openinverter.org wiki - User contributions [en]

State of Charge meter using a Teensy 4.0

2021-08-11T13:11:56Z

Clanger9: /* Wiring */

[[File:Prototype CAN SoC display.jpg|alt=Prototype CAN SoC display|thumb|Prototype CAN SoC display]]
This is a CAN bus state-of-charge meter based on a Teensy 4.0. Teensy's aren't the cheapest boards (an STM32 is a tenth of the price), but they are tiny, have on-board CAN and are very easy to develop for.

It displays a state-of-charge or voltage value according the integer number sent over CAN bus to the configured address(es)

SoC values between 0 and 1000 will be displayed as " 0.0" to "100 ". The display flashes " 0.0" when it reaches zero. Anything else (or no data) will be displayed as "----"

Voltage values between 1 and 999 will be displayed as " 1V" to "999V ". Anything else (or no data) will be displayed as "---V"

A touch sensor allows you to toggle the display between SoC and voltage.

It includes automatic night time dimming.

== Component list ==

* Teensy 4.0 board
* SN65HVD230-based CAN transceiver
* 3461BS-1 4 digit common anode 7 segment display
* 8x 220R resistors
* Photocell
* 10k resistor
* 47uF capacitor
* TTP223 Capacitive Touch Switch

== Wiring ==
[[File:Screenshot 2021-08-10 at 20.27.30.png|alt=Teensy 4.0 connections|thumb|Teensy 4.0 connections]]
Follow the Teensy 4.0 connection schematic

# Connect the CAN transceiver to Teensy 3.3V, GND, CRX2 and CTX2
# Connect the LED D1, D2, D3 and D4 digit pins to Teensy 5, 4, 3, 2
# Connect the LED a, b, c, d, e, f, g and DP segments to Teensy 16, 17, 18, 19, 20, 21, 22, 23 via 220R resistors
# Connect the Photocell to Teensy 3.3V and A0. Connect A0 to GND via a 10k resistor and 47uF capacitor in parallel.
# Connect the Touch Switch to Teensy 3.3V, GND and 15
You'll need suitable 12V -> 5V power supply for automotive use. For development, it'll work fine off 5V USB.

== Code ==
Fire up [https://www.pjrc.com/teensy/teensyduino.html Teensyduino].

Install the [https://github.com/tonton81/FlexCAN_T4 FlexCAN_T4] library

Paste in the following code:
// CAN bus state-of-charge meter for Teensy 4.x and 4-digit 7-segment display
// Includes automatic LED brightness control
//
// Usage: send integer number over CAN bus to configured address
// SoC values between 0 and 1000 will be displayed as " 0.0" to "100 "
// The display flashes " 0.0" when it reaches zero
// Anything else (or no data) will be displayed as "----"
// Voltage values between 1 and 999 will be displayed as " 1V" to "999V "
// Anything else (or no data) will be displayed as "---V"
// Touch selection to toggle display between SoC and voltage
//
// electric_dart 2021

// define display
// values below are for 3461BS-1 4 digit common anode 7 segment display
const int ledDigits = 4; // 4 digits
const int ledSegments = 7; // 7 segments
const int pinSegment[ledSegments] = {16, 17, 18, 19, 20, 21, 22}; // pins for a,b,c,d,e,f,g segments
const int pinDecimalPoint = 23; // pin for decimal point
const int pinDigit[ledDigits] = {5, 4, 3, 2}; // common digit pins, left to right
const boolean ledIsCommonAnode = 1; // 1=common anode 0=common cathode
const int ledRefreshHz = 100; // minimum 50Hz to avoid flicker
const int ledFlashHz = 2; // for flashing display

// define display characters
const int zero[ledSegments] = {HIGH, HIGH, HIGH, HIGH, HIGH, HIGH, LOW};
const int one[ledSegments] = {LOW, HIGH, HIGH, LOW, LOW, LOW, LOW};
const int two[ledSegments] = {HIGH, HIGH, LOW, HIGH, HIGH, LOW, HIGH};
const int three[ledSegments] = {HIGH, HIGH, HIGH, HIGH, LOW, LOW, HIGH};
const int four[ledSegments] = {LOW, HIGH, HIGH, LOW, LOW, HIGH, HIGH};
const int five[ledSegments] = {HIGH, LOW, HIGH, HIGH, LOW, HIGH, HIGH};
const int six[ledSegments] = {HIGH, LOW, HIGH, HIGH, HIGH, HIGH, HIGH};
const int seven[ledSegments] = {HIGH, HIGH, HIGH, LOW, LOW, LOW, LOW};
const int eight[ledSegments] = {HIGH, HIGH, HIGH, HIGH, HIGH, HIGH, HIGH};
const int nine[ledSegments] = {HIGH, HIGH, HIGH, LOW, LOW, HIGH, HIGH};
const int blank[ledSegments] = {LOW, LOW, LOW, LOW, LOW, LOW, LOW};
const int dash[ledSegments] = {LOW, LOW, LOW, LOW, LOW, LOW, HIGH};
const int volt[ledSegments] = {LOW, LOW, HIGH, HIGH, HIGH, LOW, LOW};
// add additional characters here if required
const int* character[13] = {zero, one, two, three, four, five, six, seven, eight, nine, blank, dash, volt};

// photocell parameters
int pinPhotocell = 14; // photocell pin
int photocellDark = 500; // adjust dark level for your photocell
int photocellLight = 1000; // adjust light level for your photocell

// touch parameters
int pinOnboardLED = 13;
int pinTouch = 15;
int touchCurrentState;
int touchLastState;

// CAN bus setup
const long canIDsoc = 0x350; // set this to match your SoC CAN bus ID
const long canIDvoltage = 0x522; // set this to match your voltage CAN bus ID
const long canSpeed = 500000; // set this to match your CAN bus speed
const long canTimeout = 10; // seconds to wait without data before showing error
#include <FlexCAN_T4.h>
FlexCAN_T4<CAN2, RX_SIZE_256, TX_SIZE_16> Can0; // Using CAN2 on pins 0 & 1

// internal variables
int ledRefreshMilliseconds = 1000 / (ledDigits * ledRefreshHz); // milliseconds
int ledOnMicroseconds; // microseconds
unsigned long nowMilliseconds;
unsigned long nowMicroseconds;
unsigned long nextRefreshMilliseconds = 0;
unsigned long nextBlankMicroseconds = 0;
unsigned long nextTimeoutMilliseconds = 0;
unsigned long nextFlashMilliseconds = 0;
boolean ledFlashState = 1;
int digitSelect = 0;
int readingSoC = -1;
int readingVoltage = -1;
int photocellReading;
int ledBrightness; // score 1 to 10
int displayMode = 0; // 0=SoC, 1=Voltage

void clearDisplay()
{
for (int i = 0; i < ledDigits; ++i)
{
digitalWrite(pinDigit[i], HIGH ^ ledIsCommonAnode);
}
}

void writeDisplayDigit(int digit, int value, boolean decimal)
// digit: numbered left-to-right, beginning at zero
// value: the character to display from character[] array
// decimal: set this to 1 to switch the decimal point on
{
for (int i = 0; i < ledSegments; ++i)
{
digitalWrite(pinSegment[i], character[value][i] ^ ledIsCommonAnode);
}
digitalWrite(pinDecimalPoint, decimal ^ ledIsCommonAnode);
digitalWrite(pinDigit[digit], LOW ^ ledIsCommonAnode);
}

void writeDisplaySoC(int digit, int value) // customise this section according to what you want to display
{
if (value == 1000) { // display "100 " if the input value is 1000
switch (digit) {
case 0:
writeDisplayDigit(0, 1, 0);
break;
case 1:
writeDisplayDigit(1, 0, 0);
break;
case 2:
writeDisplayDigit(2, 0, 0);
break;
}
}
else if (value >= 100 and value < 1000) { // display " 99 " to " 10 " for input values from 999 to 100
switch (digit) {
case 1:
writeDisplayDigit(1, value / 100, 0);
break;
case 2:
writeDisplayDigit(2, (value / 10) % 10, 0);
break;
}
}
else if (value >= 1 and value < 100) { // display " 9.9" to " 0.1" for input values from 99 to 1
switch (digit) {
case 2:
writeDisplayDigit(2, value / 10, 1);
break;
case 3:
writeDisplayDigit(3, value % 10, 0);
break;
}
}
else if (value == 0) { // display flashing " 0.0" for input value 0
if (nowMilliseconds > nextFlashMilliseconds) {
nextFlashMilliseconds = nowMilliseconds + ( 1000 / ledFlashHz );
ledFlashState = ledFlashState ^ 1;
}
if (ledFlashState == 1) {
switch (digit) {
case 2:
writeDisplayDigit(2, 0, 1);
break;
case 3:
writeDisplayDigit(3, 0, 0);
break;
}
}
else {
switch (digit) {
case 2:
writeDisplayDigit(2, 10, 1);
break;
case 3:
writeDisplayDigit(3, 10, 0);
break;
}
}
}
else { // display "----" for anything else
writeDisplayDigit(digit, 11, 0);
}
}

void writeDisplayVoltage(int digit, int value) // customise this section according to what you want to display
{
if (value >= 100 and value < 1000) { // display "100V" to "999V" for input values 100 to 999
switch (digit) {
case 0:
writeDisplayDigit(0, (value / 100) % 10, 0);
break;
case 1:
writeDisplayDigit(1, (value / 10) % 10, 0);
break;
case 2:
writeDisplayDigit(2, value % 10 , 0);
break;
case 3:
writeDisplayDigit(3, 12, 0);
break;
}
}
else if (value >= 10 and value < 100) { // display " 10V" to " 99V " for input values from 10 to 99
switch (digit) {
case 1:
writeDisplayDigit(1, value / 10, 0);
break;
case 2:
writeDisplayDigit(2, value % 10, 0);
break;
case 3:
writeDisplayDigit(3, 12, 0);
break;
}
}
else if (value >= 1 and value < 10) { // display " 1V" to " 9V " for input values from 1 to 9
switch (digit) {
case 2:
writeDisplayDigit(2, value % 10, 0);
break;
case 3:
writeDisplayDigit(3, 12, 0);
break;
}
}
else { // display "---V" for anything else
switch (digit) {
case 0:
writeDisplayDigit(0, 11, 0);
break;
case 1:
writeDisplayDigit(1, 11, 0);
break;
case 2:
writeDisplayDigit(2, 11, 0);
break;
case 3:
writeDisplayDigit(3, 12, 0);
break;
}
}
}

void setup() {
Serial.begin(9600); //initialise serial communications at 9600 bps

// Initialise CAN bus
delay(1000); // allow CAN hardware to stabilise
Can0.begin();
Can0.setBaudRate(canSpeed);
Can0.setMaxMB(16);
Can0.enableFIFO();
Can0.enableFIFOInterrupt();
Can0.onReceive(canDataReceived);
Can0.mailboxStatus();

// Initialise LED display

// segement pins
for (int i = 0; i < ledSegments; ++i)
{
pinMode(pinSegment[i], OUTPUT);
}

// decimal point pin
pinMode(pinDecimalPoint, OUTPUT);

// digit pins
for (int i = 0; i < ledDigits; ++i)
{
pinMode(pinDigit[i], OUTPUT);
}
clearDisplay();

pinMode(pinOnboardLED, OUTPUT);
pinMode(pinPhotocell, INPUT);
pinMode(pinTouch, INPUT);
touchCurrentState = digitalRead(pinTouch);

}

void canDataReceived(const CAN_message_t &msg) {
// Serial.print("MB "); Serial.print(msg.mb);
// Serial.print(" OVERRUN: "); Serial.print(msg.flags.overrun);
// Serial.print(" LEN: "); Serial.print(msg.len);
// Serial.print(" EXT: "); Serial.print(msg.flags.extended);
// Serial.print(" TS: "); Serial.print(msg.timestamp);
// Serial.print(" ID: "); Serial.print(msg.id, HEX);
// Serial.print(" Buffer: ");
// for ( uint8_t i = 0; i < msg.len; i++ ) {
// Serial.print(msg.buf[i], HEX); Serial.print(" ");
// } Serial.println();

switch (displayMode) { // according to display mode
case 1:
if (msg.id == canIDvoltage) {
// Matching voltage CAN bus frame arrived!
//readingVoltage = (msg.buf[2] << 24) | (msg.buf[3] << 16) | (msg.buf[4] << 8) | (msg.buf[5]); // now piece it together
readingVoltage = (msg.buf[6] << 8) | (msg.buf[7]); // now piece it together
nextTimeoutMilliseconds = nowMilliseconds + (canTimeout * 1000); // set next timeout
}
break;
default:
if (msg.id == canIDsoc) {
// Matching SoC CAN bus frame arrived!
readingSoC = (msg.buf[6] << 8) | (msg.buf[7]); // now piece it together
nextTimeoutMilliseconds = nowMilliseconds + (canTimeout * 1000); // set next timeout
}
break;
}
}

void loop() {

// add extra code here

// pot input for testing without CAN bus
//reading = analogRead(pin_pot);
//reading = map(reading, 10, 1023, 0, 1000);

touchLastState = touchCurrentState;
touchCurrentState = digitalRead(pinTouch);
if(touchLastState == LOW && touchCurrentState == HIGH) {
// toggle display
displayMode = !displayMode;
// control LED arccoding to the toggled state
digitalWrite(pinOnboardLED, displayMode);
}
//
//

Can0.events();

// take a timestamp
nowMilliseconds = millis();
nowMicroseconds = micros();

// calculate required LED brightness score (1-10) and set time to remain on (in microseconds) as a proportion of the refresh interval
photocellReading = analogRead(pinPhotocell);
photocellReading = constrain(photocellReading, photocellDark, photocellLight);
ledBrightness = map(photocellReading, photocellDark, photocellLight, 1, 10);
ledOnMicroseconds = ledBrightness * ledRefreshMilliseconds * 100; // microseconds

// timeout if no data received
if (nowMilliseconds > nextTimeoutMilliseconds) {
readingSoC = -1; // display "----"
readingVoltage = -1; // display "----"
}

// is it time to refresh display?
if (nowMilliseconds > nextRefreshMilliseconds) {
nextRefreshMilliseconds = nowMilliseconds + ledRefreshMilliseconds; // set the time in milliseconds for the next refresh
nextBlankMicroseconds = nowMicroseconds + ledOnMicroseconds; // set the time in microseconds for LEDs to remain on (for dimming)
// multiplexed display, so enable one digit at at time
switch (displayMode) { // according to display mode
case 1:
writeDisplayVoltage(digitSelect, readingVoltage);
break;
default:
writeDisplaySoC(digitSelect, readingSoC);
break;
}
++digitSelect; // we'll do the next digit on the next pass
if (digitSelect > ledDigits - 1 ) { // all digits done?
digitSelect = 0; // wrap around to first digit again.
}
}

// is it time to switch the LEDs off?
if (nowMicroseconds > nextBlankMicroseconds ) {
clearDisplay();
}
}

== Try it out! ==
Compile and upload the code to your Teensy board. The code isn't very complicated, so I set mine to run at 150MHz.

If you send CAN data to the specified node ID, the display should spring into life.

<YouTube></nowiki>https://youtu.be/s-Gadj3Rnxw<nowiki></youtube>

State of Charge meter using a Teensy 4.0

2021-08-11T13:10:51Z

Clanger9: /* Wiring */

[[File:Prototype CAN SoC display.jpg|alt=Prototype CAN SoC display|thumb|Prototype CAN SoC display]]
This is a CAN bus state-of-charge meter based on a Teensy 4.0. Teensy's aren't the cheapest boards (an STM32 is a tenth of the price), but they are tiny, have on-board CAN and are very easy to develop for.

It displays a state-of-charge or voltage value according the integer number sent over CAN bus to the configured address(es)

SoC values between 0 and 1000 will be displayed as " 0.0" to "100 ". The display flashes " 0.0" when it reaches zero. Anything else (or no data) will be displayed as "----"

Voltage values between 1 and 999 will be displayed as " 1V" to "999V ". Anything else (or no data) will be displayed as "---V"

A touch sensor allows you to toggle the display between SoC and voltage.

It includes automatic night time dimming.

== Component list ==

* Teensy 4.0 board
* SN65HVD230-based CAN transceiver
* 3461BS-1 4 digit common anode 7 segment display
* 8x 220R resistors
* Photocell
* 10k resistor
* 47uF capacitor
* TTP223 Capacitive Touch Switch

== Wiring ==
[[File:Screenshot 2021-08-10 at 20.27.30.png|alt=Teensy 4.0 connections|thumb|Teensy 4.0 connections]]
Follow the Teensy 4.0 connection schematic

# Connect the CAN transceiver to Teensy 3.3V, GND, CRX2 and CTX2
# Connect the LED D1, D2, D3 and D4 digit pins to Teensy 5, 4, 3, 2
# Connect the LED a, b, c, d, e, f, g and DP segments to Teensy 16, 17, 18, 19, 20, 21, 22, 23 via 220R resistors
# Connect the Photocell to Teensy 3.3V and A0. Connect A0 to GND via a 10k resistor and 47uF capacitor in parallel.
# Connect the Touch Switch to Teensy 3.3V, GND and 15
You'll need suitable 12V -> 3.3V power supply for automotive use. For development, it'll work fine off 5V USB.

== Code ==
Fire up [https://www.pjrc.com/teensy/teensyduino.html Teensyduino].

Install the [https://github.com/tonton81/FlexCAN_T4 FlexCAN_T4] library

Paste in the following code:
// CAN bus state-of-charge meter for Teensy 4.x and 4-digit 7-segment display
// Includes automatic LED brightness control
//
// Usage: send integer number over CAN bus to configured address
// SoC values between 0 and 1000 will be displayed as " 0.0" to "100 "
// The display flashes " 0.0" when it reaches zero
// Anything else (or no data) will be displayed as "----"
// Voltage values between 1 and 999 will be displayed as " 1V" to "999V "
// Anything else (or no data) will be displayed as "---V"
// Touch selection to toggle display between SoC and voltage
//
// electric_dart 2021

// define display
// values below are for 3461BS-1 4 digit common anode 7 segment display
const int ledDigits = 4; // 4 digits
const int ledSegments = 7; // 7 segments
const int pinSegment[ledSegments] = {16, 17, 18, 19, 20, 21, 22}; // pins for a,b,c,d,e,f,g segments
const int pinDecimalPoint = 23; // pin for decimal point
const int pinDigit[ledDigits] = {5, 4, 3, 2}; // common digit pins, left to right
const boolean ledIsCommonAnode = 1; // 1=common anode 0=common cathode
const int ledRefreshHz = 100; // minimum 50Hz to avoid flicker
const int ledFlashHz = 2; // for flashing display

// define display characters
const int zero[ledSegments] = {HIGH, HIGH, HIGH, HIGH, HIGH, HIGH, LOW};
const int one[ledSegments] = {LOW, HIGH, HIGH, LOW, LOW, LOW, LOW};
const int two[ledSegments] = {HIGH, HIGH, LOW, HIGH, HIGH, LOW, HIGH};
const int three[ledSegments] = {HIGH, HIGH, HIGH, HIGH, LOW, LOW, HIGH};
const int four[ledSegments] = {LOW, HIGH, HIGH, LOW, LOW, HIGH, HIGH};
const int five[ledSegments] = {HIGH, LOW, HIGH, HIGH, LOW, HIGH, HIGH};
const int six[ledSegments] = {HIGH, LOW, HIGH, HIGH, HIGH, HIGH, HIGH};
const int seven[ledSegments] = {HIGH, HIGH, HIGH, LOW, LOW, LOW, LOW};
const int eight[ledSegments] = {HIGH, HIGH, HIGH, HIGH, HIGH, HIGH, HIGH};
const int nine[ledSegments] = {HIGH, HIGH, HIGH, LOW, LOW, HIGH, HIGH};
const int blank[ledSegments] = {LOW, LOW, LOW, LOW, LOW, LOW, LOW};
const int dash[ledSegments] = {LOW, LOW, LOW, LOW, LOW, LOW, HIGH};
const int volt[ledSegments] = {LOW, LOW, HIGH, HIGH, HIGH, LOW, LOW};
// add additional characters here if required
const int* character[13] = {zero, one, two, three, four, five, six, seven, eight, nine, blank, dash, volt};

// photocell parameters
int pinPhotocell = 14; // photocell pin
int photocellDark = 500; // adjust dark level for your photocell
int photocellLight = 1000; // adjust light level for your photocell

// touch parameters
int pinOnboardLED = 13;
int pinTouch = 15;
int touchCurrentState;
int touchLastState;

// CAN bus setup
const long canIDsoc = 0x350; // set this to match your SoC CAN bus ID
const long canIDvoltage = 0x522; // set this to match your voltage CAN bus ID
const long canSpeed = 500000; // set this to match your CAN bus speed
const long canTimeout = 10; // seconds to wait without data before showing error
#include <FlexCAN_T4.h>
FlexCAN_T4<CAN2, RX_SIZE_256, TX_SIZE_16> Can0; // Using CAN2 on pins 0 & 1

// internal variables
int ledRefreshMilliseconds = 1000 / (ledDigits * ledRefreshHz); // milliseconds
int ledOnMicroseconds; // microseconds
unsigned long nowMilliseconds;
unsigned long nowMicroseconds;
unsigned long nextRefreshMilliseconds = 0;
unsigned long nextBlankMicroseconds = 0;
unsigned long nextTimeoutMilliseconds = 0;
unsigned long nextFlashMilliseconds = 0;
boolean ledFlashState = 1;
int digitSelect = 0;
int readingSoC = -1;
int readingVoltage = -1;
int photocellReading;
int ledBrightness; // score 1 to 10
int displayMode = 0; // 0=SoC, 1=Voltage

void clearDisplay()
{
for (int i = 0; i < ledDigits; ++i)
{
digitalWrite(pinDigit[i], HIGH ^ ledIsCommonAnode);
}
}

void writeDisplayDigit(int digit, int value, boolean decimal)
// digit: numbered left-to-right, beginning at zero
// value: the character to display from character[] array
// decimal: set this to 1 to switch the decimal point on
{
for (int i = 0; i < ledSegments; ++i)
{
digitalWrite(pinSegment[i], character[value][i] ^ ledIsCommonAnode);
}
digitalWrite(pinDecimalPoint, decimal ^ ledIsCommonAnode);
digitalWrite(pinDigit[digit], LOW ^ ledIsCommonAnode);
}

void writeDisplaySoC(int digit, int value) // customise this section according to what you want to display
{
if (value == 1000) { // display "100 " if the input value is 1000
switch (digit) {
case 0:
writeDisplayDigit(0, 1, 0);
break;
case 1:
writeDisplayDigit(1, 0, 0);
break;
case 2:
writeDisplayDigit(2, 0, 0);
break;
}
}
else if (value >= 100 and value < 1000) { // display " 99 " to " 10 " for input values from 999 to 100
switch (digit) {
case 1:
writeDisplayDigit(1, value / 100, 0);
break;
case 2:
writeDisplayDigit(2, (value / 10) % 10, 0);
break;
}
}
else if (value >= 1 and value < 100) { // display " 9.9" to " 0.1" for input values from 99 to 1
switch (digit) {
case 2:
writeDisplayDigit(2, value / 10, 1);
break;
case 3:
writeDisplayDigit(3, value % 10, 0);
break;
}
}
else if (value == 0) { // display flashing " 0.0" for input value 0
if (nowMilliseconds > nextFlashMilliseconds) {
nextFlashMilliseconds = nowMilliseconds + ( 1000 / ledFlashHz );
ledFlashState = ledFlashState ^ 1;
}
if (ledFlashState == 1) {
switch (digit) {
case 2:
writeDisplayDigit(2, 0, 1);
break;
case 3:
writeDisplayDigit(3, 0, 0);
break;
}
}
else {
switch (digit) {
case 2:
writeDisplayDigit(2, 10, 1);
break;
case 3:
writeDisplayDigit(3, 10, 0);
break;
}
}
}
else { // display "----" for anything else
writeDisplayDigit(digit, 11, 0);
}
}

void writeDisplayVoltage(int digit, int value) // customise this section according to what you want to display
{
if (value >= 100 and value < 1000) { // display "100V" to "999V" for input values 100 to 999
switch (digit) {
case 0:
writeDisplayDigit(0, (value / 100) % 10, 0);
break;
case 1:
writeDisplayDigit(1, (value / 10) % 10, 0);
break;
case 2:
writeDisplayDigit(2, value % 10 , 0);
break;
case 3:
writeDisplayDigit(3, 12, 0);
break;
}
}
else if (value >= 10 and value < 100) { // display " 10V" to " 99V " for input values from 10 to 99
switch (digit) {
case 1:
writeDisplayDigit(1, value / 10, 0);
break;
case 2:
writeDisplayDigit(2, value % 10, 0);
break;
case 3:
writeDisplayDigit(3, 12, 0);
break;
}
}
else if (value >= 1 and value < 10) { // display " 1V" to " 9V " for input values from 1 to 9
switch (digit) {
case 2:
writeDisplayDigit(2, value % 10, 0);
break;
case 3:
writeDisplayDigit(3, 12, 0);
break;
}
}
else { // display "---V" for anything else
switch (digit) {
case 0:
writeDisplayDigit(0, 11, 0);
break;
case 1:
writeDisplayDigit(1, 11, 0);
break;
case 2:
writeDisplayDigit(2, 11, 0);
break;
case 3:
writeDisplayDigit(3, 12, 0);
break;
}
}
}

void setup() {
Serial.begin(9600); //initialise serial communications at 9600 bps

// Initialise CAN bus
delay(1000); // allow CAN hardware to stabilise
Can0.begin();
Can0.setBaudRate(canSpeed);
Can0.setMaxMB(16);
Can0.enableFIFO();
Can0.enableFIFOInterrupt();
Can0.onReceive(canDataReceived);
Can0.mailboxStatus();

// Initialise LED display

// segement pins
for (int i = 0; i < ledSegments; ++i)
{
pinMode(pinSegment[i], OUTPUT);
}

// decimal point pin
pinMode(pinDecimalPoint, OUTPUT);

// digit pins
for (int i = 0; i < ledDigits; ++i)
{
pinMode(pinDigit[i], OUTPUT);
}
clearDisplay();

pinMode(pinOnboardLED, OUTPUT);
pinMode(pinPhotocell, INPUT);
pinMode(pinTouch, INPUT);
touchCurrentState = digitalRead(pinTouch);

}

void canDataReceived(const CAN_message_t &msg) {
// Serial.print("MB "); Serial.print(msg.mb);
// Serial.print(" OVERRUN: "); Serial.print(msg.flags.overrun);
// Serial.print(" LEN: "); Serial.print(msg.len);
// Serial.print(" EXT: "); Serial.print(msg.flags.extended);
// Serial.print(" TS: "); Serial.print(msg.timestamp);
// Serial.print(" ID: "); Serial.print(msg.id, HEX);
// Serial.print(" Buffer: ");
// for ( uint8_t i = 0; i < msg.len; i++ ) {
// Serial.print(msg.buf[i], HEX); Serial.print(" ");
// } Serial.println();

switch (displayMode) { // according to display mode
case 1:
if (msg.id == canIDvoltage) {
// Matching voltage CAN bus frame arrived!
//readingVoltage = (msg.buf[2] << 24) | (msg.buf[3] << 16) | (msg.buf[4] << 8) | (msg.buf[5]); // now piece it together
readingVoltage = (msg.buf[6] << 8) | (msg.buf[7]); // now piece it together
nextTimeoutMilliseconds = nowMilliseconds + (canTimeout * 1000); // set next timeout
}
break;
default:
if (msg.id == canIDsoc) {
// Matching SoC CAN bus frame arrived!
readingSoC = (msg.buf[6] << 8) | (msg.buf[7]); // now piece it together
nextTimeoutMilliseconds = nowMilliseconds + (canTimeout * 1000); // set next timeout
}
break;
}
}

void loop() {

// add extra code here

// pot input for testing without CAN bus
//reading = analogRead(pin_pot);
//reading = map(reading, 10, 1023, 0, 1000);

touchLastState = touchCurrentState;
touchCurrentState = digitalRead(pinTouch);
if(touchLastState == LOW && touchCurrentState == HIGH) {
// toggle display
displayMode = !displayMode;
// control LED arccoding to the toggled state
digitalWrite(pinOnboardLED, displayMode);
}
//
//

Can0.events();

// take a timestamp
nowMilliseconds = millis();
nowMicroseconds = micros();

// calculate required LED brightness score (1-10) and set time to remain on (in microseconds) as a proportion of the refresh interval
photocellReading = analogRead(pinPhotocell);
photocellReading = constrain(photocellReading, photocellDark, photocellLight);
ledBrightness = map(photocellReading, photocellDark, photocellLight, 1, 10);
ledOnMicroseconds = ledBrightness * ledRefreshMilliseconds * 100; // microseconds

// timeout if no data received
if (nowMilliseconds > nextTimeoutMilliseconds) {
readingSoC = -1; // display "----"
readingVoltage = -1; // display "----"
}

// is it time to refresh display?
if (nowMilliseconds > nextRefreshMilliseconds) {
nextRefreshMilliseconds = nowMilliseconds + ledRefreshMilliseconds; // set the time in milliseconds for the next refresh
nextBlankMicroseconds = nowMicroseconds + ledOnMicroseconds; // set the time in microseconds for LEDs to remain on (for dimming)
// multiplexed display, so enable one digit at at time
switch (displayMode) { // according to display mode
case 1:
writeDisplayVoltage(digitSelect, readingVoltage);
break;
default:
writeDisplaySoC(digitSelect, readingSoC);
break;
}
++digitSelect; // we'll do the next digit on the next pass
if (digitSelect > ledDigits - 1 ) { // all digits done?
digitSelect = 0; // wrap around to first digit again.
}
}

// is it time to switch the LEDs off?
if (nowMicroseconds > nextBlankMicroseconds ) {
clearDisplay();
}
}

== Try it out! ==
Compile and upload the code to your Teensy board. The code isn't very complicated, so I set mine to run at 150MHz.

If you send CAN data to the specified node ID, the display should spring into life.

<YouTube></nowiki>https://youtu.be/s-Gadj3Rnxw<nowiki></youtube>

State of Charge meter using a Teensy 4.0

2021-08-10T20:01:12Z

Clanger9:

[[File:Prototype CAN SoC display.jpg|alt=Prototype CAN SoC display|thumb|Prototype CAN SoC display]]
This is a CAN bus state-of-charge meter based on a Teensy 4.0. Teensy's aren't the cheapest boards (an STM32 is a tenth of the price), but they are tiny, have on-board CAN and are very easy to develop for.

It displays a state-of-charge or voltage value according the integer number sent over CAN bus to the configured address(es)

SoC values between 0 and 1000 will be displayed as " 0.0" to "100 ". The display flashes " 0.0" when it reaches zero. Anything else (or no data) will be displayed as "----"

Voltage values between 1 and 999 will be displayed as " 1V" to "999V ". Anything else (or no data) will be displayed as "---V"

A touch sensor allows you to toggle the display between SoC and voltage.

It includes automatic night time dimming.

== Component list ==

* Teensy 4.0 board
* SN65HVD230-based CAN transceiver
* 3461BS-1 4 digit common anode 7 segment display
* 8x 220R resistors
* Photocell
* 10k resistor
* 47uF capacitor
* TTP223 Capacitive Touch Switch

== Wiring ==
[[File:Screenshot 2021-08-10 at 20.27.30.png|alt=Teensy 4.0 connections|thumb|Teensy 4.0 connections]]
Follow the Teensy 4.0 connection schematic

# Connect the CAN transceiver to Teensy 3.3V, GND, CRX2 and CTX2
# Connect the LED D1, D2, D3 and D4 digit pins to Teensy 5, 4, 3, 2
# Connect the LED a, b, c, d, e, f, g and DP segments to Teensy 16, 17, 18, 19, 20, 21, 22, 23 via 220R resistors
# Connect the Photocell to Teensy 3.3V and A0. Connect A0 to GND via a 10k resistor and 47uF capacitor in parallel.
# Connect the Touch Switch to Teensy 3.3V, GND and 15

== Code ==
Fire up [https://www.pjrc.com/teensy/teensyduino.html Teensyduino].

Install the [https://github.com/tonton81/FlexCAN_T4 FlexCAN_T4] library

Paste in the following code:
// CAN bus state-of-charge meter for Teensy 4.x and 4-digit 7-segment display
// Includes automatic LED brightness control
//
// Usage: send integer number over CAN bus to configured address
// SoC values between 0 and 1000 will be displayed as " 0.0" to "100 "
// The display flashes " 0.0" when it reaches zero
// Anything else (or no data) will be displayed as "----"
// Voltage values between 1 and 999 will be displayed as " 1V" to "999V "
// Anything else (or no data) will be displayed as "---V"
// Touch selection to toggle display between SoC and voltage
//
// electric_dart 2021

// define display
// values below are for 3461BS-1 4 digit common anode 7 segment display
const int ledDigits = 4; // 4 digits
const int ledSegments = 7; // 7 segments
const int pinSegment[ledSegments] = {16, 17, 18, 19, 20, 21, 22}; // pins for a,b,c,d,e,f,g segments
const int pinDecimalPoint = 23; // pin for decimal point
const int pinDigit[ledDigits] = {5, 4, 3, 2}; // common digit pins, left to right
const boolean ledIsCommonAnode = 1; // 1=common anode 0=common cathode
const int ledRefreshHz = 100; // minimum 50Hz to avoid flicker
const int ledFlashHz = 2; // for flashing display

// define display characters
const int zero[ledSegments] = {HIGH, HIGH, HIGH, HIGH, HIGH, HIGH, LOW};
const int one[ledSegments] = {LOW, HIGH, HIGH, LOW, LOW, LOW, LOW};
const int two[ledSegments] = {HIGH, HIGH, LOW, HIGH, HIGH, LOW, HIGH};
const int three[ledSegments] = {HIGH, HIGH, HIGH, HIGH, LOW, LOW, HIGH};
const int four[ledSegments] = {LOW, HIGH, HIGH, LOW, LOW, HIGH, HIGH};
const int five[ledSegments] = {HIGH, LOW, HIGH, HIGH, LOW, HIGH, HIGH};
const int six[ledSegments] = {HIGH, LOW, HIGH, HIGH, HIGH, HIGH, HIGH};
const int seven[ledSegments] = {HIGH, HIGH, HIGH, LOW, LOW, LOW, LOW};
const int eight[ledSegments] = {HIGH, HIGH, HIGH, HIGH, HIGH, HIGH, HIGH};
const int nine[ledSegments] = {HIGH, HIGH, HIGH, LOW, LOW, HIGH, HIGH};
const int blank[ledSegments] = {LOW, LOW, LOW, LOW, LOW, LOW, LOW};
const int dash[ledSegments] = {LOW, LOW, LOW, LOW, LOW, LOW, HIGH};
const int volt[ledSegments] = {LOW, LOW, HIGH, HIGH, HIGH, LOW, LOW};
// add additional characters here if required
const int* character[13] = {zero, one, two, three, four, five, six, seven, eight, nine, blank, dash, volt};

// photocell parameters
int pinPhotocell = 14; // photocell pin
int photocellDark = 500; // adjust dark level for your photocell
int photocellLight = 1000; // adjust light level for your photocell

// touch parameters
int pinOnboardLED = 13;
int pinTouch = 15;
int touchCurrentState;
int touchLastState;

// CAN bus setup
const long canIDsoc = 0x350; // set this to match your SoC CAN bus ID
const long canIDvoltage = 0x522; // set this to match your voltage CAN bus ID
const long canSpeed = 500000; // set this to match your CAN bus speed
const long canTimeout = 10; // seconds to wait without data before showing error
#include <FlexCAN_T4.h>
FlexCAN_T4<CAN2, RX_SIZE_256, TX_SIZE_16> Can0; // Using CAN2 on pins 0 & 1

// internal variables
int ledRefreshMilliseconds = 1000 / (ledDigits * ledRefreshHz); // milliseconds
int ledOnMicroseconds; // microseconds
unsigned long nowMilliseconds;
unsigned long nowMicroseconds;
unsigned long nextRefreshMilliseconds = 0;
unsigned long nextBlankMicroseconds = 0;
unsigned long nextTimeoutMilliseconds = 0;
unsigned long nextFlashMilliseconds = 0;
boolean ledFlashState = 1;
int digitSelect = 0;
int readingSoC = -1;
int readingVoltage = -1;
int photocellReading;
int ledBrightness; // score 1 to 10
int displayMode = 0; // 0=SoC, 1=Voltage

void clearDisplay()
{
for (int i = 0; i < ledDigits; ++i)
{
digitalWrite(pinDigit[i], HIGH ^ ledIsCommonAnode);
}
}

void writeDisplayDigit(int digit, int value, boolean decimal)
// digit: numbered left-to-right, beginning at zero
// value: the character to display from character[] array
// decimal: set this to 1 to switch the decimal point on
{
for (int i = 0; i < ledSegments; ++i)
{
digitalWrite(pinSegment[i], character[value][i] ^ ledIsCommonAnode);
}
digitalWrite(pinDecimalPoint, decimal ^ ledIsCommonAnode);
digitalWrite(pinDigit[digit], LOW ^ ledIsCommonAnode);
}

void writeDisplaySoC(int digit, int value) // customise this section according to what you want to display
{
if (value == 1000) { // display "100 " if the input value is 1000
switch (digit) {
case 0:
writeDisplayDigit(0, 1, 0);
break;
case 1:
writeDisplayDigit(1, 0, 0);
break;
case 2:
writeDisplayDigit(2, 0, 0);
break;
}
}
else if (value >= 100 and value < 1000) { // display " 99 " to " 10 " for input values from 999 to 100
switch (digit) {
case 1:
writeDisplayDigit(1, value / 100, 0);
break;
case 2:
writeDisplayDigit(2, (value / 10) % 10, 0);
break;
}
}
else if (value >= 1 and value < 100) { // display " 9.9" to " 0.1" for input values from 99 to 1
switch (digit) {
case 2:
writeDisplayDigit(2, value / 10, 1);
break;
case 3:
writeDisplayDigit(3, value % 10, 0);
break;
}
}
else if (value == 0) { // display flashing " 0.0" for input value 0
if (nowMilliseconds > nextFlashMilliseconds) {
nextFlashMilliseconds = nowMilliseconds + ( 1000 / ledFlashHz );
ledFlashState = ledFlashState ^ 1;
}
if (ledFlashState == 1) {
switch (digit) {
case 2:
writeDisplayDigit(2, 0, 1);
break;
case 3:
writeDisplayDigit(3, 0, 0);
break;
}
}
else {
switch (digit) {
case 2:
writeDisplayDigit(2, 10, 1);
break;
case 3:
writeDisplayDigit(3, 10, 0);
break;
}
}
}
else { // display "----" for anything else
writeDisplayDigit(digit, 11, 0);
}
}

void writeDisplayVoltage(int digit, int value) // customise this section according to what you want to display
{
if (value >= 100 and value < 1000) { // display "100V" to "999V" for input values 100 to 999
switch (digit) {
case 0:
writeDisplayDigit(0, (value / 100) % 10, 0);
break;
case 1:
writeDisplayDigit(1, (value / 10) % 10, 0);
break;
case 2:
writeDisplayDigit(2, value % 10 , 0);
break;
case 3:
writeDisplayDigit(3, 12, 0);
break;
}
}
else if (value >= 10 and value < 100) { // display " 10V" to " 99V " for input values from 10 to 99
switch (digit) {
case 1:
writeDisplayDigit(1, value / 10, 0);
break;
case 2:
writeDisplayDigit(2, value % 10, 0);
break;
case 3:
writeDisplayDigit(3, 12, 0);
break;
}
}
else if (value >= 1 and value < 10) { // display " 1V" to " 9V " for input values from 1 to 9
switch (digit) {
case 2:
writeDisplayDigit(2, value % 10, 0);
break;
case 3:
writeDisplayDigit(3, 12, 0);
break;
}
}
else { // display "---V" for anything else
switch (digit) {
case 0:
writeDisplayDigit(0, 11, 0);
break;
case 1:
writeDisplayDigit(1, 11, 0);
break;
case 2:
writeDisplayDigit(2, 11, 0);
break;
case 3:
writeDisplayDigit(3, 12, 0);
break;
}
}
}

void setup() {
Serial.begin(9600); //initialise serial communications at 9600 bps

// Initialise CAN bus
delay(1000); // allow CAN hardware to stabilise
Can0.begin();
Can0.setBaudRate(canSpeed);
Can0.setMaxMB(16);
Can0.enableFIFO();
Can0.enableFIFOInterrupt();
Can0.onReceive(canDataReceived);
Can0.mailboxStatus();

// Initialise LED display

// segement pins
for (int i = 0; i < ledSegments; ++i)
{
pinMode(pinSegment[i], OUTPUT);
}

// decimal point pin
pinMode(pinDecimalPoint, OUTPUT);

// digit pins
for (int i = 0; i < ledDigits; ++i)
{
pinMode(pinDigit[i], OUTPUT);
}
clearDisplay();

pinMode(pinOnboardLED, OUTPUT);
pinMode(pinPhotocell, INPUT);
pinMode(pinTouch, INPUT);
touchCurrentState = digitalRead(pinTouch);

}

void canDataReceived(const CAN_message_t &msg) {
// Serial.print("MB "); Serial.print(msg.mb);
// Serial.print(" OVERRUN: "); Serial.print(msg.flags.overrun);
// Serial.print(" LEN: "); Serial.print(msg.len);
// Serial.print(" EXT: "); Serial.print(msg.flags.extended);
// Serial.print(" TS: "); Serial.print(msg.timestamp);
// Serial.print(" ID: "); Serial.print(msg.id, HEX);
// Serial.print(" Buffer: ");
// for ( uint8_t i = 0; i < msg.len; i++ ) {
// Serial.print(msg.buf[i], HEX); Serial.print(" ");
// } Serial.println();

switch (displayMode) { // according to display mode
case 1:
if (msg.id == canIDvoltage) {
// Matching voltage CAN bus frame arrived!
//readingVoltage = (msg.buf[2] << 24) | (msg.buf[3] << 16) | (msg.buf[4] << 8) | (msg.buf[5]); // now piece it together
readingVoltage = (msg.buf[6] << 8) | (msg.buf[7]); // now piece it together
nextTimeoutMilliseconds = nowMilliseconds + (canTimeout * 1000); // set next timeout
}
break;
default:
if (msg.id == canIDsoc) {
// Matching SoC CAN bus frame arrived!
readingSoC = (msg.buf[6] << 8) | (msg.buf[7]); // now piece it together
nextTimeoutMilliseconds = nowMilliseconds + (canTimeout * 1000); // set next timeout
}
break;
}
}

void loop() {

// add extra code here

// pot input for testing without CAN bus
//reading = analogRead(pin_pot);
//reading = map(reading, 10, 1023, 0, 1000);

touchLastState = touchCurrentState;
touchCurrentState = digitalRead(pinTouch);
if(touchLastState == LOW && touchCurrentState == HIGH) {
// toggle display
displayMode = !displayMode;
// control LED arccoding to the toggled state
digitalWrite(pinOnboardLED, displayMode);
}
//
//

Can0.events();

// take a timestamp
nowMilliseconds = millis();
nowMicroseconds = micros();

// calculate required LED brightness score (1-10) and set time to remain on (in microseconds) as a proportion of the refresh interval
photocellReading = analogRead(pinPhotocell);
photocellReading = constrain(photocellReading, photocellDark, photocellLight);
ledBrightness = map(photocellReading, photocellDark, photocellLight, 1, 10);
ledOnMicroseconds = ledBrightness * ledRefreshMilliseconds * 100; // microseconds

// timeout if no data received
if (nowMilliseconds > nextTimeoutMilliseconds) {
readingSoC = -1; // display "----"
readingVoltage = -1; // display "----"
}

// is it time to refresh display?
if (nowMilliseconds > nextRefreshMilliseconds) {
nextRefreshMilliseconds = nowMilliseconds + ledRefreshMilliseconds; // set the time in milliseconds for the next refresh
nextBlankMicroseconds = nowMicroseconds + ledOnMicroseconds; // set the time in microseconds for LEDs to remain on (for dimming)
// multiplexed display, so enable one digit at at time
switch (displayMode) { // according to display mode
case 1:
writeDisplayVoltage(digitSelect, readingVoltage);
break;
default:
writeDisplaySoC(digitSelect, readingSoC);
break;
}
++digitSelect; // we'll do the next digit on the next pass
if (digitSelect > ledDigits - 1 ) { // all digits done?
digitSelect = 0; // wrap around to first digit again.
}
}

// is it time to switch the LEDs off?
if (nowMicroseconds > nextBlankMicroseconds ) {
clearDisplay();
}
}

== Try it out! ==
Compile and upload the code to your Teensy board. The code isn't very complicated, so I set mine to run at 150MHz.

If you send CAN data to the specified node ID, the display should spring into life.

<YouTube></nowiki>https://youtu.be/s-Gadj3Rnxw<nowiki></youtube>

State of Charge meter using a Teensy 4.0

2021-08-10T19:57:42Z

Clanger9:

[[File:Prototype CAN SoC display.jpg|alt=Prototype CAN SoC display|thumb|Prototype CAN SoC display]]
This is a CAN bus state-of-charge meter based on a Teensy 4.0. Teensy's aren't the cheapest boards (an STM32 is a tenth of the price), but they are tiny, have on-board CAN and are very easy to develop for.

It displays a state-of-charge or voltage value according the integer number sent over CAN bus to the configured address(es)

SoC values between 0 and 1000 will be displayed as " 0.0" to "100 ". The display flashes " 0.0" when it reaches zero. Anything else (or no data) will be displayed as "----"

Voltage values between 1 and 999 will be displayed as " 1V" to "999V ". Anything else (or no data) will be displayed as "---V"

A touch sensor allows you to toggle the display between SoC and voltage.

It includes automatic night time dimming.

== Component list ==

* Teensy 4.0 board
* SN65HVD230-based CAN transceiver
* 3461BS-1 4 digit common anode 7 segment display
* 8x 220R resistors
* Photocell
* 10k resistor
* 47uF capacitor
* TTP223 Capacitive Touch Switch

== Wiring ==
[[File:Screenshot 2021-08-10 at 20.27.30.png|alt=Teensy 4.0 connections|thumb|Teensy 4.0 connections]]
Follow the Teensy 4.0 connection schematic

# Connect the CAN transceiver to Teensy 3.3V, GND, CRX2 and CTX2
# Connect the LED D1, D2, D3 and D4 digit pins to Teensy 5, 4, 3, 2
# Connect the LED a, b, c, d, e, f, g and DP segments to Teensy 16, 17, 18, 19, 20, 21, 22, 23 via 220R resistors
# Connect the Photocell to Teensy 3.3V and A0. Connect A0 to GND via a 10k resistor and 47uF capacitor in parallel.
# Connect the Touch Switch to Teensy 3.3V, GND and 15

== Code ==
Fire up [https://www.pjrc.com/teensy/teensyduino.html Teensyduino] and paste in the following code:
// CAN bus state-of-charge meter for Teensy 4.x and 4-digit 7-segment display
// Includes automatic LED brightness control
//
// Usage: send integer number over CAN bus to configured address
// SoC values between 0 and 1000 will be displayed as " 0.0" to "100 "
// The display flashes " 0.0" when it reaches zero
// Anything else (or no data) will be displayed as "----"
// Voltage values between 1 and 999 will be displayed as " 1V" to "999V "
// Anything else (or no data) will be displayed as "---V"
// Touch selection to toggle display between SoC and voltage
//
// electric_dart 2021

// define display
// values below are for 3461BS-1 4 digit common anode 7 segment display
const int ledDigits = 4; // 4 digits
const int ledSegments = 7; // 7 segments
const int pinSegment[ledSegments] = {16, 17, 18, 19, 20, 21, 22}; // pins for a,b,c,d,e,f,g segments
const int pinDecimalPoint = 23; // pin for decimal point
const int pinDigit[ledDigits] = {5, 4, 3, 2}; // common digit pins, left to right
const boolean ledIsCommonAnode = 1; // 1=common anode 0=common cathode
const int ledRefreshHz = 100; // minimum 50Hz to avoid flicker
const int ledFlashHz = 2; // for flashing display

// define display characters
const int zero[ledSegments] = {HIGH, HIGH, HIGH, HIGH, HIGH, HIGH, LOW};
const int one[ledSegments] = {LOW, HIGH, HIGH, LOW, LOW, LOW, LOW};
const int two[ledSegments] = {HIGH, HIGH, LOW, HIGH, HIGH, LOW, HIGH};
const int three[ledSegments] = {HIGH, HIGH, HIGH, HIGH, LOW, LOW, HIGH};
const int four[ledSegments] = {LOW, HIGH, HIGH, LOW, LOW, HIGH, HIGH};
const int five[ledSegments] = {HIGH, LOW, HIGH, HIGH, LOW, HIGH, HIGH};
const int six[ledSegments] = {HIGH, LOW, HIGH, HIGH, HIGH, HIGH, HIGH};
const int seven[ledSegments] = {HIGH, HIGH, HIGH, LOW, LOW, LOW, LOW};
const int eight[ledSegments] = {HIGH, HIGH, HIGH, HIGH, HIGH, HIGH, HIGH};
const int nine[ledSegments] = {HIGH, HIGH, HIGH, LOW, LOW, HIGH, HIGH};
const int blank[ledSegments] = {LOW, LOW, LOW, LOW, LOW, LOW, LOW};
const int dash[ledSegments] = {LOW, LOW, LOW, LOW, LOW, LOW, HIGH};
const int volt[ledSegments] = {LOW, LOW, HIGH, HIGH, HIGH, LOW, LOW};
// add additional characters here if required
const int* character[13] = {zero, one, two, three, four, five, six, seven, eight, nine, blank, dash, volt};

// photocell parameters
int pinPhotocell = 14; // photocell pin
int photocellDark = 500; // adjust dark level for your photocell
int photocellLight = 1000; // adjust light level for your photocell

// touch parameters
int pinOnboardLED = 13;
int pinTouch = 15;
int touchCurrentState;
int touchLastState;

// CAN bus setup
const long canIDsoc = 0x350; // set this to match your SoC CAN bus ID
const long canIDvoltage = 0x522; // set this to match your voltage CAN bus ID
const long canSpeed = 500000; // set this to match your CAN bus speed
const long canTimeout = 10; // seconds to wait without data before showing error
#include <FlexCAN_T4.h>
FlexCAN_T4<CAN2, RX_SIZE_256, TX_SIZE_16> Can0; // Using CAN2 on pins 0 & 1

// internal variables
int ledRefreshMilliseconds = 1000 / (ledDigits * ledRefreshHz); // milliseconds
int ledOnMicroseconds; // microseconds
unsigned long nowMilliseconds;
unsigned long nowMicroseconds;
unsigned long nextRefreshMilliseconds = 0;
unsigned long nextBlankMicroseconds = 0;
unsigned long nextTimeoutMilliseconds = 0;
unsigned long nextFlashMilliseconds = 0;
boolean ledFlashState = 1;
int digitSelect = 0;
int readingSoC = -1;
int readingVoltage = -1;
int photocellReading;
int ledBrightness; // score 1 to 10
int displayMode = 0; // 0=SoC, 1=Voltage

void clearDisplay()
{
for (int i = 0; i < ledDigits; ++i)
{
digitalWrite(pinDigit[i], HIGH ^ ledIsCommonAnode);
}
}

void writeDisplayDigit(int digit, int value, boolean decimal)
// digit: numbered left-to-right, beginning at zero
// value: the character to display from character[] array
// decimal: set this to 1 to switch the decimal point on
{
for (int i = 0; i < ledSegments; ++i)
{
digitalWrite(pinSegment[i], character[value][i] ^ ledIsCommonAnode);
}
digitalWrite(pinDecimalPoint, decimal ^ ledIsCommonAnode);
digitalWrite(pinDigit[digit], LOW ^ ledIsCommonAnode);
}

void writeDisplaySoC(int digit, int value) // customise this section according to what you want to display
{
if (value == 1000) { // display "100 " if the input value is 1000
switch (digit) {
case 0:
writeDisplayDigit(0, 1, 0);
break;
case 1:
writeDisplayDigit(1, 0, 0);
break;
case 2:
writeDisplayDigit(2, 0, 0);
break;
}
}
else if (value >= 100 and value < 1000) { // display " 99 " to " 10 " for input values from 999 to 100
switch (digit) {
case 1:
writeDisplayDigit(1, value / 100, 0);
break;
case 2:
writeDisplayDigit(2, (value / 10) % 10, 0);
break;
}
}
else if (value >= 1 and value < 100) { // display " 9.9" to " 0.1" for input values from 99 to 1
switch (digit) {
case 2:
writeDisplayDigit(2, value / 10, 1);
break;
case 3:
writeDisplayDigit(3, value % 10, 0);
break;
}
}
else if (value == 0) { // display flashing " 0.0" for input value 0
if (nowMilliseconds > nextFlashMilliseconds) {
nextFlashMilliseconds = nowMilliseconds + ( 1000 / ledFlashHz );
ledFlashState = ledFlashState ^ 1;
}
if (ledFlashState == 1) {
switch (digit) {
case 2:
writeDisplayDigit(2, 0, 1);
break;
case 3:
writeDisplayDigit(3, 0, 0);
break;
}
}
else {
switch (digit) {
case 2:
writeDisplayDigit(2, 10, 1);
break;
case 3:
writeDisplayDigit(3, 10, 0);
break;
}
}
}
else { // display "----" for anything else
writeDisplayDigit(digit, 11, 0);
}
}

void writeDisplayVoltage(int digit, int value) // customise this section according to what you want to display
{
if (value >= 100 and value < 1000) { // display "100V" to "999V" for input values 100 to 999
switch (digit) {
case 0:
writeDisplayDigit(0, (value / 100) % 10, 0);
break;
case 1:
writeDisplayDigit(1, (value / 10) % 10, 0);
break;
case 2:
writeDisplayDigit(2, value % 10 , 0);
break;
case 3:
writeDisplayDigit(3, 12, 0);
break;
}
}
else if (value >= 10 and value < 100) { // display " 10V" to " 99V " for input values from 10 to 99
switch (digit) {
case 1:
writeDisplayDigit(1, value / 10, 0);
break;
case 2:
writeDisplayDigit(2, value % 10, 0);
break;
case 3:
writeDisplayDigit(3, 12, 0);
break;
}
}
else if (value >= 1 and value < 10) { // display " 1V" to " 9V " for input values from 1 to 9
switch (digit) {
case 2:
writeDisplayDigit(2, value % 10, 0);
break;
case 3:
writeDisplayDigit(3, 12, 0);
break;
}
}
else { // display "---V" for anything else
switch (digit) {
case 0:
writeDisplayDigit(0, 11, 0);
break;
case 1:
writeDisplayDigit(1, 11, 0);
break;
case 2:
writeDisplayDigit(2, 11, 0);
break;
case 3:
writeDisplayDigit(3, 12, 0);
break;
}
}
}

void setup() {
Serial.begin(9600); //initialise serial communications at 9600 bps

// Initialise CAN bus
delay(1000); // allow CAN hardware to stabilise
Can0.begin();
Can0.setBaudRate(canSpeed);
Can0.setMaxMB(16);
Can0.enableFIFO();
Can0.enableFIFOInterrupt();
Can0.onReceive(canDataReceived);
Can0.mailboxStatus();

// Initialise LED display

// segement pins
for (int i = 0; i < ledSegments; ++i)
{
pinMode(pinSegment[i], OUTPUT);
}

// decimal point pin
pinMode(pinDecimalPoint, OUTPUT);

// digit pins
for (int i = 0; i < ledDigits; ++i)
{
pinMode(pinDigit[i], OUTPUT);
}
clearDisplay();

pinMode(pinOnboardLED, OUTPUT);
pinMode(pinPhotocell, INPUT);
pinMode(pinTouch, INPUT);
touchCurrentState = digitalRead(pinTouch);

}

void canDataReceived(const CAN_message_t &msg) {
// Serial.print("MB "); Serial.print(msg.mb);
// Serial.print(" OVERRUN: "); Serial.print(msg.flags.overrun);
// Serial.print(" LEN: "); Serial.print(msg.len);
// Serial.print(" EXT: "); Serial.print(msg.flags.extended);
// Serial.print(" TS: "); Serial.print(msg.timestamp);
// Serial.print(" ID: "); Serial.print(msg.id, HEX);
// Serial.print(" Buffer: ");
// for ( uint8_t i = 0; i < msg.len; i++ ) {
// Serial.print(msg.buf[i], HEX); Serial.print(" ");
// } Serial.println();

switch (displayMode) { // according to display mode
case 1:
if (msg.id == canIDvoltage) {
// Matching voltage CAN bus frame arrived!
//readingVoltage = (msg.buf[2] << 24) | (msg.buf[3] << 16) | (msg.buf[4] << 8) | (msg.buf[5]); // now piece it together
readingVoltage = (msg.buf[6] << 8) | (msg.buf[7]); // now piece it together
nextTimeoutMilliseconds = nowMilliseconds + (canTimeout * 1000); // set next timeout
}
break;
default:
if (msg.id == canIDsoc) {
// Matching SoC CAN bus frame arrived!
readingSoC = (msg.buf[6] << 8) | (msg.buf[7]); // now piece it together
nextTimeoutMilliseconds = nowMilliseconds + (canTimeout * 1000); // set next timeout
}
break;
}
}

void loop() {

// add extra code here

// pot input for testing without CAN bus
//reading = analogRead(pin_pot);
//reading = map(reading, 10, 1023, 0, 1000);

touchLastState = touchCurrentState;
touchCurrentState = digitalRead(pinTouch);
if(touchLastState == LOW && touchCurrentState == HIGH) {
// toggle display
displayMode = !displayMode;
// control LED arccoding to the toggled state
digitalWrite(pinOnboardLED, displayMode);
}
//
//

Can0.events();

// take a timestamp
nowMilliseconds = millis();
nowMicroseconds = micros();

// calculate required LED brightness score (1-10) and set time to remain on (in microseconds) as a proportion of the refresh interval
photocellReading = analogRead(pinPhotocell);
photocellReading = constrain(photocellReading, photocellDark, photocellLight);
ledBrightness = map(photocellReading, photocellDark, photocellLight, 1, 10);
ledOnMicroseconds = ledBrightness * ledRefreshMilliseconds * 100; // microseconds

// timeout if no data received
if (nowMilliseconds > nextTimeoutMilliseconds) {
readingSoC = -1; // display "----"
readingVoltage = -1; // display "----"
}

// is it time to refresh display?
if (nowMilliseconds > nextRefreshMilliseconds) {
nextRefreshMilliseconds = nowMilliseconds + ledRefreshMilliseconds; // set the time in milliseconds for the next refresh
nextBlankMicroseconds = nowMicroseconds + ledOnMicroseconds; // set the time in microseconds for LEDs to remain on (for dimming)
// multiplexed display, so enable one digit at at time
switch (displayMode) { // according to display mode
case 1:
writeDisplayVoltage(digitSelect, readingVoltage);
break;
default:
writeDisplaySoC(digitSelect, readingSoC);
break;
}
++digitSelect; // we'll do the next digit on the next pass
if (digitSelect > ledDigits - 1 ) { // all digits done?
digitSelect = 0; // wrap around to first digit again.
}
}

// is it time to switch the LEDs off?
if (nowMicroseconds > nextBlankMicroseconds ) {
clearDisplay();
}
}

== Try it out! ==
Compile and upload the code to your Teensy board. The code isn't very complicated, so I set mine to run at 150MHz.

If you send CAN data to the specified node ID, the display should spring into life.

<YouTube></nowiki>https://youtu.be/s-Gadj3Rnxw<nowiki></youtube>

State of Charge meter using a Teensy 4.0

2021-08-10T19:49:34Z

Clanger9: Created page with "Prototype CAN SoC display This is a CAN bus state-of-charge meter based on a Teensy 4.0. Teensy's ar..."

[[File:Prototype CAN SoC display.jpg|alt=Prototype CAN SoC display|thumb|Prototype CAN SoC display]]
This is a CAN bus state-of-charge meter based on a Teensy 4.0. Teensy's aren't the cheapest boards (an STM32 is a tenth of the price), but they are tiny, have on-board CAN and are very easy to develop for.

It displays a state-of-charge or voltage value according the integer number sent over CAN bus to the configured address(es)

SoC values between 0 and 1000 will be displayed as " 0.0" to "100 ". The display flashes " 0.0" when it reaches zero. Anything else (or no data) will be displayed as "----"

Voltage values between 1 and 999 will be displayed as " 1V" to "999V ". Anything else (or no data) will be displayed as "---V"

A touch sensor allows you to toggle the display between SoC and voltage.

It includes automatic night time dimming.

== Component list ==

* Teensy 4.0 board
* SN65HVD230-based CAN transceiver
* 3461BS-1 4 digit common anode 7 segment display
* 8x 220R resistors
* Photocell
* 10k resistor
* 47uF capacitor
* TTP223 Capacitive Touch Switch

== Wiring ==
[[File:Screenshot 2021-08-10 at 20.27.30.png|alt=Teensy 4.0 connections|thumb|Teensy 4.0 connections]]
Follow the Teensy 4.0 connection schematic

# Connect the CAN transceiver to Teensy 3.3V, GND, CRX2 and CTX2
# Connect the LED D1, D2, D3 and D4 digit pins to Teensy 5, 4, 3, 2
# Connect the LED a, b, c, d, e, f, g and DP segments to Teensy 16, 17, 18, 19, 20, 21, 22, 23 via 220R resistors
# Connect the Photocell to Teensy 3.3V and A0. Connect A0 to GND via a 10k resistor and 47uF capacitor in parallel.
# Connect the Touch Switch to Teensy 3.3V, GND and 15

== Code ==
Fire up [https://www.pjrc.com/teensy/teensyduino.html Teensyduino] and paste in the following code:
// CAN bus state-of-charge meter for Teensy 4.x and 4-digit 7-segment display
// Includes automatic LED brightness control
//
// Usage: send integer number over CAN bus to configured address
// SoC values between 0 and 1000 will be displayed as " 0.0" to "100 "
// The display flashes " 0.0" when it reaches zero
// Anything else (or no data) will be displayed as "----"
// Voltage values between 1 and 999 will be displayed as " 1V" to "999V "
// Anything else (or no data) will be displayed as "---V"
// Touch selection to toggle display between SoC and voltage
//
// electric_dart 2021

// define display
// values below are for 3461BS-1 4 digit common anode 7 segment display
const int ledDigits = 4; // 4 digits
const int ledSegments = 7; // 7 segments
const int pinSegment[ledSegments] = {16, 17, 18, 19, 20, 21, 22}; // pins for a,b,c,d,e,f,g segments
const int pinDecimalPoint = 23; // pin for decimal point
const int pinDigit[ledDigits] = {5, 4, 3, 2}; // common digit pins, left to right
const boolean ledIsCommonAnode = 1; // 1=common anode 0=common cathode
const int ledRefreshHz = 100; // minimum 50Hz to avoid flicker
const int ledFlashHz = 2; // for flashing display

// define display characters
const int zero[ledSegments] = {HIGH, HIGH, HIGH, HIGH, HIGH, HIGH, LOW};
const int one[ledSegments] = {LOW, HIGH, HIGH, LOW, LOW, LOW, LOW};
const int two[ledSegments] = {HIGH, HIGH, LOW, HIGH, HIGH, LOW, HIGH};
const int three[ledSegments] = {HIGH, HIGH, HIGH, HIGH, LOW, LOW, HIGH};
const int four[ledSegments] = {LOW, HIGH, HIGH, LOW, LOW, HIGH, HIGH};
const int five[ledSegments] = {HIGH, LOW, HIGH, HIGH, LOW, HIGH, HIGH};
const int six[ledSegments] = {HIGH, LOW, HIGH, HIGH, HIGH, HIGH, HIGH};
const int seven[ledSegments] = {HIGH, HIGH, HIGH, LOW, LOW, LOW, LOW};
const int eight[ledSegments] = {HIGH, HIGH, HIGH, HIGH, HIGH, HIGH, HIGH};
const int nine[ledSegments] = {HIGH, HIGH, HIGH, LOW, LOW, HIGH, HIGH};
const int blank[ledSegments] = {LOW, LOW, LOW, LOW, LOW, LOW, LOW};
const int dash[ledSegments] = {LOW, LOW, LOW, LOW, LOW, LOW, HIGH};
const int volt[ledSegments] = {LOW, LOW, HIGH, HIGH, HIGH, LOW, LOW};
// add additional characters here if required
const int* character[13] = {zero, one, two, three, four, five, six, seven, eight, nine, blank, dash, volt};

// photocell parameters
int pinPhotocell = 14; // photocell pin
int photocellDark = 500; // adjust dark level for your photocell
int photocellLight = 1000; // adjust light level for your photocell

// touch parameters
int pinOnboardLED = 13;
int pinTouch = 15;
int touchCurrentState;
int touchLastState;

// CAN bus setup
const long canIDsoc = 0x350; // set this to match your SoC CAN bus ID
const long canIDvoltage = 0x522; // set this to match your voltage CAN bus ID
const long canSpeed = 500000; // set this to match your CAN bus speed
const long canTimeout = 10; // seconds to wait without data before showing error
#include <FlexCAN_T4.h>
FlexCAN_T4<CAN2, RX_SIZE_256, TX_SIZE_16> Can0; // Using CAN2 on pins 0 & 1

// internal variables
int ledRefreshMilliseconds = 1000 / (ledDigits * ledRefreshHz); // milliseconds
int ledOnMicroseconds; // microseconds
unsigned long nowMilliseconds;
unsigned long nowMicroseconds;
unsigned long nextRefreshMilliseconds = 0;
unsigned long nextBlankMicroseconds = 0;
unsigned long nextTimeoutMilliseconds = 0;
unsigned long nextFlashMilliseconds = 0;
boolean ledFlashState = 1;
int digitSelect = 0;
int readingSoC = -1;
int readingVoltage = -1;
int photocellReading;
int ledBrightness; // score 1 to 10
int displayMode = 0; // 0=SoC, 1=Voltage

void clearDisplay()
{
for (int i = 0; i < ledDigits; ++i)
{
digitalWrite(pinDigit[i], HIGH ^ ledIsCommonAnode);
}
}

void writeDisplayDigit(int digit, int value, boolean decimal)
// digit: numbered left-to-right, beginning at zero
// value: the character to display from character[] array
// decimal: set this to 1 to switch the decimal point on
{
for (int i = 0; i < ledSegments; ++i)
{
digitalWrite(pinSegment[i], character[value][i] ^ ledIsCommonAnode);
}
digitalWrite(pinDecimalPoint, decimal ^ ledIsCommonAnode);
digitalWrite(pinDigit[digit], LOW ^ ledIsCommonAnode);
}

void writeDisplaySoC(int digit, int value) // customise this section according to what you want to display
{
if (value == 1000) { // display "100 " if the input value is 1000
switch (digit) {
case 0:
writeDisplayDigit(0, 1, 0);
break;
case 1:
writeDisplayDigit(1, 0, 0);
break;
case 2:
writeDisplayDigit(2, 0, 0);
break;
}
}
else if (value >= 100 and value < 1000) { // display " 99 " to " 10 " for input values from 999 to 100
switch (digit) {
case 1:
writeDisplayDigit(1, value / 100, 0);
break;
case 2:
writeDisplayDigit(2, (value / 10) % 10, 0);
break;
}
}
else if (value >= 1 and value < 100) { // display " 9.9" to " 0.1" for input values from 99 to 1
switch (digit) {
case 2:
writeDisplayDigit(2, value / 10, 1);
break;
case 3:
writeDisplayDigit(3, value % 10, 0);
break;
}
}
else if (value == 0) { // display flashing " 0.0" for input value 0
if (nowMilliseconds > nextFlashMilliseconds) {
nextFlashMilliseconds = nowMilliseconds + ( 1000 / ledFlashHz );
ledFlashState = ledFlashState ^ 1;
}
if (ledFlashState == 1) {
switch (digit) {
case 2:
writeDisplayDigit(2, 0, 1);
break;
case 3:
writeDisplayDigit(3, 0, 0);
break;
}
}
else {
switch (digit) {
case 2:
writeDisplayDigit(2, 10, 1);
break;
case 3:
writeDisplayDigit(3, 10, 0);
break;
}
}
}
else { // display "----" for anything else
writeDisplayDigit(digit, 11, 0);
}
}

void writeDisplayVoltage(int digit, int value) // customise this section according to what you want to display
{
if (value >= 100 and value < 1000) { // display "100V" to "999V" for input values 100 to 999
switch (digit) {
case 0:
writeDisplayDigit(0, (value / 100) % 10, 0);
break;
case 1:
writeDisplayDigit(1, (value / 10) % 10, 0);
break;
case 2:
writeDisplayDigit(2, value % 10 , 0);
break;
case 3:
writeDisplayDigit(3, 12, 0);
break;
}
}
else if (value >= 10 and value < 100) { // display " 10V" to " 99V " for input values from 10 to 99
switch (digit) {
case 1:
writeDisplayDigit(1, value / 10, 0);
break;
case 2:
writeDisplayDigit(2, value % 10, 0);
break;
case 3:
writeDisplayDigit(3, 12, 0);
break;
}
}
else if (value >= 1 and value < 10) { // display " 1V" to " 9V " for input values from 1 to 9
switch (digit) {
case 2:
writeDisplayDigit(2, value % 10, 0);
break;
case 3:
writeDisplayDigit(3, 12, 0);
break;
}
}
else { // display "---V" for anything else
switch (digit) {
case 0:
writeDisplayDigit(0, 11, 0);
break;
case 1:
writeDisplayDigit(1, 11, 0);
break;
case 2:
writeDisplayDigit(2, 11, 0);
break;
case 3:
writeDisplayDigit(3, 12, 0);
break;
}
}
}

void setup() {
Serial.begin(9600); //initialise serial communications at 9600 bps

// Initialise CAN bus
delay(1000); // allow CAN hardware to stabilise
Can0.begin();
Can0.setBaudRate(canSpeed);
Can0.setMaxMB(16);
Can0.enableFIFO();
Can0.enableFIFOInterrupt();
Can0.onReceive(canDataReceived);
Can0.mailboxStatus();

// Initialise LED display

// segement pins
for (int i = 0; i < ledSegments; ++i)
{
pinMode(pinSegment[i], OUTPUT);
}

// decimal point pin
pinMode(pinDecimalPoint, OUTPUT);

// digit pins
for (int i = 0; i < ledDigits; ++i)
{
pinMode(pinDigit[i], OUTPUT);
}
clearDisplay();

pinMode(pinOnboardLED, OUTPUT);
pinMode(pinPhotocell, INPUT);
pinMode(pinTouch, INPUT);
touchCurrentState = digitalRead(pinTouch);

}

void canDataReceived(const CAN_message_t &msg) {
// Serial.print("MB "); Serial.print(msg.mb);
// Serial.print(" OVERRUN: "); Serial.print(msg.flags.overrun);
// Serial.print(" LEN: "); Serial.print(msg.len);
// Serial.print(" EXT: "); Serial.print(msg.flags.extended);
// Serial.print(" TS: "); Serial.print(msg.timestamp);
// Serial.print(" ID: "); Serial.print(msg.id, HEX);
// Serial.print(" Buffer: ");
// for ( uint8_t i = 0; i < msg.len; i++ ) {
// Serial.print(msg.buf[i], HEX); Serial.print(" ");
// } Serial.println();

switch (displayMode) { // according to display mode
case 1:
if (msg.id == canIDvoltage) {
// Matching voltage CAN bus frame arrived!
//readingVoltage = (msg.buf[2] << 24) | (msg.buf[3] << 16) | (msg.buf[4] << 8) | (msg.buf[5]); // now piece it together
readingVoltage = (msg.buf[6] << 8) | (msg.buf[7]); // now piece it together
nextTimeoutMilliseconds = nowMilliseconds + (canTimeout * 1000); // set next timeout
}
break;
default:
if (msg.id == canIDsoc) {
// Matching SoC CAN bus frame arrived!
readingSoC = (msg.buf[6] << 8) | (msg.buf[7]); // now piece it together
nextTimeoutMilliseconds = nowMilliseconds + (canTimeout * 1000); // set next timeout
}
break;
}
}

void loop() {

// add extra code here

// pot input for testing without CAN bus
//reading = analogRead(pin_pot);
//reading = map(reading, 10, 1023, 0, 1000);

touchLastState = touchCurrentState;
touchCurrentState = digitalRead(pinTouch);
if(touchLastState == LOW && touchCurrentState == HIGH) {
// toggle display
displayMode = !displayMode;
// control LED arccoding to the toggled state
digitalWrite(pinOnboardLED, displayMode);
}
//
//

Can0.events();

// take a timestamp
nowMilliseconds = millis();
nowMicroseconds = micros();

// calculate required LED brightness score (1-10) and set time to remain on (in microseconds) as a proportion of the refresh interval
photocellReading = analogRead(pinPhotocell);
photocellReading = constrain(photocellReading, photocellDark, photocellLight);
ledBrightness = map(photocellReading, photocellDark, photocellLight, 1, 10);
ledOnMicroseconds = ledBrightness * ledRefreshMilliseconds * 100; // microseconds

// timeout if no data received
if (nowMilliseconds > nextTimeoutMilliseconds) {
readingSoC = -1; // display "----"
readingVoltage = -1; // display "----"
}

// is it time to refresh display?
if (nowMilliseconds > nextRefreshMilliseconds) {
nextRefreshMilliseconds = nowMilliseconds + ledRefreshMilliseconds; // set the time in milliseconds for the next refresh
nextBlankMicroseconds = nowMicroseconds + ledOnMicroseconds; // set the time in microseconds for LEDs to remain on (for dimming)
// multiplexed display, so enable one digit at at time
switch (displayMode) { // according to display mode
case 1:
writeDisplayVoltage(digitSelect, readingVoltage);
break;
default:
writeDisplaySoC(digitSelect, readingSoC);
break;
}
++digitSelect; // we'll do the next digit on the next pass
if (digitSelect > ledDigits - 1 ) { // all digits done?
digitSelect = 0; // wrap around to first digit again.
}
}

// is it time to switch the LEDs off?
if (nowMicroseconds > nextBlankMicroseconds ) {
clearDisplay();
}
}

File:Prototype CAN SoC display.jpg

2021-08-10T19:41:29Z

Clanger9:

Prototype CAN SoC display

File:Screenshot 2021-08-10 at 20.27.30.png

2021-08-10T19:29:57Z

Clanger9:

Teensy 4.0 connections

File:Teensy 4.0 connections.png

2021-08-10T19:25:26Z

Clanger9:

Teensy 4.0 connections

Getting started with CAN bus

2021-08-10T19:05:47Z

Clanger9: /* I want to build a CAN bus device... */

This page will help get you started with CAN bus.

Some people will tell you CAN is hard or complicated. They're wrong. The hardware you need isn't expensive and you don't need to be a programming whiz. Even Damien can do it.

<youtube>https://youtu.be/K4HwHQOluSg</youtube>

There are a few routes you can take, depending on what you want to do:

== I want to receive or send simple CAN bus messages... ==
If you already know which CAN bus messages you want to send or receive, one of the cheapest ways to do this is with an [[Getting started with CAN bus and an Arduino Uno|Arduino Uno and a suitable CAN bus shield]].

== I want to analyse CAN bus traffic and possibly do some serious hacking... ==
If you want to analyse CAN bus messages on an existing vehicle, you'll need the help of some software. You can use the free [https://www.savvycan.com SavvyCAN software] together with a [[CAN bus with Arduino Due|suitably configured Arduino Due]] or [[Getting CAN working on a Teensy 3.6|Teensy]]. Alternatively, you can buy a [http://store.evtv.me/proddetail.php?prod=ArduinoDueCANBUS pre-configured Due-based kit from EVTV].

<youtube>https://www.youtube.com/watch?v=MsrXs-tJKaY</youtube>

== I want to build a CAN bus device... ==
Once you've got your CAN messages sorted, you can build a dedicated device to send or receive those messages. For example, you could build a custom battery gauge. Or add a touch screen controller. Anything is possible! If you want, you can just use the Arduino hardware described above. Alternatively, something small and reasonably robust like a [https://www.pjrc.com/teensy/techspecs.html Teensy 3.x] might be a better choice for a permanent solution.

Here's a quick-start guide to [[getting CAN working on a Teensy 3.6]].

Here's a simple CAN bus [[State of Charge meter using a Teensy 4.0]].

CAN bus with Arduino Due

2021-02-11T20:59:00Z

Clanger9:

You can analyse CAN bus traffic using an Arduino Due.

You will need the following:
* An Arduino Due board
* Two SN65HVD230-based CAN transceivers
* An SPI Micro SD storage module (optional)
Here are the steps:

== Configure your Arduino IDE ==
Download and install the [https://www.arduino.cc/en/Main/Software Arduino IDE] on your computer

''Tools -> Board -> Boards Manager''. Type "due" in the search box and install "Arduino SAM Boards (32-bits ARM Cortex-M3)"

Connect your computer to the "native" USB port on the Arduino Due board with a USB cable. The Due has two USB ports and they're used for different purposes.

Make sure your Arduino board is selected with ''Tools -> Board: "Arduino Due (Native USB port)"''

''File -> Examples -> 01.Basics -> Blink''

''Sketch -> Upload''

Push the reset button on your Due. You should now see a blinking light. Congratulations! You've successfully compiled and loaded your first program and your IDE is working.
== Get CAN transceivers working ==
The Due has two on-board CAN interfaces. However, the board lacks the necessary CAN transceivers to make then useful. You will need to add the transceivers yourself. You can find suitable 3.3V SN65HVD230-based CAN transceivers easily on eBay. They are very cheap. Unfortunately, not all of them work.
[[File:SN65HVD230 CAN bus transceiver faulty.jpg|thumb|This SN65HVD230 transceiver did not work]]
Initially, I tried tiny ones that look like this. They were all faulty.
[[File:SN65HVD230 CAN bus transceiver working.jpg|thumb|This SN65HVD230 transceiver worked]]
I tried some bigger ones with screw terminals. These all worked perfectly.

Connect your transceivers to the Due board

The CAN0 interface is on the pins marked CANRX and CANTX

The CAN1 interface is on the pins marked DAC0 (RX) and 53 (TX)
[[File:Due CAN loopback test.jpg|alt=Due CAN loopback test|thumb|Due CAN loopback test]]
Connect the CAN bus on the two transceivers together (CANL to CANL, CANH to CANH)

Connect your computer to the the "native" USB port on the Arduino Due board with a USB cable and make sure ''Tools -> Board: "Arduino Due (Native USB port)"'' is selected.

''Tools -> Manage Libraries...'' Type "due_can" in the search box and install "due_can"

''File -> Examples -> due_can -> CAN_ExtendedPingPong''

''Sketch -> Upload''

''Tools -> Serial Monitor''

If your CAN transceivers are working properly, you should be rewarded with incrementing numbers in the serial monitor window.

== Install GV-RET ==
Once you've confirmed that your CAN transceivers are working, you can move on to installing the [https://github.com/collin80/GVRET Generalized Electric Vehicle Reverse Engineering Tool (GV-RET)]. This software will allow your Due CAN transceivers to talk to SavvyCAN.

You need to install a number of libraries (in addition to the due_can library installed in the last section). These are all linked to on the GV-RET website, but a couple of them may not work properly if you install them via that method. I recommend you install the following via the Arduino IDE Library Manager with ''Tools -> Manage Libraries...'' :
* SdFat
* DueFlashStorage
Now install the remaining libraries manually. In each case, the installation procedure is:
# Download the .zip file
# Rename the file to remove "-master" or any other postfixes. This is important!
# Install the library with ''Sketch -> Include Library -> Add .ZIP Library...'' and select the file.
You need all of these:
* [https://github.com/collin80/due_can due_can]
* [https://github.com/collin80/can_common can_common]
* [https://github.com/macchina/mcp2515 MCP2515]
* [https://github.com/collin80/due_wire due_wire]
* [https://github.com/collin80/Wire_EEPROM Wire_EEPROM]
Once the libraries are all installed, you can install GV-RET. Go to the [https://github.com/collin80/GVRET GitHub webpage], and click on Code -> Download .ZIP.

Expand the .zip file and put the folder in your Arduino sketchbook location. Open the GV-RET project and install it as follows:

''File -> Open -> GVRET.ino''

''Sketch -> Upload''

''Tools -> Serial Monitor''

If it doesn't compile and complains about missing libraries or headers, check the folder names in the Library folder. Remove any "-master" suffixes from the folder names. The folder names should match the library names listed above.

If everything worked, you should be rewarded with the following messages in the serial console:

<code>Resetting to factory defaults</code>

<code>Using stored values for digital toggling system</code>

<code>Running on CANDue hardware</code>

<code>11977 - ERROR: Could not initialize SDCard! No file logging will be possible!</code>

<code>Build number: 343</code>

<code>Done with init</code>

Congratulations! Your Due is now a powerful CAN sniffer and injection tool. You can connect the CAN-H and CAN-L terminals of a CAN bus transceiver to the CAN bus in your vehicle.

== Add logging to SD card (optional) ==
You may have noticed the error message about the SD card. If you have an SPI SD card storage module, your Due will log CAN traffic to this for later analysis. This is ideal if you don't want to have to drive around with a laptop on the passenger seat...

The SD card module needs to be connected to the SPI header (in the middle of the Due board), plus one additional wire to data line 10.
[[File:Due SPI pins.png|alt=Due SPI pins|thumb|Due SPI pins]]
Here are the connections:
{| class="wikitable"
|+SD module wiring
!Pin on Due
!Pin on SD module
|-
|SPI MISO
|MISO
|-
|SPI SCK
|SCK
|-
|SPI VCC
|VCC
|-
|SPI MOSI
|MOSI
|-
|SPI GND
|GND
|-
|10
|CS
|}
The SD module can be a bit finicky. The GV-RET software defaults to running the SPI bus at 50MHz, but this didn't work for me. So you will need to do a bit of tweaking to fix this.

First of all, check your SD card is working with File -> Examples -> SdFat -> QuickStart. Connect your Due to the '''Programming USB Port''' (not the Native USB Port) and upload the program. In the serial console, it will ask for the CS pin. Enter '10'. You should see a little report in the serial console that shows it is working.

It may say you need to reformat your SD card. To do this, go to File -> Examples -> SdFat -> SdFormatter. Edit the source code to set the CS pin to 10 and limit SD clock speed to 4MHz:
const uint8_t chipSelect = 10;

#define SPI_SPEED SD_SCK_MHZ(4)
Upload the program and follow the instructions to format your SD card.

Now go to your GVRET code. Add this line after the line 'SdFat sd;' :
#define SPI_SPEED SD_SCK_MHZ(4)
Find the line 'if (!sd.begin(SysSettings.SDCardSelPin, SPI_FULL_SPEED)) {' and change it to:
if (!sd.begin(SysSettings.SDCardSelPin, SPI_SPEED)) {
[[File:Due CAN bus logger with SD card storage.jpg|alt=Due CAN bus logger with SD card storage|thumb|Due CAN bus logger with SD card storage]]
That should be enough to get it working. Upload the sketch (this time using the '''Native USB Port''') and you should be rewarded with:

<code>Resetting to factory defaults</code>

<code>Using stored values for digital toggling system</code>

<code>Running on CANDue hardware</code>

<code>Build number: 343</code>

<code>Done with init</code>

At least the error message is gone. So far I haven't managed to get it to log anything to the SD card. It may be the GV-RET configuration needs to be tweaked...

== Get started with SavvyCAN ==

SavvyCAN is a free, open source tool for analysing CAN traffic. Download and install it on your computer.
It can be a bit intimidating, so here's a 30 minute tutorial to help you find your feet:

<youtube>kdA5Gdf3FAk</youtube>

If you're too impatient to sit through a tutorial, just dive straight in and connect to your Due. Go back to the Arduino IDE and note down the name of your Due's USB connection. On my Mac, it's "/dev/cu.usbmodem2441". You're now finished with the Arduino IDE, so quit it just in case it interferes with the next step...

In SavvyCAN:

''Connection -> Open Connection Window''

''Add New Device Connection'' and select the USB connection you noted earlier

''Create New Connection''

Check "Enable Bus" and set the Speed to match your CAN bus. 500000 is a good guess. You can always change it later.

After a few seconds, you should see "Connected" in the Status field. If it doesn't connect, try pushing the reset button on your Due or click "Reset Selected Device" in SavvyCAN.

Now on to the fun part...
== Start hacking ==
Feel free to add SavvyCAN examples here.

I will add something on my Ampera BMS (once I figure out an easy way to connect to the CAN bus...)

CAN bus with Arduino Due

2021-02-11T08:01:04Z

Clanger9: Add further guidance on missing libraries

You can analyse CAN bus traffic using an Arduino Due.

You will need the following:
* An Arduino Due board
* Two SN65HVD230-based CAN transceivers
* An SPI Micro SD storage module (optional)
Here are the steps:

== Configure your Arduino IDE ==
Download and install the [https://www.arduino.cc/en/Main/Software Arduino IDE] on your computer

''Tools -> Board -> Boards Manager''. Type "due" in the search box and install "Arduino SAM Boards (32-bits ARM Cortex-M3)"

Connect your computer to the "native" USB port on the Arduino Due board with a USB cable. The Due has two USB ports and they're used for different purposes.

Make sure your Arduino board is selected with ''Tools -> Board: "Arduino Due (Native USB port)"''

''File -> Examples -> 01.Basics -> Blink''

''Sketch -> Upload''

Push the reset button on your Due. You should now see a blinking light. Congratulations! You've successfully compiled and loaded your first program and your IDE is working.
== Get CAN transceivers working ==
The Due has two on-board CAN interfaces. However, the board lacks the necessary CAN transceivers to make then useful. You will need to add the transceivers yourself. You can find suitable 3.3V SN65HVD230-based CAN transceivers easily on eBay. They are very cheap. Unfortunately, not all of them work.
[[File:SN65HVD230 CAN bus transceiver faulty.jpg|thumb|This SN65HVD230 transceiver did not work]]
Initially, I tried tiny ones that look like this. They were all faulty.
[[File:SN65HVD230 CAN bus transceiver working.jpg|thumb|This SN65HVD230 transceiver worked]]
I tried some bigger ones with screw terminals. These all worked perfectly.

Connect your transceivers to the Due board

The CAN0 interface is on the pins marked CANRX and CANTX

The CAN1 interface is on the pins marked DAC0 (RX) and 53 (TX)
[[File:Due CAN loopback test.jpg|alt=Due CAN loopback test|thumb|Due CAN loopback test]]
Connect the CAN bus on the two transceivers together (CANL to CANL, CANH to CANH)

Connect your computer to the the "native" USB port on the Arduino Due board with a USB cable and make sure ''Tools -> Board: "Arduino Due (Native USB port)"'' is selected.

''Tools -> Manage Libraries...'' Type "due_can" in the search box and install "due_can"

''File -> Examples -> due_can -> CAN_ExtendedPingPong''

''Sketch -> Upload''

''Tools -> Serial Monitor''

If your CAN transceivers are working properly, you should be rewarded with incrementing numbers in the serial monitor window.

== Install GV-RET ==
Once you've confirmed that your CAN transceivers are working, you can move on to installing the [https://github.com/collin80/GVRET Generalized Electric Vehicle Reverse Engineering Tool (GV-RET)]. This software will allow your Due CAN transceivers to talk to SavvyCAN.

You need to install a number of libraries (in addition to the due_can library installed in the last section). These are all linked to on the GV-RET website, but a couple of them may not work properly if you install them via that method. I recommend you install the following via the Arduino IDE Library Manager with ''Tools -> Manage Libraries...'' :
* SdFat
* DueFlashStorage
Now install the remaining libraries manually. In each case, the installation procedure is:
# Download the .zip file
# Rename the file to remove "-master" or any other postfixes. This is important!
# Install the library with ''Sketch -> Include Library -> Add .ZIP Library...'' and select the file.
You need all of these:
* [https://github.com/collin80/due_can due_can]
* [https://github.com/collin80/can_common can_common]
* [https://github.com/macchina/mcp2515 MCP2515]
* [https://github.com/collin80/due_wire due_wire]
* [https://github.com/collin80/Wire_EEPROM Wire_EEPROM]
Once the libraries are all installed, you can install GV-RET. Go to the [https://github.com/collin80/GVRET GitHub webpage], and click on Code -> Download .ZIP.

Expand the .zip file and put the folder in your Arduino sketchbook location. Open the GV-RET project and install it as follows:

''File -> Open -> GVRET.ino''

''Sketch -> Upload''

''Tools -> Serial Monitor''

If it doesn't compile and complains about missing libraries or headers, check the folder names in the Library folder. Remove any "-master" suffix from the folder names.

If everything worked, you should be rewarded with the following messages in the serial console:

<code>Resetting to factory defaults</code>

<code>Using stored values for digital toggling system</code>

<code>Running on CANDue hardware</code>

<code>11977 - ERROR: Could not initialize SDCard! No file logging will be possible!</code>

<code>Build number: 343</code>

<code>Done with init</code>

Congratulations! Your Due is now a powerful CAN sniffer and injection tool. You can connect the CAN-H and CAN-L terminals of a CAN bus transceiver to the CAN bus in your vehicle.

== Add logging to SD card (optional) ==
You may have noticed the error message about the SD card. If you have an SPI SD card storage module, your Due will log CAN traffic to this for later analysis. This is ideal if you don't want to have to drive around with a laptop on the passenger seat...

The SD card module needs to be connected to the SPI header (in the middle of the Due board), plus one additional wire to data line 10.
[[File:Due SPI pins.png|alt=Due SPI pins|thumb|Due SPI pins]]
Here are the connections:
{| class="wikitable"
|+SD module wiring
!Pin on Due
!Pin on SD module
|-
|SPI MISO
|MISO
|-
|SPI SCK
|SCK
|-
|SPI VCC
|VCC
|-
|SPI MOSI
|MOSI
|-
|SPI GND
|GND
|-
|10
|CS
|}
The SD module can be a bit finicky. The GV-RET software defaults to running the SPI bus at 50MHz, but this didn't work for me. So you will need to do a bit of tweaking to fix this.

First of all, check your SD card is working with File -> Examples -> SdFat -> QuickStart. Connect your Due to the '''Programming USB Port''' (not the Native USB Port) and upload the program. In the serial console, it will ask for the CS pin. Enter '10'. You should see a little report in the serial console that shows it is working.

It may say you need to reformat your SD card. To do this, go to File -> Examples -> SdFat -> SdFormatter. Edit the source code to set the CS pin to 10 and limit SD clock speed to 4MHz:
const uint8_t chipSelect = 10;

#define SPI_SPEED SD_SCK_MHZ(4)
Upload the program and follow the instructions to format your SD card.

Now go to your GVRET code. Add this line after the line 'SdFat sd;' :
#define SPI_SPEED SD_SCK_MHZ(4)
Find the line 'if (!sd.begin(SysSettings.SDCardSelPin, SPI_FULL_SPEED)) {' and change it to:
if (!sd.begin(SysSettings.SDCardSelPin, SPI_SPEED)) {
[[File:Due CAN bus logger with SD card storage.jpg|alt=Due CAN bus logger with SD card storage|thumb|Due CAN bus logger with SD card storage]]
That should be enough to get it working. Upload the sketch (this time using the '''Native USB Port''') and you should be rewarded with:

<code>Resetting to factory defaults</code>

<code>Using stored values for digital toggling system</code>

<code>Running on CANDue hardware</code>

<code>Build number: 343</code>

<code>Done with init</code>

At least the error message is gone. So far I haven't managed to get it to log anything to the SD card. It may be the GV-RET configuration needs to be tweaked...

== Get started with SavvyCAN ==

SavvyCAN is a free, open source tool for analysing CAN traffic. Download and install it on your computer.
It can be a bit intimidating, so here's a 30 minute tutorial to help you find your feet:

<youtube>kdA5Gdf3FAk</youtube>

If you're too impatient to sit through a tutorial, just dive straight in and connect to your Due. Go back to the Arduino IDE and note down the name of your Due's USB connection. On my Mac, it's "/dev/cu.usbmodem2441". You're now finished with the Arduino IDE, so quit it just in case it interferes with the next step...

In SavvyCAN:

''Connection -> Open Connection Window''

''Add New Device Connection'' and select the USB connection you noted earlier

''Create New Connection''

Check "Enable Bus" and set the Speed to match your CAN bus. 500000 is a good guess. You can always change it later.

After a few seconds, you should see "Connected" in the Status field. If it doesn't connect, try pushing the reset button on your Due or click "Reset Selected Device" in SavvyCAN.

Now on to the fun part...
== Start hacking ==
Feel free to add SavvyCAN examples here.

I will add something on my Ampera BMS (once I figure out an easy way to connect to the CAN bus...)

Batteries

2021-02-10T17:18:49Z

Clanger9:

== Introduction ==
There are a wide variety of battery chemistries available for use as the main traction battery of an EV. To use each chemistry safely, and to ensure an adequate service life from the battery pack it is important to understand the requirements for the chemistry you are using. Failure to do so may lead to premature or catastrophic failure of the pack.

Good pack design will allow for a nominal amount of abuse. People make mistakes and the pack should allow a margin for safety - and for longevity!

== Battery pack specification ==
When deciding on your battery pack, here are some basic parameters to consider:

=== Capacity (kWh) ===
'''How far do you want to go?''' A standard car conversion will need a kWh for each 3, maybe 4 miles of range (very approximately). For a middleweight motorcycle, a kWh should give around 9 miles. Your mileage may vary, ''as they say.''

=== Voltage (V) ===
'''How fast do you want to go?''' The pack voltage defines the maximum speed your motor can spin. Motors are usually specified with "KV" - or RPM-per-volt. Check the KV of your motor and how fast it needs to spin to get your desired top speed. e.g. if you need 3,000 RPM from a 25 KV motor then your pack voltage needs to be 3,000 / 25 = 120 V. The exact number of cells in series you need depends on the cell design, but 3.8 V for Li-ion and 3.2 V for LiFePO4 is a reasonable guess.

=== Maximum current (A) ===
'''How quickly do you want to accelerate?''' Your motor's maximum power will be specified in kW. To estimate your maximum current draw, divide the peak power by the battery voltage. e.g. a 30 kW motor with a 120 V battery pack will pull 30,000 / 120 = 250 A. The higher the current rating of the cells, the heavier they will be for a given capacity. Ideally, you want "enough" current capacity for full throttle acceleration, but no more. You can put cells in parallel to double the current rating of your pack (which of course will half the voltage). Running cells in parallel is easy, but don't attempt to parallel battery packs unless you really know what you are doing. It's [https://www.orionbms.com/manuals/pdf/parallel_strings.pdf complicated].

=== Mass (kg) ===
'''Can your vehicle carry the weight?''' You'll need to keep the kerb weight within the original design limits. For a car, your pack could be a few hundred kg. For a motorcycle, likely less than 100 kg. This is a huge variable - and each new generation of battery tech seems to be a little lighter. For older EV or hybrid batteries, you can reckon on approximately 10 kg/kWh. Nissan Leaf batteries are relatively light (7.5 kg/kWh). With the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 5-6 kg/kWh.

=== Volume (L) ===
'''Will it fit?''' Batteries are bulky. They are getting smaller, but finding enough space might be your biggest challenge. You could be looking at over 5 L/kWh for older EV or hybrid batteries. Current state-of-the-art is the Tesla Model 3, which gets this down to 2.5 L/kWh by using 2170 cylindrical cells.

There is much, much more to battery design than this (e.g. maximum charge rate, terminations, cooling, clamping), but the above should help work out which options will or won't work for your project...

== Cell chemistry ==

=== Lithium Iron Phosphate (LiFePO4) ===
Lithium Iron Phosphate (also known as LFP, or LiFePO4) batteries offer a good compromise between safety, energy density and ease of use for DIY conversions. They are available in a number of formats, commonly pouch cells, prismatic cells and cylindrical cells.

==== LiFePO4 pouch cells ====
The majority of this content is drawn from this thread: [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761&start=900 https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761] discussing the use of the A123 20Ah pouch cell. However, many of the general points apply equally to other similar pouch cells.

===== General build requirements =====
Pouch cells are vulnerable to damage from debris, and must be held in compression (see the datasheet for your battery, but 10-12 psi is recommended for the A123 pouch cells as a guide). A rigid container capable of preventing damage and providing compression is therefore required. Be aware the cells expand and contract in use, so allowance for this must be included in the structure of the case.

The pouch cells should be separated to prevent abrasion between cells, and also to avoid the development of hot spots. Prebuilt modules from A123 systems had thin foam sheets or heatsinks between each cell. Be sure to avoid any debris that could rub on the pouch surface, particularly if using recycled cells.

Mylar, '[https://www.americanmicroinc.com/fish-paper/ Fish paper]' or a [https://www.rogerscorp.com/elastomeric-material-solutions/poron-industrial-polyurethanes compliant foam] may be appropriate materials to serve this purpose. This material should not be flammable. If the material is heat insulating, it is important to address thermal management.

===== Compression =====
Compression is required to prevent premature failure of the cell. Without compression electrolyte will become unevenly distributed, causing current gradients in the cell and uneven heating. Local temperatures can become high enough to form gas formation leading to cells 'puffing up' even when the pack is otherwise held within temperature and voltage constraints. This will be exacerbated in packs with otherwise poor thermal management. Compression forces gas generated to the margins of the cell, outside of the cell stack, minimising its effect cell performance. Gas in the middle cells will create a dead space which does not store or release energy.

There is ~1% expansion through a discharge cycle. As the cell ages, the nominal cell thickness can grow by 3-5%. For A123 cells the ideal pressure is between 4 and 18psi with the ideal pressure being ~12psi. Maintaining 12psi can increase the life by 500 cycles over that of 4 or 18psi

There is some suggestion that in uses where 1C is never exceeded compression ''may'' not be required.

Highly rigid endplates with a mechanism to allow for a limited degree of expansion (e.g. steel bands) are considered an effective solution to this challenge.

It should be noted that compression is a challenge specific to pouch cells. Cylindrical cells are designed to maintain their own compression within the cell's electrode stack by their design.

This thread provides more information and experimentation relating to pack compression: <nowiki>https://endless-sphere.com/forums/viewtopic.php?f=14&t=52244</nowiki>

===== Pouch Cell Pack Design Examples =====
<nowiki>*</nowiki>placeholder*

===== Notes regarding recycled pouch cells =====
Pouch cells are somewhat fragile, and breaching the insulation is not difficult, especially in a cells removed from existing packs and repurposed. If the pouch has had their poly-layers compromised you may see a number of faults:
* Black spots around the perimeter of the cell indicate electrolyte leakage
* Voltage on the outside of the bag. Note that microvoltage between the pouch and the electrode is normal (and due to a capacitive effect).
While the majority of these cells should no longer be in the market, a significant number of faulty cells made it back into the 'greymarket' in around 2013. These cells had misaligned tabs which can also lead to isolation failures between the tab and the pack. These cells should be avoided, particularly in high demand applications.

===== Situations likely to cause pouch cell failure =====
''Taken directly from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''
# '''Overcharge'''. Any extended time above 3.8 Volts will generate enough heat and electrochemical activity to puff a cell, especially one that is improperly compressed.
# '''Overdischarge followed by charge'''. Any A123 cell that has been pulled low enough to come to rest at <300 mV should be immediately scrapped. The published number for that is 500 mV, but the real figure is closer to 300, so that's a "safety buffer" if you will. Below this Voltage, the Cu electrodes start to dissolve into the electrolyte. When charge is applied, the Cu forms dendrites that puncture the separator layer, forming an internal short in the cell. This can puff a cell in a hurry---the more charge current on tap, the worse it's prone to be.
# '''Driving a cell negative'''. I've neglected to mention this before, but it is a possibility. I don't know much about the specific mechanism at this time.
# '''Malfunctioning or misinformed electronics'''. This is the most common cause of all of the above in my experience. At this stage of the game, it is critical for YOU to understand how your BMS functions on at least a cursory level. Choose your BMS very carefully and periodically verify that it is operating properly. They're not all created equal. Make sure V sense lines are securely connected and free of corrosion. Just because your BMS says there was never a problem doesn't necessarily make it so. Avoid harnesses or ribbon cables between multiple modules if possible--they are problematic wherever they are used in any mobile electronics.
# '''Exposure to or generation of sufficient heat'''. I don't know exactly at what temperature gas formation begins in the electrolyte, but we spec a max storage temp of 80 (or 85?) degrees C and I suspect this is the reason. The hotter, the puffier--to a point. This is why soldering tabs poses a real hazard to cell health. If you feel you must solder, sink or blow the heat away from the body of the cell. Use a big iron that can make sufficient local heat quickly, before the whole mass of the cell gets hot. You might even get the cell warm enough to melt separator if not careful.
# '''No compression, not enough compression, improperly distributed compression'''. This is a pack/module design issue. Apply 10, maybe 15 psi to your cell stack end to end and then band snugly and evenly. Use hard endplates of some sort--never wrap cells directly or allow their shape to become distorted. Protect all areas of the pouch from impact damage. This obviously does not apply to cylindrical cells.

==== LiFePO4 prismatic cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cylindrical cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cell ageing ====
''Derived (barely paraphrased) from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''

Capacity loss is caused by the lithium that was available for storage becoming permanently plated on the cathode. Being unable to move within the cell it is no longer available to store energy. The impact of this plating is greater than the amount of lithium 'lost' to plating because not only is the lithium no longer available, it is also preventing access to that part of the cathode meaning Li that can still move has to take a longer path to reach the cathode. Lithium plating is one cause of increased cell resistance (there are others), a sign of worsening cell health.

There is no linear relationship between actual capacity loss and impedance rise. However some cell defects will also increase impedance.

Increasing cell resistance may cause a number of symptoms which may be confused with [https://earthshipbiotecture.com/a-lithium-ion-battery-primer/ High Self Discharge.]
# Elevated Peukert Losses. As more energy per amount of current through the cell is lost as heat, the cells useable capacity decreases. So the apparent capacity loss is higher than the actual capacity loss of cycleable lithium. When used in low current applications (e.g. solar energy storage) the actual and apparent decrease in capacity will be small. In high current draw applications (like EV traction packs), the Peukert loss increases proportionally, so the apparent capacity loss increases much faster than the actual capacity loss.
# Greater voltage excursion under the same load. Due to increased cell resistancethe voltage will sag further under the same load than a cell in optimal condition. The inverse is also true, the voltage will be higher for the same amount of charging current applied. The cell will then rebound to a voltage further from the loaded and charging voltages. This, obviously, can look like high self discharge but is a different phenomenon.
# Absolute maximum current decrease.
Elevated impedance causes a more complex constellation of symptoms, some of which may be easy to confuse with High Self Discharge (HSD). Ohm's law (E=I/R) holds the key to understanding here.

'''1) Elevated Peukert losses.''' Because more energy per unit of current through the cell is lost as heat, less of the cell's capacity is actually USABLE. Thus, apparent capacity loss can be significantly greater than actual capacity loss caused by the loss of cycleable Li alone. In low current applications, the two numbers will be close together. In high current applications, Peukert losses increase in proportion, so apparent loss of capacity breaks further and further away from actual capacity loss as current increases.

'''2) Greater voltage excursion under the same load.''' Elevated resistance across the cell means that voltage will sag more under the same load than it did when the cell was healthier. Conversely, voltage will rise higher with the same amount of applied charge current than it did when it was healthier. At the same time, rebound/settling voltages will be further away from loaded/charging voltages. In other words, the cell will rebound to a voltage further away from loaded voltage, all else being equal. Similarly, voltage will settle farther from the charge voltage with the same charge applied. This can give the illusion of elevated self-discharge, but the phenomenon is actually not the same thing. Again, the greater the charge and load currents, the greater the effect becomes.

'''3) Absolute max current decreases.''' Because the cell's series resistance is elevated, the maximum possible current through the cell is decreased.

Just to confuse things further, there can be many factors that lead to impedance rise. Some are related to Li plating, others are not.

=== Lithium-ion ===
Lithium-ion (Li-ion) batteries have a greater energy density than Lithium Iron Phosphate batteries, but have more challenging needs to use safely. The ideal operating range of Li-ion batteries is between +15 and +45°C. The upper limit of temperature is particularly important as Li-ion batteries experience thermal runaway - an unstoppable chain reaction that can occur in milliseconds releasing the stored energy in the cell. This can produce temperatures of 400°C and a fire that is extremely difficult to put out. Thermal runaway can start as low as 60°C and becomes much more likely at 100°C

Risk factors for thermal runaway:
* Short Circuits - either internally or externally
* Overcharging
* Excessive current draw or when charging

==== Li-ion pouch cells ====
[https://kokam.com/cell Kokam] produce high-performance Li-ion pouch cells. These combine relative ease of use and pack construction with performance close to cylindrical cells.

==== Li-ion 18650 and other cylindrical cells ====
Cylindrical cells are favoured by Tesla, and are probably the main reason why their cars achieve such excellent performance. They are light, compact, powerful and expensive. Unfortunately, cylindrical cells are difficult (and potentially dangerous) to use in DIY conversions. There are two good reasons for this: thermal management and cell configuration.

As stated above, Li-ion cells are prone to thermal runaway. So you need perfect battery and thermal management to ensure that no cell ever exceeds the critical voltage or temperature. If this happens, a cell can short-circuit internally, releasing a lot of energy - potentially explosively. Furthermore, the individual cells are small, so need to be arranged in parallel. In the case of the Tesla Model S 85kW pack, there are 74 cells in parallel. Imagine if one of those cells fails and becomes short circuited internally. You now have 73 very high power cells all feeding in to that short circuit...

In fact, you don't have to imagine: you can watch this famous video instead (courtesy of Rich Rebuilds).

<youtube>WdDi1haA71Q</youtube>

== OEM modules ==
Using an OEM module means a lot of the difficulties and safety issues associated with battery design are taken care of e.g. cooling, clamping, etc.

Here is a handy list of OEM modules:
{| class="wikitable sortable mw-collapsible"
|+
!Manufacturer
!Model
!Capacity (kWh)
!Weight (kg)
!w (mm)
!d (mm)
!h (mm)
!Gravity (kg/kWh)
!Volume (L/kWh)
!Voltage (V)
!Current (cont A)
!Current (peak A)
!Cell arrangement
!Cell type
!Chemistry
|-
|Tesla
|Model S 85kWh
|5.3
|26
|690
|315
|80
|4.9
|3.3
|22.8
|500
|750
|74p6s
|18650
|Li-ion
|-
|Tesla
|Model S 100kWh
|6.4
|28
|680
|315
|80
|4.4
|2.7
|22.8
|
|870
|86p6s
|18650
|Li-ion
|-
|Tesla
|Model 3 LR (inner)
|19.2
|98.9
|1854
|292
|90
|5.2
|2.5
|91.1
|
|971
|46p25s
|2170
|Li-ion
|-
|Tesla
|Model 3 LR (outer)
|17.7
|86.6
|1715
|292
|90
|4.9
|2.5
|83.9
|
|971
|46p23s
|2170
|Li-ion
|-
|Tesla
|Model 3 SR (inner)
|13.0
|
|1854
|292
|90
|
|3.7
|91.1
|
|603
|31p25s
|2170
|Li-ion
|-
|Tesla
|Model 3 SR (outer)
|12.0
|
|1715
|292
|90
|
|3.8
|83.9
|
|603
|31p23s
|2170
|Li-ion
|-
|Calb
|4S3P
|2.19
|12
|355
|151
|108
|5.5
|2.6
|14.6
|
|900
|3p4s
|Pouch
|Li-ion
|-
|Calb
|6S2P
|2.19
|12
|355
|151
|108
|5.5
|2.6
|22.2
|
|600
|2p6s
|Pouch
|Li-ion
|-
|Chevrolet
|Volt 2012
|4
|38
|470
|180
|280
|9.5
|5.9
|88.8
|
|676
|3p24s
|Pouch
|Li-ion
|-
|BMW
|i3 60Ah
|2
|13
|368
|178
|102
|6.5
|3.3
|28.8
|210
|350
|2p8s
|Prismatic
|Li-ion
|-
|BMW
|i3 94Ah
|4.15
|28
|410
|310
|150
|6.7
|4.6
|45.6
|
|409
|12s
|Prismatic
|Li-ion
|-
|BMW
|i3 120Ah
|5.3
|28
|410
|310
|150
|5.3
|3.6
|45.6
|
|360
|12s
|Prismatic
|Li-ion
|-
|Jaguar
|iPace
|2.5
|12
|340
|155
|112
|4.8
|2.4
|10.8
|720
|1200
|4p3s
|Pouch
|Li-ion
|-
|LG
|4P3S
|2.6
|12.8
|357
|151
|110
|4.9
|2.3
|11
|
|
|4p3s
|Pouch
|Li-ion
|-
|Mitsubishi
|Outlander
|2.4
|26
|646
|184
|130
|10.8
|6.4
|60
|
|240
|16s
|
|Li-ion
|-
|Nissan
|Leaf 24kWh
|0.5
|3.65
|300
|222
|34
|7.3
|4.5
|7.2
|130
|228
|2p2s
|Pouch
|Li-ion LMO
|-
|Nissan
|Leaf 30kWh
|1.25
|
|300
|222
|34
|
|3.6
|14.4
|
|
|2p4s
|Pouch
|Li-ion
|-
|Nissan
|Leaf 40kWh
|1.6
|8.7
|300
|222
|68
|5.4
|2.8
|14.4
|
|314
|2p4s
|Pouch
|Li-ion NMC
|-
|Nissan
|Leaf 62kWh
|2.58
|
|
|
|
|
|
|14.4
|
|
|3p4s
|
|Li-ion
|-
|Volvo
|XC90 T8
|2.01
|12.1
|300
|180
|150
|6.0
|4.0
|59.2
|170
|340
|16s
|
|Li-ion
|-
|VW
|[[VW Hybrid Battery Packs|Passet GTE]]
|
|23.4
|
|
|
|
|
|
|
|
|24s
|
|
|-
|VW
|[[VW Hybrid Battery Packs|Golf GTE]]
|
|
|
|
|
|
|
|
|
|
|
|
|
|}

Batteries

2021-02-10T17:17:57Z

Clanger9:

== Introduction ==
There are a wide variety of battery chemistries available for use as the main traction battery of an EV. To use each chemistry safely, and to ensure an adequate service life from the battery pack it is important to understand the requirements for the chemistry you are using. Failure to do so may lead to premature or catastrophic failure of the pack.

Good pack design will allow for a nominal amount of abuse. People make mistakes and the pack should allow a margin for safety - and for longevity!

== Battery pack specification ==
When deciding on your battery pack, here are some basic parameters to consider:

=== Capacity (kWh) ===
'''How far do you want to go?''' A standard car conversion will need a kWh for each 3, maybe 4 miles of range (very approximately). For a middleweight motorcycle, a kWh should give around 9 miles. Your mileage may vary, ''as they say.''

=== Voltage (V) ===
'''How fast do you want to go?''' The pack voltage defines the maximum speed your motor can spin. Motors are usually specified with "KV" - or RPM-per-volt. Check the KV of your motor and how fast it needs to spin to get your desired top speed. e.g. if you need 3,000 RPM from a 25 KV motor then your pack voltage needs to be 3,000 / 25 = 120 V. The exact number of cells in series you need depends on the cell design, but 3.8 V for Li-ion and 3.2 V for LiFePO4 is a reasonable guess.

=== Maximum current (A) ===
'''How quickly do you want to accelerate?''' Your motor's maximum power will be specified in kW. To estimate your maximum current draw, divide the peak power by the battery voltage. e.g. a 30 kW motor with a 120 V battery pack will pull 30,000 / 120 = 250 A. The higher the current rating of the cells, the heavier they will be for a given capacity. Ideally, you want "enough" current capacity for full throttle acceleration, but no more. You can put cells in parallel to double the current rating of your pack (which of course will half the voltage). Running cells in parallel is easy, but don't attempt to parallel battery packs unless you really know what you are doing. It's [https://www.orionbms.com/manuals/pdf/parallel_strings.pdf complicated].

=== Mass (kg) ===
'''Can your vehicle carry the weight?''' You'll need to keep the kerb weight within the original design limits. For a car, this could be a few hundred kg. For a motorcycle, likely less than 100 kg. This is a huge variable - and each new generation of battery tech seems to be a little lighter. For older EV or hybrid batteries, you can reckon on approximately 10 kg/kWh. Nissan Leaf batteries are relatively light (7.5 kg/kWh). With the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 5-6 kg/kWh.

=== Volume (L) ===
'''Will it fit?''' Batteries are bulky. They are getting smaller, but finding enough space might be your biggest challenge. You could be looking at over 5 L/kWh for older EV or hybrid batteries. Current state-of-the-art is the Tesla Model 3, which gets this down to 2.5 L/kWh by using 2170 cylindrical cells.

There is much, much more to battery design than this (e.g. maximum charge rate, terminations, cooling, clamping), but the above should help work out which options will or won't work for your project...

== Cell chemistry ==

=== Lithium Iron Phosphate (LiFePO4) ===
Lithium Iron Phosphate (also known as LFP, or LiFePO4) batteries offer a good compromise between safety, energy density and ease of use for DIY conversions. They are available in a number of formats, commonly pouch cells, prismatic cells and cylindrical cells.

==== LiFePO4 pouch cells ====
The majority of this content is drawn from this thread: [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761&start=900 https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761] discussing the use of the A123 20Ah pouch cell. However, many of the general points apply equally to other similar pouch cells.

===== General build requirements =====
Pouch cells are vulnerable to damage from debris, and must be held in compression (see the datasheet for your battery, but 10-12 psi is recommended for the A123 pouch cells as a guide). A rigid container capable of preventing damage and providing compression is therefore required. Be aware the cells expand and contract in use, so allowance for this must be included in the structure of the case.

The pouch cells should be separated to prevent abrasion between cells, and also to avoid the development of hot spots. Prebuilt modules from A123 systems had thin foam sheets or heatsinks between each cell. Be sure to avoid any debris that could rub on the pouch surface, particularly if using recycled cells.

Mylar, '[https://www.americanmicroinc.com/fish-paper/ Fish paper]' or a [https://www.rogerscorp.com/elastomeric-material-solutions/poron-industrial-polyurethanes compliant foam] may be appropriate materials to serve this purpose. This material should not be flammable. If the material is heat insulating, it is important to address thermal management.

===== Compression =====
Compression is required to prevent premature failure of the cell. Without compression electrolyte will become unevenly distributed, causing current gradients in the cell and uneven heating. Local temperatures can become high enough to form gas formation leading to cells 'puffing up' even when the pack is otherwise held within temperature and voltage constraints. This will be exacerbated in packs with otherwise poor thermal management. Compression forces gas generated to the margins of the cell, outside of the cell stack, minimising its effect cell performance. Gas in the middle cells will create a dead space which does not store or release energy.

There is ~1% expansion through a discharge cycle. As the cell ages, the nominal cell thickness can grow by 3-5%. For A123 cells the ideal pressure is between 4 and 18psi with the ideal pressure being ~12psi. Maintaining 12psi can increase the life by 500 cycles over that of 4 or 18psi

There is some suggestion that in uses where 1C is never exceeded compression ''may'' not be required.

Highly rigid endplates with a mechanism to allow for a limited degree of expansion (e.g. steel bands) are considered an effective solution to this challenge.

It should be noted that compression is a challenge specific to pouch cells. Cylindrical cells are designed to maintain their own compression within the cell's electrode stack by their design.

This thread provides more information and experimentation relating to pack compression: <nowiki>https://endless-sphere.com/forums/viewtopic.php?f=14&t=52244</nowiki>

===== Pouch Cell Pack Design Examples =====
<nowiki>*</nowiki>placeholder*

===== Notes regarding recycled pouch cells =====
Pouch cells are somewhat fragile, and breaching the insulation is not difficult, especially in a cells removed from existing packs and repurposed. If the pouch has had their poly-layers compromised you may see a number of faults:
* Black spots around the perimeter of the cell indicate electrolyte leakage
* Voltage on the outside of the bag. Note that microvoltage between the pouch and the electrode is normal (and due to a capacitive effect).
While the majority of these cells should no longer be in the market, a significant number of faulty cells made it back into the 'greymarket' in around 2013. These cells had misaligned tabs which can also lead to isolation failures between the tab and the pack. These cells should be avoided, particularly in high demand applications.

===== Situations likely to cause pouch cell failure =====
''Taken directly from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''
# '''Overcharge'''. Any extended time above 3.8 Volts will generate enough heat and electrochemical activity to puff a cell, especially one that is improperly compressed.
# '''Overdischarge followed by charge'''. Any A123 cell that has been pulled low enough to come to rest at <300 mV should be immediately scrapped. The published number for that is 500 mV, but the real figure is closer to 300, so that's a "safety buffer" if you will. Below this Voltage, the Cu electrodes start to dissolve into the electrolyte. When charge is applied, the Cu forms dendrites that puncture the separator layer, forming an internal short in the cell. This can puff a cell in a hurry---the more charge current on tap, the worse it's prone to be.
# '''Driving a cell negative'''. I've neglected to mention this before, but it is a possibility. I don't know much about the specific mechanism at this time.
# '''Malfunctioning or misinformed electronics'''. This is the most common cause of all of the above in my experience. At this stage of the game, it is critical for YOU to understand how your BMS functions on at least a cursory level. Choose your BMS very carefully and periodically verify that it is operating properly. They're not all created equal. Make sure V sense lines are securely connected and free of corrosion. Just because your BMS says there was never a problem doesn't necessarily make it so. Avoid harnesses or ribbon cables between multiple modules if possible--they are problematic wherever they are used in any mobile electronics.
# '''Exposure to or generation of sufficient heat'''. I don't know exactly at what temperature gas formation begins in the electrolyte, but we spec a max storage temp of 80 (or 85?) degrees C and I suspect this is the reason. The hotter, the puffier--to a point. This is why soldering tabs poses a real hazard to cell health. If you feel you must solder, sink or blow the heat away from the body of the cell. Use a big iron that can make sufficient local heat quickly, before the whole mass of the cell gets hot. You might even get the cell warm enough to melt separator if not careful.
# '''No compression, not enough compression, improperly distributed compression'''. This is a pack/module design issue. Apply 10, maybe 15 psi to your cell stack end to end and then band snugly and evenly. Use hard endplates of some sort--never wrap cells directly or allow their shape to become distorted. Protect all areas of the pouch from impact damage. This obviously does not apply to cylindrical cells.

==== LiFePO4 prismatic cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cylindrical cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cell ageing ====
''Derived (barely paraphrased) from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''

Capacity loss is caused by the lithium that was available for storage becoming permanently plated on the cathode. Being unable to move within the cell it is no longer available to store energy. The impact of this plating is greater than the amount of lithium 'lost' to plating because not only is the lithium no longer available, it is also preventing access to that part of the cathode meaning Li that can still move has to take a longer path to reach the cathode. Lithium plating is one cause of increased cell resistance (there are others), a sign of worsening cell health.

There is no linear relationship between actual capacity loss and impedance rise. However some cell defects will also increase impedance.

Increasing cell resistance may cause a number of symptoms which may be confused with [https://earthshipbiotecture.com/a-lithium-ion-battery-primer/ High Self Discharge.]
# Elevated Peukert Losses. As more energy per amount of current through the cell is lost as heat, the cells useable capacity decreases. So the apparent capacity loss is higher than the actual capacity loss of cycleable lithium. When used in low current applications (e.g. solar energy storage) the actual and apparent decrease in capacity will be small. In high current draw applications (like EV traction packs), the Peukert loss increases proportionally, so the apparent capacity loss increases much faster than the actual capacity loss.
# Greater voltage excursion under the same load. Due to increased cell resistancethe voltage will sag further under the same load than a cell in optimal condition. The inverse is also true, the voltage will be higher for the same amount of charging current applied. The cell will then rebound to a voltage further from the loaded and charging voltages. This, obviously, can look like high self discharge but is a different phenomenon.
# Absolute maximum current decrease.
Elevated impedance causes a more complex constellation of symptoms, some of which may be easy to confuse with High Self Discharge (HSD). Ohm's law (E=I/R) holds the key to understanding here.

'''1) Elevated Peukert losses.''' Because more energy per unit of current through the cell is lost as heat, less of the cell's capacity is actually USABLE. Thus, apparent capacity loss can be significantly greater than actual capacity loss caused by the loss of cycleable Li alone. In low current applications, the two numbers will be close together. In high current applications, Peukert losses increase in proportion, so apparent loss of capacity breaks further and further away from actual capacity loss as current increases.

'''2) Greater voltage excursion under the same load.''' Elevated resistance across the cell means that voltage will sag more under the same load than it did when the cell was healthier. Conversely, voltage will rise higher with the same amount of applied charge current than it did when it was healthier. At the same time, rebound/settling voltages will be further away from loaded/charging voltages. In other words, the cell will rebound to a voltage further away from loaded voltage, all else being equal. Similarly, voltage will settle farther from the charge voltage with the same charge applied. This can give the illusion of elevated self-discharge, but the phenomenon is actually not the same thing. Again, the greater the charge and load currents, the greater the effect becomes.

'''3) Absolute max current decreases.''' Because the cell's series resistance is elevated, the maximum possible current through the cell is decreased.

Just to confuse things further, there can be many factors that lead to impedance rise. Some are related to Li plating, others are not.

=== Lithium-ion ===
Lithium-ion (Li-ion) batteries have a greater energy density than Lithium Iron Phosphate batteries, but have more challenging needs to use safely. The ideal operating range of Li-ion batteries is between +15 and +45°C. The upper limit of temperature is particularly important as Li-ion batteries experience thermal runaway - an unstoppable chain reaction that can occur in milliseconds releasing the stored energy in the cell. This can produce temperatures of 400°C and a fire that is extremely difficult to put out. Thermal runaway can start as low as 60°C and becomes much more likely at 100°C

Risk factors for thermal runaway:
* Short Circuits - either internally or externally
* Overcharging
* Excessive current draw or when charging

==== Li-ion pouch cells ====
[https://kokam.com/cell Kokam] produce high-performance Li-ion pouch cells. These combine relative ease of use and pack construction with performance close to cylindrical cells.

==== Li-ion 18650 and other cylindrical cells ====
Cylindrical cells are favoured by Tesla, and are probably the main reason why their cars achieve such excellent performance. They are light, compact, powerful and expensive. Unfortunately, cylindrical cells are difficult (and potentially dangerous) to use in DIY conversions. There are two good reasons for this: thermal management and cell configuration.

As stated above, Li-ion cells are prone to thermal runaway. So you need perfect battery and thermal management to ensure that no cell ever exceeds the critical voltage or temperature. If this happens, a cell can short-circuit internally, releasing a lot of energy - potentially explosively. Furthermore, the individual cells are small, so need to be arranged in parallel. In the case of the Tesla Model S 85kW pack, there are 74 cells in parallel. Imagine if one of those cells fails and becomes short circuited internally. You now have 73 very high power cells all feeding in to that short circuit...

In fact, you don't have to imagine: you can watch this famous video instead (courtesy of Rich Rebuilds).

<youtube>WdDi1haA71Q</youtube>

== OEM modules ==
Using an OEM module means a lot of the difficulties and safety issues associated with battery design are taken care of e.g. cooling, clamping, etc.

Here is a handy list of OEM modules:
{| class="wikitable sortable mw-collapsible"
|+
!Manufacturer
!Model
!Capacity (kWh)
!Weight (kg)
!w (mm)
!d (mm)
!h (mm)
!Gravity (kg/kWh)
!Volume (L/kWh)
!Voltage (V)
!Current (cont A)
!Current (peak A)
!Cell arrangement
!Cell type
!Chemistry
|-
|Tesla
|Model S 85kWh
|5.3
|26
|690
|315
|80
|4.9
|3.3
|22.8
|500
|750
|74p6s
|18650
|Li-ion
|-
|Tesla
|Model S 100kWh
|6.4
|28
|680
|315
|80
|4.4
|2.7
|22.8
|
|870
|86p6s
|18650
|Li-ion
|-
|Tesla
|Model 3 LR (inner)
|19.2
|98.9
|1854
|292
|90
|5.2
|2.5
|91.1
|
|971
|46p25s
|2170
|Li-ion
|-
|Tesla
|Model 3 LR (outer)
|17.7
|86.6
|1715
|292
|90
|4.9
|2.5
|83.9
|
|971
|46p23s
|2170
|Li-ion
|-
|Tesla
|Model 3 SR (inner)
|13.0
|
|1854
|292
|90
|
|3.7
|91.1
|
|603
|31p25s
|2170
|Li-ion
|-
|Tesla
|Model 3 SR (outer)
|12.0
|
|1715
|292
|90
|
|3.8
|83.9
|
|603
|31p23s
|2170
|Li-ion
|-
|Calb
|4S3P
|2.19
|12
|355
|151
|108
|5.5
|2.6
|14.6
|
|900
|3p4s
|Pouch
|Li-ion
|-
|Calb
|6S2P
|2.19
|12
|355
|151
|108
|5.5
|2.6
|22.2
|
|600
|2p6s
|Pouch
|Li-ion
|-
|Chevrolet
|Volt 2012
|4
|38
|470
|180
|280
|9.5
|5.9
|88.8
|
|676
|3p24s
|Pouch
|Li-ion
|-
|BMW
|i3 60Ah
|2
|13
|368
|178
|102
|6.5
|3.3
|28.8
|210
|350
|2p8s
|Prismatic
|Li-ion
|-
|BMW
|i3 94Ah
|4.15
|28
|410
|310
|150
|6.7
|4.6
|45.6
|
|409
|12s
|Prismatic
|Li-ion
|-
|BMW
|i3 120Ah
|5.3
|28
|410
|310
|150
|5.3
|3.6
|45.6
|
|360
|12s
|Prismatic
|Li-ion
|-
|Jaguar
|iPace
|2.5
|12
|340
|155
|112
|4.8
|2.4
|10.8
|720
|1200
|4p3s
|Pouch
|Li-ion
|-
|LG
|4P3S
|2.6
|12.8
|357
|151
|110
|4.9
|2.3
|11
|
|
|4p3s
|Pouch
|Li-ion
|-
|Mitsubishi
|Outlander
|2.4
|26
|646
|184
|130
|10.8
|6.4
|60
|
|240
|16s
|
|Li-ion
|-
|Nissan
|Leaf 24kWh
|0.5
|3.65
|300
|222
|34
|7.3
|4.5
|7.2
|130
|228
|2p2s
|Pouch
|Li-ion LMO
|-
|Nissan
|Leaf 30kWh
|1.25
|
|300
|222
|34
|
|3.6
|14.4
|
|
|2p4s
|Pouch
|Li-ion
|-
|Nissan
|Leaf 40kWh
|1.6
|8.7
|300
|222
|68
|5.4
|2.8
|14.4
|
|314
|2p4s
|Pouch
|Li-ion NMC
|-
|Nissan
|Leaf 62kWh
|2.58
|
|
|
|
|
|
|14.4
|
|
|3p4s
|
|Li-ion
|-
|Volvo
|XC90 T8
|2.01
|12.1
|300
|180
|150
|6.0
|4.0
|59.2
|170
|340
|16s
|
|Li-ion
|-
|VW
|[[VW Hybrid Battery Packs|Passet GTE]]
|
|23.4
|
|
|
|
|
|
|
|
|24s
|
|
|-
|VW
|[[VW Hybrid Battery Packs|Golf GTE]]
|
|
|
|
|
|
|
|
|
|
|
|
|
|}

Batteries

2021-02-10T17:17:26Z

Clanger9: /* Maximum current (A) */ Add link to Orion BMS guide for parallel packs

== Introduction ==
There are a wide variety of battery chemistries available for use as the main traction battery of an EV. To use each chemistry safely, and to ensure an adequate service life from the battery pack it is important to understand the requirements for the chemistry you are using. Failure to do so may lead to premature or catastrophic failure of the pack.

Good pack design will allow for a nominal amount of abuse. People make mistakes and the pack should allow a margin for safety - and for longevity!

== Battery pack specification ==
When deciding on your battery pack, here are some basic parameters to consider:

=== Capacity (kWh) ===
'''How far do you want to go?''' A standard car conversion will need a kWh for each 3, maybe 4 miles of range (very approximately). For a middleweight motorcycle, a kWh should give around 9 miles. Your mileage may vary, ''as they say.''

=== Voltage (V) ===
'''How fast do you want to go?''' The pack voltage defines the maximum speed your motor can spin. Motors are usually specified with "KV" - or RPM-per-volt. Check the KV of your motor and how fast it needs to spin to get your desired top speed. e.g. if you need 3,000 RPM from a 25 KV motor then your pack voltage needs to be 3,000 / 25 = 120 V. The exact number of cells in series you need depends on the cell design, but 3.8 V for Li-ion and 3.2 V for LiFePO4 is a reasonable guess.

=== Maximum current (A) ===
'''How quickly do you want to accelerate?''' Your motor's maximum power will be specified in kW. To estimate your maximum current draw, divide the peak power by the battery voltage. e.g. a 30 kW motor with a 120 V battery pack will pull 30,000 / 120 = 250 A. The higher the current rating of the cells, the heavier they will be for a given capacity. Ideally, you want "enough" current capacity for full throttle acceleration, but no more. You can put cells in parallel to double the current rating of your pack (which of course will half the voltage). Running cells in parallel is easy, but don't attempt to parallel battery packs, unless you really know what you are doing. It's [https://www.orionbms.com/manuals/pdf/parallel_strings.pdf complicated].

=== Mass (kg) ===
'''Can your vehicle carry the weight?''' You'll need to keep the kerb weight within the original design limits. For a car, this could be a few hundred kg. For a motorcycle, likely less than 100 kg. This is a huge variable - and each new generation of battery tech seems to be a little lighter. For older EV or hybrid batteries, you can reckon on approximately 10 kg/kWh. Nissan Leaf batteries are relatively light (7.5 kg/kWh). With the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 5-6 kg/kWh.

=== Volume (L) ===
'''Will it fit?''' Batteries are bulky. They are getting smaller, but finding enough space might be your biggest challenge. You could be looking at over 5 L/kWh for older EV or hybrid batteries. Current state-of-the-art is the Tesla Model 3, which gets this down to 2.5 L/kWh by using 2170 cylindrical cells.

There is much, much more to battery design than this (e.g. maximum charge rate, terminations, cooling, clamping), but the above should help work out which options will or won't work for your project...

== Cell chemistry ==

=== Lithium Iron Phosphate (LiFePO4) ===
Lithium Iron Phosphate (also known as LFP, or LiFePO4) batteries offer a good compromise between safety, energy density and ease of use for DIY conversions. They are available in a number of formats, commonly pouch cells, prismatic cells and cylindrical cells.

==== LiFePO4 pouch cells ====
The majority of this content is drawn from this thread: [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761&start=900 https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761] discussing the use of the A123 20Ah pouch cell. However, many of the general points apply equally to other similar pouch cells.

===== General build requirements =====
Pouch cells are vulnerable to damage from debris, and must be held in compression (see the datasheet for your battery, but 10-12 psi is recommended for the A123 pouch cells as a guide). A rigid container capable of preventing damage and providing compression is therefore required. Be aware the cells expand and contract in use, so allowance for this must be included in the structure of the case.

The pouch cells should be separated to prevent abrasion between cells, and also to avoid the development of hot spots. Prebuilt modules from A123 systems had thin foam sheets or heatsinks between each cell. Be sure to avoid any debris that could rub on the pouch surface, particularly if using recycled cells.

Mylar, '[https://www.americanmicroinc.com/fish-paper/ Fish paper]' or a [https://www.rogerscorp.com/elastomeric-material-solutions/poron-industrial-polyurethanes compliant foam] may be appropriate materials to serve this purpose. This material should not be flammable. If the material is heat insulating, it is important to address thermal management.

===== Compression =====
Compression is required to prevent premature failure of the cell. Without compression electrolyte will become unevenly distributed, causing current gradients in the cell and uneven heating. Local temperatures can become high enough to form gas formation leading to cells 'puffing up' even when the pack is otherwise held within temperature and voltage constraints. This will be exacerbated in packs with otherwise poor thermal management. Compression forces gas generated to the margins of the cell, outside of the cell stack, minimising its effect cell performance. Gas in the middle cells will create a dead space which does not store or release energy.

There is ~1% expansion through a discharge cycle. As the cell ages, the nominal cell thickness can grow by 3-5%. For A123 cells the ideal pressure is between 4 and 18psi with the ideal pressure being ~12psi. Maintaining 12psi can increase the life by 500 cycles over that of 4 or 18psi

There is some suggestion that in uses where 1C is never exceeded compression ''may'' not be required.

Highly rigid endplates with a mechanism to allow for a limited degree of expansion (e.g. steel bands) are considered an effective solution to this challenge.

It should be noted that compression is a challenge specific to pouch cells. Cylindrical cells are designed to maintain their own compression within the cell's electrode stack by their design.

This thread provides more information and experimentation relating to pack compression: <nowiki>https://endless-sphere.com/forums/viewtopic.php?f=14&t=52244</nowiki>

===== Pouch Cell Pack Design Examples =====
<nowiki>*</nowiki>placeholder*

===== Notes regarding recycled pouch cells =====
Pouch cells are somewhat fragile, and breaching the insulation is not difficult, especially in a cells removed from existing packs and repurposed. If the pouch has had their poly-layers compromised you may see a number of faults:
* Black spots around the perimeter of the cell indicate electrolyte leakage
* Voltage on the outside of the bag. Note that microvoltage between the pouch and the electrode is normal (and due to a capacitive effect).
While the majority of these cells should no longer be in the market, a significant number of faulty cells made it back into the 'greymarket' in around 2013. These cells had misaligned tabs which can also lead to isolation failures between the tab and the pack. These cells should be avoided, particularly in high demand applications.

===== Situations likely to cause pouch cell failure =====
''Taken directly from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''
# '''Overcharge'''. Any extended time above 3.8 Volts will generate enough heat and electrochemical activity to puff a cell, especially one that is improperly compressed.
# '''Overdischarge followed by charge'''. Any A123 cell that has been pulled low enough to come to rest at <300 mV should be immediately scrapped. The published number for that is 500 mV, but the real figure is closer to 300, so that's a "safety buffer" if you will. Below this Voltage, the Cu electrodes start to dissolve into the electrolyte. When charge is applied, the Cu forms dendrites that puncture the separator layer, forming an internal short in the cell. This can puff a cell in a hurry---the more charge current on tap, the worse it's prone to be.
# '''Driving a cell negative'''. I've neglected to mention this before, but it is a possibility. I don't know much about the specific mechanism at this time.
# '''Malfunctioning or misinformed electronics'''. This is the most common cause of all of the above in my experience. At this stage of the game, it is critical for YOU to understand how your BMS functions on at least a cursory level. Choose your BMS very carefully and periodically verify that it is operating properly. They're not all created equal. Make sure V sense lines are securely connected and free of corrosion. Just because your BMS says there was never a problem doesn't necessarily make it so. Avoid harnesses or ribbon cables between multiple modules if possible--they are problematic wherever they are used in any mobile electronics.
# '''Exposure to or generation of sufficient heat'''. I don't know exactly at what temperature gas formation begins in the electrolyte, but we spec a max storage temp of 80 (or 85?) degrees C and I suspect this is the reason. The hotter, the puffier--to a point. This is why soldering tabs poses a real hazard to cell health. If you feel you must solder, sink or blow the heat away from the body of the cell. Use a big iron that can make sufficient local heat quickly, before the whole mass of the cell gets hot. You might even get the cell warm enough to melt separator if not careful.
# '''No compression, not enough compression, improperly distributed compression'''. This is a pack/module design issue. Apply 10, maybe 15 psi to your cell stack end to end and then band snugly and evenly. Use hard endplates of some sort--never wrap cells directly or allow their shape to become distorted. Protect all areas of the pouch from impact damage. This obviously does not apply to cylindrical cells.

==== LiFePO4 prismatic cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cylindrical cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cell ageing ====
''Derived (barely paraphrased) from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''

Capacity loss is caused by the lithium that was available for storage becoming permanently plated on the cathode. Being unable to move within the cell it is no longer available to store energy. The impact of this plating is greater than the amount of lithium 'lost' to plating because not only is the lithium no longer available, it is also preventing access to that part of the cathode meaning Li that can still move has to take a longer path to reach the cathode. Lithium plating is one cause of increased cell resistance (there are others), a sign of worsening cell health.

There is no linear relationship between actual capacity loss and impedance rise. However some cell defects will also increase impedance.

Increasing cell resistance may cause a number of symptoms which may be confused with [https://earthshipbiotecture.com/a-lithium-ion-battery-primer/ High Self Discharge.]
# Elevated Peukert Losses. As more energy per amount of current through the cell is lost as heat, the cells useable capacity decreases. So the apparent capacity loss is higher than the actual capacity loss of cycleable lithium. When used in low current applications (e.g. solar energy storage) the actual and apparent decrease in capacity will be small. In high current draw applications (like EV traction packs), the Peukert loss increases proportionally, so the apparent capacity loss increases much faster than the actual capacity loss.
# Greater voltage excursion under the same load. Due to increased cell resistancethe voltage will sag further under the same load than a cell in optimal condition. The inverse is also true, the voltage will be higher for the same amount of charging current applied. The cell will then rebound to a voltage further from the loaded and charging voltages. This, obviously, can look like high self discharge but is a different phenomenon.
# Absolute maximum current decrease.
Elevated impedance causes a more complex constellation of symptoms, some of which may be easy to confuse with High Self Discharge (HSD). Ohm's law (E=I/R) holds the key to understanding here.

'''1) Elevated Peukert losses.''' Because more energy per unit of current through the cell is lost as heat, less of the cell's capacity is actually USABLE. Thus, apparent capacity loss can be significantly greater than actual capacity loss caused by the loss of cycleable Li alone. In low current applications, the two numbers will be close together. In high current applications, Peukert losses increase in proportion, so apparent loss of capacity breaks further and further away from actual capacity loss as current increases.

'''2) Greater voltage excursion under the same load.''' Elevated resistance across the cell means that voltage will sag more under the same load than it did when the cell was healthier. Conversely, voltage will rise higher with the same amount of applied charge current than it did when it was healthier. At the same time, rebound/settling voltages will be further away from loaded/charging voltages. In other words, the cell will rebound to a voltage further away from loaded voltage, all else being equal. Similarly, voltage will settle farther from the charge voltage with the same charge applied. This can give the illusion of elevated self-discharge, but the phenomenon is actually not the same thing. Again, the greater the charge and load currents, the greater the effect becomes.

'''3) Absolute max current decreases.''' Because the cell's series resistance is elevated, the maximum possible current through the cell is decreased.

Just to confuse things further, there can be many factors that lead to impedance rise. Some are related to Li plating, others are not.

=== Lithium-ion ===
Lithium-ion (Li-ion) batteries have a greater energy density than Lithium Iron Phosphate batteries, but have more challenging needs to use safely. The ideal operating range of Li-ion batteries is between +15 and +45°C. The upper limit of temperature is particularly important as Li-ion batteries experience thermal runaway - an unstoppable chain reaction that can occur in milliseconds releasing the stored energy in the cell. This can produce temperatures of 400°C and a fire that is extremely difficult to put out. Thermal runaway can start as low as 60°C and becomes much more likely at 100°C

Risk factors for thermal runaway:
* Short Circuits - either internally or externally
* Overcharging
* Excessive current draw or when charging

==== Li-ion pouch cells ====
[https://kokam.com/cell Kokam] produce high-performance Li-ion pouch cells. These combine relative ease of use and pack construction with performance close to cylindrical cells.

==== Li-ion 18650 and other cylindrical cells ====
Cylindrical cells are favoured by Tesla, and are probably the main reason why their cars achieve such excellent performance. They are light, compact, powerful and expensive. Unfortunately, cylindrical cells are difficult (and potentially dangerous) to use in DIY conversions. There are two good reasons for this: thermal management and cell configuration.

As stated above, Li-ion cells are prone to thermal runaway. So you need perfect battery and thermal management to ensure that no cell ever exceeds the critical voltage or temperature. If this happens, a cell can short-circuit internally, releasing a lot of energy - potentially explosively. Furthermore, the individual cells are small, so need to be arranged in parallel. In the case of the Tesla Model S 85kW pack, there are 74 cells in parallel. Imagine if one of those cells fails and becomes short circuited internally. You now have 73 very high power cells all feeding in to that short circuit...

In fact, you don't have to imagine: you can watch this famous video instead (courtesy of Rich Rebuilds).

<youtube>WdDi1haA71Q</youtube>

== OEM modules ==
Using an OEM module means a lot of the difficulties and safety issues associated with battery design are taken care of e.g. cooling, clamping, etc.

Here is a handy list of OEM modules:
{| class="wikitable sortable mw-collapsible"
|+
!Manufacturer
!Model
!Capacity (kWh)
!Weight (kg)
!w (mm)
!d (mm)
!h (mm)
!Gravity (kg/kWh)
!Volume (L/kWh)
!Voltage (V)
!Current (cont A)
!Current (peak A)
!Cell arrangement
!Cell type
!Chemistry
|-
|Tesla
|Model S 85kWh
|5.3
|26
|690
|315
|80
|4.9
|3.3
|22.8
|500
|750
|74p6s
|18650
|Li-ion
|-
|Tesla
|Model S 100kWh
|6.4
|28
|680
|315
|80
|4.4
|2.7
|22.8
|
|870
|86p6s
|18650
|Li-ion
|-
|Tesla
|Model 3 LR (inner)
|19.2
|98.9
|1854
|292
|90
|5.2
|2.5
|91.1
|
|971
|46p25s
|2170
|Li-ion
|-
|Tesla
|Model 3 LR (outer)
|17.7
|86.6
|1715
|292
|90
|4.9
|2.5
|83.9
|
|971
|46p23s
|2170
|Li-ion
|-
|Tesla
|Model 3 SR (inner)
|13.0
|
|1854
|292
|90
|
|3.7
|91.1
|
|603
|31p25s
|2170
|Li-ion
|-
|Tesla
|Model 3 SR (outer)
|12.0
|
|1715
|292
|90
|
|3.8
|83.9
|
|603
|31p23s
|2170
|Li-ion
|-
|Calb
|4S3P
|2.19
|12
|355
|151
|108
|5.5
|2.6
|14.6
|
|900
|3p4s
|Pouch
|Li-ion
|-
|Calb
|6S2P
|2.19
|12
|355
|151
|108
|5.5
|2.6
|22.2
|
|600
|2p6s
|Pouch
|Li-ion
|-
|Chevrolet
|Volt 2012
|4
|38
|470
|180
|280
|9.5
|5.9
|88.8
|
|676
|3p24s
|Pouch
|Li-ion
|-
|BMW
|i3 60Ah
|2
|13
|368
|178
|102
|6.5
|3.3
|28.8
|210
|350
|2p8s
|Prismatic
|Li-ion
|-
|BMW
|i3 94Ah
|4.15
|28
|410
|310
|150
|6.7
|4.6
|45.6
|
|409
|12s
|Prismatic
|Li-ion
|-
|BMW
|i3 120Ah
|5.3
|28
|410
|310
|150
|5.3
|3.6
|45.6
|
|360
|12s
|Prismatic
|Li-ion
|-
|Jaguar
|iPace
|2.5
|12
|340
|155
|112
|4.8
|2.4
|10.8
|720
|1200
|4p3s
|Pouch
|Li-ion
|-
|LG
|4P3S
|2.6
|12.8
|357
|151
|110
|4.9
|2.3
|11
|
|
|4p3s
|Pouch
|Li-ion
|-
|Mitsubishi
|Outlander
|2.4
|26
|646
|184
|130
|10.8
|6.4
|60
|
|240
|16s
|
|Li-ion
|-
|Nissan
|Leaf 24kWh
|0.5
|3.65
|300
|222
|34
|7.3
|4.5
|7.2
|130
|228
|2p2s
|Pouch
|Li-ion LMO
|-
|Nissan
|Leaf 30kWh
|1.25
|
|300
|222
|34
|
|3.6
|14.4
|
|
|2p4s
|Pouch
|Li-ion
|-
|Nissan
|Leaf 40kWh
|1.6
|8.7
|300
|222
|68
|5.4
|2.8
|14.4
|
|314
|2p4s
|Pouch
|Li-ion NMC
|-
|Nissan
|Leaf 62kWh
|2.58
|
|
|
|
|
|
|14.4
|
|
|3p4s
|
|Li-ion
|-
|Volvo
|XC90 T8
|2.01
|12.1
|300
|180
|150
|6.0
|4.0
|59.2
|170
|340
|16s
|
|Li-ion
|-
|VW
|[[VW Hybrid Battery Packs|Passet GTE]]
|
|23.4
|
|
|
|
|
|
|
|
|24s
|
|
|-
|VW
|[[VW Hybrid Battery Packs|Golf GTE]]
|
|
|
|
|
|
|
|
|
|
|
|
|
|}

Batteries

2021-01-19T21:39:58Z

Clanger9: /* OEM modules */ Correct Chevy Volt specs

== Introduction ==
There are a wide variety of battery chemistries available for use as the main traction battery of an EV. To use each chemistry safely, and to ensure an adequate service life from the battery pack it is important to understand the requirements for the chemistry you are using. Failure to do so may lead to premature or catastrophic failure of the pack.

Good pack design will allow for a nominal amount of abuse. People make mistakes and the pack should allow a margin for safety - and for longevity!

== Battery pack specification ==
When deciding on your battery pack, here are some basic parameters to consider:

=== Capacity (kWh) ===
'''How far do you want to go?''' A standard car conversion will need a kWh for each 3, maybe 4 miles of range (very approximately). For a middleweight motorcycle, a kWh should give around 9 miles. Your mileage may vary, ''as they say.''

=== Voltage (V) ===
'''How fast do you want to go?''' The pack voltage defines the maximum speed your motor can spin. Motors are usually specified with "KV" - or RPM-per-volt. Check the KV of your motor and how fast it needs to spin to get your desired top speed. e.g. if you need 3,000 RPM from a 25 KV motor then your pack voltage needs to be 3,000 / 25 = 120 V. The exact number of cells in series you need depends on the cell design, but 3.8 V for Li-ion and 3.2 V for LiFePO4 is a reasonable guess.

=== Maximum current (A) ===
'''How quickly do you want to accelerate?''' Your motor's maximum power will be specified in kW. To estimate your maximum current draw, divide the peak power by the battery voltage. e.g. a 30 kW motor with a 120 V battery pack will pull 30,000 / 120 = 250 A. The higher the current rating of the cells, the heavier they will be for a given capacity. Ideally, you want "enough" current capacity for full throttle acceleration, but no more. You can put cells in parallel to double the current rating of your pack (which of course will half the voltage).

=== Mass (kg) ===
'''Can your vehicle carry the weight?''' You'll need to keep the kerb weight within the original design limits. For a car, this could be a few hundred kg. For a motorcycle, likely less than 100 kg. This is a huge variable - and each new generation of battery tech seems to be a little lighter. For older EV or hybrid batteries, you can reckon on approximately 10 kg/kWh. Nissan Leaf batteries are relatively light (7.5 kg/kWh). With the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 5-6 kg/kWh.

=== Volume (L) ===
'''Will it fit?''' Batteries are bulky. They are getting smaller, but finding enough space might be your biggest challenge. You could be looking at over 5 L/kWh for older EV or hybrid batteries. Current state-of-the-art is the Tesla Model 3, which gets this down to 2.5 L/kWh by using 2170 cylindrical cells.

There is much, much more to battery design than this (e.g. maximum charge rate, terminations, cooling, clamping), but the above should help work out which options will or won't work for your project...

== Cell chemistry ==

=== Lithium Iron Phosphate (LiFePO4) ===
Lithium Iron Phosphate (also known as LFP, or LiFePO4) batteries offer a good compromise between safety, energy density and ease of use for DIY conversions. They are available in a number of formats, commonly pouch cells, prismatic cells and cylindrical cells.

==== LiFePO4 pouch cells ====
The majority of this content is drawn from this thread: [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761&start=900 https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761] discussing the use of the A123 20Ah pouch cell. However, many of the general points apply equally to other similar pouch cells.

===== General build requirements =====
Pouch cells are vulnerable to damage from debris, and must be held in compression (see the datasheet for your battery, but 10-12 psi is recommended for the A123 pouch cells as a guide). A rigid container capable of preventing damage and providing compression is therefore required. Be aware the cells expand and contract in use, so allowance for this must be included in the structure of the case.

The pouch cells should be separated to prevent abrasion between cells, and also to avoid the development of hot spots. Prebuilt modules from A123 systems had thin foam sheets or heatsinks between each cell. Be sure to avoid any debris that could rub on the pouch surface, particularly if using recycled cells.

Mylar, '[https://www.americanmicroinc.com/fish-paper/ Fish paper]' or a [https://www.rogerscorp.com/elastomeric-material-solutions/poron-industrial-polyurethanes compliant foam] may be appropriate materials to serve this purpose. This material should not be flammable. If the material is heat insulating, it is important to address thermal management.

===== Compression =====
Compression is required to prevent premature failure of the cell. Without compression electrolyte will become unevenly distributed, causing current gradients in the cell and uneven heating. Local temperatures can become high enough to form gas formation leading to cells 'puffing up' even when the pack is otherwise held within temperature and voltage constraints. This will be exacerbated in packs with otherwise poor thermal management. Compression forces gas generated to the margins of the cell, outside of the cell stack, minimising its effect cell performance. Gas in the middle cells will create a dead space which does not store or release energy.

There is ~1% expansion through a discharge cycle. As the cell ages, the nominal cell thickness can grow by 3-5%. For A123 cells the ideal pressure is between 4 and 18psi with the ideal pressure being ~12psi. Maintaining 12psi can increase the life by 500 cycles over that of 4 or 18psi

There is some suggestion that in uses where 1C is never exceeded compression ''may'' not be required.

Highly rigid endplates with a mechanism to allow for a limited degree of expansion (e.g. steel bands) are considered an effective solution to this challenge.

It should be noted that compression is a challenge specific to pouch cells. Cylindrical cells are designed to maintain their own compression within the cell's electrode stack by their design.

This thread provides more information and experimentation relating to pack compression: <nowiki>https://endless-sphere.com/forums/viewtopic.php?f=14&t=52244</nowiki>

===== Pouch Cell Pack Design Examples =====
<nowiki>*</nowiki>placeholder*

===== Notes regarding recycled pouch cells =====
Pouch cells are somewhat fragile, and breaching the insulation is not difficult, especially in a cells removed from existing packs and repurposed. If the pouch has had their poly-layers compromised you may see a number of faults:
* Black spots around the perimeter of the cell indicate electrolyte leakage
* Voltage on the outside of the bag. Note that microvoltage between the pouch and the electrode is normal (and due to a capacitive effect).
While the majority of these cells should no longer be in the market, a significant number of faulty cells made it back into the 'greymarket' in around 2013. These cells had misaligned tabs which can also lead to isolation failures between the tab and the pack. These cells should be avoided, particularly in high demand applications.

===== Situations likely to cause pouch cell failure =====
''Taken directly from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''
# '''Overcharge'''. Any extended time above 3.8 Volts will generate enough heat and electrochemical activity to puff a cell, especially one that is improperly compressed.
# '''Overdischarge followed by charge'''. Any A123 cell that has been pulled low enough to come to rest at <300 mV should be immediately scrapped. The published number for that is 500 mV, but the real figure is closer to 300, so that's a "safety buffer" if you will. Below this Voltage, the Cu electrodes start to dissolve into the electrolyte. When charge is applied, the Cu forms dendrites that puncture the separator layer, forming an internal short in the cell. This can puff a cell in a hurry---the more charge current on tap, the worse it's prone to be.
# '''Driving a cell negative'''. I've neglected to mention this before, but it is a possibility. I don't know much about the specific mechanism at this time.
# '''Malfunctioning or misinformed electronics'''. This is the most common cause of all of the above in my experience. At this stage of the game, it is critical for YOU to understand how your BMS functions on at least a cursory level. Choose your BMS very carefully and periodically verify that it is operating properly. They're not all created equal. Make sure V sense lines are securely connected and free of corrosion. Just because your BMS says there was never a problem doesn't necessarily make it so. Avoid harnesses or ribbon cables between multiple modules if possible--they are problematic wherever they are used in any mobile electronics.
# '''Exposure to or generation of sufficient heat'''. I don't know exactly at what temperature gas formation begins in the electrolyte, but we spec a max storage temp of 80 (or 85?) degrees C and I suspect this is the reason. The hotter, the puffier--to a point. This is why soldering tabs poses a real hazard to cell health. If you feel you must solder, sink or blow the heat away from the body of the cell. Use a big iron that can make sufficient local heat quickly, before the whole mass of the cell gets hot. You might even get the cell warm enough to melt separator if not careful.
# '''No compression, not enough compression, improperly distributed compression'''. This is a pack/module design issue. Apply 10, maybe 15 psi to your cell stack end to end and then band snugly and evenly. Use hard endplates of some sort--never wrap cells directly or allow their shape to become distorted. Protect all areas of the pouch from impact damage. This obviously does not apply to cylindrical cells.

==== LiFePO4 prismatic cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cylindrical cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cell ageing ====
''Derived (barely paraphrased) from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''

Capacity loss is caused by the lithium that was available for storage becoming permanently plated on the cathode. Being unable to move within the cell it is no longer available to store energy. The impact of this plating is greater than the amount of lithium 'lost' to plating because not only is the lithium no longer available, it is also preventing access to that part of the cathode meaning Li that can still move has to take a longer path to reach the cathode. Lithium plating is one cause of increased cell resistance (there are others), a sign of worsening cell health.

There is no linear relationship between actual capacity loss and impedance rise. However some cell defects will also increase impedance.

Increasing cell resistance may cause a number of symptoms which may be confused with [https://earthshipbiotecture.com/a-lithium-ion-battery-primer/ High Self Discharge.]
# Elevated Peukert Losses. As more energy per amount of current through the cell is lost as heat, the cells useable capacity decreases. So the apparent capacity loss is higher than the actual capacity loss of cycleable lithium. When used in low current applications (e.g. solar energy storage) the actual and apparent decrease in capacity will be small. In high current draw applications (like EV traction packs), the Peukert loss increases proportionally, so the apparent capacity loss increases much faster than the actual capacity loss.
# Greater voltage excursion under the same load. Due to increased cell resistancethe voltage will sag further under the same load than a cell in optimal condition. The inverse is also true, the voltage will be higher for the same amount of charging current applied. The cell will then rebound to a voltage further from the loaded and charging voltages. This, obviously, can look like high self discharge but is a different phenomenon.
# Absolute maximum current decrease.
Elevated impedance causes a more complex constellation of symptoms, some of which may be easy to confuse with High Self Discharge (HSD). Ohm's law (E=I/R) holds the key to understanding here.

'''1) Elevated Peukert losses.''' Because more energy per unit of current through the cell is lost as heat, less of the cell's capacity is actually USABLE. Thus, apparent capacity loss can be significantly greater than actual capacity loss caused by the loss of cycleable Li alone. In low current applications, the two numbers will be close together. In high current applications, Peukert losses increase in proportion, so apparent loss of capacity breaks further and further away from actual capacity loss as current increases.

'''2) Greater voltage excursion under the same load.''' Elevated resistance across the cell means that voltage will sag more under the same load than it did when the cell was healthier. Conversely, voltage will rise higher with the same amount of applied charge current than it did when it was healthier. At the same time, rebound/settling voltages will be further away from loaded/charging voltages. In other words, the cell will rebound to a voltage further away from loaded voltage, all else being equal. Similarly, voltage will settle farther from the charge voltage with the same charge applied. This can give the illusion of elevated self-discharge, but the phenomenon is actually not the same thing. Again, the greater the charge and load currents, the greater the effect becomes.

'''3) Absolute max current decreases.''' Because the cell's series resistance is elevated, the maximum possible current through the cell is decreased.

Just to confuse things further, there can be many factors that lead to impedance rise. Some are related to Li plating, others are not.

=== Lithium-ion ===
Lithium-ion (Li-ion) batteries have a greater energy density than Lithium Iron Phosphate batteries, but have more challenging needs to use safely. The ideal operating range of Li-ion batteries is between +15 and +45°C. The upper limit of temperature is particularly important as Li-ion batteries experience thermal runaway - an unstoppable chain reaction that can occur in milliseconds releasing the stored energy in the cell. This can produce temperatures of 400°C and a fire that is extremely difficult to put out. Thermal runaway can start as low as 60°C and becomes much more likely at 100°C

Risk factors for thermal runaway:
* Short Circuits - either internally or externally
* Overcharging
* Excessive current draw or when charging

==== Li-ion pouch cells ====
[https://kokam.com/cell Kokam] produce high-performance Li-ion pouch cells. These combine relative ease of use and pack construction with performance close to cylindrical cells.

==== Li-ion 18650 and other cylindrical cells ====
Cylindrical cells are favoured by Tesla, and are probably the main reason why their cars achieve such excellent performance. They are light, compact, powerful and expensive. Unfortunately, cylindrical cells are difficult (and potentially dangerous) to use in DIY conversions. There are two good reasons for this: thermal management and cell configuration.

As stated above, Li-ion cells are prone to thermal runaway. So you need perfect battery and thermal management to ensure that no cell ever exceeds the critical voltage or temperature. If this happens, a cell can short-circuit internally, releasing a lot of energy - potentially explosively. Furthermore, the individual cells are small, so need to be arranged in parallel. In the case of the Tesla Model S 85kW pack, there are 74 cells in parallel. Imagine if one of those cells fails and becomes short circuited internally. You now have 73 very high power cells all feeding in to that short circuit...

In fact, you don't have to imagine: you can watch this famous video instead (courtesy of Rich Rebuilds).

<youtube>WdDi1haA71Q</youtube>

== OEM modules ==
Using an OEM module means a lot of the difficulties and safety issues associated with battery design are taken care of e.g. cooling, clamping, etc.

Here is a handy list of OEM modules:
{| class="wikitable sortable mw-collapsible"
|+
!Manufacturer
!Model
!Capacity (kWh)
!Weight (kg)
!w (mm)
!d (mm)
!h (mm)
!Gravity (kg/kWh)
!Volume (L/kWh)
!Voltage (V)
!Current (cont A)
!Current (peak A)
!Cell arrangement
!Cell type
!Chemistry
|-
|Tesla
|Model S 85kWh
|5.3
|26
|690
|315
|80
|4.9
|3.3
|22.8
|500
|750
|74p6s
|18650
|Li-ion
|-
|Tesla
|Model S 100kWh
|6.4
|28
|680
|315
|80
|4.4
|2.7
|22.8
|
|870
|86p6s
|18650
|Li-ion
|-
|Tesla
|Model 3 LR (inner)
|19.2
|98.9
|1854
|292
|90
|5.2
|2.5
|91.1
|
|971
|46p25s
|2170
|Li-ion
|-
|Tesla
|Model 3 LR (outer)
|17.7
|86.6
|1715
|292
|90
|4.9
|2.5
|83.9
|
|971
|46p23s
|2170
|Li-ion
|-
|Tesla
|Model 3 SR (inner)
|13.0
|
|1854
|292
|90
|
|3.7
|91.1
|
|603
|31p25s
|2170
|Li-ion
|-
|Tesla
|Model 3 SR (outer)
|12.0
|
|1715
|292
|90
|
|3.8
|83.9
|
|603
|31p23s
|2170
|Li-ion
|-
|Calb
|4S3P
|2.19
|12
|355
|151
|108
|5.5
|2.6
|14.6
|
|900
|3p4s
|Pouch
|Li-ion
|-
|Calb
|6S2P
|2.19
|12
|355
|151
|108
|5.5
|2.6
|22.2
|
|600
|2p6s
|Pouch
|Li-ion
|-
|Chevrolet
|Volt 2012
|4
|38
|470
|180
|280
|9.5
|5.9
|88.8
|
|676
|3p24s
|Pouch
|Li-ion
|-
|BMW
|i3 60Ah
|2
|13
|368
|178
|102
|6.5
|3.3
|28.8
|210
|350
|2p8s
|Prismatic
|Li-ion
|-
|BMW
|i3 94Ah
|4.15
|28
|410
|310
|150
|6.7
|4.6
|45.6
|
|409
|12s
|Prismatic
|Li-ion
|-
|BMW
|i3 120Ah
|5.3
|28
|410
|310
|150
|5.3
|3.6
|45.6
|
|360
|12s
|Prismatic
|Li-ion
|-
|Jaguar
|iPace
|2.5
|12
|340
|155
|112
|4.8
|2.4
|10.8
|720
|1200
|4p3s
|Pouch
|Li-ion
|-
|LG
|4P3S
|2.6
|12.8
|357
|151
|110
|4.9
|2.3
|11
|
|
|4p3s
|Pouch
|Li-ion
|-
|Mitsubishi
|Outlander
|2.4
|26
|646
|184
|130
|10.8
|6.4
|60
|
|240
|16s
|
|Li-ion
|-
|Nissan
|Leaf 24kWh
|0.5
|3.65
|300
|222
|34
|7.3
|4.5
|7.2
|130
|228
|2p2s
|Pouch
|Li-ion LMO
|-
|Nissan
|Leaf 30kWh
|1.25
|
|300
|222
|34
|
|3.6
|14.4
|
|
|2p4s
|Pouch
|Li-ion
|-
|Nissan
|Leaf 40kWh
|1.6
|8.7
|300
|222
|68
|5.4
|2.8
|14.4
|
|314
|2p4s
|Pouch
|Li-ion NMC
|-
|Nissan
|Leaf 62kWh
|2.58
|
|
|
|
|
|
|14.4
|
|
|3p4s
|
|Li-ion
|-
|Volvo
|XC90 T8
|2.01
|12.1
|300
|180
|150
|6.0
|4.0
|59.2
|170
|340
|16s
|
|Li-ion
|}

Batteries

2020-12-31T09:59:24Z

Clanger9: /* OEM modules */ Add Calb & LG modules

== Introduction ==
There are a wide variety of battery chemistries available for use as the main traction battery of an EV. To use each chemistry safely, and to ensure an adequate service life from the battery pack it is important to understand the requirements for the chemistry you are using. Failure to do so may lead to premature or catastrophic failure of the pack.

Good pack design will allow for a nominal amount of abuse. People make mistakes and the pack should allow a margin for safety - and for longevity!

== Battery pack specification ==
When deciding on your battery pack, here are some basic parameters to consider:

=== Capacity (kWh) ===
'''How far do you want to go?''' A standard car conversion will need a kWh for each 3, maybe 4 miles of range (very approximately). For a middleweight motorcycle, a kWh should give around 9 miles. Your mileage may vary, ''as they say.''

=== Voltage (V) ===
'''How fast do you want to go?''' The pack voltage defines the maximum speed your motor can spin. Motors are usually specified with "KV" - or RPM-per-volt. Check the KV of your motor and how fast it needs to spin to get your desired top speed. e.g. if you need 3,000 RPM from a 25 KV motor then your pack voltage needs to be 3,000 / 25 = 120 V. The exact number of cells in series you need depends on the cell design, but 3.8 V for Li-ion and 3.2 V for LiFePO4 is a reasonable guess.

=== Maximum current (A) ===
'''How quickly do you want to accelerate?''' Your motor's maximum power will be specified in kW. To estimate your maximum current draw, divide the peak power by the battery voltage. e.g. a 30 kW motor with a 120 V battery pack will pull 30,000 / 120 = 250 A. The higher the current rating of the cells, the heavier they will be for a given capacity. Ideally, you want "enough" current capacity for full throttle acceleration, but no more. You can put cells in parallel to double the current rating of your pack (which of course will half the voltage).

=== Mass (kg) ===
'''Can your vehicle carry the weight?''' You'll need to keep the kerb weight within the original design limits. For a car, this could be a few hundred kg. For a motorcycle, likely less than 100 kg. This is a huge variable - and each new generation of battery tech seems to be a little lighter. For older EV or hybrid batteries, you can reckon on approximately 10 kg/kWh. Nissan Leaf batteries are relatively light (7.5 kg/kWh). With the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 5-6 kg/kWh.

=== Volume (L) ===
'''Will it fit?''' Batteries are bulky. They are getting smaller, but finding enough space might be your biggest challenge. You could be looking at over 5 L/kWh for older EV or hybrid batteries. Current state-of-the-art is the Tesla Model 3, which gets this down to 2.5 L/kWh by using 2170 cylindrical cells.

There is much, much more to battery design than this (e.g. maximum charge rate, terminations, cooling, clamping), but the above should help work out which options will or won't work for your project...

== Cell chemistry ==

=== Lithium Iron Phosphate (LiFePO4) ===
Lithium Iron Phosphate (also known as LFP, or LiFePO4) batteries offer a good compromise between safety, energy density and ease of use for DIY conversions. They are available in a number of formats, commonly pouch cells, prismatic cells and cylindrical cells.

==== LiFePO4 pouch cells ====
The majority of this content is drawn from this thread: [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761&start=900 https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761] discussing the use of the A123 20Ah pouch cell. However, many of the general points apply equally to other similar pouch cells.

===== General build requirements =====
Pouch cells are vulnerable to damage from debris, and must be held in compression (see the datasheet for your battery, but 10-12 psi is recommended for the A123 pouch cells as a guide). A rigid container capable of preventing damage and providing compression is therefore required. Be aware the cells expand and contract in use, so allowance for this must be included in the structure of the case.

The pouch cells should be separated to prevent abrasion between cells, and also to avoid the development of hot spots. Prebuilt modules from A123 systems had thin foam sheets or heatsinks between each cell. Be sure to avoid any debris that could rub on the pouch surface, particularly if using recycled cells.

Mylar, '[https://www.americanmicroinc.com/fish-paper/ Fish paper]' or a [https://www.rogerscorp.com/elastomeric-material-solutions/poron-industrial-polyurethanes compliant foam] may be appropriate materials to serve this purpose. This material should not be flammable. If the material is heat insulating, it is important to address thermal management.

===== Compression =====
Compression is required to prevent premature failure of the cell. Without compression electrolyte will become unevenly distributed, causing current gradients in the cell and uneven heating. Local temperatures can become high enough to form gas formation leading to cells 'puffing up' even when the pack is otherwise held within temperature and voltage constraints. This will be exacerbated in packs with otherwise poor thermal management. Compression forces gas generated to the margins of the cell, outside of the cell stack, minimising its effect cell performance. Gas in the middle cells will create a dead space which does not store or release energy.

There is ~1% expansion through a discharge cycle. As the cell ages, the nominal cell thickness can grow by 3-5%. For A123 cells the ideal pressure is between 4 and 18psi with the ideal pressure being ~12psi. Maintaining 12psi can increase the life by 500 cycles over that of 4 or 18psi

There is some suggestion that in uses where 1C is never exceeded compression ''may'' not be required.

Highly rigid endplates with a mechanism to allow for a limited degree of expansion (e.g. steel bands) are considered an effective solution to this challenge.

It should be noted that compression is a challenge specific to pouch cells. Cylindrical cells are designed to maintain their own compression within the cell's electrode stack by their design.

This thread provides more information and experimentation relating to pack compression: <nowiki>https://endless-sphere.com/forums/viewtopic.php?f=14&t=52244</nowiki>

===== Pouch Cell Pack Design Examples =====
<nowiki>*</nowiki>placeholder*

===== Notes regarding recycled pouch cells =====
Pouch cells are somewhat fragile, and breaching the insulation is not difficult, especially in a cells removed from existing packs and repurposed. If the pouch has had their poly-layers compromised you may see a number of faults:
* Black spots around the perimeter of the cell indicate electrolyte leakage
* Voltage on the outside of the bag. Note that microvoltage between the pouch and the electrode is normal (and due to a capacitive effect).
While the majority of these cells should no longer be in the market, a significant number of faulty cells made it back into the 'greymarket' in around 2013. These cells had misaligned tabs which can also lead to isolation failures between the tab and the pack. These cells should be avoided, particularly in high demand applications.

===== Situations likely to cause pouch cell failure =====
''Taken directly from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''
# '''Overcharge'''. Any extended time above 3.8 Volts will generate enough heat and electrochemical activity to puff a cell, especially one that is improperly compressed.
# '''Overdischarge followed by charge'''. Any A123 cell that has been pulled low enough to come to rest at <300 mV should be immediately scrapped. The published number for that is 500 mV, but the real figure is closer to 300, so that's a "safety buffer" if you will. Below this Voltage, the Cu electrodes start to dissolve into the electrolyte. When charge is applied, the Cu forms dendrites that puncture the separator layer, forming an internal short in the cell. This can puff a cell in a hurry---the more charge current on tap, the worse it's prone to be.
# '''Driving a cell negative'''. I've neglected to mention this before, but it is a possibility. I don't know much about the specific mechanism at this time.
# '''Malfunctioning or misinformed electronics'''. This is the most common cause of all of the above in my experience. At this stage of the game, it is critical for YOU to understand how your BMS functions on at least a cursory level. Choose your BMS very carefully and periodically verify that it is operating properly. They're not all created equal. Make sure V sense lines are securely connected and free of corrosion. Just because your BMS says there was never a problem doesn't necessarily make it so. Avoid harnesses or ribbon cables between multiple modules if possible--they are problematic wherever they are used in any mobile electronics.
# '''Exposure to or generation of sufficient heat'''. I don't know exactly at what temperature gas formation begins in the electrolyte, but we spec a max storage temp of 80 (or 85?) degrees C and I suspect this is the reason. The hotter, the puffier--to a point. This is why soldering tabs poses a real hazard to cell health. If you feel you must solder, sink or blow the heat away from the body of the cell. Use a big iron that can make sufficient local heat quickly, before the whole mass of the cell gets hot. You might even get the cell warm enough to melt separator if not careful.
# '''No compression, not enough compression, improperly distributed compression'''. This is a pack/module design issue. Apply 10, maybe 15 psi to your cell stack end to end and then band snugly and evenly. Use hard endplates of some sort--never wrap cells directly or allow their shape to become distorted. Protect all areas of the pouch from impact damage. This obviously does not apply to cylindrical cells.

==== LiFePO4 prismatic cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cylindrical cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cell ageing ====
''Derived (barely paraphrased) from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''

Capacity loss is caused by the lithium that was available for storage becoming permanently plated on the cathode. Being unable to move within the cell it is no longer available to store energy. The impact of this plating is greater than the amount of lithium 'lost' to plating because not only is the lithium no longer available, it is also preventing access to that part of the cathode meaning Li that can still move has to take a longer path to reach the cathode. Lithium plating is one cause of increased cell resistance (there are others), a sign of worsening cell health.

There is no linear relationship between actual capacity loss and impedance rise. However some cell defects will also increase impedance.

Increasing cell resistance may cause a number of symptoms which may be confused with [https://earthshipbiotecture.com/a-lithium-ion-battery-primer/ High Self Discharge.]
# Elevated Peukert Losses. As more energy per amount of current through the cell is lost as heat, the cells useable capacity decreases. So the apparent capacity loss is higher than the actual capacity loss of cycleable lithium. When used in low current applications (e.g. solar energy storage) the actual and apparent decrease in capacity will be small. In high current draw applications (like EV traction packs), the Peukert loss increases proportionally, so the apparent capacity loss increases much faster than the actual capacity loss.
# Greater voltage excursion under the same load. Due to increased cell resistancethe voltage will sag further under the same load than a cell in optimal condition. The inverse is also true, the voltage will be higher for the same amount of charging current applied. The cell will then rebound to a voltage further from the loaded and charging voltages. This, obviously, can look like high self discharge but is a different phenomenon.
# Absolute maximum current decrease.
Elevated impedance causes a more complex constellation of symptoms, some of which may be easy to confuse with High Self Discharge (HSD). Ohm's law (E=I/R) holds the key to understanding here.

'''1) Elevated Peukert losses.''' Because more energy per unit of current through the cell is lost as heat, less of the cell's capacity is actually USABLE. Thus, apparent capacity loss can be significantly greater than actual capacity loss caused by the loss of cycleable Li alone. In low current applications, the two numbers will be close together. In high current applications, Peukert losses increase in proportion, so apparent loss of capacity breaks further and further away from actual capacity loss as current increases.

'''2) Greater voltage excursion under the same load.''' Elevated resistance across the cell means that voltage will sag more under the same load than it did when the cell was healthier. Conversely, voltage will rise higher with the same amount of applied charge current than it did when it was healthier. At the same time, rebound/settling voltages will be further away from loaded/charging voltages. In other words, the cell will rebound to a voltage further away from loaded voltage, all else being equal. Similarly, voltage will settle farther from the charge voltage with the same charge applied. This can give the illusion of elevated self-discharge, but the phenomenon is actually not the same thing. Again, the greater the charge and load currents, the greater the effect becomes.

'''3) Absolute max current decreases.''' Because the cell's series resistance is elevated, the maximum possible current through the cell is decreased.

Just to confuse things further, there can be many factors that lead to impedance rise. Some are related to Li plating, others are not.

=== Lithium-ion ===
Lithium-ion (Li-ion) batteries have a greater energy density than Lithium Iron Phosphate batteries, but have more challenging needs to use safely. The ideal operating range of Li-ion batteries is between +15 and +45°C. The upper limit of temperature is particularly important as Li-ion batteries experience thermal runaway - an unstoppable chain reaction that can occur in milliseconds releasing the stored energy in the cell. This can produce temperatures of 400°C and a fire that is extremely difficult to put out. Thermal runaway can start as low as 60°C and becomes much more likely at 100°C

Risk factors for thermal runaway:
* Short Circuits - either internally or externally
* Overcharging
* Excessive current draw or when charging

==== Li-ion pouch cells ====
[https://kokam.com/cell Kokam] produce high-performance Li-ion pouch cells. These combine relative ease of use and pack construction with performance close to cylindrical cells.

==== Li-ion 18650 and other cylindrical cells ====
Cylindrical cells are favoured by Tesla, and are probably the main reason why their cars achieve such excellent performance. They are light, compact, powerful and expensive. Unfortunately, cylindrical cells are difficult (and potentially dangerous) to use in DIY conversions. There are two good reasons for this: thermal management and cell configuration.

As stated above, Li-ion cells are prone to thermal runaway. So you need perfect battery and thermal management to ensure that no cell ever exceeds the critical voltage or temperature. If this happens, a cell can short-circuit internally, releasing a lot of energy - potentially explosively. Furthermore, the individual cells are small, so need to be arranged in parallel. In the case of the Tesla Model S 85kW pack, there are 74 cells in parallel. Imagine if one of those cells fails and becomes short circuited internally. You now have 73 very high power cells all feeding in to that short circuit...

In fact, you don't have to imagine: you can watch this famous video instead (courtesy of Rich Rebuilds).

<youtube>WdDi1haA71Q</youtube>

== OEM modules ==
Using an OEM module means a lot of the difficulties and safety issues associated with battery design are taken care of e.g. cooling, clamping, etc.

Here is a handy list of OEM modules:
{| class="wikitable sortable mw-collapsible"
|+
!Manufacturer
!Model
!Capacity (kWh)
!Weight (kg)
!w (mm)
!d (mm)
!h (mm)
!Gravity (kg/kWh)
!Volume (L/kWh)
!Voltage (V)
!Current (cont A)
!Current (peak A)
!Cell arrangement
!Cell type
!Chemistry
|-
|Tesla
|Model S 85kWh
|5.3
|26
|690
|315
|80
|4.9
|3.3
|22.8
|500
|750
|74p6s
|18650
|Li-ion
|-
|Tesla
|Model S 100kWh
|6.4
|28
|680
|315
|80
|4.4
|2.7
|22.8
|
|870
|86p6s
|18650
|Li-ion
|-
|Tesla
|Model 3 LR (inner)
|19.2
|98.9
|1854
|292
|90
|5.2
|2.5
|91.1
|
|971
|46p25s
|2170
|Li-ion
|-
|Tesla
|Model 3 LR (outer)
|17.7
|86.6
|1715
|292
|90
|4.9
|2.5
|83.9
|
|971
|46p23s
|2170
|Li-ion
|-
|Tesla
|Model 3 SR (inner)
|13.0
|
|1854
|292
|90
|
|3.7
|91.1
|
|603
|31p25s
|2170
|Li-ion
|-
|Tesla
|Model 3 SR (outer)
|12.0
|
|1715
|292
|90
|
|3.8
|83.9
|
|603
|31p23s
|2170
|Li-ion
|-
|Calb
|4S3P
|2.19
|12
|355
|151
|108
|5.5
|2.6
|14.6
|
|900
|3p4s
|Pouch
|Li-ion
|-
|Calb
|6S2P
|2.19
|12
|355
|151
|108
|5.5
|2.6
|22.2
|
|600
|2p6s
|Pouch
|Li-ion
|-
|Chevrolet
|Volt 2012
|4
|38
|470
|180
|280
|9.5
|5.9
|88
|140
|210
|24s
|Pouch
|Li-ion
|-
|BMW
|i3 60Ah
|2
|13
|368
|178
|102
|6.5
|3.3
|28.8
|210
|350
|2p8s
|Prismatic
|Li-ion
|-
|BMW
|i3 94Ah
|4.15
|28
|410
|310
|150
|6.7
|4.6
|45.6
|
|409
|12s
|Prismatic
|Li-ion
|-
|BMW
|i3 120Ah
|5.3
|28
|410
|310
|150
|5.3
|3.6
|45.6
|
|360
|12s
|Prismatic
|Li-ion
|-
|Jaguar
|iPace
|2.5
|12
|340
|155
|112
|4.8
|2.4
|10.8
|720
|1200
|4p3s
|Pouch
|Li-ion
|-
|LG
|4P3S
|2.6
|12.8
|357
|151
|110
|4.9
|2.3
|11
|
|
|4p3s
|Pouch
|Li-ion
|-
|Mitsubishi
|Outlander
|2.4
|26
|646
|184
|130
|10.8
|6.4
|60
|
|240
|16s
|
|Li-ion
|-
|Nissan
|Leaf 24kWh
|0.5
|3.65
|300
|222
|34
|7.3
|4.5
|7.2
|130
|228
|2p2s
|Pouch
|Li-ion LMO
|-
|Nissan
|Leaf 30kWh
|1.25
|
|300
|222
|34
|
|3.6
|14.4
|
|
|2p4s
|Pouch
|Li-ion
|-
|Nissan
|Leaf 40kWh
|1.6
|8.7
|300
|222
|68
|5.4
|2.8
|14.4
|
|314
|2p4s
|Pouch
|Li-ion NMC
|-
|Nissan
|Leaf 62kWh
|2.58
|
|
|
|
|
|
|14.4
|
|
|3p4s
|
|Li-ion
|-
|Volvo
|XC90 T8
|2.01
|12.1
|300
|180
|150
|6.0
|4.0
|59.2
|170
|340
|16s
|
|Li-ion
|}

Batteries

2020-12-07T16:59:11Z

Clanger9: /* OEM modules */

== Introduction ==
There are a wide variety of battery chemistries available for use as the main traction battery of an EV. To use each chemistry safely, and to ensure an adequate service life from the battery pack it is important to understand the requirements for the chemistry you are using. Failure to do so may lead to premature or catastrophic failure of the pack.

Good pack design will allow for a nominal amount of abuse. People make mistakes and the pack should allow a margin for safety - and for longevity!

== Battery pack specification ==
When deciding on your battery pack, here are some basic parameters to consider:

=== Capacity (kWh) ===
'''How far do you want to go?''' A standard car conversion will need a kWh for each 3, maybe 4 miles of range (very approximately). For a middleweight motorcycle, a kWh should give around 9 miles. Your mileage may vary, ''as they say.''

=== Voltage (V) ===
'''How fast do you want to go?''' The pack voltage defines the maximum speed your motor can spin. Motors are usually specified with "KV" - or RPM-per-volt. Check the KV of your motor and how fast it needs to spin to get your desired top speed. e.g. if you need 3,000 RPM from a 25 KV motor then your pack voltage needs to be 3,000 / 25 = 120 V. The exact number of cells in series you need depends on the cell design, but 3.8 V for Li-ion and 3.2 V for LiFePO4 is a reasonable guess.

=== Maximum current (A) ===
'''How quickly do you want to accelerate?''' Your motor's maximum power will be specified in kW. To estimate your maximum current draw, divide the peak power by the battery voltage. e.g. a 30 kW motor with a 120 V battery pack will pull 30,000 / 120 = 250 A. The higher the current rating of the cells, the heavier they will be for a given capacity. Ideally, you want "enough" current capacity for full throttle acceleration, but no more. You can put cells in parallel to double the current rating of your pack (which of course will half the voltage).

=== Mass (kg) ===
'''Can your vehicle carry the weight?''' You'll need to keep the kerb weight within the original design limits. For a car, this could be a few hundred kg. For a motorcycle, likely less than 100 kg. This is a huge variable - and each new generation of battery tech seems to be a little lighter. For older EV or hybrid batteries, you can reckon on approximately 10 kg/kWh. Nissan Leaf batteries are relatively light (7.5 kg/kWh). With the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 5-6 kg/kWh.

=== Volume (L) ===
'''Will it fit?''' Batteries are bulky. They are getting smaller, but finding enough space might be your biggest challenge. You could be looking at over 5 L/kWh for older EV or hybrid batteries. Current state-of-the-art is the Tesla Model 3, which gets this down to 2.5 L/kWh by using 2170 cylindrical cells.

There is much, much more to battery design than this (e.g. maximum charge rate, terminations, cooling, clamping), but the above should help work out which options will or won't work for your project...

== Cell chemistry ==

=== Lithium Iron Phosphate (LiFePO4) ===
Lithium Iron Phosphate (also known as LFP, or LiFePO4) batteries offer a good compromise between safety, energy density and ease of use for DIY conversions. They are available in a number of formats, commonly pouch cells, prismatic cells and cylindrical cells.

==== LiFePO4 pouch cells ====
The majority of this content is drawn from this thread: [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761&start=900 https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761] discussing the use of the A123 20Ah pouch cell. However, many of the general points apply equally to other similar pouch cells.

===== General build requirements =====
Pouch cells are vulnerable to damage from debris, and must be held in compression (see the datasheet for your battery, but 10-12 psi is recommended for the A123 pouch cells as a guide). A rigid container capable of preventing damage and providing compression is therefore required. Be aware the cells expand and contract in use, so allowance for this must be included in the structure of the case.

The pouch cells should be separated to prevent abrasion between cells, and also to avoid the development of hot spots. Prebuilt modules from A123 systems had thin foam sheets or heatsinks between each cell. Be sure to avoid any debris that could rub on the pouch surface, particularly if using recycled cells.

Mylar, '[https://www.americanmicroinc.com/fish-paper/ Fish paper]' or a [https://www.rogerscorp.com/elastomeric-material-solutions/poron-industrial-polyurethanes compliant foam] may be appropriate materials to serve this purpose. This material should not be flammable. If the material is heat insulating, it is important to address thermal management.

===== Compression =====
Compression is required to prevent premature failure of the cell. Without compression electrolyte will become unevenly distributed, causing current gradients in the cell and uneven heating. Local temperatures can become high enough to form gas formation leading to cells 'puffing up' even when the pack is otherwise held within temperature and voltage constraints. This will be exacerbated in packs with otherwise poor thermal management. Compression forces gas generated to the margins of the cell, outside of the cell stack, minimising its effect cell performance. Gas in the middle cells will create a dead space which does not store or release energy.

There is ~1% expansion through a discharge cycle. As the cell ages, the nominal cell thickness can grow by 3-5%. For A123 cells the ideal pressure is between 4 and 18psi with the ideal pressure being ~12psi. Maintaining 12psi can increase the life by 500 cycles over that of 4 or 18psi

There is some suggestion that in uses where 1C is never exceeded compression ''may'' not be required.

Highly rigid endplates with a mechanism to allow for a limited degree of expansion (e.g. steel bands) are considered an effective solution to this challenge.

It should be noted that compression is a challenge specific to pouch cells. Cylindrical cells are designed to maintain their own compression within the cell's electrode stack by their design.

This thread provides more information and experimentation relating to pack compression: <nowiki>https://endless-sphere.com/forums/viewtopic.php?f=14&t=52244</nowiki>

===== Pouch Cell Pack Design Examples =====
<nowiki>*</nowiki>placeholder*

===== Notes regarding recycled pouch cells =====
Pouch cells are somewhat fragile, and breaching the insulation is not difficult, especially in a cells removed from existing packs and repurposed. If the pouch has had their poly-layers compromised you may see a number of faults:
* Black spots around the perimeter of the cell indicate electrolyte leakage
* Voltage on the outside of the bag. Note that microvoltage between the pouch and the electrode is normal (and due to a capacitive effect).
While the majority of these cells should no longer be in the market, a significant number of faulty cells made it back into the 'greymarket' in around 2013. These cells had misaligned tabs which can also lead to isolation failures between the tab and the pack. These cells should be avoided, particularly in high demand applications.

===== Situations likely to cause pouch cell failure =====
''Taken directly from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''
# '''Overcharge'''. Any extended time above 3.8 Volts will generate enough heat and electrochemical activity to puff a cell, especially one that is improperly compressed.
# '''Overdischarge followed by charge'''. Any A123 cell that has been pulled low enough to come to rest at <300 mV should be immediately scrapped. The published number for that is 500 mV, but the real figure is closer to 300, so that's a "safety buffer" if you will. Below this Voltage, the Cu electrodes start to dissolve into the electrolyte. When charge is applied, the Cu forms dendrites that puncture the separator layer, forming an internal short in the cell. This can puff a cell in a hurry---the more charge current on tap, the worse it's prone to be.
# '''Driving a cell negative'''. I've neglected to mention this before, but it is a possibility. I don't know much about the specific mechanism at this time.
# '''Malfunctioning or misinformed electronics'''. This is the most common cause of all of the above in my experience. At this stage of the game, it is critical for YOU to understand how your BMS functions on at least a cursory level. Choose your BMS very carefully and periodically verify that it is operating properly. They're not all created equal. Make sure V sense lines are securely connected and free of corrosion. Just because your BMS says there was never a problem doesn't necessarily make it so. Avoid harnesses or ribbon cables between multiple modules if possible--they are problematic wherever they are used in any mobile electronics.
# '''Exposure to or generation of sufficient heat'''. I don't know exactly at what temperature gas formation begins in the electrolyte, but we spec a max storage temp of 80 (or 85?) degrees C and I suspect this is the reason. The hotter, the puffier--to a point. This is why soldering tabs poses a real hazard to cell health. If you feel you must solder, sink or blow the heat away from the body of the cell. Use a big iron that can make sufficient local heat quickly, before the whole mass of the cell gets hot. You might even get the cell warm enough to melt separator if not careful.
# '''No compression, not enough compression, improperly distributed compression'''. This is a pack/module design issue. Apply 10, maybe 15 psi to your cell stack end to end and then band snugly and evenly. Use hard endplates of some sort--never wrap cells directly or allow their shape to become distorted. Protect all areas of the pouch from impact damage. This obviously does not apply to cylindrical cells.

==== LiFePO4 prismatic cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cylindrical cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cell ageing ====
''Derived (barely paraphrased) from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''

Capacity loss is caused by the lithium that was available for storage becoming permanently plated on the cathode. Being unable to move within the cell it is no longer available to store energy. The impact of this plating is greater than the amount of lithium 'lost' to plating because not only is the lithium no longer available, it is also preventing access to that part of the cathode meaning Li that can still move has to take a longer path to reach the cathode. Lithium plating is one cause of increased cell resistance (there are others), a sign of worsening cell health.

There is no linear relationship between actual capacity loss and impedance rise. However some cell defects will also increase impedance.

Increasing cell resistance may cause a number of symptoms which may be confused with [https://earthshipbiotecture.com/a-lithium-ion-battery-primer/ High Self Discharge.]
# Elevated Peukert Losses. As more energy per amount of current through the cell is lost as heat, the cells useable capacity decreases. So the apparent capacity loss is higher than the actual capacity loss of cycleable lithium. When used in low current applications (e.g. solar energy storage) the actual and apparent decrease in capacity will be small. In high current draw applications (like EV traction packs), the Peukert loss increases proportionally, so the apparent capacity loss increases much faster than the actual capacity loss.
# Greater voltage excursion under the same load. Due to increased cell resistancethe voltage will sag further under the same load than a cell in optimal condition. The inverse is also true, the voltage will be higher for the same amount of charging current applied. The cell will then rebound to a voltage further from the loaded and charging voltages. This, obviously, can look like high self discharge but is a different phenomenon.
# Absolute maximum current decrease.
Elevated impedance causes a more complex constellation of symptoms, some of which may be easy to confuse with High Self Discharge (HSD). Ohm's law (E=I/R) holds the key to understanding here.

'''1) Elevated Peukert losses.''' Because more energy per unit of current through the cell is lost as heat, less of the cell's capacity is actually USABLE. Thus, apparent capacity loss can be significantly greater than actual capacity loss caused by the loss of cycleable Li alone. In low current applications, the two numbers will be close together. In high current applications, Peukert losses increase in proportion, so apparent loss of capacity breaks further and further away from actual capacity loss as current increases.

'''2) Greater voltage excursion under the same load.''' Elevated resistance across the cell means that voltage will sag more under the same load than it did when the cell was healthier. Conversely, voltage will rise higher with the same amount of applied charge current than it did when it was healthier. At the same time, rebound/settling voltages will be further away from loaded/charging voltages. In other words, the cell will rebound to a voltage further away from loaded voltage, all else being equal. Similarly, voltage will settle farther from the charge voltage with the same charge applied. This can give the illusion of elevated self-discharge, but the phenomenon is actually not the same thing. Again, the greater the charge and load currents, the greater the effect becomes.

'''3) Absolute max current decreases.''' Because the cell's series resistance is elevated, the maximum possible current through the cell is decreased.

Just to confuse things further, there can be many factors that lead to impedance rise. Some are related to Li plating, others are not.

=== Lithium-ion ===
Lithium-ion (Li-ion) batteries have a greater energy density than Lithium Iron Phosphate batteries, but have more challenging needs to use safely. The ideal operating range of Li-ion batteries is between +15 and +45°C. The upper limit of temperature is particularly important as Li-ion batteries experience thermal runaway - an unstoppable chain reaction that can occur in milliseconds releasing the stored energy in the cell. This can produce temperatures of 400°C and a fire that is extremely difficult to put out. Thermal runaway can start as low as 60°C and becomes much more likely at 100°C

Risk factors for thermal runaway:
* Short Circuits - either internally or externally
* Overcharging
* Excessive current draw or when charging

==== Li-ion pouch cells ====
[https://kokam.com/cell Kokam] produce high-performance Li-ion pouch cells. These combine relative ease of use and pack construction with performance close to cylindrical cells.

==== Li-ion 18650 and other cylindrical cells ====
Cylindrical cells are favoured by Tesla, and are probably the main reason why their cars achieve such excellent performance. They are light, compact, powerful and expensive. Unfortunately, cylindrical cells are difficult (and potentially dangerous) to use in DIY conversions. There are two good reasons for this: thermal management and cell configuration.

As stated above, Li-ion cells are prone to thermal runaway. So you need perfect battery and thermal management to ensure that no cell ever exceeds the critical voltage or temperature. If this happens, a cell can short-circuit internally, releasing a lot of energy - potentially explosively. Furthermore, the individual cells are small, so need to be arranged in parallel. In the case of the Tesla Model S 85kW pack, there are 74 cells in parallel. Imagine if one of those cells fails and becomes short circuited internally. You now have 73 very high power cells all feeding in to that short circuit...

In fact, you don't have to imagine: you can watch this famous video instead (courtesy of Rich Rebuilds).

<youtube>WdDi1haA71Q</youtube>

== OEM modules ==
Using an OEM module means a lot of the difficulties and safety issues associated with battery design are taken care of e.g. cooling, clamping, etc.

Here is a handy list of OEM modules:
{| class="wikitable sortable mw-collapsible"
|+
!Manufacturer
!Model
!Capacity (kWh)
!Weight (kg)
!w (mm)
!d (mm)
!h (mm)
!Gravity (kg/kWh)
!Volume (L/kWh)
!Voltage (V)
!Current (cont A)
!Current (peak A)
!Cell arrangement
!Cell type
!Chemistry
|-
|Tesla
|Model S 85kWh
|5.3
|26
|690
|315
|80
|4.9
|3.3
|22.8
|500
|750
|74p6s
|18650
|Li-ion
|-
|Tesla
|Model S 100kWh
|6.4
|28
|680
|315
|80
|4.4
|2.7
|22.8
|
|870
|86p6s
|18650
|Li-ion
|-
|Tesla
|Model 3 LR (inner)
|19.2
|98.9
|1854
|292
|90
|5.2
|2.5
|91.1
|
|971
|46p25s
|2170
|Li-ion
|-
|Tesla
|Model 3 LR (outer)
|17.7
|86.6
|1715
|292
|90
|4.9
|2.5
|83.9
|
|971
|46p23s
|2170
|Li-ion
|-
|Tesla
|Model 3 SR (inner)
|13.0
|
|1854
|292
|90
|
|3.7
|91.1
|
|603
|31p25s
|2170
|Li-ion
|-
|Tesla
|Model 3 SR (outer)
|12.0
|
|1715
|292
|90
|
|3.8
|83.9
|
|603
|31p23s
|2170
|Li-ion
|-
|Chevrolet
|Volt 2012
|4
|38
|470
|180
|280
|9.5
|5.9
|88
|140
|210
|24s
|Pouch
|Li-ion
|-
|BMW
|i3 60Ah
|2
|13
|368
|178
|102
|6.5
|3.3
|28.8
|210
|350
|2p8s
|Prismatic
|Li-ion
|-
|BMW
|i3 94Ah
|4.15
|28
|410
|310
|150
|6.7
|4.6
|45.6
|
|409
|12s
|Prismatic
|Li-ion
|-
|BMW
|i3 120Ah
|5.3
|28
|410
|310
|150
|5.3
|3.6
|45.6
|
|360
|12s
|Prismatic
|Li-ion
|-
|Jaguar
|iPace
|2.5
|12
|340
|155
|112
|4.8
|2.4
|10.8
|720
|1200
|4p3s
|Pouch
|Li-ion
|-
|Mitsubishi
|Outlander
|2.4
|26
|646
|184
|130
|10.8
|6.4
|60
|
|240
|16s
|
|Li-ion
|-
|Nissan
|Leaf 24kWh
|0.5
|3.65
|300
|222
|34
|7.3
|4.5
|7.2
|130
|228
|2p2s
|Pouch
|Li-ion LMO
|-
|Nissan
|Leaf 30kWh
|1.25
|
|300
|222
|34
|
|3.6
|14.4
|
|
|2p4s
|Pouch
|Li-ion
|-
|Nissan
|Leaf 40kWh
|1.6
|8.7
|300
|222
|68
|5.4
|2.8
|14.4
|
|314
|2p4s
|Pouch
|Li-ion NMC
|-
|Nissan
|Leaf 62kWh
|2.58
|
|
|
|
|
|
|14.4
|
|
|3p4s
|
|Li-ion
|-
|Volvo
|XC90 T8
|2.01
|12.1
|300
|180
|150
|6.0
|4.0
|59.2
|170
|340
|16s
|
|Li-ion
|}

Batteries

2020-12-07T08:45:19Z

Clanger9: /* Capacity (kWh) */

== Introduction ==
There are a wide variety of battery chemistries available for use as the main traction battery of an EV. To use each chemistry safely, and to ensure an adequate service life from the battery pack it is important to understand the requirements for the chemistry you are using. Failure to do so may lead to premature or catastrophic failure of the pack.

Good pack design will allow for a nominal amount of abuse. People make mistakes and the pack should allow a margin for safety - and for longevity!

== Battery pack specification ==
When deciding on your battery pack, here are some basic parameters to consider:

=== Capacity (kWh) ===
'''How far do you want to go?''' A standard car conversion will need a kWh for each 3, maybe 4 miles of range (very approximately). For a middleweight motorcycle, a kWh should give around 9 miles. Your mileage may vary, ''as they say.''

=== Voltage (V) ===
'''How fast do you want to go?''' The pack voltage defines the maximum speed your motor can spin. Motors are usually specified with "KV" - or RPM-per-volt. Check the KV of your motor and how fast it needs to spin to get your desired top speed. e.g. if you need 3,000 RPM from a 25 KV motor then your pack voltage needs to be 3,000 / 25 = 120 V. The exact number of cells in series you need depends on the cell design, but 3.8 V for Li-ion and 3.2 V for LiFePO4 is a reasonable guess.

=== Maximum current (A) ===
'''How quickly do you want to accelerate?''' Your motor's maximum power will be specified in kW. To estimate your maximum current draw, divide the peak power by the battery voltage. e.g. a 30 kW motor with a 120 V battery pack will pull 30,000 / 120 = 250 A. The higher the current rating of the cells, the heavier they will be for a given capacity. Ideally, you want "enough" current capacity for full throttle acceleration, but no more. You can put cells in parallel to double the current rating of your pack (which of course will half the voltage).

=== Mass (kg) ===
'''Can your vehicle carry the weight?''' You'll need to keep the kerb weight within the original design limits. For a car, this could be a few hundred kg. For a motorcycle, likely less than 100 kg. This is a huge variable - and each new generation of battery tech seems to be a little lighter. For older EV or hybrid batteries, you can reckon on approximately 10 kg/kWh. Nissan Leaf batteries are relatively light (7.5 kg/kWh). With the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 5-6 kg/kWh.

=== Volume (L) ===
'''Will it fit?''' Batteries are bulky. They are getting smaller, but finding enough space might be your biggest challenge. You could be looking at over 5 L/kWh for older EV or hybrid batteries. Current state-of-the-art is the Tesla Model 3, which gets this down to 2.5 L/kWh by using 2170 cylindrical cells.

There is much, much more to battery design than this (e.g. maximum charge rate, terminations, cooling, clamping), but the above should help work out which options will or won't work for your project...

== Cell chemistry ==

=== Lithium Iron Phosphate (LiFePO4) ===
Lithium Iron Phosphate (also known as LFP, or LiFePO4) batteries offer a good compromise between safety, energy density and ease of use for DIY conversions. They are available in a number of formats, commonly pouch cells, prismatic cells and cylindrical cells.

==== LiFePO4 pouch cells ====
The majority of this content is drawn from this thread: [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761&start=900 https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761] discussing the use of the A123 20Ah pouch cell. However, many of the general points apply equally to other similar pouch cells.

===== General build requirements =====
Pouch cells are vulnerable to damage from debris, and must be held in compression (see the datasheet for your battery, but 10-12 psi is recommended for the A123 pouch cells as a guide). A rigid container capable of preventing damage and providing compression is therefore required. Be aware the cells expand and contract in use, so allowance for this must be included in the structure of the case.

The pouch cells should be separated to prevent abrasion between cells, and also to avoid the development of hot spots. Prebuilt modules from A123 systems had thin foam sheets or heatsinks between each cell. Be sure to avoid any debris that could rub on the pouch surface, particularly if using recycled cells.

Mylar, '[https://www.americanmicroinc.com/fish-paper/ Fish paper]' or a [https://www.rogerscorp.com/elastomeric-material-solutions/poron-industrial-polyurethanes compliant foam] may be appropriate materials to serve this purpose. This material should not be flammable. If the material is heat insulating, it is important to address thermal management.

===== Compression =====
Compression is required to prevent premature failure of the cell. Without compression electrolyte will become unevenly distributed, causing current gradients in the cell and uneven heating. Local temperatures can become high enough to form gas formation leading to cells 'puffing up' even when the pack is otherwise held within temperature and voltage constraints. This will be exacerbated in packs with otherwise poor thermal management. Compression forces gas generated to the margins of the cell, outside of the cell stack, minimising its effect cell performance. Gas in the middle cells will create a dead space which does not store or release energy.

There is ~1% expansion through a discharge cycle. As the cell ages, the nominal cell thickness can grow by 3-5%. For A123 cells the ideal pressure is between 4 and 18psi with the ideal pressure being ~12psi. Maintaining 12psi can increase the life by 500 cycles over that of 4 or 18psi

There is some suggestion that in uses where 1C is never exceeded compression ''may'' not be required.

Highly rigid endplates with a mechanism to allow for a limited degree of expansion (e.g. steel bands) are considered an effective solution to this challenge.

It should be noted that compression is a challenge specific to pouch cells. Cylindrical cells are designed to maintain their own compression within the cell's electrode stack by their design.

This thread provides more information and experimentation relating to pack compression: <nowiki>https://endless-sphere.com/forums/viewtopic.php?f=14&t=52244</nowiki>

===== Pouch Cell Pack Design Examples =====
<nowiki>*</nowiki>placeholder*

===== Notes regarding recycled pouch cells =====
Pouch cells are somewhat fragile, and breaching the insulation is not difficult, especially in a cells removed from existing packs and repurposed. If the pouch has had their poly-layers compromised you may see a number of faults:
* Black spots around the perimeter of the cell indicate electrolyte leakage
* Voltage on the outside of the bag. Note that microvoltage between the pouch and the electrode is normal (and due to a capacitive effect).
While the majority of these cells should no longer be in the market, a significant number of faulty cells made it back into the 'greymarket' in around 2013. These cells had misaligned tabs which can also lead to isolation failures between the tab and the pack. These cells should be avoided, particularly in high demand applications.

===== Situations likely to cause pouch cell failure =====
''Taken directly from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''
# '''Overcharge'''. Any extended time above 3.8 Volts will generate enough heat and electrochemical activity to puff a cell, especially one that is improperly compressed.
# '''Overdischarge followed by charge'''. Any A123 cell that has been pulled low enough to come to rest at <300 mV should be immediately scrapped. The published number for that is 500 mV, but the real figure is closer to 300, so that's a "safety buffer" if you will. Below this Voltage, the Cu electrodes start to dissolve into the electrolyte. When charge is applied, the Cu forms dendrites that puncture the separator layer, forming an internal short in the cell. This can puff a cell in a hurry---the more charge current on tap, the worse it's prone to be.
# '''Driving a cell negative'''. I've neglected to mention this before, but it is a possibility. I don't know much about the specific mechanism at this time.
# '''Malfunctioning or misinformed electronics'''. This is the most common cause of all of the above in my experience. At this stage of the game, it is critical for YOU to understand how your BMS functions on at least a cursory level. Choose your BMS very carefully and periodically verify that it is operating properly. They're not all created equal. Make sure V sense lines are securely connected and free of corrosion. Just because your BMS says there was never a problem doesn't necessarily make it so. Avoid harnesses or ribbon cables between multiple modules if possible--they are problematic wherever they are used in any mobile electronics.
# '''Exposure to or generation of sufficient heat'''. I don't know exactly at what temperature gas formation begins in the electrolyte, but we spec a max storage temp of 80 (or 85?) degrees C and I suspect this is the reason. The hotter, the puffier--to a point. This is why soldering tabs poses a real hazard to cell health. If you feel you must solder, sink or blow the heat away from the body of the cell. Use a big iron that can make sufficient local heat quickly, before the whole mass of the cell gets hot. You might even get the cell warm enough to melt separator if not careful.
# '''No compression, not enough compression, improperly distributed compression'''. This is a pack/module design issue. Apply 10, maybe 15 psi to your cell stack end to end and then band snugly and evenly. Use hard endplates of some sort--never wrap cells directly or allow their shape to become distorted. Protect all areas of the pouch from impact damage. This obviously does not apply to cylindrical cells.

==== LiFePO4 prismatic cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cylindrical cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cell ageing ====
''Derived (barely paraphrased) from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''

Capacity loss is caused by the lithium that was available for storage becoming permanently plated on the cathode. Being unable to move within the cell it is no longer available to store energy. The impact of this plating is greater than the amount of lithium 'lost' to plating because not only is the lithium no longer available, it is also preventing access to that part of the cathode meaning Li that can still move has to take a longer path to reach the cathode. Lithium plating is one cause of increased cell resistance (there are others), a sign of worsening cell health.

There is no linear relationship between actual capacity loss and impedance rise. However some cell defects will also increase impedance.

Increasing cell resistance may cause a number of symptoms which may be confused with [https://earthshipbiotecture.com/a-lithium-ion-battery-primer/ High Self Discharge.]
# Elevated Peukert Losses. As more energy per amount of current through the cell is lost as heat, the cells useable capacity decreases. So the apparent capacity loss is higher than the actual capacity loss of cycleable lithium. When used in low current applications (e.g. solar energy storage) the actual and apparent decrease in capacity will be small. In high current draw applications (like EV traction packs), the Peukert loss increases proportionally, so the apparent capacity loss increases much faster than the actual capacity loss.
# Greater voltage excursion under the same load. Due to increased cell resistancethe voltage will sag further under the same load than a cell in optimal condition. The inverse is also true, the voltage will be higher for the same amount of charging current applied. The cell will then rebound to a voltage further from the loaded and charging voltages. This, obviously, can look like high self discharge but is a different phenomenon.
# Absolute maximum current decrease.
Elevated impedance causes a more complex constellation of symptoms, some of which may be easy to confuse with High Self Discharge (HSD). Ohm's law (E=I/R) holds the key to understanding here.

'''1) Elevated Peukert losses.''' Because more energy per unit of current through the cell is lost as heat, less of the cell's capacity is actually USABLE. Thus, apparent capacity loss can be significantly greater than actual capacity loss caused by the loss of cycleable Li alone. In low current applications, the two numbers will be close together. In high current applications, Peukert losses increase in proportion, so apparent loss of capacity breaks further and further away from actual capacity loss as current increases.

'''2) Greater voltage excursion under the same load.''' Elevated resistance across the cell means that voltage will sag more under the same load than it did when the cell was healthier. Conversely, voltage will rise higher with the same amount of applied charge current than it did when it was healthier. At the same time, rebound/settling voltages will be further away from loaded/charging voltages. In other words, the cell will rebound to a voltage further away from loaded voltage, all else being equal. Similarly, voltage will settle farther from the charge voltage with the same charge applied. This can give the illusion of elevated self-discharge, but the phenomenon is actually not the same thing. Again, the greater the charge and load currents, the greater the effect becomes.

'''3) Absolute max current decreases.''' Because the cell's series resistance is elevated, the maximum possible current through the cell is decreased.

Just to confuse things further, there can be many factors that lead to impedance rise. Some are related to Li plating, others are not.

=== Lithium-ion ===
Lithium-ion (Li-ion) batteries have a greater energy density than Lithium Iron Phosphate batteries, but have more challenging needs to use safely. The ideal operating range of Li-ion batteries is between +15 and +45°C. The upper limit of temperature is particularly important as Li-ion batteries experience thermal runaway - an unstoppable chain reaction that can occur in milliseconds releasing the stored energy in the cell. This can produce temperatures of 400°C and a fire that is extremely difficult to put out. Thermal runaway can start as low as 60°C and becomes much more likely at 100°C

Risk factors for thermal runaway:
* Short Circuits - either internally or externally
* Overcharging
* Excessive current draw or when charging

==== Li-ion pouch cells ====
[https://kokam.com/cell Kokam] produce high-performance Li-ion pouch cells. These combine relative ease of use and pack construction with performance close to cylindrical cells.

==== Li-ion 18650 and other cylindrical cells ====
Cylindrical cells are favoured by Tesla, and are probably the main reason why their cars achieve such excellent performance. They are light, compact, powerful and expensive. Unfortunately, cylindrical cells are difficult (and potentially dangerous) to use in DIY conversions. There are two good reasons for this: thermal management and cell configuration.

As stated above, Li-ion cells are prone to thermal runaway. So you need perfect battery and thermal management to ensure that no cell ever exceeds the critical voltage or temperature. If this happens, a cell can short-circuit internally, releasing a lot of energy - potentially explosively. Furthermore, the individual cells are small, so need to be arranged in parallel. In the case of the Tesla Model S 85kW pack, there are 74 cells in parallel. Imagine if one of those cells fails and becomes short circuited internally. You now have 73 very high power cells all feeding in to that short circuit...

In fact, you don't have to imagine: you can watch this famous video instead (courtesy of Rich Rebuilds).

<youtube>WdDi1haA71Q</youtube>

== OEM modules ==
Using an OEM module means a lot of the difficulties and safety issues associated with battery design are taken care of e.g. cooling, clamping, etc.

Here is a handy list of OEM modules:
{| class="wikitable sortable mw-collapsible"
|+
!Manufacturer
!Model
!Capacity (kWh)
!Weight (kg)
!w (mm)
!d (mm)
!h (mm)
!Gravity (kg/kWh)
!Volume (L/kWh)
!Voltage (V)
!Current (cont A)
!Current (peak A)
!Cell arrangement
!Cell type
!Chemistry
|-
|Tesla
|Model S 85kWh
|5.3
|26
|690
|315
|80
|4.9
|3.3
|22.8
|500
|750
|74p6s
|18650
|Li-ion
|-
|Tesla
|Model S 100kWh
|6.4
|28
|680
|315
|80
|4.4
|2.7
|22.8
|
|870
|86p6s
|18650
|Li-ion
|-
|Tesla
|Model 3 LR (inner)
|19.2
|98.9
|1854
|292
|90
|5.2
|2.5
|91.1
|
|971
|46p25s
|2170
|Li-ion
|-
|Tesla
|Model 3 LR (outer)
|17.7
|86.6
|1715
|292
|90
|4.9
|2.5
|83.9
|
|971
|46p23s
|2170
|Li-ion
|-
|Tesla
|Model 3 SR (inner)
|13.0
|
|1854
|292
|90
|
|3.7
|91.1
|
|603
|31p25s
|2170
|Li-ion
|-
|Tesla
|Model 3 SR (outer)
|12.0
|
|1715
|292
|90
|
|3.8
|83.9
|
|603
|31p23s
|2170
|Li-ion
|-
|Chevrolet
|Volt 2012
|4
|38
|470
|180
|280
|9.5
|5.9
|88
|140
|210
|24s
|Pouch
|Li-ion
|-
|BMW
|i3 60Ah
|2
|13
|368
|178
|102
|6.5
|3.3
|28.8
|210
|350
|2p8s
|Prismatic
|Li-ion
|-
|BMW
|i3 94Ah
|4.15
|28
|410
|310
|150
|6.7
|4.6
|45.6
|
|409
|12s
|Prismatic
|Li-ion
|-
|BMW
|i3 120Ah
|5.3
|28
|410
|310
|150
|5.3
|3.6
|45.6
|
|360
|12s
|Prismatic
|Li-ion
|-
|Jaguar
|iPace
|2.5
|12
|340
|155
|112
|4.8
|2.4
|10.8
|720
|1200
|4p3s
|Pouch
|Li-ion
|-
|Mitsubishi
|Outlander
|2.4
|26
|646
|184
|130
|10.8
|6.4
|60
|
|240
|16s
|
|Li-ion
|-
|Nissan
|Leaf 24kWh
|0.5
|3.65
|300
|222
|34
|7.3
|4.5
|7.4
|130
|228
|2p2s
|Pouch
|Li-ion LMO
|-
|Nissan
|Leaf 40kWh
|1.6
|8.7
|300
|222
|68
|5.4
|2.8
|14.6
|
|314
|2p4s
|Pouch
|Li-ion NMC
|-
|Volvo
|XC90 T8
|2.01
|12.1
|300
|180
|150
|6.0
|4.0
|59.2
|170
|340
|16s
|
|Li-ion
|}

Batteries

2020-12-06T18:35:38Z

Clanger9: /* OEM modules */

== Introduction ==
There are a wide variety of battery chemistries available for use as the main traction battery of an EV. To use each chemistry safely, and to ensure an adequate service life from the battery pack it is important to understand the requirements for the chemistry you are using. Failure to do so may lead to premature or catastrophic failure of the pack.

Good pack design will allow for a nominal amount of abuse. People make mistakes and the pack should allow a margin for safety - and for longevity!

== Battery pack specification ==
When deciding on your battery pack, here are some basic parameters to consider:

=== Capacity (kWh) ===
'''How far do you want to go?''' A standard car conversion will need a kWh for each 3 miles of range (very approximately). For a middleweight motorcycle, a kWh should give around 9 miles. Your mileage may vary, ''as they say.''

=== Voltage (V) ===
'''How fast do you want to go?''' The pack voltage defines the maximum speed your motor can spin. Motors are usually specified with "KV" - or RPM-per-volt. Check the KV of your motor and how fast it needs to spin to get your desired top speed. e.g. if you need 3,000 RPM from a 25 KV motor then your pack voltage needs to be 3,000 / 25 = 120 V. The exact number of cells in series you need depends on the cell design, but 3.8 V for Li-ion and 3.2 V for LiFePO4 is a reasonable guess.

=== Maximum current (A) ===
'''How quickly do you want to accelerate?''' Your motor's maximum power will be specified in kW. To estimate your maximum current draw, divide the peak power by the battery voltage. e.g. a 30 kW motor with a 120 V battery pack will pull 30,000 / 120 = 250 A. The higher the current rating of the cells, the heavier they will be for a given capacity. Ideally, you want "enough" current capacity for full throttle acceleration, but no more. You can put cells in parallel to double the current rating of your pack (which of course will half the voltage).

=== Mass (kg) ===
'''Can your vehicle carry the weight?''' You'll need to keep the kerb weight within the original design limits. For a car, this could be a few hundred kg. For a motorcycle, likely less than 100 kg. This is a huge variable - and each new generation of battery tech seems to be a little lighter. For older EV or hybrid batteries, you can reckon on approximately 10 kg/kWh. Nissan Leaf batteries are relatively light (7.5 kg/kWh). With the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 5-6 kg/kWh.

=== Volume (L) ===
'''Will it fit?''' Batteries are bulky. They are getting smaller, but finding enough space might be your biggest challenge. You could be looking at over 5 L/kWh for older EV or hybrid batteries. Current state-of-the-art is the Tesla Model 3, which gets this down to 2.5 L/kWh by using 2170 cylindrical cells.

There is much, much more to battery design than this (e.g. maximum charge rate, terminations, cooling, clamping), but the above should help work out which options will or won't work for your project...

== Cell chemistry ==

=== Lithium Iron Phosphate (LiFePO4) ===
Lithium Iron Phosphate (also known as LFP, or LiFePO4) batteries offer a good compromise between safety, energy density and ease of use for DIY conversions. They are available in a number of formats, commonly pouch cells, prismatic cells and cylindrical cells.

==== LiFePO4 pouch cells ====
The majority of this content is drawn from this thread: [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761&start=900 https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761] discussing the use of the A123 20Ah pouch cell. However, many of the general points apply equally to other similar pouch cells.

===== General build requirements =====
Pouch cells are vulnerable to damage from debris, and must be held in compression (see the datasheet for your battery, but 10-12 psi is recommended for the A123 pouch cells as a guide). A rigid container capable of preventing damage and providing compression is therefore required. Be aware the cells expand and contract in use, so allowance for this must be included in the structure of the case.

The pouch cells should be separated to prevent abrasion between cells, and also to avoid the development of hot spots. Prebuilt modules from A123 systems had thin foam sheets or heatsinks between each cell. Be sure to avoid any debris that could rub on the pouch surface, particularly if using recycled cells.

Mylar, '[https://www.americanmicroinc.com/fish-paper/ Fish paper]' or a [https://www.rogerscorp.com/elastomeric-material-solutions/poron-industrial-polyurethanes compliant foam] may be appropriate materials to serve this purpose. This material should not be flammable. If the material is heat insulating, it is important to address thermal management.

===== Compression =====
Compression is required to prevent premature failure of the cell. Without compression electrolyte will become unevenly distributed, causing current gradients in the cell and uneven heating. Local temperatures can become high enough to form gas formation leading to cells 'puffing up' even when the pack is otherwise held within temperature and voltage constraints. This will be exacerbated in packs with otherwise poor thermal management. Compression forces gas generated to the margins of the cell, outside of the cell stack, minimising its effect cell performance. Gas in the middle cells will create a dead space which does not store or release energy.

There is ~1% expansion through a discharge cycle. As the cell ages, the nominal cell thickness can grow by 3-5%. For A123 cells the ideal pressure is between 4 and 18psi with the ideal pressure being ~12psi. Maintaining 12psi can increase the life by 500 cycles over that of 4 or 18psi

There is some suggestion that in uses where 1C is never exceeded compression ''may'' not be required.

Highly rigid endplates with a mechanism to allow for a limited degree of expansion (e.g. steel bands) are considered an effective solution to this challenge.

It should be noted that compression is a challenge specific to pouch cells. Cylindrical cells are designed to maintain their own compression within the cell's electrode stack by their design.

This thread provides more information and experimentation relating to pack compression: <nowiki>https://endless-sphere.com/forums/viewtopic.php?f=14&t=52244</nowiki>

===== Pouch Cell Pack Design Examples =====
<nowiki>*</nowiki>placeholder*

===== Notes regarding recycled pouch cells =====
Pouch cells are somewhat fragile, and breaching the insulation is not difficult, especially in a cells removed from existing packs and repurposed. If the pouch has had their poly-layers compromised you may see a number of faults:
* Black spots around the perimeter of the cell indicate electrolyte leakage
* Voltage on the outside of the bag. Note that microvoltage between the pouch and the electrode is normal (and due to a capacitive effect).
While the majority of these cells should no longer be in the market, a significant number of faulty cells made it back into the 'greymarket' in around 2013. These cells had misaligned tabs which can also lead to isolation failures between the tab and the pack. These cells should be avoided, particularly in high demand applications.

===== Situations likely to cause pouch cell failure =====
''Taken directly from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''
# '''Overcharge'''. Any extended time above 3.8 Volts will generate enough heat and electrochemical activity to puff a cell, especially one that is improperly compressed.
# '''Overdischarge followed by charge'''. Any A123 cell that has been pulled low enough to come to rest at <300 mV should be immediately scrapped. The published number for that is 500 mV, but the real figure is closer to 300, so that's a "safety buffer" if you will. Below this Voltage, the Cu electrodes start to dissolve into the electrolyte. When charge is applied, the Cu forms dendrites that puncture the separator layer, forming an internal short in the cell. This can puff a cell in a hurry---the more charge current on tap, the worse it's prone to be.
# '''Driving a cell negative'''. I've neglected to mention this before, but it is a possibility. I don't know much about the specific mechanism at this time.
# '''Malfunctioning or misinformed electronics'''. This is the most common cause of all of the above in my experience. At this stage of the game, it is critical for YOU to understand how your BMS functions on at least a cursory level. Choose your BMS very carefully and periodically verify that it is operating properly. They're not all created equal. Make sure V sense lines are securely connected and free of corrosion. Just because your BMS says there was never a problem doesn't necessarily make it so. Avoid harnesses or ribbon cables between multiple modules if possible--they are problematic wherever they are used in any mobile electronics.
# '''Exposure to or generation of sufficient heat'''. I don't know exactly at what temperature gas formation begins in the electrolyte, but we spec a max storage temp of 80 (or 85?) degrees C and I suspect this is the reason. The hotter, the puffier--to a point. This is why soldering tabs poses a real hazard to cell health. If you feel you must solder, sink or blow the heat away from the body of the cell. Use a big iron that can make sufficient local heat quickly, before the whole mass of the cell gets hot. You might even get the cell warm enough to melt separator if not careful.
# '''No compression, not enough compression, improperly distributed compression'''. This is a pack/module design issue. Apply 10, maybe 15 psi to your cell stack end to end and then band snugly and evenly. Use hard endplates of some sort--never wrap cells directly or allow their shape to become distorted. Protect all areas of the pouch from impact damage. This obviously does not apply to cylindrical cells.

==== LiFePO4 prismatic cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cylindrical cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cell ageing ====
''Derived (barely paraphrased) from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''

Capacity loss is caused by the lithium that was available for storage becoming permanently plated on the cathode. Being unable to move within the cell it is no longer available to store energy. The impact of this plating is greater than the amount of lithium 'lost' to plating because not only is the lithium no longer available, it is also preventing access to that part of the cathode meaning Li that can still move has to take a longer path to reach the cathode. Lithium plating is one cause of increased cell resistance (there are others), a sign of worsening cell health.

There is no linear relationship between actual capacity loss and impedance rise. However some cell defects will also increase impedance.

Increasing cell resistance may cause a number of symptoms which may be confused with [https://earthshipbiotecture.com/a-lithium-ion-battery-primer/ High Self Discharge.]
# Elevated Peukert Losses. As more energy per amount of current through the cell is lost as heat, the cells useable capacity decreases. So the apparent capacity loss is higher than the actual capacity loss of cycleable lithium. When used in low current applications (e.g. solar energy storage) the actual and apparent decrease in capacity will be small. In high current draw applications (like EV traction packs), the Peukert loss increases proportionally, so the apparent capacity loss increases much faster than the actual capacity loss.
# Greater voltage excursion under the same load. Due to increased cell resistancethe voltage will sag further under the same load than a cell in optimal condition. The inverse is also true, the voltage will be higher for the same amount of charging current applied. The cell will then rebound to a voltage further from the loaded and charging voltages. This, obviously, can look like high self discharge but is a different phenomenon.
# Absolute maximum current decrease.
Elevated impedance causes a more complex constellation of symptoms, some of which may be easy to confuse with High Self Discharge (HSD). Ohm's law (E=I/R) holds the key to understanding here.

'''1) Elevated Peukert losses.''' Because more energy per unit of current through the cell is lost as heat, less of the cell's capacity is actually USABLE. Thus, apparent capacity loss can be significantly greater than actual capacity loss caused by the loss of cycleable Li alone. In low current applications, the two numbers will be close together. In high current applications, Peukert losses increase in proportion, so apparent loss of capacity breaks further and further away from actual capacity loss as current increases.

'''2) Greater voltage excursion under the same load.''' Elevated resistance across the cell means that voltage will sag more under the same load than it did when the cell was healthier. Conversely, voltage will rise higher with the same amount of applied charge current than it did when it was healthier. At the same time, rebound/settling voltages will be further away from loaded/charging voltages. In other words, the cell will rebound to a voltage further away from loaded voltage, all else being equal. Similarly, voltage will settle farther from the charge voltage with the same charge applied. This can give the illusion of elevated self-discharge, but the phenomenon is actually not the same thing. Again, the greater the charge and load currents, the greater the effect becomes.

'''3) Absolute max current decreases.''' Because the cell's series resistance is elevated, the maximum possible current through the cell is decreased.

Just to confuse things further, there can be many factors that lead to impedance rise. Some are related to Li plating, others are not.

=== Lithium-ion ===
Lithium-ion (Li-ion) batteries have a greater energy density than Lithium Iron Phosphate batteries, but have more challenging needs to use safely. The ideal operating range of Li-ion batteries is between +15 and +45°C. The upper limit of temperature is particularly important as Li-ion batteries experience thermal runaway - an unstoppable chain reaction that can occur in milliseconds releasing the stored energy in the cell. This can produce temperatures of 400°C and a fire that is extremely difficult to put out. Thermal runaway can start as low as 60°C and becomes much more likely at 100°C

Risk factors for thermal runaway:
* Short Circuits - either internally or externally
* Overcharging
* Excessive current draw or when charging

==== Li-ion pouch cells ====
[https://kokam.com/cell Kokam] produce high-performance Li-ion pouch cells. These combine relative ease of use and pack construction with performance close to cylindrical cells.

==== Li-ion 18650 and other cylindrical cells ====
Cylindrical cells are favoured by Tesla, and are probably the main reason why their cars achieve such excellent performance. They are light, compact, powerful and expensive. Unfortunately, cylindrical cells are difficult (and potentially dangerous) to use in DIY conversions. There are two good reasons for this: thermal management and cell configuration.

As stated above, Li-ion cells are prone to thermal runaway. So you need perfect battery and thermal management to ensure that no cell ever exceeds the critical voltage or temperature. If this happens, a cell can short-circuit internally, releasing a lot of energy - potentially explosively. Furthermore, the individual cells are small, so need to be arranged in parallel. In the case of the Tesla Model S 85kW pack, there are 74 cells in parallel. Imagine if one of those cells fails and becomes short circuited internally. You now have 73 very high power cells all feeding in to that short circuit...

In fact, you don't have to imagine: you can watch this famous video instead (courtesy of Rich Rebuilds).

<youtube>WdDi1haA71Q</youtube>

== OEM modules ==
Using an OEM module means a lot of the difficulties and safety issues associated with battery design are taken care of e.g. cooling, clamping, etc.

Here is a handy list of OEM modules:
{| class="wikitable sortable mw-collapsible"
|+
!Manufacturer
!Model
!Capacity (kWh)
!Weight (kg)
!w (mm)
!d (mm)
!h (mm)
!Gravity (kg/kWh)
!Volume (L/kWh)
!Voltage (V)
!Current (cont A)
!Current (peak A)
!Cell arrangement
!Cell type
!Chemistry
|-
|Tesla
|Model S 85kWh
|5.3
|26
|690
|315
|80
|4.9
|3.3
|22.8
|500
|750
|74p6s
|18650
|Li-ion
|-
|Tesla
|Model S 100kWh
|6.4
|28
|680
|315
|80
|4.4
|2.7
|22.8
|
|870
|86p6s
|18650
|Li-ion
|-
|Tesla
|Model 3 LR (inner)
|19.2
|98.9
|1854
|292
|90
|5.2
|2.5
|91.1
|
|971
|46p25s
|2170
|Li-ion
|-
|Tesla
|Model 3 LR (outer)
|17.7
|86.6
|1715
|292
|90
|4.9
|2.5
|83.9
|
|971
|46p23s
|2170
|Li-ion
|-
|Tesla
|Model 3 SR (inner)
|13.0
|
|1854
|292
|90
|
|3.7
|91.1
|
|603
|31p25s
|2170
|Li-ion
|-
|Tesla
|Model 3 SR (outer)
|12.0
|
|1715
|292
|90
|
|3.8
|83.9
|
|603
|31p23s
|2170
|Li-ion
|-
|Chevrolet
|Volt 2012
|4
|38
|470
|180
|280
|9.5
|5.9
|88
|140
|210
|24s
|Pouch
|Li-ion
|-
|BMW
|i3 60Ah
|2
|13
|368
|178
|102
|6.5
|3.3
|28.8
|210
|350
|2p8s
|Prismatic
|Li-ion
|-
|BMW
|i3 94Ah
|4.15
|28
|410
|310
|150
|6.7
|4.6
|45.6
|
|409
|12s
|Prismatic
|Li-ion
|-
|BMW
|i3 120Ah
|5.3
|28
|410
|310
|150
|5.3
|3.6
|45.6
|
|360
|12s
|Prismatic
|Li-ion
|-
|Jaguar
|iPace
|2.5
|12
|340
|155
|112
|4.8
|2.4
|10.8
|720
|1200
|4p3s
|Pouch
|Li-ion
|-
|Mitsubishi
|Outlander
|2.4
|26
|646
|184
|130
|10.8
|6.4
|60
|
|240
|16s
|
|Li-ion
|-
|Nissan
|Leaf 24kWh
|0.5
|3.65
|300
|222
|34
|7.3
|4.5
|7.4
|130
|228
|2p2s
|Pouch
|Li-ion LMO
|-
|Nissan
|Leaf 40kWh
|1.6
|8.7
|300
|222
|68
|5.4
|2.8
|14.6
|
|314
|2p4s
|Pouch
|Li-ion NMC
|-
|Volvo
|XC90 T8
|2.01
|12.1
|300
|180
|150
|6.0
|4.0
|59.2
|170
|340
|16s
|
|Li-ion
|}

Batteries

2020-12-06T18:33:26Z

Clanger9: /* OEM modules */ Correct iPace entry

== Introduction ==
There are a wide variety of battery chemistries available for use as the main traction battery of an EV. To use each chemistry safely, and to ensure an adequate service life from the battery pack it is important to understand the requirements for the chemistry you are using. Failure to do so may lead to premature or catastrophic failure of the pack.

Good pack design will allow for a nominal amount of abuse. People make mistakes and the pack should allow a margin for safety - and for longevity!

== Battery pack specification ==
When deciding on your battery pack, here are some basic parameters to consider:

=== Capacity (kWh) ===
'''How far do you want to go?''' A standard car conversion will need a kWh for each 3 miles of range (very approximately). For a middleweight motorcycle, a kWh should give around 9 miles. Your mileage may vary, ''as they say.''

=== Voltage (V) ===
'''How fast do you want to go?''' The pack voltage defines the maximum speed your motor can spin. Motors are usually specified with "KV" - or RPM-per-volt. Check the KV of your motor and how fast it needs to spin to get your desired top speed. e.g. if you need 3,000 RPM from a 25 KV motor then your pack voltage needs to be 3,000 / 25 = 120 V. The exact number of cells in series you need depends on the cell design, but 3.8 V for Li-ion and 3.2 V for LiFePO4 is a reasonable guess.

=== Maximum current (A) ===
'''How quickly do you want to accelerate?''' Your motor's maximum power will be specified in kW. To estimate your maximum current draw, divide the peak power by the battery voltage. e.g. a 30 kW motor with a 120 V battery pack will pull 30,000 / 120 = 250 A. The higher the current rating of the cells, the heavier they will be for a given capacity. Ideally, you want "enough" current capacity for full throttle acceleration, but no more. You can put cells in parallel to double the current rating of your pack (which of course will half the voltage).

=== Mass (kg) ===
'''Can your vehicle carry the weight?''' You'll need to keep the kerb weight within the original design limits. For a car, this could be a few hundred kg. For a motorcycle, likely less than 100 kg. This is a huge variable - and each new generation of battery tech seems to be a little lighter. For older EV or hybrid batteries, you can reckon on approximately 10 kg/kWh. Nissan Leaf batteries are relatively light (7.5 kg/kWh). With the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 5-6 kg/kWh.

=== Volume (L) ===
'''Will it fit?''' Batteries are bulky. They are getting smaller, but finding enough space might be your biggest challenge. You could be looking at over 5 L/kWh for older EV or hybrid batteries. Current state-of-the-art is the Tesla Model 3, which gets this down to 2.5 L/kWh by using 2170 cylindrical cells.

There is much, much more to battery design than this (e.g. maximum charge rate, terminations, cooling, clamping), but the above should help work out which options will or won't work for your project...

== Cell chemistry ==

=== Lithium Iron Phosphate (LiFePO4) ===
Lithium Iron Phosphate (also known as LFP, or LiFePO4) batteries offer a good compromise between safety, energy density and ease of use for DIY conversions. They are available in a number of formats, commonly pouch cells, prismatic cells and cylindrical cells.

==== LiFePO4 pouch cells ====
The majority of this content is drawn from this thread: [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761&start=900 https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761] discussing the use of the A123 20Ah pouch cell. However, many of the general points apply equally to other similar pouch cells.

===== General build requirements =====
Pouch cells are vulnerable to damage from debris, and must be held in compression (see the datasheet for your battery, but 10-12 psi is recommended for the A123 pouch cells as a guide). A rigid container capable of preventing damage and providing compression is therefore required. Be aware the cells expand and contract in use, so allowance for this must be included in the structure of the case.

The pouch cells should be separated to prevent abrasion between cells, and also to avoid the development of hot spots. Prebuilt modules from A123 systems had thin foam sheets or heatsinks between each cell. Be sure to avoid any debris that could rub on the pouch surface, particularly if using recycled cells.

Mylar, '[https://www.americanmicroinc.com/fish-paper/ Fish paper]' or a [https://www.rogerscorp.com/elastomeric-material-solutions/poron-industrial-polyurethanes compliant foam] may be appropriate materials to serve this purpose. This material should not be flammable. If the material is heat insulating, it is important to address thermal management.

===== Compression =====
Compression is required to prevent premature failure of the cell. Without compression electrolyte will become unevenly distributed, causing current gradients in the cell and uneven heating. Local temperatures can become high enough to form gas formation leading to cells 'puffing up' even when the pack is otherwise held within temperature and voltage constraints. This will be exacerbated in packs with otherwise poor thermal management. Compression forces gas generated to the margins of the cell, outside of the cell stack, minimising its effect cell performance. Gas in the middle cells will create a dead space which does not store or release energy.

There is ~1% expansion through a discharge cycle. As the cell ages, the nominal cell thickness can grow by 3-5%. For A123 cells the ideal pressure is between 4 and 18psi with the ideal pressure being ~12psi. Maintaining 12psi can increase the life by 500 cycles over that of 4 or 18psi

There is some suggestion that in uses where 1C is never exceeded compression ''may'' not be required.

Highly rigid endplates with a mechanism to allow for a limited degree of expansion (e.g. steel bands) are considered an effective solution to this challenge.

It should be noted that compression is a challenge specific to pouch cells. Cylindrical cells are designed to maintain their own compression within the cell's electrode stack by their design.

This thread provides more information and experimentation relating to pack compression: <nowiki>https://endless-sphere.com/forums/viewtopic.php?f=14&t=52244</nowiki>

===== Pouch Cell Pack Design Examples =====
<nowiki>*</nowiki>placeholder*

===== Notes regarding recycled pouch cells =====
Pouch cells are somewhat fragile, and breaching the insulation is not difficult, especially in a cells removed from existing packs and repurposed. If the pouch has had their poly-layers compromised you may see a number of faults:
* Black spots around the perimeter of the cell indicate electrolyte leakage
* Voltage on the outside of the bag. Note that microvoltage between the pouch and the electrode is normal (and due to a capacitive effect).
While the majority of these cells should no longer be in the market, a significant number of faulty cells made it back into the 'greymarket' in around 2013. These cells had misaligned tabs which can also lead to isolation failures between the tab and the pack. These cells should be avoided, particularly in high demand applications.

===== Situations likely to cause pouch cell failure =====
''Taken directly from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''
# '''Overcharge'''. Any extended time above 3.8 Volts will generate enough heat and electrochemical activity to puff a cell, especially one that is improperly compressed.
# '''Overdischarge followed by charge'''. Any A123 cell that has been pulled low enough to come to rest at <300 mV should be immediately scrapped. The published number for that is 500 mV, but the real figure is closer to 300, so that's a "safety buffer" if you will. Below this Voltage, the Cu electrodes start to dissolve into the electrolyte. When charge is applied, the Cu forms dendrites that puncture the separator layer, forming an internal short in the cell. This can puff a cell in a hurry---the more charge current on tap, the worse it's prone to be.
# '''Driving a cell negative'''. I've neglected to mention this before, but it is a possibility. I don't know much about the specific mechanism at this time.
# '''Malfunctioning or misinformed electronics'''. This is the most common cause of all of the above in my experience. At this stage of the game, it is critical for YOU to understand how your BMS functions on at least a cursory level. Choose your BMS very carefully and periodically verify that it is operating properly. They're not all created equal. Make sure V sense lines are securely connected and free of corrosion. Just because your BMS says there was never a problem doesn't necessarily make it so. Avoid harnesses or ribbon cables between multiple modules if possible--they are problematic wherever they are used in any mobile electronics.
# '''Exposure to or generation of sufficient heat'''. I don't know exactly at what temperature gas formation begins in the electrolyte, but we spec a max storage temp of 80 (or 85?) degrees C and I suspect this is the reason. The hotter, the puffier--to a point. This is why soldering tabs poses a real hazard to cell health. If you feel you must solder, sink or blow the heat away from the body of the cell. Use a big iron that can make sufficient local heat quickly, before the whole mass of the cell gets hot. You might even get the cell warm enough to melt separator if not careful.
# '''No compression, not enough compression, improperly distributed compression'''. This is a pack/module design issue. Apply 10, maybe 15 psi to your cell stack end to end and then band snugly and evenly. Use hard endplates of some sort--never wrap cells directly or allow their shape to become distorted. Protect all areas of the pouch from impact damage. This obviously does not apply to cylindrical cells.

==== LiFePO4 prismatic cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cylindrical cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cell ageing ====
''Derived (barely paraphrased) from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''

Capacity loss is caused by the lithium that was available for storage becoming permanently plated on the cathode. Being unable to move within the cell it is no longer available to store energy. The impact of this plating is greater than the amount of lithium 'lost' to plating because not only is the lithium no longer available, it is also preventing access to that part of the cathode meaning Li that can still move has to take a longer path to reach the cathode. Lithium plating is one cause of increased cell resistance (there are others), a sign of worsening cell health.

There is no linear relationship between actual capacity loss and impedance rise. However some cell defects will also increase impedance.

Increasing cell resistance may cause a number of symptoms which may be confused with [https://earthshipbiotecture.com/a-lithium-ion-battery-primer/ High Self Discharge.]
# Elevated Peukert Losses. As more energy per amount of current through the cell is lost as heat, the cells useable capacity decreases. So the apparent capacity loss is higher than the actual capacity loss of cycleable lithium. When used in low current applications (e.g. solar energy storage) the actual and apparent decrease in capacity will be small. In high current draw applications (like EV traction packs), the Peukert loss increases proportionally, so the apparent capacity loss increases much faster than the actual capacity loss.
# Greater voltage excursion under the same load. Due to increased cell resistancethe voltage will sag further under the same load than a cell in optimal condition. The inverse is also true, the voltage will be higher for the same amount of charging current applied. The cell will then rebound to a voltage further from the loaded and charging voltages. This, obviously, can look like high self discharge but is a different phenomenon.
# Absolute maximum current decrease.
Elevated impedance causes a more complex constellation of symptoms, some of which may be easy to confuse with High Self Discharge (HSD). Ohm's law (E=I/R) holds the key to understanding here.

'''1) Elevated Peukert losses.''' Because more energy per unit of current through the cell is lost as heat, less of the cell's capacity is actually USABLE. Thus, apparent capacity loss can be significantly greater than actual capacity loss caused by the loss of cycleable Li alone. In low current applications, the two numbers will be close together. In high current applications, Peukert losses increase in proportion, so apparent loss of capacity breaks further and further away from actual capacity loss as current increases.

'''2) Greater voltage excursion under the same load.''' Elevated resistance across the cell means that voltage will sag more under the same load than it did when the cell was healthier. Conversely, voltage will rise higher with the same amount of applied charge current than it did when it was healthier. At the same time, rebound/settling voltages will be further away from loaded/charging voltages. In other words, the cell will rebound to a voltage further away from loaded voltage, all else being equal. Similarly, voltage will settle farther from the charge voltage with the same charge applied. This can give the illusion of elevated self-discharge, but the phenomenon is actually not the same thing. Again, the greater the charge and load currents, the greater the effect becomes.

'''3) Absolute max current decreases.''' Because the cell's series resistance is elevated, the maximum possible current through the cell is decreased.

Just to confuse things further, there can be many factors that lead to impedance rise. Some are related to Li plating, others are not.

=== Lithium-ion ===
Lithium-ion (Li-ion) batteries have a greater energy density than Lithium Iron Phosphate batteries, but have more challenging needs to use safely. The ideal operating range of Li-ion batteries is between +15 and +45°C. The upper limit of temperature is particularly important as Li-ion batteries experience thermal runaway - an unstoppable chain reaction that can occur in milliseconds releasing the stored energy in the cell. This can produce temperatures of 400°C and a fire that is extremely difficult to put out. Thermal runaway can start as low as 60°C and becomes much more likely at 100°C

Risk factors for thermal runaway:
* Short Circuits - either internally or externally
* Overcharging
* Excessive current draw or when charging

==== Li-ion pouch cells ====
[https://kokam.com/cell Kokam] produce high-performance Li-ion pouch cells. These combine relative ease of use and pack construction with performance close to cylindrical cells.

==== Li-ion 18650 and other cylindrical cells ====
Cylindrical cells are favoured by Tesla, and are probably the main reason why their cars achieve such excellent performance. They are light, compact, powerful and expensive. Unfortunately, cylindrical cells are difficult (and potentially dangerous) to use in DIY conversions. There are two good reasons for this: thermal management and cell configuration.

As stated above, Li-ion cells are prone to thermal runaway. So you need perfect battery and thermal management to ensure that no cell ever exceeds the critical voltage or temperature. If this happens, a cell can short-circuit internally, releasing a lot of energy - potentially explosively. Furthermore, the individual cells are small, so need to be arranged in parallel. In the case of the Tesla Model S 85kW pack, there are 74 cells in parallel. Imagine if one of those cells fails and becomes short circuited internally. You now have 73 very high power cells all feeding in to that short circuit...

In fact, you don't have to imagine: you can watch this famous video instead (courtesy of Rich Rebuilds).

<youtube>WdDi1haA71Q</youtube>

== OEM modules ==
Using an OEM module means a lot of the difficulties and safety issues associated with battery design are taken care of e.g. cooling, clamping, etc.

Here is a handy list of OEM modules:
{| class="wikitable sortable mw-collapsible"
|+
!Manufacturer
!Model
!Capacity (kWh)
!Weight (kg)
!w (mm)
!d (mm)
!h (mm)
!Gravity (kg/kWh)
!Volume (L/kWh)
!Voltage (V)
!Current (cont A)
!Current (peak A)
!Cell arrangement
!Cell type
!Chemistry
|-
|Tesla
|Model S 85kWh
|5.3
|26
|690
|315
|80
|4.9
|3.3
|22.8
|500
|750
|74p6s
|18650
|Li-ion
|-
|Tesla
|Model S 100kWh
|6.4
|28
|680
|315
|80
|4.4
|2.7
|22.8
|
|870
|86p6s
|18650
|Li-ion
|-
|Tesla
|Model 3 LR (inner)
|19.2
|98.9
|1854
|292
|90
|5.2
|2.5
|91.1
|
|971
|46p25s
|2170
|Li-ion
|-
|Tesla
|Model 3 LR (outer)
|17.7
|86.6
|1715
|292
|90
|4.9
|2.5
|83.9
|
|971
|46p23s
|2170
|Li-ion
|-
|Tesla
|Model 3 SR (inner)
|13.0
|
|1854
|292
|90
|
|3.7
|91.1
|
|603
|31p25s
|2170
|Li-ion
|-
|Tesla
|Model 3 SR (outer)
|12.0
|
|1715
|292
|90
|
|3.8
|83.9
|
|603
|31p23s
|2170
|Li-ion
|-
|Chevrolet
|Volt 2012
|4
|38
|470
|180
|280
|9.5
|5.9
|88
|140
|210
|24s
|Pouch
|Li-ion
|-
|BMW
|i3 60Ah
|2
|13
|368
|178
|102
|6.5
|3.3
|28.8
|210
|350
|8s2p
|Prismatic
|Li-ion
|-
|BMW
|i3 94Ah
|4.15
|28
|410
|310
|150
|6.7
|4.6
|45.6
|
|409
|12s
|Prismatic
|Li-ion
|-
|BMW
|i3 120Ah
|5.3
|28
|410
|310
|150
|5.3
|3.6
|45.6
|
|360
|12s
|Prismatic
|Li-ion
|-
|Jaguar
|iPace
|2.5
|12
|340
|155
|112
|4.8
|2.4
|10.8
|720
|1200
|3s4p
|Pouch
|Li-ion
|-
|Mitsubishi
|Outlander
|2.4
|26
|646
|184
|130
|10.8
|6.4
|60
|
|240
|16s
|
|Li-ion
|-
|Nissan
|Leaf 24kWh
|0.5
|3.65
|300
|222
|34
|7.3
|4.5
|7.4
|130
|228
|2s2p
|Pouch
|Li-ion LMO
|-
|Nissan
|Leaf 40kWh
|1.6
|8.7
|300
|222
|68
|5.4
|2.8
|14.6
|
|314
|4s2p
|Pouch
|Li-ion NMC
|-
|Volvo
|XC90 T8
|2.01
|12.1
|300
|180
|150
|6.0
|4.0
|59.2
|170
|340
|16s
|
|Li-ion
|}

Batteries

2020-12-06T17:52:51Z

Clanger9: /* OEM modules */

== Introduction ==
There are a wide variety of battery chemistries available for use as the main traction battery of an EV. To use each chemistry safely, and to ensure an adequate service life from the battery pack it is important to understand the requirements for the chemistry you are using. Failure to do so may lead to premature or catastrophic failure of the pack.

Good pack design will allow for a nominal amount of abuse. People make mistakes and the pack should allow a margin for safety - and for longevity!

== Battery pack specification ==
When deciding on your battery pack, here are some basic parameters to consider:

=== Capacity (kWh) ===
'''How far do you want to go?''' A standard car conversion will need a kWh for each 3 miles of range (very approximately). For a middleweight motorcycle, a kWh should give around 9 miles. Your mileage may vary, ''as they say.''

=== Voltage (V) ===
'''How fast do you want to go?''' The pack voltage defines the maximum speed your motor can spin. Motors are usually specified with "KV" - or RPM-per-volt. Check the KV of your motor and how fast it needs to spin to get your desired top speed. e.g. if you need 3,000 RPM from a 25 KV motor then your pack voltage needs to be 3,000 / 25 = 120 V. The exact number of cells in series you need depends on the cell design, but 3.8 V for Li-ion and 3.2 V for LiFePO4 is a reasonable guess.

=== Maximum current (A) ===
'''How quickly do you want to accelerate?''' Your motor's maximum power will be specified in kW. To estimate your maximum current draw, divide the peak power by the battery voltage. e.g. a 30 kW motor with a 120 V battery pack will pull 30,000 / 120 = 250 A. The higher the current rating of the cells, the heavier they will be for a given capacity. Ideally, you want "enough" current capacity for full throttle acceleration, but no more. You can put cells in parallel to double the current rating of your pack (which of course will half the voltage).

=== Mass (kg) ===
'''Can your vehicle carry the weight?''' You'll need to keep the kerb weight within the original design limits. For a car, this could be a few hundred kg. For a motorcycle, likely less than 100 kg. This is a huge variable - and each new generation of battery tech seems to be a little lighter. For older EV or hybrid batteries, you can reckon on approximately 10 kg/kWh. Nissan Leaf batteries are relatively light (7.5 kg/kWh). With the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 5-6 kg/kWh.

=== Volume (L) ===
'''Will it fit?''' Batteries are bulky. They are getting smaller, but finding enough space might be your biggest challenge. You could be looking at over 5 L/kWh for older EV or hybrid batteries. Current state-of-the-art is the Tesla Model 3, which gets this down to 2.5 L/kWh by using 2170 cylindrical cells.

There is much, much more to battery design than this (e.g. maximum charge rate, terminations, cooling, clamping), but the above should help work out which options will or won't work for your project...

== Cell chemistry ==

=== Lithium Iron Phosphate (LiFePO4) ===
Lithium Iron Phosphate (also known as LFP, or LiFePO4) batteries offer a good compromise between safety, energy density and ease of use for DIY conversions. They are available in a number of formats, commonly pouch cells, prismatic cells and cylindrical cells.

==== LiFePO4 pouch cells ====
The majority of this content is drawn from this thread: [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761&start=900 https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761] discussing the use of the A123 20Ah pouch cell. However, many of the general points apply equally to other similar pouch cells.

===== General build requirements =====
Pouch cells are vulnerable to damage from debris, and must be held in compression (see the datasheet for your battery, but 10-12 psi is recommended for the A123 pouch cells as a guide). A rigid container capable of preventing damage and providing compression is therefore required. Be aware the cells expand and contract in use, so allowance for this must be included in the structure of the case.

The pouch cells should be separated to prevent abrasion between cells, and also to avoid the development of hot spots. Prebuilt modules from A123 systems had thin foam sheets or heatsinks between each cell. Be sure to avoid any debris that could rub on the pouch surface, particularly if using recycled cells.

Mylar, '[https://www.americanmicroinc.com/fish-paper/ Fish paper]' or a [https://www.rogerscorp.com/elastomeric-material-solutions/poron-industrial-polyurethanes compliant foam] may be appropriate materials to serve this purpose. This material should not be flammable. If the material is heat insulating, it is important to address thermal management.

===== Compression =====
Compression is required to prevent premature failure of the cell. Without compression electrolyte will become unevenly distributed, causing current gradients in the cell and uneven heating. Local temperatures can become high enough to form gas formation leading to cells 'puffing up' even when the pack is otherwise held within temperature and voltage constraints. This will be exacerbated in packs with otherwise poor thermal management. Compression forces gas generated to the margins of the cell, outside of the cell stack, minimising its effect cell performance. Gas in the middle cells will create a dead space which does not store or release energy.

There is ~1% expansion through a discharge cycle. As the cell ages, the nominal cell thickness can grow by 3-5%. For A123 cells the ideal pressure is between 4 and 18psi with the ideal pressure being ~12psi. Maintaining 12psi can increase the life by 500 cycles over that of 4 or 18psi

There is some suggestion that in uses where 1C is never exceeded compression ''may'' not be required.

Highly rigid endplates with a mechanism to allow for a limited degree of expansion (e.g. steel bands) are considered an effective solution to this challenge.

It should be noted that compression is a challenge specific to pouch cells. Cylindrical cells are designed to maintain their own compression within the cell's electrode stack by their design.

This thread provides more information and experimentation relating to pack compression: <nowiki>https://endless-sphere.com/forums/viewtopic.php?f=14&t=52244</nowiki>

===== Pouch Cell Pack Design Examples =====
<nowiki>*</nowiki>placeholder*

===== Notes regarding recycled pouch cells =====
Pouch cells are somewhat fragile, and breaching the insulation is not difficult, especially in a cells removed from existing packs and repurposed. If the pouch has had their poly-layers compromised you may see a number of faults:
* Black spots around the perimeter of the cell indicate electrolyte leakage
* Voltage on the outside of the bag. Note that microvoltage between the pouch and the electrode is normal (and due to a capacitive effect).
While the majority of these cells should no longer be in the market, a significant number of faulty cells made it back into the 'greymarket' in around 2013. These cells had misaligned tabs which can also lead to isolation failures between the tab and the pack. These cells should be avoided, particularly in high demand applications.

===== Situations likely to cause pouch cell failure =====
''Taken directly from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''
# '''Overcharge'''. Any extended time above 3.8 Volts will generate enough heat and electrochemical activity to puff a cell, especially one that is improperly compressed.
# '''Overdischarge followed by charge'''. Any A123 cell that has been pulled low enough to come to rest at <300 mV should be immediately scrapped. The published number for that is 500 mV, but the real figure is closer to 300, so that's a "safety buffer" if you will. Below this Voltage, the Cu electrodes start to dissolve into the electrolyte. When charge is applied, the Cu forms dendrites that puncture the separator layer, forming an internal short in the cell. This can puff a cell in a hurry---the more charge current on tap, the worse it's prone to be.
# '''Driving a cell negative'''. I've neglected to mention this before, but it is a possibility. I don't know much about the specific mechanism at this time.
# '''Malfunctioning or misinformed electronics'''. This is the most common cause of all of the above in my experience. At this stage of the game, it is critical for YOU to understand how your BMS functions on at least a cursory level. Choose your BMS very carefully and periodically verify that it is operating properly. They're not all created equal. Make sure V sense lines are securely connected and free of corrosion. Just because your BMS says there was never a problem doesn't necessarily make it so. Avoid harnesses or ribbon cables between multiple modules if possible--they are problematic wherever they are used in any mobile electronics.
# '''Exposure to or generation of sufficient heat'''. I don't know exactly at what temperature gas formation begins in the electrolyte, but we spec a max storage temp of 80 (or 85?) degrees C and I suspect this is the reason. The hotter, the puffier--to a point. This is why soldering tabs poses a real hazard to cell health. If you feel you must solder, sink or blow the heat away from the body of the cell. Use a big iron that can make sufficient local heat quickly, before the whole mass of the cell gets hot. You might even get the cell warm enough to melt separator if not careful.
# '''No compression, not enough compression, improperly distributed compression'''. This is a pack/module design issue. Apply 10, maybe 15 psi to your cell stack end to end and then band snugly and evenly. Use hard endplates of some sort--never wrap cells directly or allow their shape to become distorted. Protect all areas of the pouch from impact damage. This obviously does not apply to cylindrical cells.

==== LiFePO4 prismatic cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cylindrical cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cell ageing ====
''Derived (barely paraphrased) from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''

Capacity loss is caused by the lithium that was available for storage becoming permanently plated on the cathode. Being unable to move within the cell it is no longer available to store energy. The impact of this plating is greater than the amount of lithium 'lost' to plating because not only is the lithium no longer available, it is also preventing access to that part of the cathode meaning Li that can still move has to take a longer path to reach the cathode. Lithium plating is one cause of increased cell resistance (there are others), a sign of worsening cell health.

There is no linear relationship between actual capacity loss and impedance rise. However some cell defects will also increase impedance.

Increasing cell resistance may cause a number of symptoms which may be confused with [https://earthshipbiotecture.com/a-lithium-ion-battery-primer/ High Self Discharge.]
# Elevated Peukert Losses. As more energy per amount of current through the cell is lost as heat, the cells useable capacity decreases. So the apparent capacity loss is higher than the actual capacity loss of cycleable lithium. When used in low current applications (e.g. solar energy storage) the actual and apparent decrease in capacity will be small. In high current draw applications (like EV traction packs), the Peukert loss increases proportionally, so the apparent capacity loss increases much faster than the actual capacity loss.
# Greater voltage excursion under the same load. Due to increased cell resistancethe voltage will sag further under the same load than a cell in optimal condition. The inverse is also true, the voltage will be higher for the same amount of charging current applied. The cell will then rebound to a voltage further from the loaded and charging voltages. This, obviously, can look like high self discharge but is a different phenomenon.
# Absolute maximum current decrease.
Elevated impedance causes a more complex constellation of symptoms, some of which may be easy to confuse with High Self Discharge (HSD). Ohm's law (E=I/R) holds the key to understanding here.

'''1) Elevated Peukert losses.''' Because more energy per unit of current through the cell is lost as heat, less of the cell's capacity is actually USABLE. Thus, apparent capacity loss can be significantly greater than actual capacity loss caused by the loss of cycleable Li alone. In low current applications, the two numbers will be close together. In high current applications, Peukert losses increase in proportion, so apparent loss of capacity breaks further and further away from actual capacity loss as current increases.

'''2) Greater voltage excursion under the same load.''' Elevated resistance across the cell means that voltage will sag more under the same load than it did when the cell was healthier. Conversely, voltage will rise higher with the same amount of applied charge current than it did when it was healthier. At the same time, rebound/settling voltages will be further away from loaded/charging voltages. In other words, the cell will rebound to a voltage further away from loaded voltage, all else being equal. Similarly, voltage will settle farther from the charge voltage with the same charge applied. This can give the illusion of elevated self-discharge, but the phenomenon is actually not the same thing. Again, the greater the charge and load currents, the greater the effect becomes.

'''3) Absolute max current decreases.''' Because the cell's series resistance is elevated, the maximum possible current through the cell is decreased.

Just to confuse things further, there can be many factors that lead to impedance rise. Some are related to Li plating, others are not.

=== Lithium-ion ===
Lithium-ion (Li-ion) batteries have a greater energy density than Lithium Iron Phosphate batteries, but have more challenging needs to use safely. The ideal operating range of Li-ion batteries is between +15 and +45°C. The upper limit of temperature is particularly important as Li-ion batteries experience thermal runaway - an unstoppable chain reaction that can occur in milliseconds releasing the stored energy in the cell. This can produce temperatures of 400°C and a fire that is extremely difficult to put out. Thermal runaway can start as low as 60°C and becomes much more likely at 100°C

Risk factors for thermal runaway:
* Short Circuits - either internally or externally
* Overcharging
* Excessive current draw or when charging

==== Li-ion pouch cells ====
[https://kokam.com/cell Kokam] produce high-performance Li-ion pouch cells. These combine relative ease of use and pack construction with performance close to cylindrical cells.

==== Li-ion 18650 and other cylindrical cells ====
Cylindrical cells are favoured by Tesla, and are probably the main reason why their cars achieve such excellent performance. They are light, compact, powerful and expensive. Unfortunately, cylindrical cells are difficult (and potentially dangerous) to use in DIY conversions. There are two good reasons for this: thermal management and cell configuration.

As stated above, Li-ion cells are prone to thermal runaway. So you need perfect battery and thermal management to ensure that no cell ever exceeds the critical voltage or temperature. If this happens, a cell can short-circuit internally, releasing a lot of energy - potentially explosively. Furthermore, the individual cells are small, so need to be arranged in parallel. In the case of the Tesla Model S 85kW pack, there are 74 cells in parallel. Imagine if one of those cells fails and becomes short circuited internally. You now have 73 very high power cells all feeding in to that short circuit...

In fact, you don't have to imagine: you can watch this famous video instead (courtesy of Rich Rebuilds).

<youtube>WdDi1haA71Q</youtube>

== OEM modules ==
Using an OEM module means a lot of the difficulties and safety issues associated with battery design are taken care of e.g. cooling, clamping, etc.

Here is a handy list of OEM modules:
{| class="wikitable sortable mw-collapsible"
|+
!Manufacturer
!Model
!Capacity (kWh)
!Weight (kg)
!w (mm)
!d (mm)
!h (mm)
!Gravity (kg/kWh)
!Volume (L/kWh)
!Voltage (V)
!Current (cont A)
!Current (peak A)
!Cell arrangement
!Cell type
!Chemistry
|-
|Tesla
|Model S 85kWh
|5.3
|26
|690
|315
|80
|4.9
|3.3
|22.8
|500
|750
|74p6s
|18650
|Li-ion
|-
|Tesla
|Model S 100kWh
|6.4
|28
|680
|315
|80
|4.4
|2.7
|22.8
|
|870
|86p6s
|18650
|Li-ion
|-
|Tesla
|Model 3 LR (inner)
|19.2
|98.9
|1854
|292
|90
|5.2
|2.5
|91.1
|
|971
|46p25s
|2170
|Li-ion
|-
|Tesla
|Model 3 LR (outer)
|17.7
|86.6
|1715
|292
|90
|4.9
|2.5
|83.9
|
|971
|46p23s
|2170
|Li-ion
|-
|Tesla
|Model 3 SR (inner)
|13.0
|
|1854
|292
|90
|
|3.7
|91.1
|
|603
|31p25s
|2170
|Li-ion
|-
|Tesla
|Model 3 SR (outer)
|12.0
|
|1715
|292
|90
|
|3.8
|83.9
|
|603
|31p23s
|2170
|Li-ion
|-
|Chevrolet
|Volt 2012
|4
|38
|470
|180
|280
|9.5
|5.9
|88
|140
|210
|24s
|Pouch
|Li-ion
|-
|BMW
|i3 60Ah
|2
|13
|368
|178
|102
|6.5
|3.3
|28.8
|210
|350
|8s2p
|Prismatic
|Li-ion
|-
|BMW
|i3 94Ah
|4.15
|28
|410
|310
|150
|6.7
|4.6
|45.6
|
|409
|12s
|Prismatic
|Li-ion
|-
|BMW
|i3 120Ah
|5.3
|28
|410
|310
|150
|5.3
|3.6
|45.6
|
|360
|12s
|Prismatic
|Li-ion
|-
|Jaguar
|iPace
|2.5
|12
|340
|155
|112
|4.8
|2.4
|43.1
|720
|1200
|12s4p
|Pouch
|Li-ion
|-
|Mitsubishi
|Outlander
|2.4
|26
|646
|184
|130
|10.8
|6.4
|60
|
|240
|16s
|
|Li-ion
|-
|Nissan
|Leaf 24kWh
|0.5
|3.65
|300
|222
|34
|7.3
|4.5
|7.4
|130
|228
|2s2p
|Pouch
|Li-ion LMO
|-
|Nissan
|Leaf 40kWh
|1.6
|8.7
|300
|222
|68
|5.4
|2.8
|14.6
|
|314
|4s2p
|Pouch
|Li-ion NMC
|-
|Volvo
|XC90 T8
|2.01
|12.1
|300
|180
|150
|6.0
|4.0
|59.2
|170
|340
|16s
|
|Li-ion
|}

Batteries

2020-12-06T17:51:51Z

Clanger9:

== Introduction ==
There are a wide variety of battery chemistries available for use as the main traction battery of an EV. To use each chemistry safely, and to ensure an adequate service life from the battery pack it is important to understand the requirements for the chemistry you are using. Failure to do so may lead to premature or catastrophic failure of the pack.

Good pack design will allow for a nominal amount of abuse. People make mistakes and the pack should allow a margin for safety - and for longevity!

== Battery pack specification ==
When deciding on your battery pack, here are some basic parameters to consider:

=== Capacity (kWh) ===
'''How far do you want to go?''' A standard car conversion will need a kWh for each 3 miles of range (very approximately). For a middleweight motorcycle, a kWh should give around 9 miles. Your mileage may vary, ''as they say.''

=== Voltage (V) ===
'''How fast do you want to go?''' The pack voltage defines the maximum speed your motor can spin. Motors are usually specified with "KV" - or RPM-per-volt. Check the KV of your motor and how fast it needs to spin to get your desired top speed. e.g. if you need 3,000 RPM from a 25 KV motor then your pack voltage needs to be 3,000 / 25 = 120 V. The exact number of cells in series you need depends on the cell design, but 3.8 V for Li-ion and 3.2 V for LiFePO4 is a reasonable guess.

=== Maximum current (A) ===
'''How quickly do you want to accelerate?''' Your motor's maximum power will be specified in kW. To estimate your maximum current draw, divide the peak power by the battery voltage. e.g. a 30 kW motor with a 120 V battery pack will pull 30,000 / 120 = 250 A. The higher the current rating of the cells, the heavier they will be for a given capacity. Ideally, you want "enough" current capacity for full throttle acceleration, but no more. You can put cells in parallel to double the current rating of your pack (which of course will half the voltage).

=== Mass (kg) ===
'''Can your vehicle carry the weight?''' You'll need to keep the kerb weight within the original design limits. For a car, this could be a few hundred kg. For a motorcycle, likely less than 100 kg. This is a huge variable - and each new generation of battery tech seems to be a little lighter. For older EV or hybrid batteries, you can reckon on approximately 10 kg/kWh. Nissan Leaf batteries are relatively light (7.5 kg/kWh). With the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 5-6 kg/kWh.

=== Volume (L) ===
'''Will it fit?''' Batteries are bulky. They are getting smaller, but finding enough space might be your biggest challenge. You could be looking at over 5 L/kWh for older EV or hybrid batteries. Current state-of-the-art is the Tesla Model 3, which gets this down to 2.5 L/kWh by using 2170 cylindrical cells.

There is much, much more to battery design than this (e.g. maximum charge rate, terminations, cooling, clamping), but the above should help work out which options will or won't work for your project...

== Cell chemistry ==

=== Lithium Iron Phosphate (LiFePO4) ===
Lithium Iron Phosphate (also known as LFP, or LiFePO4) batteries offer a good compromise between safety, energy density and ease of use for DIY conversions. They are available in a number of formats, commonly pouch cells, prismatic cells and cylindrical cells.

==== LiFePO4 pouch cells ====
The majority of this content is drawn from this thread: [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761&start=900 https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761] discussing the use of the A123 20Ah pouch cell. However, many of the general points apply equally to other similar pouch cells.

===== General build requirements =====
Pouch cells are vulnerable to damage from debris, and must be held in compression (see the datasheet for your battery, but 10-12 psi is recommended for the A123 pouch cells as a guide). A rigid container capable of preventing damage and providing compression is therefore required. Be aware the cells expand and contract in use, so allowance for this must be included in the structure of the case.

The pouch cells should be separated to prevent abrasion between cells, and also to avoid the development of hot spots. Prebuilt modules from A123 systems had thin foam sheets or heatsinks between each cell. Be sure to avoid any debris that could rub on the pouch surface, particularly if using recycled cells.

Mylar, '[https://www.americanmicroinc.com/fish-paper/ Fish paper]' or a [https://www.rogerscorp.com/elastomeric-material-solutions/poron-industrial-polyurethanes compliant foam] may be appropriate materials to serve this purpose. This material should not be flammable. If the material is heat insulating, it is important to address thermal management.

===== Compression =====
Compression is required to prevent premature failure of the cell. Without compression electrolyte will become unevenly distributed, causing current gradients in the cell and uneven heating. Local temperatures can become high enough to form gas formation leading to cells 'puffing up' even when the pack is otherwise held within temperature and voltage constraints. This will be exacerbated in packs with otherwise poor thermal management. Compression forces gas generated to the margins of the cell, outside of the cell stack, minimising its effect cell performance. Gas in the middle cells will create a dead space which does not store or release energy.

There is ~1% expansion through a discharge cycle. As the cell ages, the nominal cell thickness can grow by 3-5%. For A123 cells the ideal pressure is between 4 and 18psi with the ideal pressure being ~12psi. Maintaining 12psi can increase the life by 500 cycles over that of 4 or 18psi

There is some suggestion that in uses where 1C is never exceeded compression ''may'' not be required.

Highly rigid endplates with a mechanism to allow for a limited degree of expansion (e.g. steel bands) are considered an effective solution to this challenge.

It should be noted that compression is a challenge specific to pouch cells. Cylindrical cells are designed to maintain their own compression within the cell's electrode stack by their design.

This thread provides more information and experimentation relating to pack compression: <nowiki>https://endless-sphere.com/forums/viewtopic.php?f=14&t=52244</nowiki>

===== Pouch Cell Pack Design Examples =====
<nowiki>*</nowiki>placeholder*

===== Notes regarding recycled pouch cells =====
Pouch cells are somewhat fragile, and breaching the insulation is not difficult, especially in a cells removed from existing packs and repurposed. If the pouch has had their poly-layers compromised you may see a number of faults:
* Black spots around the perimeter of the cell indicate electrolyte leakage
* Voltage on the outside of the bag. Note that microvoltage between the pouch and the electrode is normal (and due to a capacitive effect).
While the majority of these cells should no longer be in the market, a significant number of faulty cells made it back into the 'greymarket' in around 2013. These cells had misaligned tabs which can also lead to isolation failures between the tab and the pack. These cells should be avoided, particularly in high demand applications.

===== Situations likely to cause pouch cell failure =====
''Taken directly from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''
# '''Overcharge'''. Any extended time above 3.8 Volts will generate enough heat and electrochemical activity to puff a cell, especially one that is improperly compressed.
# '''Overdischarge followed by charge'''. Any A123 cell that has been pulled low enough to come to rest at <300 mV should be immediately scrapped. The published number for that is 500 mV, but the real figure is closer to 300, so that's a "safety buffer" if you will. Below this Voltage, the Cu electrodes start to dissolve into the electrolyte. When charge is applied, the Cu forms dendrites that puncture the separator layer, forming an internal short in the cell. This can puff a cell in a hurry---the more charge current on tap, the worse it's prone to be.
# '''Driving a cell negative'''. I've neglected to mention this before, but it is a possibility. I don't know much about the specific mechanism at this time.
# '''Malfunctioning or misinformed electronics'''. This is the most common cause of all of the above in my experience. At this stage of the game, it is critical for YOU to understand how your BMS functions on at least a cursory level. Choose your BMS very carefully and periodically verify that it is operating properly. They're not all created equal. Make sure V sense lines are securely connected and free of corrosion. Just because your BMS says there was never a problem doesn't necessarily make it so. Avoid harnesses or ribbon cables between multiple modules if possible--they are problematic wherever they are used in any mobile electronics.
# '''Exposure to or generation of sufficient heat'''. I don't know exactly at what temperature gas formation begins in the electrolyte, but we spec a max storage temp of 80 (or 85?) degrees C and I suspect this is the reason. The hotter, the puffier--to a point. This is why soldering tabs poses a real hazard to cell health. If you feel you must solder, sink or blow the heat away from the body of the cell. Use a big iron that can make sufficient local heat quickly, before the whole mass of the cell gets hot. You might even get the cell warm enough to melt separator if not careful.
# '''No compression, not enough compression, improperly distributed compression'''. This is a pack/module design issue. Apply 10, maybe 15 psi to your cell stack end to end and then band snugly and evenly. Use hard endplates of some sort--never wrap cells directly or allow their shape to become distorted. Protect all areas of the pouch from impact damage. This obviously does not apply to cylindrical cells.

==== LiFePO4 prismatic cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cylindrical cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cell ageing ====
''Derived (barely paraphrased) from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''

Capacity loss is caused by the lithium that was available for storage becoming permanently plated on the cathode. Being unable to move within the cell it is no longer available to store energy. The impact of this plating is greater than the amount of lithium 'lost' to plating because not only is the lithium no longer available, it is also preventing access to that part of the cathode meaning Li that can still move has to take a longer path to reach the cathode. Lithium plating is one cause of increased cell resistance (there are others), a sign of worsening cell health.

There is no linear relationship between actual capacity loss and impedance rise. However some cell defects will also increase impedance.

Increasing cell resistance may cause a number of symptoms which may be confused with [https://earthshipbiotecture.com/a-lithium-ion-battery-primer/ High Self Discharge.]
# Elevated Peukert Losses. As more energy per amount of current through the cell is lost as heat, the cells useable capacity decreases. So the apparent capacity loss is higher than the actual capacity loss of cycleable lithium. When used in low current applications (e.g. solar energy storage) the actual and apparent decrease in capacity will be small. In high current draw applications (like EV traction packs), the Peukert loss increases proportionally, so the apparent capacity loss increases much faster than the actual capacity loss.
# Greater voltage excursion under the same load. Due to increased cell resistancethe voltage will sag further under the same load than a cell in optimal condition. The inverse is also true, the voltage will be higher for the same amount of charging current applied. The cell will then rebound to a voltage further from the loaded and charging voltages. This, obviously, can look like high self discharge but is a different phenomenon.
# Absolute maximum current decrease.
Elevated impedance causes a more complex constellation of symptoms, some of which may be easy to confuse with High Self Discharge (HSD). Ohm's law (E=I/R) holds the key to understanding here.

'''1) Elevated Peukert losses.''' Because more energy per unit of current through the cell is lost as heat, less of the cell's capacity is actually USABLE. Thus, apparent capacity loss can be significantly greater than actual capacity loss caused by the loss of cycleable Li alone. In low current applications, the two numbers will be close together. In high current applications, Peukert losses increase in proportion, so apparent loss of capacity breaks further and further away from actual capacity loss as current increases.

'''2) Greater voltage excursion under the same load.''' Elevated resistance across the cell means that voltage will sag more under the same load than it did when the cell was healthier. Conversely, voltage will rise higher with the same amount of applied charge current than it did when it was healthier. At the same time, rebound/settling voltages will be further away from loaded/charging voltages. In other words, the cell will rebound to a voltage further away from loaded voltage, all else being equal. Similarly, voltage will settle farther from the charge voltage with the same charge applied. This can give the illusion of elevated self-discharge, but the phenomenon is actually not the same thing. Again, the greater the charge and load currents, the greater the effect becomes.

'''3) Absolute max current decreases.''' Because the cell's series resistance is elevated, the maximum possible current through the cell is decreased.

Just to confuse things further, there can be many factors that lead to impedance rise. Some are related to Li plating, others are not.

=== Lithium-ion ===
Lithium-ion (Li-ion) batteries have a greater energy density than Lithium Iron Phosphate batteries, but have more challenging needs to use safely. The ideal operating range of Li-ion batteries is between +15 and +45°C. The upper limit of temperature is particularly important as Li-ion batteries experience thermal runaway - an unstoppable chain reaction that can occur in milliseconds releasing the stored energy in the cell. This can produce temperatures of 400°C and a fire that is extremely difficult to put out. Thermal runaway can start as low as 60°C and becomes much more likely at 100°C

Risk factors for thermal runaway:
* Short Circuits - either internally or externally
* Overcharging
* Excessive current draw or when charging

==== Li-ion pouch cells ====
[https://kokam.com/cell Kokam] produce high-performance Li-ion pouch cells. These combine relative ease of use and pack construction with performance close to cylindrical cells.

==== Li-ion 18650 and other cylindrical cells ====
Cylindrical cells are favoured by Tesla, and are probably the main reason why their cars achieve such excellent performance. They are light, compact, powerful and expensive. Unfortunately, cylindrical cells are difficult (and potentially dangerous) to use in DIY conversions. There are two good reasons for this: thermal management and cell configuration.

As stated above, Li-ion cells are prone to thermal runaway. So you need perfect battery and thermal management to ensure that no cell ever exceeds the critical voltage or temperature. If this happens, a cell can short-circuit internally, releasing a lot of energy - potentially explosively. Furthermore, the individual cells are small, so need to be arranged in parallel. In the case of the Tesla Model S 85kW pack, there are 74 cells in parallel. Imagine if one of those cells fails and becomes short circuited internally. You now have 73 very high power cells all feeding in to that short circuit...

In fact, you don't have to imagine: you can watch this famous video instead (courtesy of Rich Rebuilds).

<youtube>WdDi1haA71Q</youtube>

== OEM modules ==
Using an OEM module means a lot of the difficulties and safety issues associated with battery design are taken care of e.g. cooling, clamping, etc.

Here is a handy list of OEM modules:
{| class="wikitable sortable mw-collapsible"
|+
!Manufacturer
!Model
!Capacity (kWh)
!Weight (kg)
!w (mm)
!d (mm)
!h (mm)
!Gravity (kg/kWh)
!Volume (L/kWh)
!Voltage (V)
!Current (cont A)
!Current (peak A)
!Cell arrangement
!Cell type
!Chemistry
|-
|Tesla
|Model S 85kWh
|5.3
|26
|690
|315
|80
|4.9
|3.3
|22.8
|500
|750
|74p6s
|18650
|Li-ion
|-
|Tesla
|Model S 100kWh
|6.4
|28
|680
|315
|80
|4.4
|2.7
|22.8
|
|870
|86p6s
|18650
|Li-ion
|-
|Tesla
|Model 3 LR (inner)
|19.2
|98.9
|1854
|292
|90
|5.2
|2.5
|91.1
|
|971
|46p25s
|2170
|Li-ion
|-
|Tesla
|Model 3 LR (outer)
|17.7
|86.6
|1715
|292
|90
|4.9
|2.5
|83.9
|
|971
|46p23s
|2170
|Li-ion
|-
|Tesla
|Model 3 SR (inner)
|13.0
|
|1854
|292
|90
|
|3.7
|91.1
|
|603
|31p25s
|2170
|Li-ion
|-
|Tesla
|Model 3 SR (outer)
|12.0
|
|1715
|292
|90
|
|3.8
|83.9
|
|603
|31p23s
|2170
|Li-ion
|-
|Chevrolet
|Volt 2012
|4
|38
|470
|180
|280
|9.5
|5.9
|88
|140
|210
|24s
|Pouch
|Li-ion
|-
|BMW
|i3 60Ah
|2
|13
|368
|178
|102
|6.5
|3.3
|28.8
|210
|350
|8s2p
|Prismatic
|Li-ion
|-
|BMW
|i3 94Ah
|4.15
|28
|410
|310
|150
|6.7
|4.6
|45.6
|
|409
|12s
|Prismatic
|Li-ion
|-
|BMW
|i3 120Ah
|5.3
|28
|410
|310
|150
|5.3
|3.6
|45.6
|
|360
|12s
|Prismatic
|Li-ion
|-
|Jaguar
|iPace
|2.5
|12
|340
|115
|112
|4.8
|1.8
|43.1
|720
|1200
|12s4p
|Pouch
|Li-ion
|-
|Mitsubishi
|Outlander
|2.4
|26
|646
|184
|130
|10.8
|6.4
|60
|
|240
|16s
|
|Li-ion
|-
|Nissan
|Leaf 24kWh
|0.5
|3.65
|300
|222
|34
|7.3
|4.5
|7.4
|130
|228
|2s2p
|Pouch
|Li-ion LMO
|-
|Nissan
|Leaf 40kWh
|1.6
|8.7
|300
|222
|68
|5.4
|2.8
|14.6
|
|314
|4s2p
|Pouch
|Li-ion NMC
|-
|Volvo
|XC90 T8
|2.01
|12.1
|300
|180
|150
|6.0
|4.0
|59.2
|170
|340
|16s
|
|Li-ion
|}

Batteries

2020-12-06T16:49:48Z

Clanger9: /* OEM modules */ Add iPace

== Introduction ==
There are a wide variety of battery chemistries available for use as the main traction battery of an EV. To use each chemistry safely, and to ensure an adequate service life from the battery pack it is important to understand the requirements for the chemistry you are using. Failure to do so may lead to premature or catastrophic failure of the pack.

Good pack design will allow for a nominal amount of abuse. People make mistakes and the pack should allow a margin for safety - and for longevity!

== Battery pack specification ==
When deciding on your battery pack, here are some basic parameters to consider:

=== Capacity (kWh) ===
'''How far do you want to go?''' A standard car conversion will need a kWh for each 3 miles of range (very approximately). For a middleweight motorcycle, a kWh should give around 9 miles. Your mileage may vary, ''as they say.''

=== Voltage (V) ===
'''How fast do you want to go?''' The pack voltage defines the maximum speed your motor can spin. Motors are usually specified with "KV" - or RPM-per-volt. Check the KV of your motor and how fast it needs to spin to get your desired top speed. e.g. if you need 3,000 RPM from a 25 KV motor then your pack voltage needs to be 3,000 / 25 = 120 V. The exact number of cells in series you need depends on the cell design, but 3.8 V for Li-ion and 3.2 V for LiFePO4 is a reasonable guess.

=== Maximum current (A) ===
'''How quickly do you want to accelerate?''' Your motor's maximum power will be specified in kW. To estimate your maximum current draw, divide the peak power by the battery voltage. e.g. a 30 kW motor with a 120 V battery pack will pull 30,000 / 120 = 250 A. The higher the current rating of the cells, the heavier they will be for a given capacity. Ideally, you want "enough" current capacity for full throttle acceleration, but no more. You can put cells in parallel to double the current rating of your pack (which of course will half the voltage).

=== Mass (kg) ===
'''Can your vehicle carry the weight?''' You'll need to keep the kerb weight within the original design limits. For a car, this could be a few hundred kg. For a motorcycle, likely less than 100 kg. This is a huge variable - and each new generation of battery tech seems to be a little lighter. For older EV or hybrid batteries, you can reckon on approximately 10 kg/kWh. Nissan Leaf batteries are relatively light (7.5 kg/kWh). With the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 5-6 kg/kWh.

=== Volume (L) ===
'''Will it fit?''' Batteries are bulky. They are getting smaller, but finding enough space might be your biggest challenge. You could be looking at over 5 L/kWh for older EV or hybrid batteries. Current state-of-the-art is the Tesla Model 3, which gets this down to 2.5 L/kWh by using 2170 cylindrical cells.

There is much, much more to battery design than this (e.g. maximum charge rate, terminations, cooling, clamping), but the above should help work out which options will or won't work for your project...

== Cell chemistry ==

=== Lithium Iron Phosphate (LiFePO4) ===
Lithium Iron Phosphate (also known as LFP, or LiFePO4) batteries offer a good compromise between safety, energy density and ease of use for DIY conversions. They are available in a number of formats, commonly pouch cells, prismatic cells and cylindrical cells.

==== LiFePO4 pouch cells ====
The majority of this content is drawn from this thread: [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761&start=900 https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761] discussing the use of the A123 20Ah pouch cell. However, many of the general points apply equally to other similar pouch cells.

===== General build requirements =====
Pouch cells are vulnerable to damage from debris, and must be held in compression (see the datasheet for your battery, but 10-12 psi is recommended for the A123 pouch cells as a guide). A rigid container capable of preventing damage and providing compression is therefore required. Be aware the cells expand and contract in use, so allowance for this must be included in the structure of the case.

The pouch cells should be separated to prevent abrasion between cells, and also to avoid the development of hot spots. Prebuilt modules from A123 systems had thin foam sheets or heatsinks between each cell. Be sure to avoid any debris that could rub on the pouch surface, particularly if using recycled cells.

Mylar, '[https://www.americanmicroinc.com/fish-paper/ Fish paper]' or a [https://www.rogerscorp.com/elastomeric-material-solutions/poron-industrial-polyurethanes compliant foam] may be appropriate materials to serve this purpose. This material should not be flammable. If the material is heat insulating, it is important to address thermal management.

===== Compression =====
Compression is required to prevent premature failure of the cell. Without compression electrolyte will become unevenly distributed, causing current gradients in the cell and uneven heating. Local temperatures can become high enough to form gas formation leading to cells 'puffing up' even when the pack is otherwise held within temperature and voltage constraints. This will be exacerbated in packs with otherwise poor thermal management. Compression forces gas generated to the margins of the cell, outside of the cell stack, minimising its effect cell performance. Gas in the middle cells will create a dead space which does not store or release energy.

There is ~1% expansion through a discharge cycle. As the cell ages, the nominal cell thickness can grow by 3-5%. For A123 cells the ideal pressure is between 4 and 18psi with the ideal pressure being ~12psi. Maintaining 12psi can increase the life by 500 cycles over that of 4 or 18psi

There is some suggestion that in uses where 1C is never exceeded compression ''may'' not be required.

Highly rigid endplates with a mechanism to allow for a limited degree of expansion (e.g. steel bands) are considered an effective solution to this challenge.

It should be noted that compression is a challenge specific to pouch cells. Cylindrical cells are designed to maintain their own compression within the cell's electrode stack by their design.

This thread provides more information and experimentation relating to pack compression: <nowiki>https://endless-sphere.com/forums/viewtopic.php?f=14&t=52244</nowiki>

===== Pouch Cell Pack Design Examples =====
<nowiki>*</nowiki>placeholder*

===== Notes regarding recycled pouch cells =====
Pouch cells are somewhat fragile, and breaching the insulation is not difficult, especially in a cells removed from existing packs and repurposed. If the pouch has had their poly-layers compromised you may see a number of faults:
* Black spots around the perimeter of the cell indicate electrolyte leakage
* Voltage on the outside of the bag. Note that microvoltage between the pouch and the electrode is normal (and due to a capacitive effect).
While the majority of these cells should no longer be in the market, a significant number of faulty cells made it back into the 'greymarket' in around 2013. These cells had misaligned tabs which can also lead to isolation failures between the tab and the pack. These cells should be avoided, particularly in high demand applications.

===== Situations likely to cause pouch cell failure =====
''Taken directly from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''
# '''Overcharge'''. Any extended time above 3.8 Volts will generate enough heat and electrochemical activity to puff a cell, especially one that is improperly compressed.
# '''Overdischarge followed by charge'''. Any A123 cell that has been pulled low enough to come to rest at <300 mV should be immediately scrapped. The published number for that is 500 mV, but the real figure is closer to 300, so that's a "safety buffer" if you will. Below this Voltage, the Cu electrodes start to dissolve into the electrolyte. When charge is applied, the Cu forms dendrites that puncture the separator layer, forming an internal short in the cell. This can puff a cell in a hurry---the more charge current on tap, the worse it's prone to be.
# '''Driving a cell negative'''. I've neglected to mention this before, but it is a possibility. I don't know much about the specific mechanism at this time.
# '''Malfunctioning or misinformed electronics'''. This is the most common cause of all of the above in my experience. At this stage of the game, it is critical for YOU to understand how your BMS functions on at least a cursory level. Choose your BMS very carefully and periodically verify that it is operating properly. They're not all created equal. Make sure V sense lines are securely connected and free of corrosion. Just because your BMS says there was never a problem doesn't necessarily make it so. Avoid harnesses or ribbon cables between multiple modules if possible--they are problematic wherever they are used in any mobile electronics.
# '''Exposure to or generation of sufficient heat'''. I don't know exactly at what temperature gas formation begins in the electrolyte, but we spec a max storage temp of 80 (or 85?) degrees C and I suspect this is the reason. The hotter, the puffier--to a point. This is why soldering tabs poses a real hazard to cell health. If you feel you must solder, sink or blow the heat away from the body of the cell. Use a big iron that can make sufficient local heat quickly, before the whole mass of the cell gets hot. You might even get the cell warm enough to melt separator if not careful.
# '''No compression, not enough compression, improperly distributed compression'''. This is a pack/module design issue. Apply 10, maybe 15 psi to your cell stack end to end and then band snugly and evenly. Use hard endplates of some sort--never wrap cells directly or allow their shape to become distorted. Protect all areas of the pouch from impact damage. This obviously does not apply to cylindrical cells.

==== LiFePO4 prismatic cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cylindrical cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cell ageing ====
''Derived (barely paraphrased) from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''

Capacity loss is caused by the lithium that was available for storage becoming permanently plated on the cathode. Being unable to move within the cell it is no longer available to store energy. The impact of this plating is greater than the amount of lithium 'lost' to plating because not only is the lithium no longer available, it is also preventing access to that part of the cathode meaning Li that can still move has to take a longer path to reach the cathode. Lithium plating is one cause of increased cell resistance (there are others), a sign of worsening cell health.

There is no linear relationship between actual capacity loss and impedance rise. However some cell defects will also increase impedance.

Increasing cell resistance may cause a number of symptoms which may be confused with [https://earthshipbiotecture.com/a-lithium-ion-battery-primer/ High Self Discharge.]
# Elevated Peukert Losses. As more energy per amount of current through the cell is lost as heat, the cells useable capacity decreases. So the apparent capacity loss is higher than the actual capacity loss of cycleable lithium. When used in low current applications (e.g. solar energy storage) the actual and apparent decrease in capacity will be small. In high current draw applications (like EV traction packs), the Peukert loss increases proportionally, so the apparent capacity loss increases much faster than the actual capacity loss.
# Greater voltage excursion under the same load. Due to increased cell resistancethe voltage will sag further under the same load than a cell in optimal condition. The inverse is also true, the voltage will be higher for the same amount of charging current applied. The cell will then rebound to a voltage further from the loaded and charging voltages. This, obviously, can look like high self discharge but is a different phenomenon.
# Absolute maximum current decrease.
Elevated impedance causes a more complex constellation of symptoms, some of which may be easy to confuse with High Self Discharge (HSD). Ohm's law (E=I/R) holds the key to understanding here.

'''1) Elevated Peukert losses.''' Because more energy per unit of current through the cell is lost as heat, less of the cell's capacity is actually USABLE. Thus, apparent capacity loss can be significantly greater than actual capacity loss caused by the loss of cycleable Li alone. In low current applications, the two numbers will be close together. In high current applications, Peukert losses increase in proportion, so apparent loss of capacity breaks further and further away from actual capacity loss as current increases.

'''2) Greater voltage excursion under the same load.''' Elevated resistance across the cell means that voltage will sag more under the same load than it did when the cell was healthier. Conversely, voltage will rise higher with the same amount of applied charge current than it did when it was healthier. At the same time, rebound/settling voltages will be further away from loaded/charging voltages. In other words, the cell will rebound to a voltage further away from loaded voltage, all else being equal. Similarly, voltage will settle farther from the charge voltage with the same charge applied. This can give the illusion of elevated self-discharge, but the phenomenon is actually not the same thing. Again, the greater the charge and load currents, the greater the effect becomes.

'''3) Absolute max current decreases.''' Because the cell's series resistance is elevated, the maximum possible current through the cell is decreased.

Just to confuse things further, there can be many factors that lead to impedance rise. Some are related to Li plating, others are not.

=== Lithium-ion ===
Lithium-ion (Li-ion) batteries have a greater energy density than Lithium Iron Phosphate batteries, but have more challenging needs to use safely. The ideal operating range of Li-ion batteries is between +15 and +45°C. The upper limit of temperature is particularly important as Li-ion batteries experience thermal runaway - an unstoppable chain reaction that can occur in milliseconds releasing the stored energy in the cell. This can produce temperatures of 400°C and a fire that is extremely difficult to put out. Thermal runaway can start as low as 60°C and becomes much more likely at 100°C

Risk factors for thermal runaway:
* Short Circuits - either internally or externally
* Overcharging
* Excessive current draw or when charging

==== Li-ion pouch cells ====
[https://kokam.com/cell Kokam] produce high-performance Li-ion pouch cells. These combine relative ease of use and pack construction with performance close to cylindrical cells.

==== Li-ion 18650 and other cylindrical cells ====
Cylindrical cells are favoured by Tesla, and are probably the main reason why their cars achieve such excellent performance. They are light, compact, powerful and expensive. Unfortunately, cylindrical cells are difficult (and potentially dangerous) to use in DIY conversions. There are two good reasons for this: thermal management and cell configuration.

As stated above, Li-ion cells are prone to thermal runaway. So you need perfect battery and thermal management to ensure that no cell ever exceeds the critical voltage or temperature. If this happens, a cell can short-circuit internally, releasing a lot of energy - potentially explosively. Furthermore, the individual cells are small, so need to be arranged in parallel. In the case of the Tesla Model S 85kW pack, there are 74 cells in parallel. Imagine if one of those cells fails and becomes short circuited internally. You now have 73 very high power cells all feeding in to that short circuit...

In fact, you don't have to imagine: you can watch this famous video instead (courtesy of Rich Rebuilds).

<youtube>WdDi1haA71Q</youtube>

== OEM modules ==
Using an OEM module means a lot of the difficulties and safety issues associated with battery design are taken care of e.g. cooling, clamping, etc.

Here is a handy list of OEM modules:
{| class="wikitable sortable mw-collapsible"
|+
!Manufacturer
!Model
!Capacity (kWh)
!Weight (kg)
!w (mm)
!d (mm)
!h (mm)
!Gravity (kg/kWh)
!Volume (L/kWh)
!Voltage (V)
!Current (cont A)
!Current (peak A)
!Cell arrangement
!Cell type
!Chemistry
|-
|Tesla
|Model S 85kWh
|5.3
|26
|690
|315
|80
|4.9
|3.3
|22.8
|500
|750
|74p6s
|18650
|Li-ion
|-
|Tesla
|Model S 100kWh
|6.4
|28
|680
|315
|80
|4.4
|2.7
|22.8
|
|870
|86p6s
|18650
|Li-ion
|-
|Tesla
|Model 3 LR (inner)
|19.2
|98.9
|1854
|292
|90
|5.2
|2.5
|91.1
|
|971
|46p25s
|2170
|Li-ion
|-
|Tesla
|Model 3 LR (outer)
|17.7
|86.6
|1715
|292
|90
|4.9
|2.5
|83.9
|
|971
|46p23s
|2170
|Li-ion
|-
|Tesla
|Model 3 SR (inner)
|13.0
|
|1854
|292
|90
|
|3.7
|91.1
|
|603
|31p25s
|2170
|Li-ion
|-
|Tesla
|Model 3 SR (outer)
|12.0
|
|1715
|292
|90
|
|3.8
|83.9
|
|603
|31p23s
|2170
|Li-ion
|-
|Chevrolet
|Volt 2012
|4
|38
|470
|180
|280
|9.5
|5.9
|88
|140
|210
|24s
|Pouch
|Li-ion
|-
|BMW
|i3 60Ah
|2
|13
|368
|178
|102
|6.5
|3.3
|28.8
|210
|350
|8s2p
|Prismatic
|Li-ion
|-
|BMW
|i3 94Ah
|4.15
|28
|410
|310
|150
|6.7
|4.6
|45.6
|
|409
|12s
|Prismatic
|Li-ion
|-
|BMW
|i3 120Ah
|5.3
|28
|410
|310
|150
|5.3
|3.6
|45.6
|
|360
|12s
|Prismatic
|Li-ion
|-
|Jaguar
|iPace
|2.5
|12
|
|
|
|4.8
|
|43.1
|
|
|12s4p
|Pouch
|Li-ion
|-
|Mitsubishi
|Outlander
|2.4
|26
|646
|184
|130
|10.8
|6.4
|60
|
|240
|16s
|
|Li-ion
|-
|Nissan
|Leaf 24kWh
|0.5
|3.65
|300
|222
|34
|7.3
|4.5
|7.4
|130
|228
|2s2p
|Pouch
|Li-ion LMO
|-
|Nissan
|Leaf 40kWh
|1.6
|8.7
|300
|222
|68
|5.4
|2.8
|14.6
|
|314
|4s2p
|Pouch
|Li-ion NMC
|-
|Volvo
|XC90 T8
|2.01
|12.1
|300
|180
|150
|6.0
|4.0
|59.2
|170
|340
|16s
|
|Li-ion
|}

Batteries

2020-12-05T22:15:47Z

Clanger9: /* Volume (L) */

== Introduction ==
There are a wide variety of battery chemistries available for use as the main traction battery of an EV. To use each chemistry safely, and to ensure an adequate service life from the battery pack it is important to understand the requirements for the chemistry you are using. Failure to do so may lead to premature or catastrophic failure of the pack.

Good pack design will allow for a nominal amount of abuse. People make mistakes and the pack should allow a margin for safety - and for longevity!

== Battery pack specification ==
When deciding on your battery pack, here are some basic parameters to consider:

=== Capacity (kWh) ===
'''How far do you want to go?''' A standard car conversion will need a kWh for each 3 miles of range (very approximately). For a middleweight motorcycle, a kWh should give around 9 miles. Your mileage may vary, ''as they say.''

=== Voltage (V) ===
'''How fast do you want to go?''' The pack voltage defines the maximum speed your motor can spin. Motors are usually specified with "KV" - or RPM-per-volt. Check the KV of your motor and how fast it needs to spin to get your desired top speed. e.g. if you need 3,000 RPM from a 25 KV motor then your pack voltage needs to be 3,000 / 25 = 120 V. The exact number of cells in series you need depends on the cell design, but 3.8 V for Li-ion and 3.2 V for LiFePO4 is a reasonable guess.

=== Maximum current (A) ===
'''How quickly do you want to accelerate?''' Your motor's maximum power will be specified in kW. To estimate your maximum current draw, divide the peak power by the battery voltage. e.g. a 30 kW motor with a 120 V battery pack will pull 30,000 / 120 = 250 A. The higher the current rating of the cells, the heavier they will be for a given capacity. Ideally, you want "enough" current capacity for full throttle acceleration, but no more. You can put cells in parallel to double the current rating of your pack (which of course will half the voltage).

=== Mass (kg) ===
'''Can your vehicle carry the weight?''' You'll need to keep the kerb weight within the original design limits. For a car, this could be a few hundred kg. For a motorcycle, likely less than 100 kg. This is a huge variable - and each new generation of battery tech seems to be a little lighter. For older EV or hybrid batteries, you can reckon on approximately 10 kg/kWh. Nissan Leaf batteries are relatively light (7.5 kg/kWh). With the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 5-6 kg/kWh.

=== Volume (L) ===
'''Will it fit?''' Batteries are bulky. They are getting smaller, but finding enough space might be your biggest challenge. You could be looking at over 5 L/kWh for older EV or hybrid batteries. Current state-of-the-art is the Tesla Model 3, which gets this down to 2.5 L/kWh by using 2170 cylindrical cells.

There is much, much more to battery design than this (e.g. maximum charge rate, terminations, cooling, clamping), but the above should help work out which options will or won't work for your project...

== Cell chemistry ==

=== Lithium Iron Phosphate (LiFePO4) ===
Lithium Iron Phosphate (also known as LFP, or LiFePO4) batteries offer a good compromise between safety, energy density and ease of use for DIY conversions. They are available in a number of formats, commonly pouch cells, prismatic cells and cylindrical cells.

==== LiFePO4 pouch cells ====
The majority of this content is drawn from this thread: [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761&start=900 https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761] discussing the use of the A123 20Ah pouch cell. However, many of the general points apply equally to other similar pouch cells.

===== General build requirements =====
Pouch cells are vulnerable to damage from debris, and must be held in compression (see the datasheet for your battery, but 10-12 psi is recommended for the A123 pouch cells as a guide). A rigid container capable of preventing damage and providing compression is therefore required. Be aware the cells expand and contract in use, so allowance for this must be included in the structure of the case.

The pouch cells should be separated to prevent abrasion between cells, and also to avoid the development of hot spots. Prebuilt modules from A123 systems had thin foam sheets or heatsinks between each cell. Be sure to avoid any debris that could rub on the pouch surface, particularly if using recycled cells.

Mylar, '[https://www.americanmicroinc.com/fish-paper/ Fish paper]' or a [https://www.rogerscorp.com/elastomeric-material-solutions/poron-industrial-polyurethanes compliant foam] may be appropriate materials to serve this purpose. This material should not be flammable. If the material is heat insulating, it is important to address thermal management.

===== Compression =====
Compression is required to prevent premature failure of the cell. Without compression electrolyte will become unevenly distributed, causing current gradients in the cell and uneven heating. Local temperatures can become high enough to form gas formation leading to cells 'puffing up' even when the pack is otherwise held within temperature and voltage constraints. This will be exacerbated in packs with otherwise poor thermal management. Compression forces gas generated to the margins of the cell, outside of the cell stack, minimising its effect cell performance. Gas in the middle cells will create a dead space which does not store or release energy.

There is ~1% expansion through a discharge cycle. As the cell ages, the nominal cell thickness can grow by 3-5%. For A123 cells the ideal pressure is between 4 and 18psi with the ideal pressure being ~12psi. Maintaining 12psi can increase the life by 500 cycles over that of 4 or 18psi

There is some suggestion that in uses where 1C is never exceeded compression ''may'' not be required.

Highly rigid endplates with a mechanism to allow for a limited degree of expansion (e.g. steel bands) are considered an effective solution to this challenge.

It should be noted that compression is a challenge specific to pouch cells. Cylindrical cells are designed to maintain their own compression within the cell's electrode stack by their design.

This thread provides more information and experimentation relating to pack compression: <nowiki>https://endless-sphere.com/forums/viewtopic.php?f=14&t=52244</nowiki>

===== Pouch Cell Pack Design Examples =====
<nowiki>*</nowiki>placeholder*

===== Notes regarding recycled pouch cells =====
Pouch cells are somewhat fragile, and breaching the insulation is not difficult, especially in a cells removed from existing packs and repurposed. If the pouch has had their poly-layers compromised you may see a number of faults:
* Black spots around the perimeter of the cell indicate electrolyte leakage
* Voltage on the outside of the bag. Note that microvoltage between the pouch and the electrode is normal (and due to a capacitive effect).
While the majority of these cells should no longer be in the market, a significant number of faulty cells made it back into the 'greymarket' in around 2013. These cells had misaligned tabs which can also lead to isolation failures between the tab and the pack. These cells should be avoided, particularly in high demand applications.

===== Situations likely to cause pouch cell failure =====
''Taken directly from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''
# '''Overcharge'''. Any extended time above 3.8 Volts will generate enough heat and electrochemical activity to puff a cell, especially one that is improperly compressed.
# '''Overdischarge followed by charge'''. Any A123 cell that has been pulled low enough to come to rest at <300 mV should be immediately scrapped. The published number for that is 500 mV, but the real figure is closer to 300, so that's a "safety buffer" if you will. Below this Voltage, the Cu electrodes start to dissolve into the electrolyte. When charge is applied, the Cu forms dendrites that puncture the separator layer, forming an internal short in the cell. This can puff a cell in a hurry---the more charge current on tap, the worse it's prone to be.
# '''Driving a cell negative'''. I've neglected to mention this before, but it is a possibility. I don't know much about the specific mechanism at this time.
# '''Malfunctioning or misinformed electronics'''. This is the most common cause of all of the above in my experience. At this stage of the game, it is critical for YOU to understand how your BMS functions on at least a cursory level. Choose your BMS very carefully and periodically verify that it is operating properly. They're not all created equal. Make sure V sense lines are securely connected and free of corrosion. Just because your BMS says there was never a problem doesn't necessarily make it so. Avoid harnesses or ribbon cables between multiple modules if possible--they are problematic wherever they are used in any mobile electronics.
# '''Exposure to or generation of sufficient heat'''. I don't know exactly at what temperature gas formation begins in the electrolyte, but we spec a max storage temp of 80 (or 85?) degrees C and I suspect this is the reason. The hotter, the puffier--to a point. This is why soldering tabs poses a real hazard to cell health. If you feel you must solder, sink or blow the heat away from the body of the cell. Use a big iron that can make sufficient local heat quickly, before the whole mass of the cell gets hot. You might even get the cell warm enough to melt separator if not careful.
# '''No compression, not enough compression, improperly distributed compression'''. This is a pack/module design issue. Apply 10, maybe 15 psi to your cell stack end to end and then band snugly and evenly. Use hard endplates of some sort--never wrap cells directly or allow their shape to become distorted. Protect all areas of the pouch from impact damage. This obviously does not apply to cylindrical cells.

==== LiFePO4 prismatic cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cylindrical cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cell ageing ====
''Derived (barely paraphrased) from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''

Capacity loss is caused by the lithium that was available for storage becoming permanently plated on the cathode. Being unable to move within the cell it is no longer available to store energy. The impact of this plating is greater than the amount of lithium 'lost' to plating because not only is the lithium no longer available, it is also preventing access to that part of the cathode meaning Li that can still move has to take a longer path to reach the cathode. Lithium plating is one cause of increased cell resistance (there are others), a sign of worsening cell health.

There is no linear relationship between actual capacity loss and impedance rise. However some cell defects will also increase impedance.

Increasing cell resistance may cause a number of symptoms which may be confused with [https://earthshipbiotecture.com/a-lithium-ion-battery-primer/ High Self Discharge.]
# Elevated Peukert Losses. As more energy per amount of current through the cell is lost as heat, the cells useable capacity decreases. So the apparent capacity loss is higher than the actual capacity loss of cycleable lithium. When used in low current applications (e.g. solar energy storage) the actual and apparent decrease in capacity will be small. In high current draw applications (like EV traction packs), the Peukert loss increases proportionally, so the apparent capacity loss increases much faster than the actual capacity loss.
# Greater voltage excursion under the same load. Due to increased cell resistancethe voltage will sag further under the same load than a cell in optimal condition. The inverse is also true, the voltage will be higher for the same amount of charging current applied. The cell will then rebound to a voltage further from the loaded and charging voltages. This, obviously, can look like high self discharge but is a different phenomenon.
# Absolute maximum current decrease.
Elevated impedance causes a more complex constellation of symptoms, some of which may be easy to confuse with High Self Discharge (HSD). Ohm's law (E=I/R) holds the key to understanding here.

'''1) Elevated Peukert losses.''' Because more energy per unit of current through the cell is lost as heat, less of the cell's capacity is actually USABLE. Thus, apparent capacity loss can be significantly greater than actual capacity loss caused by the loss of cycleable Li alone. In low current applications, the two numbers will be close together. In high current applications, Peukert losses increase in proportion, so apparent loss of capacity breaks further and further away from actual capacity loss as current increases.

'''2) Greater voltage excursion under the same load.''' Elevated resistance across the cell means that voltage will sag more under the same load than it did when the cell was healthier. Conversely, voltage will rise higher with the same amount of applied charge current than it did when it was healthier. At the same time, rebound/settling voltages will be further away from loaded/charging voltages. In other words, the cell will rebound to a voltage further away from loaded voltage, all else being equal. Similarly, voltage will settle farther from the charge voltage with the same charge applied. This can give the illusion of elevated self-discharge, but the phenomenon is actually not the same thing. Again, the greater the charge and load currents, the greater the effect becomes.

'''3) Absolute max current decreases.''' Because the cell's series resistance is elevated, the maximum possible current through the cell is decreased.

Just to confuse things further, there can be many factors that lead to impedance rise. Some are related to Li plating, others are not.

=== Lithium-ion ===
Lithium-ion (Li-ion) batteries have a greater energy density than Lithium Iron Phosphate batteries, but have more challenging needs to use safely. The ideal operating range of Li-ion batteries is between +15 and +45°C. The upper limit of temperature is particularly important as Li-ion batteries experience thermal runaway - an unstoppable chain reaction that can occur in milliseconds releasing the stored energy in the cell. This can produce temperatures of 400°C and a fire that is extremely difficult to put out. Thermal runaway can start as low as 60°C and becomes much more likely at 100°C

Risk factors for thermal runaway:
* Short Circuits - either internally or externally
* Overcharging
* Excessive current draw or when charging

==== Li-ion pouch cells ====
[https://kokam.com/cell Kokam] produce high-performance Li-ion pouch cells. These combine relative ease of use and pack construction with performance close to cylindrical cells.

==== Li-ion 18650 and other cylindrical cells ====
Cylindrical cells are favoured by Tesla, and are probably the main reason why their cars achieve such excellent performance. They are light, compact, powerful and expensive. Unfortunately, cylindrical cells are difficult (and potentially dangerous) to use in DIY conversions. There are two good reasons for this: thermal management and cell configuration.

As stated above, Li-ion cells are prone to thermal runaway. So you need perfect battery and thermal management to ensure that no cell ever exceeds the critical voltage or temperature. If this happens, a cell can short-circuit internally, releasing a lot of energy - potentially explosively. Furthermore, the individual cells are small, so need to be arranged in parallel. In the case of the Tesla Model S 85kW pack, there are 74 cells in parallel. Imagine if one of those cells fails and becomes short circuited internally. You now have 73 very high power cells all feeding in to that short circuit...

In fact, you don't have to imagine: you can watch this famous video instead (courtesy of Rich Rebuilds).

<youtube>WdDi1haA71Q</youtube>

== OEM modules ==
Using an OEM module means a lot of the difficulties and safety issues associated with battery design are taken care of e.g. cooling, clamping, etc.

Here is a handy list of OEM modules:
{| class="wikitable sortable mw-collapsible"
|+
!Manufacturer
!Model
!Capacity (kWh)
!Weight (kg)
!w (mm)
!d (mm)
!h (mm)
!Gravity (kg/kWh)
!Volume (L/kWh)
!Voltage (V)
!Current (cont A)
!Current (peak A)
!Cell arrangement
!Cell type
!Chemistry
|-
|Tesla
|Model S 85kWh
|5.3
|26
|690
|315
|80
|4.9
|3.3
|22.8
|500
|750
|74p6s
|18650
|Li-ion
|-
|Tesla
|Model S 100kWh
|6.4
|28
|680
|315
|80
|4.4
|2.7
|22.8
|
|870
|86p6s
|18650
|Li-ion
|-
|Tesla
|Model 3 LR (inner)
|19.2
|98.9
|1854
|292
|90
|5.2
|2.5
|91.1
|
|971
|46p25s
|2170
|Li-ion
|-
|Tesla
|Model 3 LR (outer)
|17.7
|86.6
|1715
|292
|90
|4.9
|2.5
|83.9
|
|971
|46p23s
|2170
|Li-ion
|-
|Tesla
|Model 3 SR (inner)
|13.0
|
|1854
|292
|90
|
|3.7
|91.1
|
|603
|31p25s
|2170
|Li-ion
|-
|Tesla
|Model 3 SR (outer)
|12.0
|
|1715
|292
|90
|
|3.8
|83.9
|
|603
|31p23s
|2170
|Li-ion
|-
|Chevrolet
|Volt 2012
|4
|38
|470
|180
|280
|9.5
|5.9
|88
|140
|210
|24s
|Pouch
|Li-ion
|-
|BMW
|i3 60Ah
|2
|13
|368
|178
|102
|6.5
|3.3
|28.8
|210
|350
|8s2p
|Prismatic
|Li-ion
|-
|BMW
|i3 94Ah
|4.15
|28
|410
|310
|150
|6.7
|4.6
|45.6
|
|409
|12s
|Prismatic
|Li-ion
|-
|BMW
|i3 120Ah
|5.3
|28
|410
|310
|150
|5.3
|3.6
|45.6
|
|360
|12s
|Prismatic
|Li-ion
|-
|Mitsubishi
|Outlander
|2.4
|26
|646
|184
|130
|10.8
|6.4
|60
|
|240
|16s
|
|Li-ion
|-
|Nissan
|Leaf 24kWh
|0.5
|3.65
|300
|222
|34
|7.3
|4.5
|7.4
|130
|228
|2s2p
|Pouch
|Li-ion LMO
|-
|Nissan
|Leaf 40kWh
|1.6
|8.7
|300
|222
|68
|5.4
|2.8
|14.6
|
|314
|4s2p
|Pouch
|Li-ion NMC
|-
|Volvo
|XC90 T8
|2.01
|12.1
|300
|180
|150
|6.0
|4.0
|59.2
|170
|340
|16s
|
|Li-ion
|}

Batteries

2020-12-05T22:13:50Z

Clanger9: /* OEM modules */ Add Tesla Model 3

== Introduction ==
There are a wide variety of battery chemistries available for use as the main traction battery of an EV. To use each chemistry safely, and to ensure an adequate service life from the battery pack it is important to understand the requirements for the chemistry you are using. Failure to do so may lead to premature or catastrophic failure of the pack.

Good pack design will allow for a nominal amount of abuse. People make mistakes and the pack should allow a margin for safety - and for longevity!

== Battery pack specification ==
When deciding on your battery pack, here are some basic parameters to consider:

=== Capacity (kWh) ===
'''How far do you want to go?''' A standard car conversion will need a kWh for each 3 miles of range (very approximately). For a middleweight motorcycle, a kWh should give around 9 miles. Your mileage may vary, ''as they say.''

=== Voltage (V) ===
'''How fast do you want to go?''' The pack voltage defines the maximum speed your motor can spin. Motors are usually specified with "KV" - or RPM-per-volt. Check the KV of your motor and how fast it needs to spin to get your desired top speed. e.g. if you need 3,000 RPM from a 25 KV motor then your pack voltage needs to be 3,000 / 25 = 120 V. The exact number of cells in series you need depends on the cell design, but 3.8 V for Li-ion and 3.2 V for LiFePO4 is a reasonable guess.

=== Maximum current (A) ===
'''How quickly do you want to accelerate?''' Your motor's maximum power will be specified in kW. To estimate your maximum current draw, divide the peak power by the battery voltage. e.g. a 30 kW motor with a 120 V battery pack will pull 30,000 / 120 = 250 A. The higher the current rating of the cells, the heavier they will be for a given capacity. Ideally, you want "enough" current capacity for full throttle acceleration, but no more. You can put cells in parallel to double the current rating of your pack (which of course will half the voltage).

=== Mass (kg) ===
'''Can your vehicle carry the weight?''' You'll need to keep the kerb weight within the original design limits. For a car, this could be a few hundred kg. For a motorcycle, likely less than 100 kg. This is a huge variable - and each new generation of battery tech seems to be a little lighter. For older EV or hybrid batteries, you can reckon on approximately 10 kg/kWh. Nissan Leaf batteries are relatively light (7.5 kg/kWh). With the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 5-6 kg/kWh.

=== Volume (L) ===
'''Will it fit?''' Batteries are bulky. They are getting smaller, but finding enough space might be your biggest challenge. You could be looking at over 5 L/kWh for older EV or hybrid batteries. For the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 3 L/kWh.

There is much, much more to battery design than this (e.g. maximum charge rate, terminations, cooling, clamping), but the above should help work out which options will or won't work for your project...

== Cell chemistry ==

=== Lithium Iron Phosphate (LiFePO4) ===
Lithium Iron Phosphate (also known as LFP, or LiFePO4) batteries offer a good compromise between safety, energy density and ease of use for DIY conversions. They are available in a number of formats, commonly pouch cells, prismatic cells and cylindrical cells.

==== LiFePO4 pouch cells ====
The majority of this content is drawn from this thread: [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761&start=900 https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761] discussing the use of the A123 20Ah pouch cell. However, many of the general points apply equally to other similar pouch cells.

===== General build requirements =====
Pouch cells are vulnerable to damage from debris, and must be held in compression (see the datasheet for your battery, but 10-12 psi is recommended for the A123 pouch cells as a guide). A rigid container capable of preventing damage and providing compression is therefore required. Be aware the cells expand and contract in use, so allowance for this must be included in the structure of the case.

The pouch cells should be separated to prevent abrasion between cells, and also to avoid the development of hot spots. Prebuilt modules from A123 systems had thin foam sheets or heatsinks between each cell. Be sure to avoid any debris that could rub on the pouch surface, particularly if using recycled cells.

Mylar, '[https://www.americanmicroinc.com/fish-paper/ Fish paper]' or a [https://www.rogerscorp.com/elastomeric-material-solutions/poron-industrial-polyurethanes compliant foam] may be appropriate materials to serve this purpose. This material should not be flammable. If the material is heat insulating, it is important to address thermal management.

===== Compression =====
Compression is required to prevent premature failure of the cell. Without compression electrolyte will become unevenly distributed, causing current gradients in the cell and uneven heating. Local temperatures can become high enough to form gas formation leading to cells 'puffing up' even when the pack is otherwise held within temperature and voltage constraints. This will be exacerbated in packs with otherwise poor thermal management. Compression forces gas generated to the margins of the cell, outside of the cell stack, minimising its effect cell performance. Gas in the middle cells will create a dead space which does not store or release energy.

There is ~1% expansion through a discharge cycle. As the cell ages, the nominal cell thickness can grow by 3-5%. For A123 cells the ideal pressure is between 4 and 18psi with the ideal pressure being ~12psi. Maintaining 12psi can increase the life by 500 cycles over that of 4 or 18psi

There is some suggestion that in uses where 1C is never exceeded compression ''may'' not be required.

Highly rigid endplates with a mechanism to allow for a limited degree of expansion (e.g. steel bands) are considered an effective solution to this challenge.

It should be noted that compression is a challenge specific to pouch cells. Cylindrical cells are designed to maintain their own compression within the cell's electrode stack by their design.

This thread provides more information and experimentation relating to pack compression: <nowiki>https://endless-sphere.com/forums/viewtopic.php?f=14&t=52244</nowiki>

===== Pouch Cell Pack Design Examples =====
<nowiki>*</nowiki>placeholder*

===== Notes regarding recycled pouch cells =====
Pouch cells are somewhat fragile, and breaching the insulation is not difficult, especially in a cells removed from existing packs and repurposed. If the pouch has had their poly-layers compromised you may see a number of faults:
* Black spots around the perimeter of the cell indicate electrolyte leakage
* Voltage on the outside of the bag. Note that microvoltage between the pouch and the electrode is normal (and due to a capacitive effect).
While the majority of these cells should no longer be in the market, a significant number of faulty cells made it back into the 'greymarket' in around 2013. These cells had misaligned tabs which can also lead to isolation failures between the tab and the pack. These cells should be avoided, particularly in high demand applications.

===== Situations likely to cause pouch cell failure =====
''Taken directly from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''
# '''Overcharge'''. Any extended time above 3.8 Volts will generate enough heat and electrochemical activity to puff a cell, especially one that is improperly compressed.
# '''Overdischarge followed by charge'''. Any A123 cell that has been pulled low enough to come to rest at <300 mV should be immediately scrapped. The published number for that is 500 mV, but the real figure is closer to 300, so that's a "safety buffer" if you will. Below this Voltage, the Cu electrodes start to dissolve into the electrolyte. When charge is applied, the Cu forms dendrites that puncture the separator layer, forming an internal short in the cell. This can puff a cell in a hurry---the more charge current on tap, the worse it's prone to be.
# '''Driving a cell negative'''. I've neglected to mention this before, but it is a possibility. I don't know much about the specific mechanism at this time.
# '''Malfunctioning or misinformed electronics'''. This is the most common cause of all of the above in my experience. At this stage of the game, it is critical for YOU to understand how your BMS functions on at least a cursory level. Choose your BMS very carefully and periodically verify that it is operating properly. They're not all created equal. Make sure V sense lines are securely connected and free of corrosion. Just because your BMS says there was never a problem doesn't necessarily make it so. Avoid harnesses or ribbon cables between multiple modules if possible--they are problematic wherever they are used in any mobile electronics.
# '''Exposure to or generation of sufficient heat'''. I don't know exactly at what temperature gas formation begins in the electrolyte, but we spec a max storage temp of 80 (or 85?) degrees C and I suspect this is the reason. The hotter, the puffier--to a point. This is why soldering tabs poses a real hazard to cell health. If you feel you must solder, sink or blow the heat away from the body of the cell. Use a big iron that can make sufficient local heat quickly, before the whole mass of the cell gets hot. You might even get the cell warm enough to melt separator if not careful.
# '''No compression, not enough compression, improperly distributed compression'''. This is a pack/module design issue. Apply 10, maybe 15 psi to your cell stack end to end and then band snugly and evenly. Use hard endplates of some sort--never wrap cells directly or allow their shape to become distorted. Protect all areas of the pouch from impact damage. This obviously does not apply to cylindrical cells.

==== LiFePO4 prismatic cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cylindrical cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cell ageing ====
''Derived (barely paraphrased) from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''

Capacity loss is caused by the lithium that was available for storage becoming permanently plated on the cathode. Being unable to move within the cell it is no longer available to store energy. The impact of this plating is greater than the amount of lithium 'lost' to plating because not only is the lithium no longer available, it is also preventing access to that part of the cathode meaning Li that can still move has to take a longer path to reach the cathode. Lithium plating is one cause of increased cell resistance (there are others), a sign of worsening cell health.

There is no linear relationship between actual capacity loss and impedance rise. However some cell defects will also increase impedance.

Increasing cell resistance may cause a number of symptoms which may be confused with [https://earthshipbiotecture.com/a-lithium-ion-battery-primer/ High Self Discharge.]
# Elevated Peukert Losses. As more energy per amount of current through the cell is lost as heat, the cells useable capacity decreases. So the apparent capacity loss is higher than the actual capacity loss of cycleable lithium. When used in low current applications (e.g. solar energy storage) the actual and apparent decrease in capacity will be small. In high current draw applications (like EV traction packs), the Peukert loss increases proportionally, so the apparent capacity loss increases much faster than the actual capacity loss.
# Greater voltage excursion under the same load. Due to increased cell resistancethe voltage will sag further under the same load than a cell in optimal condition. The inverse is also true, the voltage will be higher for the same amount of charging current applied. The cell will then rebound to a voltage further from the loaded and charging voltages. This, obviously, can look like high self discharge but is a different phenomenon.
# Absolute maximum current decrease.
Elevated impedance causes a more complex constellation of symptoms, some of which may be easy to confuse with High Self Discharge (HSD). Ohm's law (E=I/R) holds the key to understanding here.

'''1) Elevated Peukert losses.''' Because more energy per unit of current through the cell is lost as heat, less of the cell's capacity is actually USABLE. Thus, apparent capacity loss can be significantly greater than actual capacity loss caused by the loss of cycleable Li alone. In low current applications, the two numbers will be close together. In high current applications, Peukert losses increase in proportion, so apparent loss of capacity breaks further and further away from actual capacity loss as current increases.

'''2) Greater voltage excursion under the same load.''' Elevated resistance across the cell means that voltage will sag more under the same load than it did when the cell was healthier. Conversely, voltage will rise higher with the same amount of applied charge current than it did when it was healthier. At the same time, rebound/settling voltages will be further away from loaded/charging voltages. In other words, the cell will rebound to a voltage further away from loaded voltage, all else being equal. Similarly, voltage will settle farther from the charge voltage with the same charge applied. This can give the illusion of elevated self-discharge, but the phenomenon is actually not the same thing. Again, the greater the charge and load currents, the greater the effect becomes.

'''3) Absolute max current decreases.''' Because the cell's series resistance is elevated, the maximum possible current through the cell is decreased.

Just to confuse things further, there can be many factors that lead to impedance rise. Some are related to Li plating, others are not.

=== Lithium-ion ===
Lithium-ion (Li-ion) batteries have a greater energy density than Lithium Iron Phosphate batteries, but have more challenging needs to use safely. The ideal operating range of Li-ion batteries is between +15 and +45°C. The upper limit of temperature is particularly important as Li-ion batteries experience thermal runaway - an unstoppable chain reaction that can occur in milliseconds releasing the stored energy in the cell. This can produce temperatures of 400°C and a fire that is extremely difficult to put out. Thermal runaway can start as low as 60°C and becomes much more likely at 100°C

Risk factors for thermal runaway:
* Short Circuits - either internally or externally
* Overcharging
* Excessive current draw or when charging

==== Li-ion pouch cells ====
[https://kokam.com/cell Kokam] produce high-performance Li-ion pouch cells. These combine relative ease of use and pack construction with performance close to cylindrical cells.

==== Li-ion 18650 and other cylindrical cells ====
Cylindrical cells are favoured by Tesla, and are probably the main reason why their cars achieve such excellent performance. They are light, compact, powerful and expensive. Unfortunately, cylindrical cells are difficult (and potentially dangerous) to use in DIY conversions. There are two good reasons for this: thermal management and cell configuration.

As stated above, Li-ion cells are prone to thermal runaway. So you need perfect battery and thermal management to ensure that no cell ever exceeds the critical voltage or temperature. If this happens, a cell can short-circuit internally, releasing a lot of energy - potentially explosively. Furthermore, the individual cells are small, so need to be arranged in parallel. In the case of the Tesla Model S 85kW pack, there are 74 cells in parallel. Imagine if one of those cells fails and becomes short circuited internally. You now have 73 very high power cells all feeding in to that short circuit...

In fact, you don't have to imagine: you can watch this famous video instead (courtesy of Rich Rebuilds).

<youtube>WdDi1haA71Q</youtube>

== OEM modules ==
Using an OEM module means a lot of the difficulties and safety issues associated with battery design are taken care of e.g. cooling, clamping, etc.

Here is a handy list of OEM modules:
{| class="wikitable sortable mw-collapsible"
|+
!Manufacturer
!Model
!Capacity (kWh)
!Weight (kg)
!w (mm)
!d (mm)
!h (mm)
!Gravity (kg/kWh)
!Volume (L/kWh)
!Voltage (V)
!Current (cont A)
!Current (peak A)
!Cell arrangement
!Cell type
!Chemistry
|-
|Tesla
|Model S 85kWh
|5.3
|26
|690
|315
|80
|4.9
|3.3
|22.8
|500
|750
|74p6s
|18650
|Li-ion
|-
|Tesla
|Model S 100kWh
|6.4
|28
|680
|315
|80
|4.4
|2.7
|22.8
|
|870
|86p6s
|18650
|Li-ion
|-
|Tesla
|Model 3 LR (inner)
|19.2
|98.9
|1854
|292
|90
|5.2
|2.5
|91.1
|
|971
|46p25s
|2170
|Li-ion
|-
|Tesla
|Model 3 LR (outer)
|17.7
|86.6
|1715
|292
|90
|4.9
|2.5
|83.9
|
|971
|46p23s
|2170
|Li-ion
|-
|Tesla
|Model 3 SR (inner)
|13.0
|
|1854
|292
|90
|
|3.7
|91.1
|
|603
|31p25s
|2170
|Li-ion
|-
|Tesla
|Model 3 SR (outer)
|12.0
|
|1715
|292
|90
|
|3.8
|83.9
|
|603
|31p23s
|2170
|Li-ion
|-
|Chevrolet
|Volt 2012
|4
|38
|470
|180
|280
|9.5
|5.9
|88
|140
|210
|24s
|Pouch
|Li-ion
|-
|BMW
|i3 60Ah
|2
|13
|368
|178
|102
|6.5
|3.3
|28.8
|210
|350
|8s2p
|Prismatic
|Li-ion
|-
|BMW
|i3 94Ah
|4.15
|28
|410
|310
|150
|6.7
|4.6
|45.6
|
|409
|12s
|Prismatic
|Li-ion
|-
|BMW
|i3 120Ah
|5.3
|28
|410
|310
|150
|5.3
|3.6
|45.6
|
|360
|12s
|Prismatic
|Li-ion
|-
|Mitsubishi
|Outlander
|2.4
|26
|646
|184
|130
|10.8
|6.4
|60
|
|240
|16s
|
|Li-ion
|-
|Nissan
|Leaf 24kWh
|0.5
|3.65
|300
|222
|34
|7.3
|4.5
|7.4
|130
|228
|2s2p
|Pouch
|Li-ion LMO
|-
|Nissan
|Leaf 40kWh
|1.6
|8.7
|300
|222
|68
|5.4
|2.8
|14.6
|
|314
|4s2p
|Pouch
|Li-ion NMC
|-
|Volvo
|XC90 T8
|2.01
|12.1
|300
|180
|150
|6.0
|4.0
|59.2
|170
|340
|16s
|
|Li-ion
|}

Batteries

2020-12-05T21:41:55Z

Clanger9: /* OEM modules */ Add Leaf battery current

== Introduction ==
There are a wide variety of battery chemistries available for use as the main traction battery of an EV. To use each chemistry safely, and to ensure an adequate service life from the battery pack it is important to understand the requirements for the chemistry you are using. Failure to do so may lead to premature or catastrophic failure of the pack.

Good pack design will allow for a nominal amount of abuse. People make mistakes and the pack should allow a margin for safety - and for longevity!

== Battery pack specification ==
When deciding on your battery pack, here are some basic parameters to consider:

=== Capacity (kWh) ===
'''How far do you want to go?''' A standard car conversion will need a kWh for each 3 miles of range (very approximately). For a middleweight motorcycle, a kWh should give around 9 miles. Your mileage may vary, ''as they say.''

=== Voltage (V) ===
'''How fast do you want to go?''' The pack voltage defines the maximum speed your motor can spin. Motors are usually specified with "KV" - or RPM-per-volt. Check the KV of your motor and how fast it needs to spin to get your desired top speed. e.g. if you need 3,000 RPM from a 25 KV motor then your pack voltage needs to be 3,000 / 25 = 120 V. The exact number of cells in series you need depends on the cell design, but 3.8 V for Li-ion and 3.2 V for LiFePO4 is a reasonable guess.

=== Maximum current (A) ===
'''How quickly do you want to accelerate?''' Your motor's maximum power will be specified in kW. To estimate your maximum current draw, divide the peak power by the battery voltage. e.g. a 30 kW motor with a 120 V battery pack will pull 30,000 / 120 = 250 A. The higher the current rating of the cells, the heavier they will be for a given capacity. Ideally, you want "enough" current capacity for full throttle acceleration, but no more. You can put cells in parallel to double the current rating of your pack (which of course will half the voltage).

=== Mass (kg) ===
'''Can your vehicle carry the weight?''' You'll need to keep the kerb weight within the original design limits. For a car, this could be a few hundred kg. For a motorcycle, likely less than 100 kg. This is a huge variable - and each new generation of battery tech seems to be a little lighter. For older EV or hybrid batteries, you can reckon on approximately 10 kg/kWh. Nissan Leaf batteries are relatively light (7.5 kg/kWh). With the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 5-6 kg/kWh.

=== Volume (L) ===
'''Will it fit?''' Batteries are bulky. They are getting smaller, but finding enough space might be your biggest challenge. You could be looking at over 5 L/kWh for older EV or hybrid batteries. For the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 3 L/kWh.

There is much, much more to battery design than this (e.g. maximum charge rate, terminations, cooling, clamping), but the above should help work out which options will or won't work for your project...

== Cell chemistry ==

=== Lithium Iron Phosphate (LiFePO4) ===
Lithium Iron Phosphate (also known as LFP, or LiFePO4) batteries offer a good compromise between safety, energy density and ease of use for DIY conversions. They are available in a number of formats, commonly pouch cells, prismatic cells and cylindrical cells.

==== LiFePO4 pouch cells ====
The majority of this content is drawn from this thread: [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761&start=900 https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761] discussing the use of the A123 20Ah pouch cell. However, many of the general points apply equally to other similar pouch cells.

===== General build requirements =====
Pouch cells are vulnerable to damage from debris, and must be held in compression (see the datasheet for your battery, but 10-12 psi is recommended for the A123 pouch cells as a guide). A rigid container capable of preventing damage and providing compression is therefore required. Be aware the cells expand and contract in use, so allowance for this must be included in the structure of the case.

The pouch cells should be separated to prevent abrasion between cells, and also to avoid the development of hot spots. Prebuilt modules from A123 systems had thin foam sheets or heatsinks between each cell. Be sure to avoid any debris that could rub on the pouch surface, particularly if using recycled cells.

Mylar, '[https://www.americanmicroinc.com/fish-paper/ Fish paper]' or a [https://www.rogerscorp.com/elastomeric-material-solutions/poron-industrial-polyurethanes compliant foam] may be appropriate materials to serve this purpose. This material should not be flammable. If the material is heat insulating, it is important to address thermal management.

===== Compression =====
Compression is required to prevent premature failure of the cell. Without compression electrolyte will become unevenly distributed, causing current gradients in the cell and uneven heating. Local temperatures can become high enough to form gas formation leading to cells 'puffing up' even when the pack is otherwise held within temperature and voltage constraints. This will be exacerbated in packs with otherwise poor thermal management. Compression forces gas generated to the margins of the cell, outside of the cell stack, minimising its effect cell performance. Gas in the middle cells will create a dead space which does not store or release energy.

There is ~1% expansion through a discharge cycle. As the cell ages, the nominal cell thickness can grow by 3-5%. For A123 cells the ideal pressure is between 4 and 18psi with the ideal pressure being ~12psi. Maintaining 12psi can increase the life by 500 cycles over that of 4 or 18psi

There is some suggestion that in uses where 1C is never exceeded compression ''may'' not be required.

Highly rigid endplates with a mechanism to allow for a limited degree of expansion (e.g. steel bands) are considered an effective solution to this challenge.

It should be noted that compression is a challenge specific to pouch cells. Cylindrical cells are designed to maintain their own compression within the cell's electrode stack by their design.

This thread provides more information and experimentation relating to pack compression: <nowiki>https://endless-sphere.com/forums/viewtopic.php?f=14&t=52244</nowiki>

===== Pouch Cell Pack Design Examples =====
<nowiki>*</nowiki>placeholder*

===== Notes regarding recycled pouch cells =====
Pouch cells are somewhat fragile, and breaching the insulation is not difficult, especially in a cells removed from existing packs and repurposed. If the pouch has had their poly-layers compromised you may see a number of faults:
* Black spots around the perimeter of the cell indicate electrolyte leakage
* Voltage on the outside of the bag. Note that microvoltage between the pouch and the electrode is normal (and due to a capacitive effect).
While the majority of these cells should no longer be in the market, a significant number of faulty cells made it back into the 'greymarket' in around 2013. These cells had misaligned tabs which can also lead to isolation failures between the tab and the pack. These cells should be avoided, particularly in high demand applications.

===== Situations likely to cause pouch cell failure =====
''Taken directly from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''
# '''Overcharge'''. Any extended time above 3.8 Volts will generate enough heat and electrochemical activity to puff a cell, especially one that is improperly compressed.
# '''Overdischarge followed by charge'''. Any A123 cell that has been pulled low enough to come to rest at <300 mV should be immediately scrapped. The published number for that is 500 mV, but the real figure is closer to 300, so that's a "safety buffer" if you will. Below this Voltage, the Cu electrodes start to dissolve into the electrolyte. When charge is applied, the Cu forms dendrites that puncture the separator layer, forming an internal short in the cell. This can puff a cell in a hurry---the more charge current on tap, the worse it's prone to be.
# '''Driving a cell negative'''. I've neglected to mention this before, but it is a possibility. I don't know much about the specific mechanism at this time.
# '''Malfunctioning or misinformed electronics'''. This is the most common cause of all of the above in my experience. At this stage of the game, it is critical for YOU to understand how your BMS functions on at least a cursory level. Choose your BMS very carefully and periodically verify that it is operating properly. They're not all created equal. Make sure V sense lines are securely connected and free of corrosion. Just because your BMS says there was never a problem doesn't necessarily make it so. Avoid harnesses or ribbon cables between multiple modules if possible--they are problematic wherever they are used in any mobile electronics.
# '''Exposure to or generation of sufficient heat'''. I don't know exactly at what temperature gas formation begins in the electrolyte, but we spec a max storage temp of 80 (or 85?) degrees C and I suspect this is the reason. The hotter, the puffier--to a point. This is why soldering tabs poses a real hazard to cell health. If you feel you must solder, sink or blow the heat away from the body of the cell. Use a big iron that can make sufficient local heat quickly, before the whole mass of the cell gets hot. You might even get the cell warm enough to melt separator if not careful.
# '''No compression, not enough compression, improperly distributed compression'''. This is a pack/module design issue. Apply 10, maybe 15 psi to your cell stack end to end and then band snugly and evenly. Use hard endplates of some sort--never wrap cells directly or allow their shape to become distorted. Protect all areas of the pouch from impact damage. This obviously does not apply to cylindrical cells.

==== LiFePO4 prismatic cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cylindrical cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cell ageing ====
''Derived (barely paraphrased) from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''

Capacity loss is caused by the lithium that was available for storage becoming permanently plated on the cathode. Being unable to move within the cell it is no longer available to store energy. The impact of this plating is greater than the amount of lithium 'lost' to plating because not only is the lithium no longer available, it is also preventing access to that part of the cathode meaning Li that can still move has to take a longer path to reach the cathode. Lithium plating is one cause of increased cell resistance (there are others), a sign of worsening cell health.

There is no linear relationship between actual capacity loss and impedance rise. However some cell defects will also increase impedance.

Increasing cell resistance may cause a number of symptoms which may be confused with [https://earthshipbiotecture.com/a-lithium-ion-battery-primer/ High Self Discharge.]
# Elevated Peukert Losses. As more energy per amount of current through the cell is lost as heat, the cells useable capacity decreases. So the apparent capacity loss is higher than the actual capacity loss of cycleable lithium. When used in low current applications (e.g. solar energy storage) the actual and apparent decrease in capacity will be small. In high current draw applications (like EV traction packs), the Peukert loss increases proportionally, so the apparent capacity loss increases much faster than the actual capacity loss.
# Greater voltage excursion under the same load. Due to increased cell resistancethe voltage will sag further under the same load than a cell in optimal condition. The inverse is also true, the voltage will be higher for the same amount of charging current applied. The cell will then rebound to a voltage further from the loaded and charging voltages. This, obviously, can look like high self discharge but is a different phenomenon.
# Absolute maximum current decrease.
Elevated impedance causes a more complex constellation of symptoms, some of which may be easy to confuse with High Self Discharge (HSD). Ohm's law (E=I/R) holds the key to understanding here.

'''1) Elevated Peukert losses.''' Because more energy per unit of current through the cell is lost as heat, less of the cell's capacity is actually USABLE. Thus, apparent capacity loss can be significantly greater than actual capacity loss caused by the loss of cycleable Li alone. In low current applications, the two numbers will be close together. In high current applications, Peukert losses increase in proportion, so apparent loss of capacity breaks further and further away from actual capacity loss as current increases.

'''2) Greater voltage excursion under the same load.''' Elevated resistance across the cell means that voltage will sag more under the same load than it did when the cell was healthier. Conversely, voltage will rise higher with the same amount of applied charge current than it did when it was healthier. At the same time, rebound/settling voltages will be further away from loaded/charging voltages. In other words, the cell will rebound to a voltage further away from loaded voltage, all else being equal. Similarly, voltage will settle farther from the charge voltage with the same charge applied. This can give the illusion of elevated self-discharge, but the phenomenon is actually not the same thing. Again, the greater the charge and load currents, the greater the effect becomes.

'''3) Absolute max current decreases.''' Because the cell's series resistance is elevated, the maximum possible current through the cell is decreased.

Just to confuse things further, there can be many factors that lead to impedance rise. Some are related to Li plating, others are not.

=== Lithium-ion ===
Lithium-ion (Li-ion) batteries have a greater energy density than Lithium Iron Phosphate batteries, but have more challenging needs to use safely. The ideal operating range of Li-ion batteries is between +15 and +45°C. The upper limit of temperature is particularly important as Li-ion batteries experience thermal runaway - an unstoppable chain reaction that can occur in milliseconds releasing the stored energy in the cell. This can produce temperatures of 400°C and a fire that is extremely difficult to put out. Thermal runaway can start as low as 60°C and becomes much more likely at 100°C

Risk factors for thermal runaway:
* Short Circuits - either internally or externally
* Overcharging
* Excessive current draw or when charging

==== Li-ion pouch cells ====
[https://kokam.com/cell Kokam] produce high-performance Li-ion pouch cells. These combine relative ease of use and pack construction with performance close to cylindrical cells.

==== Li-ion 18650 and other cylindrical cells ====
Cylindrical cells are favoured by Tesla, and are probably the main reason why their cars achieve such excellent performance. They are light, compact, powerful and expensive. Unfortunately, cylindrical cells are difficult (and potentially dangerous) to use in DIY conversions. There are two good reasons for this: thermal management and cell configuration.

As stated above, Li-ion cells are prone to thermal runaway. So you need perfect battery and thermal management to ensure that no cell ever exceeds the critical voltage or temperature. If this happens, a cell can short-circuit internally, releasing a lot of energy - potentially explosively. Furthermore, the individual cells are small, so need to be arranged in parallel. In the case of the Tesla Model S 85kW pack, there are 74 cells in parallel. Imagine if one of those cells fails and becomes short circuited internally. You now have 73 very high power cells all feeding in to that short circuit...

In fact, you don't have to imagine: you can watch this famous video instead (courtesy of Rich Rebuilds).

<youtube>WdDi1haA71Q</youtube>

== OEM modules ==
Using an OEM module means a lot of the difficulties and safety issues associated with battery design are taken care of e.g. cooling, clamping, etc.

Here is a handy list of OEM modules:
{| class="wikitable sortable mw-collapsible"
|+
!Manufacturer
!Model
!Capacity (kWh)
!Weight (kg)
!w (mm)
!d (mm)
!h (mm)
!Gravity (kg/kWh)
!Volume (L/kWh)
!Voltage (V)
!Current (cont A)
!Current (peak A)
!Cell arrangement
!Cell type
!Chemistry
|-
|Tesla
|Model S 85kWh
|5.3
|26
|690
|315
|80
|4.9
|3.3
|22.8
|500
|750
|74p6s
|18650
|Li-ion
|-
|Tesla
|Model S 100kWh
|6.4
|28
|680
|315
|80
|4.4
|2.7
|22.8
|
|870
|86p6s
|18650
|Li-ion
|-
|Chevrolet
|Volt 2012
|4
|38
|470
|180
|280
|9.5
|5.9
|88
|140
|210
|24s
|Pouch
|Li-ion
|-
|BMW
|i3 60Ah
|2
|13
|368
|178
|102
|6.5
|3.3
|28.8
|210
|350
|8s2p
|Prismatic
|Li-ion
|-
|BMW
|i3 94Ah
|4.15
|28
|410
|310
|150
|6.7
|4.6
|45.6
|
|409
|12s
|Prismatic
|Li-ion
|-
|BMW
|i3 120Ah
|5.3
|28
|410
|310
|150
|5.3
|3.6
|45.6
|
|360
|12s
|Prismatic
|Li-ion
|-
|Mitsubishi
|Outlander
|2.4
|26
|646
|184
|130
|10.8
|6.4
|60
|
|240
|16s
|
|Li-ion
|-
|Nissan
|Leaf 24kWh
|0.5
|3.65
|300
|222
|34
|7.3
|4.5
|7.4
|130
|228
|2s2p
|Pouch
|Li-ion LMO
|-
|Nissan
|Leaf 40kWh
|1.6
|8.7
|300
|222
|68
|5.4
|2.8
|14.6
|
|314
|4s2p
|Pouch
|Li-ion NMC
|-
|Volvo
|XC90 T8
|2.01
|12.1
|300
|180
|150
|6.0
|4.0
|59.2
|170
|340
|16s
|
|Li-ion
|}

Batteries

2020-12-01T09:08:19Z

Clanger9: /* Battery pack specification */

== Introduction ==
There are a wide variety of battery chemistries available for use as the main traction battery of an EV. To use each chemistry safely, and to ensure an adequate service life from the battery pack it is important to understand the requirements for the chemistry you are using. Failure to do so may lead to premature or catastrophic failure of the pack.

Good pack design will allow for a nominal amount of abuse. People make mistakes and the pack should allow a margin for safety - and for longevity!

== Battery pack specification ==
When deciding on your battery pack, here are some basic parameters to consider:

=== Capacity (kWh) ===
'''How far do you want to go?''' A standard car conversion will need a kWh for each 3 miles of range (very approximately). For a middleweight motorcycle, a kWh should give around 9 miles. Your mileage may vary, ''as they say.''

=== Voltage (V) ===
'''How fast do you want to go?''' The pack voltage defines the maximum speed your motor can spin. Motors are usually specified with "KV" - or RPM-per-volt. Check the KV of your motor and how fast it needs to spin to get your desired top speed. e.g. if you need 3,000 RPM from a 25 KV motor then your pack voltage needs to be 3,000 / 25 = 120 V. The exact number of cells in series you need depends on the cell design, but 3.8 V for Li-ion and 3.2 V for LiFePO4 is a reasonable guess.

=== Maximum current (A) ===
'''How quickly do you want to accelerate?''' Your motor's maximum power will be specified in kW. To estimate your maximum current draw, divide the peak power by the battery voltage. e.g. a 30 kW motor with a 120 V battery pack will pull 30,000 / 120 = 250 A. The higher the current rating of the cells, the heavier they will be for a given capacity. Ideally, you want "enough" current capacity for full throttle acceleration, but no more. You can put cells in parallel to double the current rating of your pack (which of course will half the voltage).

=== Mass (kg) ===
'''Can your vehicle carry the weight?''' You'll need to keep the kerb weight within the original design limits. For a car, this could be a few hundred kg. For a motorcycle, likely less than 100 kg. This is a huge variable - and each new generation of battery tech seems to be a little lighter. For older EV or hybrid batteries, you can reckon on approximately 10 kg/kWh. Nissan Leaf batteries are relatively light (7.5 kg/kWh). With the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 5-6 kg/kWh.

=== Volume (L) ===
'''Will it fit?''' Batteries are bulky. They are getting smaller, but finding enough space might be your biggest challenge. You could be looking at over 5 L/kWh for older EV or hybrid batteries. For the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 3 L/kWh.

There is much, much more to battery design than this (e.g. maximum charge rate, terminations, cooling, clamping), but the above should help work out which options will or won't work for your project...

== Cell chemistry ==

=== Lithium Iron Phosphate (LiFePO4) ===
Lithium Iron Phosphate (also known as LFP, or LiFePO4) batteries offer a good compromise between safety, energy density and ease of use for DIY conversions. They are available in a number of formats, commonly pouch cells, prismatic cells and cylindrical cells.

==== LiFePO4 pouch cells ====
The majority of this content is drawn from this thread: [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761&start=900 https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761] discussing the use of the A123 20Ah pouch cell. However, many of the general points apply equally to other similar pouch cells.

===== General build requirements =====
Pouch cells are vulnerable to damage from debris, and must be held in compression (see the datasheet for your battery, but 10-12 psi is recommended for the A123 pouch cells as a guide). A rigid container capable of preventing damage and providing compression is therefore required. Be aware the cells expand and contract in use, so allowance for this must be included in the structure of the case.

The pouch cells should be separated to prevent abrasion between cells, and also to avoid the development of hot spots. Prebuilt modules from A123 systems had thin foam sheets or heatsinks between each cell. Be sure to avoid any debris that could rub on the pouch surface, particularly if using recycled cells.

Mylar, '[https://www.americanmicroinc.com/fish-paper/ Fish paper]' or a [https://www.rogerscorp.com/elastomeric-material-solutions/poron-industrial-polyurethanes compliant foam] may be appropriate materials to serve this purpose. This material should not be flammable. If the material is heat insulating, it is important to address thermal management.

===== Compression =====
Compression is required to prevent premature failure of the cell. Without compression electrolyte will become unevenly distributed, causing current gradients in the cell and uneven heating. Local temperatures can become high enough to form gas formation leading to cells 'puffing up' even when the pack is otherwise held within temperature and voltage constraints. This will be exacerbated in packs with otherwise poor thermal management. Compression forces gas generated to the margins of the cell, outside of the cell stack, minimising its effect cell performance. Gas in the middle cells will create a dead space which does not store or release energy.

There is ~1% expansion through a discharge cycle. As the cell ages, the nominal cell thickness can grow by 3-5%. For A123 cells the ideal pressure is between 4 and 18psi with the ideal pressure being ~12psi. Maintaining 12psi can increase the life by 500 cycles over that of 4 or 18psi

There is some suggestion that in uses where 1C is never exceeded compression ''may'' not be required.

Highly rigid endplates with a mechanism to allow for a limited degree of expansion (e.g. steel bands) are considered an effective solution to this challenge.

It should be noted that compression is a challenge specific to pouch cells. Cylindrical cells are designed to maintain their own compression within the cell's electrode stack by their design.

This thread provides more information and experimentation relating to pack compression: <nowiki>https://endless-sphere.com/forums/viewtopic.php?f=14&t=52244</nowiki>

===== Pouch Cell Pack Design Examples =====
<nowiki>*</nowiki>placeholder*

===== Notes regarding recycled pouch cells =====
Pouch cells are somewhat fragile, and breaching the insulation is not difficult, especially in a cells removed from existing packs and repurposed. If the pouch has had their poly-layers compromised you may see a number of faults:
* Black spots around the perimeter of the cell indicate electrolyte leakage
* Voltage on the outside of the bag. Note that microvoltage between the pouch and the electrode is normal (and due to a capacitive effect).
While the majority of these cells should no longer be in the market, a significant number of faulty cells made it back into the 'greymarket' in around 2013. These cells had misaligned tabs which can also lead to isolation failures between the tab and the pack. These cells should be avoided, particularly in high demand applications.

===== Situations likely to cause pouch cell failure =====
''Taken directly from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''
# '''Overcharge'''. Any extended time above 3.8 Volts will generate enough heat and electrochemical activity to puff a cell, especially one that is improperly compressed.
# '''Overdischarge followed by charge'''. Any A123 cell that has been pulled low enough to come to rest at <300 mV should be immediately scrapped. The published number for that is 500 mV, but the real figure is closer to 300, so that's a "safety buffer" if you will. Below this Voltage, the Cu electrodes start to dissolve into the electrolyte. When charge is applied, the Cu forms dendrites that puncture the separator layer, forming an internal short in the cell. This can puff a cell in a hurry---the more charge current on tap, the worse it's prone to be.
# '''Driving a cell negative'''. I've neglected to mention this before, but it is a possibility. I don't know much about the specific mechanism at this time.
# '''Malfunctioning or misinformed electronics'''. This is the most common cause of all of the above in my experience. At this stage of the game, it is critical for YOU to understand how your BMS functions on at least a cursory level. Choose your BMS very carefully and periodically verify that it is operating properly. They're not all created equal. Make sure V sense lines are securely connected and free of corrosion. Just because your BMS says there was never a problem doesn't necessarily make it so. Avoid harnesses or ribbon cables between multiple modules if possible--they are problematic wherever they are used in any mobile electronics.
# '''Exposure to or generation of sufficient heat'''. I don't know exactly at what temperature gas formation begins in the electrolyte, but we spec a max storage temp of 80 (or 85?) degrees C and I suspect this is the reason. The hotter, the puffier--to a point. This is why soldering tabs poses a real hazard to cell health. If you feel you must solder, sink or blow the heat away from the body of the cell. Use a big iron that can make sufficient local heat quickly, before the whole mass of the cell gets hot. You might even get the cell warm enough to melt separator if not careful.
# '''No compression, not enough compression, improperly distributed compression'''. This is a pack/module design issue. Apply 10, maybe 15 psi to your cell stack end to end and then band snugly and evenly. Use hard endplates of some sort--never wrap cells directly or allow their shape to become distorted. Protect all areas of the pouch from impact damage. This obviously does not apply to cylindrical cells.

==== LiFePO4 prismatic cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cylindrical cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cell ageing ====
''Derived (barely paraphrased) from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''

Capacity loss is caused by the lithium that was available for storage becoming permanently plated on the cathode. Being unable to move within the cell it is no longer available to store energy. The impact of this plating is greater than the amount of lithium 'lost' to plating because not only is the lithium no longer available, it is also preventing access to that part of the cathode meaning Li that can still move has to take a longer path to reach the cathode. Lithium plating is one cause of increased cell resistance (there are others), a sign of worsening cell health.

There is no linear relationship between actual capacity loss and impedance rise. However some cell defects will also increase impedance.

Increasing cell resistance may cause a number of symptoms which may be confused with [https://earthshipbiotecture.com/a-lithium-ion-battery-primer/ High Self Discharge.]
# Elevated Peukert Losses. As more energy per amount of current through the cell is lost as heat, the cells useable capacity decreases. So the apparent capacity loss is higher than the actual capacity loss of cycleable lithium. When used in low current applications (e.g. solar energy storage) the actual and apparent decrease in capacity will be small. In high current draw applications (like EV traction packs), the Peukert loss increases proportionally, so the apparent capacity loss increases much faster than the actual capacity loss.
# Greater voltage excursion under the same load. Due to increased cell resistancethe voltage will sag further under the same load than a cell in optimal condition. The inverse is also true, the voltage will be higher for the same amount of charging current applied. The cell will then rebound to a voltage further from the loaded and charging voltages. This, obviously, can look like high self discharge but is a different phenomenon.
# Absolute maximum current decrease.
Elevated impedance causes a more complex constellation of symptoms, some of which may be easy to confuse with High Self Discharge (HSD). Ohm's law (E=I/R) holds the key to understanding here.

'''1) Elevated Peukert losses.''' Because more energy per unit of current through the cell is lost as heat, less of the cell's capacity is actually USABLE. Thus, apparent capacity loss can be significantly greater than actual capacity loss caused by the loss of cycleable Li alone. In low current applications, the two numbers will be close together. In high current applications, Peukert losses increase in proportion, so apparent loss of capacity breaks further and further away from actual capacity loss as current increases.

'''2) Greater voltage excursion under the same load.''' Elevated resistance across the cell means that voltage will sag more under the same load than it did when the cell was healthier. Conversely, voltage will rise higher with the same amount of applied charge current than it did when it was healthier. At the same time, rebound/settling voltages will be further away from loaded/charging voltages. In other words, the cell will rebound to a voltage further away from loaded voltage, all else being equal. Similarly, voltage will settle farther from the charge voltage with the same charge applied. This can give the illusion of elevated self-discharge, but the phenomenon is actually not the same thing. Again, the greater the charge and load currents, the greater the effect becomes.

'''3) Absolute max current decreases.''' Because the cell's series resistance is elevated, the maximum possible current through the cell is decreased.

Just to confuse things further, there can be many factors that lead to impedance rise. Some are related to Li plating, others are not.

=== Lithium-ion ===
Lithium-ion (Li-ion) batteries have a greater energy density than Lithium Iron Phosphate batteries, but have more challenging needs to use safely. The ideal operating range of Li-ion batteries is between +15 and +45°C. The upper limit of temperature is particularly important as Li-ion batteries experience thermal runaway - an unstoppable chain reaction that can occur in milliseconds releasing the stored energy in the cell. This can produce temperatures of 400°C and a fire that is extremely difficult to put out. Thermal runaway can start as low as 60°C and becomes much more likely at 100°C

Risk factors for thermal runaway:
* Short Circuits - either internally or externally
* Overcharging
* Excessive current draw or when charging

==== Li-ion pouch cells ====
[https://kokam.com/cell Kokam] produce high-performance Li-ion pouch cells. These combine relative ease of use and pack construction with performance close to cylindrical cells.

==== Li-ion 18650 and other cylindrical cells ====
Cylindrical cells are favoured by Tesla, and are probably the main reason why their cars achieve such excellent performance. They are light, compact, powerful and expensive. Unfortunately, cylindrical cells are difficult (and potentially dangerous) to use in DIY conversions. There are two good reasons for this: thermal management and cell configuration.

As stated above, Li-ion cells are prone to thermal runaway. So you need perfect battery and thermal management to ensure that no cell ever exceeds the critical voltage or temperature. If this happens, a cell can short-circuit internally, releasing a lot of energy - potentially explosively. Furthermore, the individual cells are small, so need to be arranged in parallel. In the case of the Tesla Model S 85kW pack, there are 74 cells in parallel. Imagine if one of those cells fails and becomes short circuited internally. You now have 73 very high power cells all feeding in to that short circuit...

In fact, you don't have to imagine: you can watch this famous video instead (courtesy of Rich Rebuilds).

<youtube>WdDi1haA71Q</youtube>

== OEM modules ==
Using an OEM module means a lot of the difficulties and safety issues associated with battery design are taken care of e.g. cooling, clamping, etc.

Here is a handy list of OEM modules:
{| class="wikitable sortable mw-collapsible"
|+
!Manufacturer
!Type
!Capacity (kWh)
!Weight (kg)
!w (mm)
!d (mm)
!h (mm)
!Gravity (kg/kWh)
!Volume (L/kWh)
!Voltage (V)
!Current (cont A)
!Current (peak A)
!Cell arrangement
!Cell type
!Chemistry
|-
|Tesla
|Model S 85kWh
|5.3
|26
|690
|315
|80
|4.9
|3.3
|22.8
|500
|750
|74p6s
|18650
|Li-ion
|-
|Tesla
|Model S 100kWh
|6.4
|28
|680
|315
|80
|4.4
|2.7
|22.8
|
|870
|86p6s
|18650
|Li-ion
|-
|Chevrolet
|Volt 2012
|4
|38
|470
|180
|280
|9.5
|5.9
|88
|140
|210
|24s
|Pouch
|Li-ion
|-
|BMW
|i3 60Ah
|2
|13
|368
|178
|102
|6.5
|3.3
|28.8
|210
|350
|8s2p
|Prismatic
|Li-ion
|-
|BMW
|i3 94Ah
|4.15
|28
|410
|310
|150
|6.7
|4.6
|45.6
|
|409
|12s
|Prismatic
|Li-ion
|-
|BMW
|i3 120Ah
|5.3
|28
|410
|310
|150
|5.3
|3.6
|45.6
|
|360
|12s
|Prismatic
|Li-ion
|-
|Mitsubishi
|Outlander
|2.4
|26
|646
|184
|130
|10.8
|6.4
|60
|
|240
|16s
|
|Li-ion
|-
|Nissan
|Leaf 24kWh
|0.5
|3.65
|300
|222
|34
|7.3
|4.5
|7.4
|130
|
|2s2p
|Pouch
|Li-ion LMO
|-
|Nissan
|Leaf 40kWh
|1.6
|8.7
|300
|222
|68
|5.4
|2.8
|14.6
|
|
|4s2p
|Pouch
|Li-ion NMC
|-
|Volvo
|XC90 T8
|2.01
|12.1
|300
|180
|150
|6.0
|4.0
|59.2
|170
|340
|16s
|
|Li-ion
|}

Batteries

2020-11-30T22:52:47Z

Clanger9: /* OEM modules */

== Introduction ==
There are a wide variety of battery chemistries available for use as the main traction battery of an EV. To use each chemistry safely, and to ensure an adequate service life from the battery pack it is important to understand the requirements for the chemistry you are using. Failure to do so may lead to premature or catastrophic failure of the pack.

Good pack design will allow for a nominal amount of abuse. People make mistakes and the pack should allow a margin for safety - and for longevity!

== Battery pack specification ==
When deciding on your battery pack, here are some basic parameters to consider:

=== Capacity (kWh) ===
'''How far do you want to go?''' A standard car conversion will need a kWh for each 3 miles of range (very approximately). For a middleweight motorcycle, a kWh should give around 9 miles. ''Your mileage may vary'', as they say.

=== Voltage (V) ===
'''How fast do you want to go?''' The pack voltage defines the maximum speed your motor can spin. Motors are usually specified with "KV" - or RPM-per-volt. Check the KV of your motor and how fast it needs to spin to get your desired top speed. e.g. if you need 3,000 RPM from a 25 KV motor then your pack voltage needs to be 3,000 / 25 = 120 V. The exact number of cells in series you need depends on the cell design, but 3.8 V for Li-ion and 3.2 V for LiFePO4 is a reasonable guess.

=== Maximum current (A) ===
'''How quickly do you want to accelerate?''' Your motor's maximum power will be specified in kW. To estimate your maximum current draw, divide the peak power by the battery voltage. e.g. a 30 kW motor with a 120 V battery pack will pull 30,000 / 120 = 250 A. The higher the current rating of the cells, the heavier they will be for a given capacity. Ideally, you want "enough" current capacity for full throttle acceleration, but no more. You can put cells in parallel to double the current rating of your pack (which of course will half the voltage).

=== Mass (kg) ===
'''Can your vehicle carry the weight?''' You'll need to keep the kerb weight within the original design limits. For a car, this could be a few hundred kg. For a motorcycle, likely less than 100 kg. This is a huge variable - and each new generation of battery tech seems to be a little lighter. For older EV or hybrid batteries, you can reckon on approximately 10 kg/kWh. Nissan Leaf batteries are relatively light (7.5 kg/kWh). With the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 5-6 kg/kWh.

=== Volume (L) ===
'''Will it fit?''' Batteries are bulky. They are getting smaller, but finding enough space might be your biggest challenge. You could be looking at over 5 L/kWh for older EV or hybrid batteries. For the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 3 L/kWh.

There is much, much more to battery design than this (e.g. maximum charge rate, terminations, cooling, clamping), but the above should help work out which options will or won't work for your project...

== Cell chemistry ==

=== Lithium Iron Phosphate (LiFePO4) ===
Lithium Iron Phosphate (also known as LFP, or LiFePO4) batteries offer a good compromise between safety, energy density and ease of use for DIY conversions. They are available in a number of formats, commonly pouch cells, prismatic cells and cylindrical cells.

==== LiFePO4 pouch cells ====
The majority of this content is drawn from this thread: [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761&start=900 https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761] discussing the use of the A123 20Ah pouch cell. However, many of the general points apply equally to other similar pouch cells.

===== General build requirements =====
Pouch cells are vulnerable to damage from debris, and must be held in compression (see the datasheet for your battery, but 10-12 psi is recommended for the A123 pouch cells as a guide). A rigid container capable of preventing damage and providing compression is therefore required. Be aware the cells expand and contract in use, so allowance for this must be included in the structure of the case.

The pouch cells should be separated to prevent abrasion between cells, and also to avoid the development of hot spots. Prebuilt modules from A123 systems had thin foam sheets or heatsinks between each cell. Be sure to avoid any debris that could rub on the pouch surface, particularly if using recycled cells.

Mylar, '[https://www.americanmicroinc.com/fish-paper/ Fish paper]' or a [https://www.rogerscorp.com/elastomeric-material-solutions/poron-industrial-polyurethanes compliant foam] may be appropriate materials to serve this purpose. This material should not be flammable. If the material is heat insulating, it is important to address thermal management.

===== Compression =====
Compression is required to prevent premature failure of the cell. Without compression electrolyte will become unevenly distributed, causing current gradients in the cell and uneven heating. Local temperatures can become high enough to form gas formation leading to cells 'puffing up' even when the pack is otherwise held within temperature and voltage constraints. This will be exacerbated in packs with otherwise poor thermal management. Compression forces gas generated to the margins of the cell, outside of the cell stack, minimising its effect cell performance. Gas in the middle cells will create a dead space which does not store or release energy.

There is ~1% expansion through a discharge cycle. As the cell ages, the nominal cell thickness can grow by 3-5%. For A123 cells the ideal pressure is between 4 and 18psi with the ideal pressure being ~12psi. Maintaining 12psi can increase the life by 500 cycles over that of 4 or 18psi

There is some suggestion that in uses where 1C is never exceeded compression ''may'' not be required.

Highly rigid endplates with a mechanism to allow for a limited degree of expansion (e.g. steel bands) are considered an effective solution to this challenge.

It should be noted that compression is a challenge specific to pouch cells. Cylindrical cells are designed to maintain their own compression within the cell's electrode stack by their design.

This thread provides more information and experimentation relating to pack compression: <nowiki>https://endless-sphere.com/forums/viewtopic.php?f=14&t=52244</nowiki>

===== Pouch Cell Pack Design Examples =====
<nowiki>*</nowiki>placeholder*

===== Notes regarding recycled pouch cells =====
Pouch cells are somewhat fragile, and breaching the insulation is not difficult, especially in a cells removed from existing packs and repurposed. If the pouch has had their poly-layers compromised you may see a number of faults:
* Black spots around the perimeter of the cell indicate electrolyte leakage
* Voltage on the outside of the bag. Note that microvoltage between the pouch and the electrode is normal (and due to a capacitive effect).
While the majority of these cells should no longer be in the market, a significant number of faulty cells made it back into the 'greymarket' in around 2013. These cells had misaligned tabs which can also lead to isolation failures between the tab and the pack. These cells should be avoided, particularly in high demand applications.

===== Situations likely to cause pouch cell failure =====
''Taken directly from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''
# '''Overcharge'''. Any extended time above 3.8 Volts will generate enough heat and electrochemical activity to puff a cell, especially one that is improperly compressed.
# '''Overdischarge followed by charge'''. Any A123 cell that has been pulled low enough to come to rest at <300 mV should be immediately scrapped. The published number for that is 500 mV, but the real figure is closer to 300, so that's a "safety buffer" if you will. Below this Voltage, the Cu electrodes start to dissolve into the electrolyte. When charge is applied, the Cu forms dendrites that puncture the separator layer, forming an internal short in the cell. This can puff a cell in a hurry---the more charge current on tap, the worse it's prone to be.
# '''Driving a cell negative'''. I've neglected to mention this before, but it is a possibility. I don't know much about the specific mechanism at this time.
# '''Malfunctioning or misinformed electronics'''. This is the most common cause of all of the above in my experience. At this stage of the game, it is critical for YOU to understand how your BMS functions on at least a cursory level. Choose your BMS very carefully and periodically verify that it is operating properly. They're not all created equal. Make sure V sense lines are securely connected and free of corrosion. Just because your BMS says there was never a problem doesn't necessarily make it so. Avoid harnesses or ribbon cables between multiple modules if possible--they are problematic wherever they are used in any mobile electronics.
# '''Exposure to or generation of sufficient heat'''. I don't know exactly at what temperature gas formation begins in the electrolyte, but we spec a max storage temp of 80 (or 85?) degrees C and I suspect this is the reason. The hotter, the puffier--to a point. This is why soldering tabs poses a real hazard to cell health. If you feel you must solder, sink or blow the heat away from the body of the cell. Use a big iron that can make sufficient local heat quickly, before the whole mass of the cell gets hot. You might even get the cell warm enough to melt separator if not careful.
# '''No compression, not enough compression, improperly distributed compression'''. This is a pack/module design issue. Apply 10, maybe 15 psi to your cell stack end to end and then band snugly and evenly. Use hard endplates of some sort--never wrap cells directly or allow their shape to become distorted. Protect all areas of the pouch from impact damage. This obviously does not apply to cylindrical cells.

==== LiFePO4 prismatic cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cylindrical cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cell ageing ====
''Derived (barely paraphrased) from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''

Capacity loss is caused by the lithium that was available for storage becoming permanently plated on the cathode. Being unable to move within the cell it is no longer available to store energy. The impact of this plating is greater than the amount of lithium 'lost' to plating because not only is the lithium no longer available, it is also preventing access to that part of the cathode meaning Li that can still move has to take a longer path to reach the cathode. Lithium plating is one cause of increased cell resistance (there are others), a sign of worsening cell health.

There is no linear relationship between actual capacity loss and impedance rise. However some cell defects will also increase impedance.

Increasing cell resistance may cause a number of symptoms which may be confused with [https://earthshipbiotecture.com/a-lithium-ion-battery-primer/ High Self Discharge.]
# Elevated Peukert Losses. As more energy per amount of current through the cell is lost as heat, the cells useable capacity decreases. So the apparent capacity loss is higher than the actual capacity loss of cycleable lithium. When used in low current applications (e.g. solar energy storage) the actual and apparent decrease in capacity will be small. In high current draw applications (like EV traction packs), the Peukert loss increases proportionally, so the apparent capacity loss increases much faster than the actual capacity loss.
# Greater voltage excursion under the same load. Due to increased cell resistancethe voltage will sag further under the same load than a cell in optimal condition. The inverse is also true, the voltage will be higher for the same amount of charging current applied. The cell will then rebound to a voltage further from the loaded and charging voltages. This, obviously, can look like high self discharge but is a different phenomenon.
# Absolute maximum current decrease.
Elevated impedance causes a more complex constellation of symptoms, some of which may be easy to confuse with High Self Discharge (HSD). Ohm's law (E=I/R) holds the key to understanding here.

'''1) Elevated Peukert losses.''' Because more energy per unit of current through the cell is lost as heat, less of the cell's capacity is actually USABLE. Thus, apparent capacity loss can be significantly greater than actual capacity loss caused by the loss of cycleable Li alone. In low current applications, the two numbers will be close together. In high current applications, Peukert losses increase in proportion, so apparent loss of capacity breaks further and further away from actual capacity loss as current increases.

'''2) Greater voltage excursion under the same load.''' Elevated resistance across the cell means that voltage will sag more under the same load than it did when the cell was healthier. Conversely, voltage will rise higher with the same amount of applied charge current than it did when it was healthier. At the same time, rebound/settling voltages will be further away from loaded/charging voltages. In other words, the cell will rebound to a voltage further away from loaded voltage, all else being equal. Similarly, voltage will settle farther from the charge voltage with the same charge applied. This can give the illusion of elevated self-discharge, but the phenomenon is actually not the same thing. Again, the greater the charge and load currents, the greater the effect becomes.

'''3) Absolute max current decreases.''' Because the cell's series resistance is elevated, the maximum possible current through the cell is decreased.

Just to confuse things further, there can be many factors that lead to impedance rise. Some are related to Li plating, others are not.

=== Lithium-ion ===
Lithium-ion (Li-ion) batteries have a greater energy density than Lithium Iron Phosphate batteries, but have more challenging needs to use safely. The ideal operating range of Li-ion batteries is between +15 and +45°C. The upper limit of temperature is particularly important as Li-ion batteries experience thermal runaway - an unstoppable chain reaction that can occur in milliseconds releasing the stored energy in the cell. This can produce temperatures of 400°C and a fire that is extremely difficult to put out. Thermal runaway can start as low as 60°C and becomes much more likely at 100°C

Risk factors for thermal runaway:
* Short Circuits - either internally or externally
* Overcharging
* Excessive current draw or when charging

==== Li-ion pouch cells ====
[https://kokam.com/cell Kokam] produce high-performance Li-ion pouch cells. These combine relative ease of use and pack construction with performance close to cylindrical cells.

==== Li-ion 18650 and other cylindrical cells ====
Cylindrical cells are favoured by Tesla, and are probably the main reason why their cars achieve such excellent performance. They are light, compact, powerful and expensive. Unfortunately, cylindrical cells are difficult (and potentially dangerous) to use in DIY conversions. There are two good reasons for this: thermal management and cell configuration.

As stated above, Li-ion cells are prone to thermal runaway. So you need perfect battery and thermal management to ensure that no cell ever exceeds the critical voltage or temperature. If this happens, a cell can short-circuit internally, releasing a lot of energy - potentially explosively. Furthermore, the individual cells are small, so need to be arranged in parallel. In the case of the Tesla Model S 85kW pack, there are 74 cells in parallel. Imagine if one of those cells fails and becomes short circuited internally. You now have 73 very high power cells all feeding in to that short circuit...

In fact, you don't have to imagine: you can watch this famous video instead (courtesy of Rich Rebuilds).

<youtube>WdDi1haA71Q</youtube>

== OEM modules ==
Using an OEM module means a lot of the difficulties and safety issues associated with battery design are taken care of e.g. cooling, clamping, etc.

Here is a handy list of OEM modules:
{| class="wikitable sortable mw-collapsible"
|+
!Manufacturer
!Type
!Capacity (kWh)
!Weight (kg)
!w (mm)
!d (mm)
!h (mm)
!Gravity (kg/kWh)
!Volume (L/kWh)
!Voltage (V)
!Current (cont A)
!Current (peak A)
!Cell arrangement
!Cell type
!Chemistry
|-
|Tesla
|Model S 85kWh
|5.3
|26
|690
|315
|80
|4.9
|3.3
|22.8
|500
|750
|74p6s
|18650
|Li-ion
|-
|Tesla
|Model S 100kWh
|6.4
|28
|680
|315
|80
|4.4
|2.7
|22.8
|
|870
|86p6s
|18650
|Li-ion
|-
|Chevrolet
|Volt 2012
|4
|38
|470
|180
|280
|9.5
|5.9
|88
|140
|210
|24s
|Pouch
|Li-ion
|-
|BMW
|i3 60Ah
|2
|13
|368
|178
|102
|6.5
|3.3
|28.8
|210
|350
|8s2p
|Prismatic
|Li-ion
|-
|BMW
|i3 94Ah
|4.15
|28
|410
|310
|150
|6.7
|4.6
|45.6
|
|409
|12s
|Prismatic
|Li-ion
|-
|BMW
|i3 120Ah
|5.3
|28
|410
|310
|150
|5.3
|3.6
|45.6
|
|360
|12s
|Prismatic
|Li-ion
|-
|Mitsubishi
|Outlander
|2.4
|26
|646
|184
|130
|10.8
|6.4
|60
|
|240
|16s
|
|Li-ion
|-
|Nissan
|Leaf 24kWh
|0.5
|3.65
|300
|222
|34
|7.3
|4.5
|7.4
|130
|
|2s2p
|Pouch
|Li-ion LMO
|-
|Nissan
|Leaf 40kWh
|1.6
|8.7
|300
|222
|68
|5.4
|2.8
|14.6
|
|
|4s2p
|Pouch
|Li-ion NMC
|-
|Volvo
|XC90 T8
|2.01
|12.1
|300
|180
|150
|6.0
|4.0
|59.2
|170
|340
|16s
|
|Li-ion
|}

Batteries

2020-11-30T22:40:35Z

Clanger9: /* OEM modules */

== Introduction ==
There are a wide variety of battery chemistries available for use as the main traction battery of an EV. To use each chemistry safely, and to ensure an adequate service life from the battery pack it is important to understand the requirements for the chemistry you are using. Failure to do so may lead to premature or catastrophic failure of the pack.

Good pack design will allow for a nominal amount of abuse. People make mistakes and the pack should allow a margin for safety - and for longevity!

== Battery pack specification ==
When deciding on your battery pack, here are some basic parameters to consider:

=== Capacity (kWh) ===
'''How far do you want to go?''' A standard car conversion will need a kWh for each 3 miles of range (very approximately). For a middleweight motorcycle, a kWh should give around 9 miles. ''Your mileage may vary'', as they say.

=== Voltage (V) ===
'''How fast do you want to go?''' The pack voltage defines the maximum speed your motor can spin. Motors are usually specified with "KV" - or RPM-per-volt. Check the KV of your motor and how fast it needs to spin to get your desired top speed. e.g. if you need 3,000 RPM from a 25 KV motor then your pack voltage needs to be 3,000 / 25 = 120 V. The exact number of cells in series you need depends on the cell design, but 3.8 V for Li-ion and 3.2 V for LiFePO4 is a reasonable guess.

=== Maximum current (A) ===
'''How quickly do you want to accelerate?''' Your motor's maximum power will be specified in kW. To estimate your maximum current draw, divide the peak power by the battery voltage. e.g. a 30 kW motor with a 120 V battery pack will pull 30,000 / 120 = 250 A. The higher the current rating of the cells, the heavier they will be for a given capacity. Ideally, you want "enough" current capacity for full throttle acceleration, but no more. You can put cells in parallel to double the current rating of your pack (which of course will half the voltage).

=== Mass (kg) ===
'''Can your vehicle carry the weight?''' You'll need to keep the kerb weight within the original design limits. For a car, this could be a few hundred kg. For a motorcycle, likely less than 100 kg. This is a huge variable - and each new generation of battery tech seems to be a little lighter. For older EV or hybrid batteries, you can reckon on approximately 10 kg/kWh. Nissan Leaf batteries are relatively light (7.5 kg/kWh). With the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 5-6 kg/kWh.

=== Volume (L) ===
'''Will it fit?''' Batteries are bulky. They are getting smaller, but finding enough space might be your biggest challenge. You could be looking at over 5 L/kWh for older EV or hybrid batteries. For the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 3 L/kWh.

There is much, much more to battery design than this (e.g. maximum charge rate, terminations, cooling, clamping), but the above should help work out which options will or won't work for your project...

== Cell chemistry ==

=== Lithium Iron Phosphate (LiFePO4) ===
Lithium Iron Phosphate (also known as LFP, or LiFePO4) batteries offer a good compromise between safety, energy density and ease of use for DIY conversions. They are available in a number of formats, commonly pouch cells, prismatic cells and cylindrical cells.

==== LiFePO4 pouch cells ====
The majority of this content is drawn from this thread: [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761&start=900 https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761] discussing the use of the A123 20Ah pouch cell. However, many of the general points apply equally to other similar pouch cells.

===== General build requirements =====
Pouch cells are vulnerable to damage from debris, and must be held in compression (see the datasheet for your battery, but 10-12 psi is recommended for the A123 pouch cells as a guide). A rigid container capable of preventing damage and providing compression is therefore required. Be aware the cells expand and contract in use, so allowance for this must be included in the structure of the case.

The pouch cells should be separated to prevent abrasion between cells, and also to avoid the development of hot spots. Prebuilt modules from A123 systems had thin foam sheets or heatsinks between each cell. Be sure to avoid any debris that could rub on the pouch surface, particularly if using recycled cells.

Mylar, '[https://www.americanmicroinc.com/fish-paper/ Fish paper]' or a [https://www.rogerscorp.com/elastomeric-material-solutions/poron-industrial-polyurethanes compliant foam] may be appropriate materials to serve this purpose. This material should not be flammable. If the material is heat insulating, it is important to address thermal management.

===== Compression =====
Compression is required to prevent premature failure of the cell. Without compression electrolyte will become unevenly distributed, causing current gradients in the cell and uneven heating. Local temperatures can become high enough to form gas formation leading to cells 'puffing up' even when the pack is otherwise held within temperature and voltage constraints. This will be exacerbated in packs with otherwise poor thermal management. Compression forces gas generated to the margins of the cell, outside of the cell stack, minimising its effect cell performance. Gas in the middle cells will create a dead space which does not store or release energy.

There is ~1% expansion through a discharge cycle. As the cell ages, the nominal cell thickness can grow by 3-5%. For A123 cells the ideal pressure is between 4 and 18psi with the ideal pressure being ~12psi. Maintaining 12psi can increase the life by 500 cycles over that of 4 or 18psi

There is some suggestion that in uses where 1C is never exceeded compression ''may'' not be required.

Highly rigid endplates with a mechanism to allow for a limited degree of expansion (e.g. steel bands) are considered an effective solution to this challenge.

It should be noted that compression is a challenge specific to pouch cells. Cylindrical cells are designed to maintain their own compression within the cell's electrode stack by their design.

This thread provides more information and experimentation relating to pack compression: <nowiki>https://endless-sphere.com/forums/viewtopic.php?f=14&t=52244</nowiki>

===== Pouch Cell Pack Design Examples =====
<nowiki>*</nowiki>placeholder*

===== Notes regarding recycled pouch cells =====
Pouch cells are somewhat fragile, and breaching the insulation is not difficult, especially in a cells removed from existing packs and repurposed. If the pouch has had their poly-layers compromised you may see a number of faults:
* Black spots around the perimeter of the cell indicate electrolyte leakage
* Voltage on the outside of the bag. Note that microvoltage between the pouch and the electrode is normal (and due to a capacitive effect).
While the majority of these cells should no longer be in the market, a significant number of faulty cells made it back into the 'greymarket' in around 2013. These cells had misaligned tabs which can also lead to isolation failures between the tab and the pack. These cells should be avoided, particularly in high demand applications.

===== Situations likely to cause pouch cell failure =====
''Taken directly from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''
# '''Overcharge'''. Any extended time above 3.8 Volts will generate enough heat and electrochemical activity to puff a cell, especially one that is improperly compressed.
# '''Overdischarge followed by charge'''. Any A123 cell that has been pulled low enough to come to rest at <300 mV should be immediately scrapped. The published number for that is 500 mV, but the real figure is closer to 300, so that's a "safety buffer" if you will. Below this Voltage, the Cu electrodes start to dissolve into the electrolyte. When charge is applied, the Cu forms dendrites that puncture the separator layer, forming an internal short in the cell. This can puff a cell in a hurry---the more charge current on tap, the worse it's prone to be.
# '''Driving a cell negative'''. I've neglected to mention this before, but it is a possibility. I don't know much about the specific mechanism at this time.
# '''Malfunctioning or misinformed electronics'''. This is the most common cause of all of the above in my experience. At this stage of the game, it is critical for YOU to understand how your BMS functions on at least a cursory level. Choose your BMS very carefully and periodically verify that it is operating properly. They're not all created equal. Make sure V sense lines are securely connected and free of corrosion. Just because your BMS says there was never a problem doesn't necessarily make it so. Avoid harnesses or ribbon cables between multiple modules if possible--they are problematic wherever they are used in any mobile electronics.
# '''Exposure to or generation of sufficient heat'''. I don't know exactly at what temperature gas formation begins in the electrolyte, but we spec a max storage temp of 80 (or 85?) degrees C and I suspect this is the reason. The hotter, the puffier--to a point. This is why soldering tabs poses a real hazard to cell health. If you feel you must solder, sink or blow the heat away from the body of the cell. Use a big iron that can make sufficient local heat quickly, before the whole mass of the cell gets hot. You might even get the cell warm enough to melt separator if not careful.
# '''No compression, not enough compression, improperly distributed compression'''. This is a pack/module design issue. Apply 10, maybe 15 psi to your cell stack end to end and then band snugly and evenly. Use hard endplates of some sort--never wrap cells directly or allow their shape to become distorted. Protect all areas of the pouch from impact damage. This obviously does not apply to cylindrical cells.

==== LiFePO4 prismatic cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cylindrical cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cell ageing ====
''Derived (barely paraphrased) from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''

Capacity loss is caused by the lithium that was available for storage becoming permanently plated on the cathode. Being unable to move within the cell it is no longer available to store energy. The impact of this plating is greater than the amount of lithium 'lost' to plating because not only is the lithium no longer available, it is also preventing access to that part of the cathode meaning Li that can still move has to take a longer path to reach the cathode. Lithium plating is one cause of increased cell resistance (there are others), a sign of worsening cell health.

There is no linear relationship between actual capacity loss and impedance rise. However some cell defects will also increase impedance.

Increasing cell resistance may cause a number of symptoms which may be confused with [https://earthshipbiotecture.com/a-lithium-ion-battery-primer/ High Self Discharge.]
# Elevated Peukert Losses. As more energy per amount of current through the cell is lost as heat, the cells useable capacity decreases. So the apparent capacity loss is higher than the actual capacity loss of cycleable lithium. When used in low current applications (e.g. solar energy storage) the actual and apparent decrease in capacity will be small. In high current draw applications (like EV traction packs), the Peukert loss increases proportionally, so the apparent capacity loss increases much faster than the actual capacity loss.
# Greater voltage excursion under the same load. Due to increased cell resistancethe voltage will sag further under the same load than a cell in optimal condition. The inverse is also true, the voltage will be higher for the same amount of charging current applied. The cell will then rebound to a voltage further from the loaded and charging voltages. This, obviously, can look like high self discharge but is a different phenomenon.
# Absolute maximum current decrease.
Elevated impedance causes a more complex constellation of symptoms, some of which may be easy to confuse with High Self Discharge (HSD). Ohm's law (E=I/R) holds the key to understanding here.

'''1) Elevated Peukert losses.''' Because more energy per unit of current through the cell is lost as heat, less of the cell's capacity is actually USABLE. Thus, apparent capacity loss can be significantly greater than actual capacity loss caused by the loss of cycleable Li alone. In low current applications, the two numbers will be close together. In high current applications, Peukert losses increase in proportion, so apparent loss of capacity breaks further and further away from actual capacity loss as current increases.

'''2) Greater voltage excursion under the same load.''' Elevated resistance across the cell means that voltage will sag more under the same load than it did when the cell was healthier. Conversely, voltage will rise higher with the same amount of applied charge current than it did when it was healthier. At the same time, rebound/settling voltages will be further away from loaded/charging voltages. In other words, the cell will rebound to a voltage further away from loaded voltage, all else being equal. Similarly, voltage will settle farther from the charge voltage with the same charge applied. This can give the illusion of elevated self-discharge, but the phenomenon is actually not the same thing. Again, the greater the charge and load currents, the greater the effect becomes.

'''3) Absolute max current decreases.''' Because the cell's series resistance is elevated, the maximum possible current through the cell is decreased.

Just to confuse things further, there can be many factors that lead to impedance rise. Some are related to Li plating, others are not.

=== Lithium-ion ===
Lithium-ion (Li-ion) batteries have a greater energy density than Lithium Iron Phosphate batteries, but have more challenging needs to use safely. The ideal operating range of Li-ion batteries is between +15 and +45°C. The upper limit of temperature is particularly important as Li-ion batteries experience thermal runaway - an unstoppable chain reaction that can occur in milliseconds releasing the stored energy in the cell. This can produce temperatures of 400°C and a fire that is extremely difficult to put out. Thermal runaway can start as low as 60°C and becomes much more likely at 100°C

Risk factors for thermal runaway:
* Short Circuits - either internally or externally
* Overcharging
* Excessive current draw or when charging

==== Li-ion pouch cells ====
[https://kokam.com/cell Kokam] produce high-performance Li-ion pouch cells. These combine relative ease of use and pack construction with performance close to cylindrical cells.

==== Li-ion 18650 and other cylindrical cells ====
Cylindrical cells are favoured by Tesla, and are probably the main reason why their cars achieve such excellent performance. They are light, compact, powerful and expensive. Unfortunately, cylindrical cells are difficult (and potentially dangerous) to use in DIY conversions. There are two good reasons for this: thermal management and cell configuration.

As stated above, Li-ion cells are prone to thermal runaway. So you need perfect battery and thermal management to ensure that no cell ever exceeds the critical voltage or temperature. If this happens, a cell can short-circuit internally, releasing a lot of energy - potentially explosively. Furthermore, the individual cells are small, so need to be arranged in parallel. In the case of the Tesla Model S 85kW pack, there are 74 cells in parallel. Imagine if one of those cells fails and becomes short circuited internally. You now have 73 very high power cells all feeding in to that short circuit...

In fact, you don't have to imagine: you can watch this famous video instead (courtesy of Rich Rebuilds).

<youtube>WdDi1haA71Q</youtube>

== OEM modules ==
Using an OEM module means a lot of the difficulties and safety issues associated with battery design are taken care of e.g. cooling, clamping, etc.

Here is a handy list of OEM modules:
{| class="wikitable sortable mw-collapsible"
|+
!Manufacturer
!Type
!Capacity (kWh)
!Weight (kg)
!w (mm)
!d (mm)
!h (mm)
!Gravity (kg/kWh)
!Volume (L/kWh)
!Voltage (V)
!Current (cont A)
!Current (peak A)
!Cell arrangement
!Cell type
!Chemistry
|-
|Tesla
|Model S 85kWh
|5.3
|26
|690
|315
|80
|4.9
|3.3
|22.8
|500
|750
|74p6s
|18650
|Li-ion
|-
|Tesla
|Model S 100kWh
|6.4
|28
|680
|315
|80
|4.4
|2.7
|22.8
|
|870
|86p6s
|18650
|Li-ion
|-
|Chevrolet
|Volt 2012
|4
|38
|470
|180
|280
|9.5
|5.9
|88
|140
|210
|24s
|Pouch
|Li-ion
|-
|BMW
|i3 60Ah
|2
|13
|368
|178
|102
|6.5
|3.3
|28.8
|210
|350
|8s2p
|Prismatic
|Li-ion
|-
|BMW
|i3 94Ah
|4.15
|28
|410
|310
|150
|6.7
|4.6
|45.6
|
|409
|12s
|Prismatic
|Li-ion
|-
|BMW
|i3 120Ah
|5.3
|28
|410
|310
|150
|5.3
|3.6
|45.6
|
|360
|12s
|Prismatic
|Li-ion
|-
|Mitsubishi
|Outlander
|2.4
|26
|646
|184
|130
|10.8
|6.4
|60
|
|240
|16s
|
|Li-ion
|-
|Nissan
|Leaf 24kWh
|0.5
|3.65
|300
|222
|34
|7.3
|4.5
|7.4
|130
|
|2s2p
|
|Li-ion LMO
|-
|Nissan
|Leaf 40kWh
|1.6
|8.7
|300
|222
|68
|5.4
|2.8
|14.6
|
|
|4s2p
|
|Li-ion NMC
|-
|Volvo
|XC90 T8
|2.01
|12.1
|300
|180
|150
|6.0
|4.0
|59.2
|170
|340
|16s
|
|Li-ion
|}

Batteries

2020-11-30T22:03:31Z

Clanger9: /* Capacity (kWh) */

== Introduction ==
There are a wide variety of battery chemistries available for use as the main traction battery of an EV. To use each chemistry safely, and to ensure an adequate service life from the battery pack it is important to understand the requirements for the chemistry you are using. Failure to do so may lead to premature or catastrophic failure of the pack.

Good pack design will allow for a nominal amount of abuse. People make mistakes and the pack should allow a margin for safety - and for longevity!

== Battery pack specification ==
When deciding on your battery pack, here are some basic parameters to consider:

=== Capacity (kWh) ===
'''How far do you want to go?''' A standard car conversion will need a kWh for each 3 miles of range (very approximately). For a middleweight motorcycle, a kWh should give around 9 miles. ''Your mileage may vary'', as they say.

=== Voltage (V) ===
'''How fast do you want to go?''' The pack voltage defines the maximum speed your motor can spin. Motors are usually specified with "KV" - or RPM-per-volt. Check the KV of your motor and how fast it needs to spin to get your desired top speed. e.g. if you need 3,000 RPM from a 25 KV motor then your pack voltage needs to be 3,000 / 25 = 120 V. The exact number of cells in series you need depends on the cell design, but 3.8 V for Li-ion and 3.2 V for LiFePO4 is a reasonable guess.

=== Maximum current (A) ===
'''How quickly do you want to accelerate?''' Your motor's maximum power will be specified in kW. To estimate your maximum current draw, divide the peak power by the battery voltage. e.g. a 30 kW motor with a 120 V battery pack will pull 30,000 / 120 = 250 A. The higher the current rating of the cells, the heavier they will be for a given capacity. Ideally, you want "enough" current capacity for full throttle acceleration, but no more. You can put cells in parallel to double the current rating of your pack (which of course will half the voltage).

=== Mass (kg) ===
'''Can your vehicle carry the weight?''' You'll need to keep the kerb weight within the original design limits. For a car, this could be a few hundred kg. For a motorcycle, likely less than 100 kg. This is a huge variable - and each new generation of battery tech seems to be a little lighter. For older EV or hybrid batteries, you can reckon on approximately 10 kg/kWh. Nissan Leaf batteries are relatively light (7.5 kg/kWh). With the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 5-6 kg/kWh.

=== Volume (L) ===
'''Will it fit?''' Batteries are bulky. They are getting smaller, but finding enough space might be your biggest challenge. You could be looking at over 5 L/kWh for older EV or hybrid batteries. For the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 3 L/kWh.

There is much, much more to battery design than this (e.g. maximum charge rate, terminations, cooling, clamping), but the above should help work out which options will or won't work for your project...

== Cell chemistry ==

=== Lithium Iron Phosphate (LiFePO4) ===
Lithium Iron Phosphate (also known as LFP, or LiFePO4) batteries offer a good compromise between safety, energy density and ease of use for DIY conversions. They are available in a number of formats, commonly pouch cells, prismatic cells and cylindrical cells.

==== LiFePO4 pouch cells ====
The majority of this content is drawn from this thread: [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761&start=900 https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761] discussing the use of the A123 20Ah pouch cell. However, many of the general points apply equally to other similar pouch cells.

===== General build requirements =====
Pouch cells are vulnerable to damage from debris, and must be held in compression (see the datasheet for your battery, but 10-12 psi is recommended for the A123 pouch cells as a guide). A rigid container capable of preventing damage and providing compression is therefore required. Be aware the cells expand and contract in use, so allowance for this must be included in the structure of the case.

The pouch cells should be separated to prevent abrasion between cells, and also to avoid the development of hot spots. Prebuilt modules from A123 systems had thin foam sheets or heatsinks between each cell. Be sure to avoid any debris that could rub on the pouch surface, particularly if using recycled cells.

Mylar, '[https://www.americanmicroinc.com/fish-paper/ Fish paper]' or a [https://www.rogerscorp.com/elastomeric-material-solutions/poron-industrial-polyurethanes compliant foam] may be appropriate materials to serve this purpose. This material should not be flammable. If the material is heat insulating, it is important to address thermal management.

===== Compression =====
Compression is required to prevent premature failure of the cell. Without compression electrolyte will become unevenly distributed, causing current gradients in the cell and uneven heating. Local temperatures can become high enough to form gas formation leading to cells 'puffing up' even when the pack is otherwise held within temperature and voltage constraints. This will be exacerbated in packs with otherwise poor thermal management. Compression forces gas generated to the margins of the cell, outside of the cell stack, minimising its effect cell performance. Gas in the middle cells will create a dead space which does not store or release energy.

There is ~1% expansion through a discharge cycle. As the cell ages, the nominal cell thickness can grow by 3-5%. For A123 cells the ideal pressure is between 4 and 18psi with the ideal pressure being ~12psi. Maintaining 12psi can increase the life by 500 cycles over that of 4 or 18psi

There is some suggestion that in uses where 1C is never exceeded compression ''may'' not be required.

Highly rigid endplates with a mechanism to allow for a limited degree of expansion (e.g. steel bands) are considered an effective solution to this challenge.

It should be noted that compression is a challenge specific to pouch cells. Cylindrical cells are designed to maintain their own compression within the cell's electrode stack by their design.

This thread provides more information and experimentation relating to pack compression: <nowiki>https://endless-sphere.com/forums/viewtopic.php?f=14&t=52244</nowiki>

===== Pouch Cell Pack Design Examples =====
<nowiki>*</nowiki>placeholder*

===== Notes regarding recycled pouch cells =====
Pouch cells are somewhat fragile, and breaching the insulation is not difficult, especially in a cells removed from existing packs and repurposed. If the pouch has had their poly-layers compromised you may see a number of faults:
* Black spots around the perimeter of the cell indicate electrolyte leakage
* Voltage on the outside of the bag. Note that microvoltage between the pouch and the electrode is normal (and due to a capacitive effect).
While the majority of these cells should no longer be in the market, a significant number of faulty cells made it back into the 'greymarket' in around 2013. These cells had misaligned tabs which can also lead to isolation failures between the tab and the pack. These cells should be avoided, particularly in high demand applications.

===== Situations likely to cause pouch cell failure =====
''Taken directly from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''
# '''Overcharge'''. Any extended time above 3.8 Volts will generate enough heat and electrochemical activity to puff a cell, especially one that is improperly compressed.
# '''Overdischarge followed by charge'''. Any A123 cell that has been pulled low enough to come to rest at <300 mV should be immediately scrapped. The published number for that is 500 mV, but the real figure is closer to 300, so that's a "safety buffer" if you will. Below this Voltage, the Cu electrodes start to dissolve into the electrolyte. When charge is applied, the Cu forms dendrites that puncture the separator layer, forming an internal short in the cell. This can puff a cell in a hurry---the more charge current on tap, the worse it's prone to be.
# '''Driving a cell negative'''. I've neglected to mention this before, but it is a possibility. I don't know much about the specific mechanism at this time.
# '''Malfunctioning or misinformed electronics'''. This is the most common cause of all of the above in my experience. At this stage of the game, it is critical for YOU to understand how your BMS functions on at least a cursory level. Choose your BMS very carefully and periodically verify that it is operating properly. They're not all created equal. Make sure V sense lines are securely connected and free of corrosion. Just because your BMS says there was never a problem doesn't necessarily make it so. Avoid harnesses or ribbon cables between multiple modules if possible--they are problematic wherever they are used in any mobile electronics.
# '''Exposure to or generation of sufficient heat'''. I don't know exactly at what temperature gas formation begins in the electrolyte, but we spec a max storage temp of 80 (or 85?) degrees C and I suspect this is the reason. The hotter, the puffier--to a point. This is why soldering tabs poses a real hazard to cell health. If you feel you must solder, sink or blow the heat away from the body of the cell. Use a big iron that can make sufficient local heat quickly, before the whole mass of the cell gets hot. You might even get the cell warm enough to melt separator if not careful.
# '''No compression, not enough compression, improperly distributed compression'''. This is a pack/module design issue. Apply 10, maybe 15 psi to your cell stack end to end and then band snugly and evenly. Use hard endplates of some sort--never wrap cells directly or allow their shape to become distorted. Protect all areas of the pouch from impact damage. This obviously does not apply to cylindrical cells.

==== LiFePO4 prismatic cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cylindrical cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cell ageing ====
''Derived (barely paraphrased) from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''

Capacity loss is caused by the lithium that was available for storage becoming permanently plated on the cathode. Being unable to move within the cell it is no longer available to store energy. The impact of this plating is greater than the amount of lithium 'lost' to plating because not only is the lithium no longer available, it is also preventing access to that part of the cathode meaning Li that can still move has to take a longer path to reach the cathode. Lithium plating is one cause of increased cell resistance (there are others), a sign of worsening cell health.

There is no linear relationship between actual capacity loss and impedance rise. However some cell defects will also increase impedance.

Increasing cell resistance may cause a number of symptoms which may be confused with [https://earthshipbiotecture.com/a-lithium-ion-battery-primer/ High Self Discharge.]
# Elevated Peukert Losses. As more energy per amount of current through the cell is lost as heat, the cells useable capacity decreases. So the apparent capacity loss is higher than the actual capacity loss of cycleable lithium. When used in low current applications (e.g. solar energy storage) the actual and apparent decrease in capacity will be small. In high current draw applications (like EV traction packs), the Peukert loss increases proportionally, so the apparent capacity loss increases much faster than the actual capacity loss.
# Greater voltage excursion under the same load. Due to increased cell resistancethe voltage will sag further under the same load than a cell in optimal condition. The inverse is also true, the voltage will be higher for the same amount of charging current applied. The cell will then rebound to a voltage further from the loaded and charging voltages. This, obviously, can look like high self discharge but is a different phenomenon.
# Absolute maximum current decrease.
Elevated impedance causes a more complex constellation of symptoms, some of which may be easy to confuse with High Self Discharge (HSD). Ohm's law (E=I/R) holds the key to understanding here.

'''1) Elevated Peukert losses.''' Because more energy per unit of current through the cell is lost as heat, less of the cell's capacity is actually USABLE. Thus, apparent capacity loss can be significantly greater than actual capacity loss caused by the loss of cycleable Li alone. In low current applications, the two numbers will be close together. In high current applications, Peukert losses increase in proportion, so apparent loss of capacity breaks further and further away from actual capacity loss as current increases.

'''2) Greater voltage excursion under the same load.''' Elevated resistance across the cell means that voltage will sag more under the same load than it did when the cell was healthier. Conversely, voltage will rise higher with the same amount of applied charge current than it did when it was healthier. At the same time, rebound/settling voltages will be further away from loaded/charging voltages. In other words, the cell will rebound to a voltage further away from loaded voltage, all else being equal. Similarly, voltage will settle farther from the charge voltage with the same charge applied. This can give the illusion of elevated self-discharge, but the phenomenon is actually not the same thing. Again, the greater the charge and load currents, the greater the effect becomes.

'''3) Absolute max current decreases.''' Because the cell's series resistance is elevated, the maximum possible current through the cell is decreased.

Just to confuse things further, there can be many factors that lead to impedance rise. Some are related to Li plating, others are not.

=== Lithium-ion ===
Lithium-ion (Li-ion) batteries have a greater energy density than Lithium Iron Phosphate batteries, but have more challenging needs to use safely. The ideal operating range of Li-ion batteries is between +15 and +45°C. The upper limit of temperature is particularly important as Li-ion batteries experience thermal runaway - an unstoppable chain reaction that can occur in milliseconds releasing the stored energy in the cell. This can produce temperatures of 400°C and a fire that is extremely difficult to put out. Thermal runaway can start as low as 60°C and becomes much more likely at 100°C

Risk factors for thermal runaway:
* Short Circuits - either internally or externally
* Overcharging
* Excessive current draw or when charging

==== Li-ion pouch cells ====
[https://kokam.com/cell Kokam] produce high-performance Li-ion pouch cells. These combine relative ease of use and pack construction with performance close to cylindrical cells.

==== Li-ion 18650 and other cylindrical cells ====
Cylindrical cells are favoured by Tesla, and are probably the main reason why their cars achieve such excellent performance. They are light, compact, powerful and expensive. Unfortunately, cylindrical cells are difficult (and potentially dangerous) to use in DIY conversions. There are two good reasons for this: thermal management and cell configuration.

As stated above, Li-ion cells are prone to thermal runaway. So you need perfect battery and thermal management to ensure that no cell ever exceeds the critical voltage or temperature. If this happens, a cell can short-circuit internally, releasing a lot of energy - potentially explosively. Furthermore, the individual cells are small, so need to be arranged in parallel. In the case of the Tesla Model S 85kW pack, there are 74 cells in parallel. Imagine if one of those cells fails and becomes short circuited internally. You now have 73 very high power cells all feeding in to that short circuit...

In fact, you don't have to imagine: you can watch this famous video instead (courtesy of Rich Rebuilds).

<youtube>WdDi1haA71Q</youtube>

== OEM modules ==
Using an OEM module means a lot of the difficulties and safety issues associated with battery design are taken care of e.g. cooling, clamping, etc.

Here is a handy list of OEM modules:
{| class="wikitable sortable mw-collapsible"
|+
!Manufacturer
!Type
!Capacity (kWh)
!Weight (kg)
!w (mm)
!d (mm)
!h (mm)
!Gravity (kg/kWh)
!Volume (L/kWh)
!Voltage (V)
!Current (cont A)
!Current (peak A)
!Cell arrangement
!Cell type
!Chemistry
|-
|Tesla
|Model S 85kWh
|5.3
|26
|690
|315
|80
|4.9
|3.3
|22.8
|500
|750
|74p6s
|18650
|Li-ion
|-
|Tesla
|Model S 100kWh
|6.4
|28
|680
|315
|80
|4.4
|2.7
|22.8
|
|870
|86p6s
|18650
|Li-ion
|-
|Chevrolet
|Volt 2012
|4
|38
|470
|180
|280
|9.5
|5.9
|88
|140
|210
|24s
|Pouch
|Li-ion
|-
|BMW
|i3 60Ah
|2
|13
|368
|178
|102
|6.5
|3.3
|28.8
|210
|350
|8s2p
|Prismatic
|Li-ion
|-
|BMW
|i3 94Ah
|4.15
|28
|410
|310
|150
|6.7
|4.6
|45.6
|
|409
|12s
|Prismatic
|Li-ion
|-
|BMW
|i3 120Ah
|5.3
|28
|410
|310
|150
|5.3
|3.6
|45.6
|
|360
|12s
|Prismatic
|Li-ion
|-
|Mitsubishi
|Outlander
|2.4
|26
|646
|184
|130
|10.8
|6.4
|60
|
|240
|16s
|
|Li-ion
|-
|Nissan
|Leaf 24kWh
|0.5
|3.65
|300
|222
|34
|7.3
|4.5
|7.4
|130
|
|2s2p
|
|Li-ion
|-
|Nissan
|Leaf 40kWh
|1.6
|8.7
|300
|222
|68
|5.4
|2.8
|14.6
|
|
|4s2p
|
|Li-ion
|-
|Volvo
|XC90 T8
|2.01
|12.1
|300
|180
|150
|6.0
|4.0
|59.2
|170
|340
|16s
|
|Li-ion
|}

Batteries

2020-11-30T22:02:42Z

Clanger9: /* Capacity (kWh) */

== Introduction ==
There are a wide variety of battery chemistries available for use as the main traction battery of an EV. To use each chemistry safely, and to ensure an adequate service life from the battery pack it is important to understand the requirements for the chemistry you are using. Failure to do so may lead to premature or catastrophic failure of the pack.

Good pack design will allow for a nominal amount of abuse. People make mistakes and the pack should allow a margin for safety - and for longevity!

== Battery pack specification ==
When deciding on your battery pack, here are some basic parameters to consider:

=== Capacity (kWh) ===
'''How far do you want to go?''' A standard car conversion will need a kWh for approximately each 3 miles of range. For a middleweight motorcycle, a kWh should give around 9 miles. ''Your mileage may vary'', as they say.

=== Voltage (V) ===
'''How fast do you want to go?''' The pack voltage defines the maximum speed your motor can spin. Motors are usually specified with "KV" - or RPM-per-volt. Check the KV of your motor and how fast it needs to spin to get your desired top speed. e.g. if you need 3,000 RPM from a 25 KV motor then your pack voltage needs to be 3,000 / 25 = 120 V. The exact number of cells in series you need depends on the cell design, but 3.8 V for Li-ion and 3.2 V for LiFePO4 is a reasonable guess.

=== Maximum current (A) ===
'''How quickly do you want to accelerate?''' Your motor's maximum power will be specified in kW. To estimate your maximum current draw, divide the peak power by the battery voltage. e.g. a 30 kW motor with a 120 V battery pack will pull 30,000 / 120 = 250 A. The higher the current rating of the cells, the heavier they will be for a given capacity. Ideally, you want "enough" current capacity for full throttle acceleration, but no more. You can put cells in parallel to double the current rating of your pack (which of course will half the voltage).

=== Mass (kg) ===
'''Can your vehicle carry the weight?''' You'll need to keep the kerb weight within the original design limits. For a car, this could be a few hundred kg. For a motorcycle, likely less than 100 kg. This is a huge variable - and each new generation of battery tech seems to be a little lighter. For older EV or hybrid batteries, you can reckon on approximately 10 kg/kWh. Nissan Leaf batteries are relatively light (7.5 kg/kWh). With the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 5-6 kg/kWh.

=== Volume (L) ===
'''Will it fit?''' Batteries are bulky. They are getting smaller, but finding enough space might be your biggest challenge. You could be looking at over 5 L/kWh for older EV or hybrid batteries. For the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 3 L/kWh.

There is much, much more to battery design than this (e.g. maximum charge rate, terminations, cooling, clamping), but the above should help work out which options will or won't work for your project...

== Cell chemistry ==

=== Lithium Iron Phosphate (LiFePO4) ===
Lithium Iron Phosphate (also known as LFP, or LiFePO4) batteries offer a good compromise between safety, energy density and ease of use for DIY conversions. They are available in a number of formats, commonly pouch cells, prismatic cells and cylindrical cells.

==== LiFePO4 pouch cells ====
The majority of this content is drawn from this thread: [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761&start=900 https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761] discussing the use of the A123 20Ah pouch cell. However, many of the general points apply equally to other similar pouch cells.

===== General build requirements =====
Pouch cells are vulnerable to damage from debris, and must be held in compression (see the datasheet for your battery, but 10-12 psi is recommended for the A123 pouch cells as a guide). A rigid container capable of preventing damage and providing compression is therefore required. Be aware the cells expand and contract in use, so allowance for this must be included in the structure of the case.

The pouch cells should be separated to prevent abrasion between cells, and also to avoid the development of hot spots. Prebuilt modules from A123 systems had thin foam sheets or heatsinks between each cell. Be sure to avoid any debris that could rub on the pouch surface, particularly if using recycled cells.

Mylar, '[https://www.americanmicroinc.com/fish-paper/ Fish paper]' or a [https://www.rogerscorp.com/elastomeric-material-solutions/poron-industrial-polyurethanes compliant foam] may be appropriate materials to serve this purpose. This material should not be flammable. If the material is heat insulating, it is important to address thermal management.

===== Compression =====
Compression is required to prevent premature failure of the cell. Without compression electrolyte will become unevenly distributed, causing current gradients in the cell and uneven heating. Local temperatures can become high enough to form gas formation leading to cells 'puffing up' even when the pack is otherwise held within temperature and voltage constraints. This will be exacerbated in packs with otherwise poor thermal management. Compression forces gas generated to the margins of the cell, outside of the cell stack, minimising its effect cell performance. Gas in the middle cells will create a dead space which does not store or release energy.

There is ~1% expansion through a discharge cycle. As the cell ages, the nominal cell thickness can grow by 3-5%. For A123 cells the ideal pressure is between 4 and 18psi with the ideal pressure being ~12psi. Maintaining 12psi can increase the life by 500 cycles over that of 4 or 18psi

There is some suggestion that in uses where 1C is never exceeded compression ''may'' not be required.

Highly rigid endplates with a mechanism to allow for a limited degree of expansion (e.g. steel bands) are considered an effective solution to this challenge.

It should be noted that compression is a challenge specific to pouch cells. Cylindrical cells are designed to maintain their own compression within the cell's electrode stack by their design.

This thread provides more information and experimentation relating to pack compression: <nowiki>https://endless-sphere.com/forums/viewtopic.php?f=14&t=52244</nowiki>

===== Pouch Cell Pack Design Examples =====
<nowiki>*</nowiki>placeholder*

===== Notes regarding recycled pouch cells =====
Pouch cells are somewhat fragile, and breaching the insulation is not difficult, especially in a cells removed from existing packs and repurposed. If the pouch has had their poly-layers compromised you may see a number of faults:
* Black spots around the perimeter of the cell indicate electrolyte leakage
* Voltage on the outside of the bag. Note that microvoltage between the pouch and the electrode is normal (and due to a capacitive effect).
While the majority of these cells should no longer be in the market, a significant number of faulty cells made it back into the 'greymarket' in around 2013. These cells had misaligned tabs which can also lead to isolation failures between the tab and the pack. These cells should be avoided, particularly in high demand applications.

===== Situations likely to cause pouch cell failure =====
''Taken directly from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''
# '''Overcharge'''. Any extended time above 3.8 Volts will generate enough heat and electrochemical activity to puff a cell, especially one that is improperly compressed.
# '''Overdischarge followed by charge'''. Any A123 cell that has been pulled low enough to come to rest at <300 mV should be immediately scrapped. The published number for that is 500 mV, but the real figure is closer to 300, so that's a "safety buffer" if you will. Below this Voltage, the Cu electrodes start to dissolve into the electrolyte. When charge is applied, the Cu forms dendrites that puncture the separator layer, forming an internal short in the cell. This can puff a cell in a hurry---the more charge current on tap, the worse it's prone to be.
# '''Driving a cell negative'''. I've neglected to mention this before, but it is a possibility. I don't know much about the specific mechanism at this time.
# '''Malfunctioning or misinformed electronics'''. This is the most common cause of all of the above in my experience. At this stage of the game, it is critical for YOU to understand how your BMS functions on at least a cursory level. Choose your BMS very carefully and periodically verify that it is operating properly. They're not all created equal. Make sure V sense lines are securely connected and free of corrosion. Just because your BMS says there was never a problem doesn't necessarily make it so. Avoid harnesses or ribbon cables between multiple modules if possible--they are problematic wherever they are used in any mobile electronics.
# '''Exposure to or generation of sufficient heat'''. I don't know exactly at what temperature gas formation begins in the electrolyte, but we spec a max storage temp of 80 (or 85?) degrees C and I suspect this is the reason. The hotter, the puffier--to a point. This is why soldering tabs poses a real hazard to cell health. If you feel you must solder, sink or blow the heat away from the body of the cell. Use a big iron that can make sufficient local heat quickly, before the whole mass of the cell gets hot. You might even get the cell warm enough to melt separator if not careful.
# '''No compression, not enough compression, improperly distributed compression'''. This is a pack/module design issue. Apply 10, maybe 15 psi to your cell stack end to end and then band snugly and evenly. Use hard endplates of some sort--never wrap cells directly or allow their shape to become distorted. Protect all areas of the pouch from impact damage. This obviously does not apply to cylindrical cells.

==== LiFePO4 prismatic cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cylindrical cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cell ageing ====
''Derived (barely paraphrased) from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''

Capacity loss is caused by the lithium that was available for storage becoming permanently plated on the cathode. Being unable to move within the cell it is no longer available to store energy. The impact of this plating is greater than the amount of lithium 'lost' to plating because not only is the lithium no longer available, it is also preventing access to that part of the cathode meaning Li that can still move has to take a longer path to reach the cathode. Lithium plating is one cause of increased cell resistance (there are others), a sign of worsening cell health.

There is no linear relationship between actual capacity loss and impedance rise. However some cell defects will also increase impedance.

Increasing cell resistance may cause a number of symptoms which may be confused with [https://earthshipbiotecture.com/a-lithium-ion-battery-primer/ High Self Discharge.]
# Elevated Peukert Losses. As more energy per amount of current through the cell is lost as heat, the cells useable capacity decreases. So the apparent capacity loss is higher than the actual capacity loss of cycleable lithium. When used in low current applications (e.g. solar energy storage) the actual and apparent decrease in capacity will be small. In high current draw applications (like EV traction packs), the Peukert loss increases proportionally, so the apparent capacity loss increases much faster than the actual capacity loss.
# Greater voltage excursion under the same load. Due to increased cell resistancethe voltage will sag further under the same load than a cell in optimal condition. The inverse is also true, the voltage will be higher for the same amount of charging current applied. The cell will then rebound to a voltage further from the loaded and charging voltages. This, obviously, can look like high self discharge but is a different phenomenon.
# Absolute maximum current decrease.
Elevated impedance causes a more complex constellation of symptoms, some of which may be easy to confuse with High Self Discharge (HSD). Ohm's law (E=I/R) holds the key to understanding here.

'''1) Elevated Peukert losses.''' Because more energy per unit of current through the cell is lost as heat, less of the cell's capacity is actually USABLE. Thus, apparent capacity loss can be significantly greater than actual capacity loss caused by the loss of cycleable Li alone. In low current applications, the two numbers will be close together. In high current applications, Peukert losses increase in proportion, so apparent loss of capacity breaks further and further away from actual capacity loss as current increases.

'''2) Greater voltage excursion under the same load.''' Elevated resistance across the cell means that voltage will sag more under the same load than it did when the cell was healthier. Conversely, voltage will rise higher with the same amount of applied charge current than it did when it was healthier. At the same time, rebound/settling voltages will be further away from loaded/charging voltages. In other words, the cell will rebound to a voltage further away from loaded voltage, all else being equal. Similarly, voltage will settle farther from the charge voltage with the same charge applied. This can give the illusion of elevated self-discharge, but the phenomenon is actually not the same thing. Again, the greater the charge and load currents, the greater the effect becomes.

'''3) Absolute max current decreases.''' Because the cell's series resistance is elevated, the maximum possible current through the cell is decreased.

Just to confuse things further, there can be many factors that lead to impedance rise. Some are related to Li plating, others are not.

=== Lithium-ion ===
Lithium-ion (Li-ion) batteries have a greater energy density than Lithium Iron Phosphate batteries, but have more challenging needs to use safely. The ideal operating range of Li-ion batteries is between +15 and +45°C. The upper limit of temperature is particularly important as Li-ion batteries experience thermal runaway - an unstoppable chain reaction that can occur in milliseconds releasing the stored energy in the cell. This can produce temperatures of 400°C and a fire that is extremely difficult to put out. Thermal runaway can start as low as 60°C and becomes much more likely at 100°C

Risk factors for thermal runaway:
* Short Circuits - either internally or externally
* Overcharging
* Excessive current draw or when charging

==== Li-ion pouch cells ====
[https://kokam.com/cell Kokam] produce high-performance Li-ion pouch cells. These combine relative ease of use and pack construction with performance close to cylindrical cells.

==== Li-ion 18650 and other cylindrical cells ====
Cylindrical cells are favoured by Tesla, and are probably the main reason why their cars achieve such excellent performance. They are light, compact, powerful and expensive. Unfortunately, cylindrical cells are difficult (and potentially dangerous) to use in DIY conversions. There are two good reasons for this: thermal management and cell configuration.

As stated above, Li-ion cells are prone to thermal runaway. So you need perfect battery and thermal management to ensure that no cell ever exceeds the critical voltage or temperature. If this happens, a cell can short-circuit internally, releasing a lot of energy - potentially explosively. Furthermore, the individual cells are small, so need to be arranged in parallel. In the case of the Tesla Model S 85kW pack, there are 74 cells in parallel. Imagine if one of those cells fails and becomes short circuited internally. You now have 73 very high power cells all feeding in to that short circuit...

In fact, you don't have to imagine: you can watch this famous video instead (courtesy of Rich Rebuilds).

<youtube>WdDi1haA71Q</youtube>

== OEM modules ==
Using an OEM module means a lot of the difficulties and safety issues associated with battery design are taken care of e.g. cooling, clamping, etc.

Here is a handy list of OEM modules:
{| class="wikitable sortable mw-collapsible"
|+
!Manufacturer
!Type
!Capacity (kWh)
!Weight (kg)
!w (mm)
!d (mm)
!h (mm)
!Gravity (kg/kWh)
!Volume (L/kWh)
!Voltage (V)
!Current (cont A)
!Current (peak A)
!Cell arrangement
!Cell type
!Chemistry
|-
|Tesla
|Model S 85kWh
|5.3
|26
|690
|315
|80
|4.9
|3.3
|22.8
|500
|750
|74p6s
|18650
|Li-ion
|-
|Tesla
|Model S 100kWh
|6.4
|28
|680
|315
|80
|4.4
|2.7
|22.8
|
|870
|86p6s
|18650
|Li-ion
|-
|Chevrolet
|Volt 2012
|4
|38
|470
|180
|280
|9.5
|5.9
|88
|140
|210
|24s
|Pouch
|Li-ion
|-
|BMW
|i3 60Ah
|2
|13
|368
|178
|102
|6.5
|3.3
|28.8
|210
|350
|8s2p
|Prismatic
|Li-ion
|-
|BMW
|i3 94Ah
|4.15
|28
|410
|310
|150
|6.7
|4.6
|45.6
|
|409
|12s
|Prismatic
|Li-ion
|-
|BMW
|i3 120Ah
|5.3
|28
|410
|310
|150
|5.3
|3.6
|45.6
|
|360
|12s
|Prismatic
|Li-ion
|-
|Mitsubishi
|Outlander
|2.4
|26
|646
|184
|130
|10.8
|6.4
|60
|
|240
|16s
|
|Li-ion
|-
|Nissan
|Leaf 24kWh
|0.5
|3.65
|300
|222
|34
|7.3
|4.5
|7.4
|130
|
|2s2p
|
|Li-ion
|-
|Nissan
|Leaf 40kWh
|1.6
|8.7
|300
|222
|68
|5.4
|2.8
|14.6
|
|
|4s2p
|
|Li-ion
|-
|Volvo
|XC90 T8
|2.01
|12.1
|300
|180
|150
|6.0
|4.0
|59.2
|170
|340
|16s
|
|Li-ion
|}

Batteries

2020-11-30T21:54:00Z

Clanger9: /* Volume (L) */

== Introduction ==
There are a wide variety of battery chemistries available for use as the main traction battery of an EV. To use each chemistry safely, and to ensure an adequate service life from the battery pack it is important to understand the requirements for the chemistry you are using. Failure to do so may lead to premature or catastrophic failure of the pack.

Good pack design will allow for a nominal amount of abuse. People make mistakes and the pack should allow a margin for safety - and for longevity!

== Battery pack specification ==
When deciding on your battery pack, here are some basic parameters to consider:

=== Capacity (kWh) ===
'''How far do you want to go?''' A standard car conversion will need around 1kWh for 3 miles of range. For a middleweight motorcycle, 1kWh should give around 9 miles. ''Your mileage may vary'', as they say.

=== Voltage (V) ===
'''How fast do you want to go?''' The pack voltage defines the maximum speed your motor can spin. Motors are usually specified with "KV" - or RPM-per-volt. Check the KV of your motor and how fast it needs to spin to get your desired top speed. e.g. if you need 3,000 RPM from a 25 KV motor then your pack voltage needs to be 3,000 / 25 = 120 V. The exact number of cells in series you need depends on the cell design, but 3.8 V for Li-ion and 3.2 V for LiFePO4 is a reasonable guess.

=== Maximum current (A) ===
'''How quickly do you want to accelerate?''' Your motor's maximum power will be specified in kW. To estimate your maximum current draw, divide the peak power by the battery voltage. e.g. a 30 kW motor with a 120 V battery pack will pull 30,000 / 120 = 250 A. The higher the current rating of the cells, the heavier they will be for a given capacity. Ideally, you want "enough" current capacity for full throttle acceleration, but no more. You can put cells in parallel to double the current rating of your pack (which of course will half the voltage).

=== Mass (kg) ===
'''Can your vehicle carry the weight?''' You'll need to keep the kerb weight within the original design limits. For a car, this could be a few hundred kg. For a motorcycle, likely less than 100 kg. This is a huge variable - and each new generation of battery tech seems to be a little lighter. For older EV or hybrid batteries, you can reckon on approximately 10 kg/kWh. Nissan Leaf batteries are relatively light (7.5 kg/kWh). With the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 5-6 kg/kWh.

=== Volume (L) ===
'''Will it fit?''' Batteries are bulky. They are getting smaller, but finding enough space might be your biggest challenge. You could be looking at over 5 L/kWh for older EV or hybrid batteries. For the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 3 L/kWh.

There is much, much more to battery design than this (e.g. maximum charge rate, terminations, cooling, clamping), but the above should help work out which options will or won't work for your project...

== Cell chemistry ==

=== Lithium Iron Phosphate (LiFePO4) ===
Lithium Iron Phosphate (also known as LFP, or LiFePO4) batteries offer a good compromise between safety, energy density and ease of use for DIY conversions. They are available in a number of formats, commonly pouch cells, prismatic cells and cylindrical cells.

==== LiFePO4 pouch cells ====
The majority of this content is drawn from this thread: [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761&start=900 https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761] discussing the use of the A123 20Ah pouch cell. However, many of the general points apply equally to other similar pouch cells.

===== General build requirements =====
Pouch cells are vulnerable to damage from debris, and must be held in compression (see the datasheet for your battery, but 10-12 psi is recommended for the A123 pouch cells as a guide). A rigid container capable of preventing damage and providing compression is therefore required. Be aware the cells expand and contract in use, so allowance for this must be included in the structure of the case.

The pouch cells should be separated to prevent abrasion between cells, and also to avoid the development of hot spots. Prebuilt modules from A123 systems had thin foam sheets or heatsinks between each cell. Be sure to avoid any debris that could rub on the pouch surface, particularly if using recycled cells.

Mylar, '[https://www.americanmicroinc.com/fish-paper/ Fish paper]' or a [https://www.rogerscorp.com/elastomeric-material-solutions/poron-industrial-polyurethanes compliant foam] may be appropriate materials to serve this purpose. This material should not be flammable. If the material is heat insulating, it is important to address thermal management.

===== Compression =====
Compression is required to prevent premature failure of the cell. Without compression electrolyte will become unevenly distributed, causing current gradients in the cell and uneven heating. Local temperatures can become high enough to form gas formation leading to cells 'puffing up' even when the pack is otherwise held within temperature and voltage constraints. This will be exacerbated in packs with otherwise poor thermal management. Compression forces gas generated to the margins of the cell, outside of the cell stack, minimising its effect cell performance. Gas in the middle cells will create a dead space which does not store or release energy.

There is ~1% expansion through a discharge cycle. As the cell ages, the nominal cell thickness can grow by 3-5%. For A123 cells the ideal pressure is between 4 and 18psi with the ideal pressure being ~12psi. Maintaining 12psi can increase the life by 500 cycles over that of 4 or 18psi

There is some suggestion that in uses where 1C is never exceeded compression ''may'' not be required.

Highly rigid endplates with a mechanism to allow for a limited degree of expansion (e.g. steel bands) are considered an effective solution to this challenge.

It should be noted that compression is a challenge specific to pouch cells. Cylindrical cells are designed to maintain their own compression within the cell's electrode stack by their design.

This thread provides more information and experimentation relating to pack compression: <nowiki>https://endless-sphere.com/forums/viewtopic.php?f=14&t=52244</nowiki>

===== Pouch Cell Pack Design Examples =====
<nowiki>*</nowiki>placeholder*

===== Notes regarding recycled pouch cells =====
Pouch cells are somewhat fragile, and breaching the insulation is not difficult, especially in a cells removed from existing packs and repurposed. If the pouch has had their poly-layers compromised you may see a number of faults:
* Black spots around the perimeter of the cell indicate electrolyte leakage
* Voltage on the outside of the bag. Note that microvoltage between the pouch and the electrode is normal (and due to a capacitive effect).
While the majority of these cells should no longer be in the market, a significant number of faulty cells made it back into the 'greymarket' in around 2013. These cells had misaligned tabs which can also lead to isolation failures between the tab and the pack. These cells should be avoided, particularly in high demand applications.

===== Situations likely to cause pouch cell failure =====
''Taken directly from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''
# '''Overcharge'''. Any extended time above 3.8 Volts will generate enough heat and electrochemical activity to puff a cell, especially one that is improperly compressed.
# '''Overdischarge followed by charge'''. Any A123 cell that has been pulled low enough to come to rest at <300 mV should be immediately scrapped. The published number for that is 500 mV, but the real figure is closer to 300, so that's a "safety buffer" if you will. Below this Voltage, the Cu electrodes start to dissolve into the electrolyte. When charge is applied, the Cu forms dendrites that puncture the separator layer, forming an internal short in the cell. This can puff a cell in a hurry---the more charge current on tap, the worse it's prone to be.
# '''Driving a cell negative'''. I've neglected to mention this before, but it is a possibility. I don't know much about the specific mechanism at this time.
# '''Malfunctioning or misinformed electronics'''. This is the most common cause of all of the above in my experience. At this stage of the game, it is critical for YOU to understand how your BMS functions on at least a cursory level. Choose your BMS very carefully and periodically verify that it is operating properly. They're not all created equal. Make sure V sense lines are securely connected and free of corrosion. Just because your BMS says there was never a problem doesn't necessarily make it so. Avoid harnesses or ribbon cables between multiple modules if possible--they are problematic wherever they are used in any mobile electronics.
# '''Exposure to or generation of sufficient heat'''. I don't know exactly at what temperature gas formation begins in the electrolyte, but we spec a max storage temp of 80 (or 85?) degrees C and I suspect this is the reason. The hotter, the puffier--to a point. This is why soldering tabs poses a real hazard to cell health. If you feel you must solder, sink or blow the heat away from the body of the cell. Use a big iron that can make sufficient local heat quickly, before the whole mass of the cell gets hot. You might even get the cell warm enough to melt separator if not careful.
# '''No compression, not enough compression, improperly distributed compression'''. This is a pack/module design issue. Apply 10, maybe 15 psi to your cell stack end to end and then band snugly and evenly. Use hard endplates of some sort--never wrap cells directly or allow their shape to become distorted. Protect all areas of the pouch from impact damage. This obviously does not apply to cylindrical cells.

==== LiFePO4 prismatic cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cylindrical cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cell ageing ====
''Derived (barely paraphrased) from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''

Capacity loss is caused by the lithium that was available for storage becoming permanently plated on the cathode. Being unable to move within the cell it is no longer available to store energy. The impact of this plating is greater than the amount of lithium 'lost' to plating because not only is the lithium no longer available, it is also preventing access to that part of the cathode meaning Li that can still move has to take a longer path to reach the cathode. Lithium plating is one cause of increased cell resistance (there are others), a sign of worsening cell health.

There is no linear relationship between actual capacity loss and impedance rise. However some cell defects will also increase impedance.

Increasing cell resistance may cause a number of symptoms which may be confused with [https://earthshipbiotecture.com/a-lithium-ion-battery-primer/ High Self Discharge.]
# Elevated Peukert Losses. As more energy per amount of current through the cell is lost as heat, the cells useable capacity decreases. So the apparent capacity loss is higher than the actual capacity loss of cycleable lithium. When used in low current applications (e.g. solar energy storage) the actual and apparent decrease in capacity will be small. In high current draw applications (like EV traction packs), the Peukert loss increases proportionally, so the apparent capacity loss increases much faster than the actual capacity loss.
# Greater voltage excursion under the same load. Due to increased cell resistancethe voltage will sag further under the same load than a cell in optimal condition. The inverse is also true, the voltage will be higher for the same amount of charging current applied. The cell will then rebound to a voltage further from the loaded and charging voltages. This, obviously, can look like high self discharge but is a different phenomenon.
# Absolute maximum current decrease.
Elevated impedance causes a more complex constellation of symptoms, some of which may be easy to confuse with High Self Discharge (HSD). Ohm's law (E=I/R) holds the key to understanding here.

'''1) Elevated Peukert losses.''' Because more energy per unit of current through the cell is lost as heat, less of the cell's capacity is actually USABLE. Thus, apparent capacity loss can be significantly greater than actual capacity loss caused by the loss of cycleable Li alone. In low current applications, the two numbers will be close together. In high current applications, Peukert losses increase in proportion, so apparent loss of capacity breaks further and further away from actual capacity loss as current increases.

'''2) Greater voltage excursion under the same load.''' Elevated resistance across the cell means that voltage will sag more under the same load than it did when the cell was healthier. Conversely, voltage will rise higher with the same amount of applied charge current than it did when it was healthier. At the same time, rebound/settling voltages will be further away from loaded/charging voltages. In other words, the cell will rebound to a voltage further away from loaded voltage, all else being equal. Similarly, voltage will settle farther from the charge voltage with the same charge applied. This can give the illusion of elevated self-discharge, but the phenomenon is actually not the same thing. Again, the greater the charge and load currents, the greater the effect becomes.

'''3) Absolute max current decreases.''' Because the cell's series resistance is elevated, the maximum possible current through the cell is decreased.

Just to confuse things further, there can be many factors that lead to impedance rise. Some are related to Li plating, others are not.

=== Lithium-ion ===
Lithium-ion (Li-ion) batteries have a greater energy density than Lithium Iron Phosphate batteries, but have more challenging needs to use safely. The ideal operating range of Li-ion batteries is between +15 and +45°C. The upper limit of temperature is particularly important as Li-ion batteries experience thermal runaway - an unstoppable chain reaction that can occur in milliseconds releasing the stored energy in the cell. This can produce temperatures of 400°C and a fire that is extremely difficult to put out. Thermal runaway can start as low as 60°C and becomes much more likely at 100°C

Risk factors for thermal runaway:
* Short Circuits - either internally or externally
* Overcharging
* Excessive current draw or when charging

==== Li-ion pouch cells ====
[https://kokam.com/cell Kokam] produce high-performance Li-ion pouch cells. These combine relative ease of use and pack construction with performance close to cylindrical cells.

==== Li-ion 18650 and other cylindrical cells ====
Cylindrical cells are favoured by Tesla, and are probably the main reason why their cars achieve such excellent performance. They are light, compact, powerful and expensive. Unfortunately, cylindrical cells are difficult (and potentially dangerous) to use in DIY conversions. There are two good reasons for this: thermal management and cell configuration.

As stated above, Li-ion cells are prone to thermal runaway. So you need perfect battery and thermal management to ensure that no cell ever exceeds the critical voltage or temperature. If this happens, a cell can short-circuit internally, releasing a lot of energy - potentially explosively. Furthermore, the individual cells are small, so need to be arranged in parallel. In the case of the Tesla Model S 85kW pack, there are 74 cells in parallel. Imagine if one of those cells fails and becomes short circuited internally. You now have 73 very high power cells all feeding in to that short circuit...

In fact, you don't have to imagine: you can watch this famous video instead (courtesy of Rich Rebuilds).

<youtube>WdDi1haA71Q</youtube>

== OEM modules ==
Using an OEM module means a lot of the difficulties and safety issues associated with battery design are taken care of e.g. cooling, clamping, etc.

Here is a handy list of OEM modules:
{| class="wikitable sortable mw-collapsible"
|+
!Manufacturer
!Type
!Capacity (kWh)
!Weight (kg)
!w (mm)
!d (mm)
!h (mm)
!Gravity (kg/kWh)
!Volume (L/kWh)
!Voltage (V)
!Current (cont A)
!Current (peak A)
!Cell arrangement
!Cell type
!Chemistry
|-
|Tesla
|Model S 85kWh
|5.3
|26
|690
|315
|80
|4.9
|3.3
|22.8
|500
|750
|74p6s
|18650
|Li-ion
|-
|Tesla
|Model S 100kWh
|6.4
|28
|680
|315
|80
|4.4
|2.7
|22.8
|
|870
|86p6s
|18650
|Li-ion
|-
|Chevrolet
|Volt 2012
|4
|38
|470
|180
|280
|9.5
|5.9
|88
|140
|210
|24s
|Pouch
|Li-ion
|-
|BMW
|i3 60Ah
|2
|13
|368
|178
|102
|6.5
|3.3
|28.8
|210
|350
|8s2p
|Prismatic
|Li-ion
|-
|BMW
|i3 94Ah
|4.15
|28
|410
|310
|150
|6.7
|4.6
|45.6
|
|409
|12s
|Prismatic
|Li-ion
|-
|BMW
|i3 120Ah
|5.3
|28
|410
|310
|150
|5.3
|3.6
|45.6
|
|360
|12s
|Prismatic
|Li-ion
|-
|Mitsubishi
|Outlander
|2.4
|26
|646
|184
|130
|10.8
|6.4
|60
|
|240
|16s
|
|Li-ion
|-
|Nissan
|Leaf 24kWh
|0.5
|3.65
|300
|222
|34
|7.3
|4.5
|7.4
|130
|
|2s2p
|
|Li-ion
|-
|Nissan
|Leaf 40kWh
|1.6
|8.7
|300
|222
|68
|5.4
|2.8
|14.6
|
|
|4s2p
|
|Li-ion
|-
|Volvo
|XC90 T8
|2.01
|12.1
|300
|180
|150
|6.0
|4.0
|59.2
|170
|340
|16s
|
|Li-ion
|}

Batteries

2020-11-30T21:43:43Z

Clanger9: /* Li-ion 18650 and other cylindrical cells */

== Introduction ==
There are a wide variety of battery chemistries available for use as the main traction battery of an EV. To use each chemistry safely, and to ensure an adequate service life from the battery pack it is important to understand the requirements for the chemistry you are using. Failure to do so may lead to premature or catastrophic failure of the pack.

Good pack design will allow for a nominal amount of abuse. People make mistakes and the pack should allow a margin for safety - and for longevity!

== Battery pack specification ==
When deciding on your battery pack, here are some basic parameters to consider:

=== Capacity (kWh) ===
'''How far do you want to go?''' A standard car conversion will need around 1kWh for 3 miles of range. For a middleweight motorcycle, 1kWh should give around 9 miles. ''Your mileage may vary'', as they say.

=== Voltage (V) ===
'''How fast do you want to go?''' The pack voltage defines the maximum speed your motor can spin. Motors are usually specified with "KV" - or RPM-per-volt. Check the KV of your motor and how fast it needs to spin to get your desired top speed. e.g. if you need 3,000 RPM from a 25 KV motor then your pack voltage needs to be 3,000 / 25 = 120 V. The exact number of cells in series you need depends on the cell design, but 3.8 V for Li-ion and 3.2 V for LiFePO4 is a reasonable guess.

=== Maximum current (A) ===
'''How quickly do you want to accelerate?''' Your motor's maximum power will be specified in kW. To estimate your maximum current draw, divide the peak power by the battery voltage. e.g. a 30 kW motor with a 120 V battery pack will pull 30,000 / 120 = 250 A. The higher the current rating of the cells, the heavier they will be for a given capacity. Ideally, you want "enough" current capacity for full throttle acceleration, but no more. You can put cells in parallel to double the current rating of your pack (which of course will half the voltage).

=== Mass (kg) ===
'''Can your vehicle carry the weight?''' You'll need to keep the kerb weight within the original design limits. For a car, this could be a few hundred kg. For a motorcycle, likely less than 100 kg. This is a huge variable - and each new generation of battery tech seems to be a little lighter. For older EV or hybrid batteries, you can reckon on approximately 10 kg/kWh. Nissan Leaf batteries are relatively light (7.5 kg/kWh). With the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 5-6 kg/kWh.

=== Volume (L) ===
'''Will it fit?''' Batteries are bulky. They are getting smaller, but finding enough space my be your biggest challenge. You could be looking at over 5 L/kWh for older EV or hybrid batteries. For the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 3 kg/kWh.

There is much, much more to battery design than this (e.g. maximum charge rate, terminations, cooling, clamping), but the above should help work out which options will or won't work for your project...

== Cell chemistry ==

=== Lithium Iron Phosphate (LiFePO4) ===
Lithium Iron Phosphate (also known as LFP, or LiFePO4) batteries offer a good compromise between safety, energy density and ease of use for DIY conversions. They are available in a number of formats, commonly pouch cells, prismatic cells and cylindrical cells.

==== LiFePO4 pouch cells ====
The majority of this content is drawn from this thread: [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761&start=900 https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761] discussing the use of the A123 20Ah pouch cell. However, many of the general points apply equally to other similar pouch cells.

===== General build requirements =====
Pouch cells are vulnerable to damage from debris, and must be held in compression (see the datasheet for your battery, but 10-12 psi is recommended for the A123 pouch cells as a guide). A rigid container capable of preventing damage and providing compression is therefore required. Be aware the cells expand and contract in use, so allowance for this must be included in the structure of the case.

The pouch cells should be separated to prevent abrasion between cells, and also to avoid the development of hot spots. Prebuilt modules from A123 systems had thin foam sheets or heatsinks between each cell. Be sure to avoid any debris that could rub on the pouch surface, particularly if using recycled cells.

Mylar, '[https://www.americanmicroinc.com/fish-paper/ Fish paper]' or a [https://www.rogerscorp.com/elastomeric-material-solutions/poron-industrial-polyurethanes compliant foam] may be appropriate materials to serve this purpose. This material should not be flammable. If the material is heat insulating, it is important to address thermal management.

===== Compression =====
Compression is required to prevent premature failure of the cell. Without compression electrolyte will become unevenly distributed, causing current gradients in the cell and uneven heating. Local temperatures can become high enough to form gas formation leading to cells 'puffing up' even when the pack is otherwise held within temperature and voltage constraints. This will be exacerbated in packs with otherwise poor thermal management. Compression forces gas generated to the margins of the cell, outside of the cell stack, minimising its effect cell performance. Gas in the middle cells will create a dead space which does not store or release energy.

There is ~1% expansion through a discharge cycle. As the cell ages, the nominal cell thickness can grow by 3-5%. For A123 cells the ideal pressure is between 4 and 18psi with the ideal pressure being ~12psi. Maintaining 12psi can increase the life by 500 cycles over that of 4 or 18psi

There is some suggestion that in uses where 1C is never exceeded compression ''may'' not be required.

Highly rigid endplates with a mechanism to allow for a limited degree of expansion (e.g. steel bands) are considered an effective solution to this challenge.

It should be noted that compression is a challenge specific to pouch cells. Cylindrical cells are designed to maintain their own compression within the cell's electrode stack by their design.

This thread provides more information and experimentation relating to pack compression: <nowiki>https://endless-sphere.com/forums/viewtopic.php?f=14&t=52244</nowiki>

===== Pouch Cell Pack Design Examples =====
<nowiki>*</nowiki>placeholder*

===== Notes regarding recycled pouch cells =====
Pouch cells are somewhat fragile, and breaching the insulation is not difficult, especially in a cells removed from existing packs and repurposed. If the pouch has had their poly-layers compromised you may see a number of faults:
* Black spots around the perimeter of the cell indicate electrolyte leakage
* Voltage on the outside of the bag. Note that microvoltage between the pouch and the electrode is normal (and due to a capacitive effect).
While the majority of these cells should no longer be in the market, a significant number of faulty cells made it back into the 'greymarket' in around 2013. These cells had misaligned tabs which can also lead to isolation failures between the tab and the pack. These cells should be avoided, particularly in high demand applications.

===== Situations likely to cause pouch cell failure =====
''Taken directly from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''
# '''Overcharge'''. Any extended time above 3.8 Volts will generate enough heat and electrochemical activity to puff a cell, especially one that is improperly compressed.
# '''Overdischarge followed by charge'''. Any A123 cell that has been pulled low enough to come to rest at <300 mV should be immediately scrapped. The published number for that is 500 mV, but the real figure is closer to 300, so that's a "safety buffer" if you will. Below this Voltage, the Cu electrodes start to dissolve into the electrolyte. When charge is applied, the Cu forms dendrites that puncture the separator layer, forming an internal short in the cell. This can puff a cell in a hurry---the more charge current on tap, the worse it's prone to be.
# '''Driving a cell negative'''. I've neglected to mention this before, but it is a possibility. I don't know much about the specific mechanism at this time.
# '''Malfunctioning or misinformed electronics'''. This is the most common cause of all of the above in my experience. At this stage of the game, it is critical for YOU to understand how your BMS functions on at least a cursory level. Choose your BMS very carefully and periodically verify that it is operating properly. They're not all created equal. Make sure V sense lines are securely connected and free of corrosion. Just because your BMS says there was never a problem doesn't necessarily make it so. Avoid harnesses or ribbon cables between multiple modules if possible--they are problematic wherever they are used in any mobile electronics.
# '''Exposure to or generation of sufficient heat'''. I don't know exactly at what temperature gas formation begins in the electrolyte, but we spec a max storage temp of 80 (or 85?) degrees C and I suspect this is the reason. The hotter, the puffier--to a point. This is why soldering tabs poses a real hazard to cell health. If you feel you must solder, sink or blow the heat away from the body of the cell. Use a big iron that can make sufficient local heat quickly, before the whole mass of the cell gets hot. You might even get the cell warm enough to melt separator if not careful.
# '''No compression, not enough compression, improperly distributed compression'''. This is a pack/module design issue. Apply 10, maybe 15 psi to your cell stack end to end and then band snugly and evenly. Use hard endplates of some sort--never wrap cells directly or allow their shape to become distorted. Protect all areas of the pouch from impact damage. This obviously does not apply to cylindrical cells.

==== LiFePO4 prismatic cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cylindrical cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cell ageing ====
''Derived (barely paraphrased) from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''

Capacity loss is caused by the lithium that was available for storage becoming permanently plated on the cathode. Being unable to move within the cell it is no longer available to store energy. The impact of this plating is greater than the amount of lithium 'lost' to plating because not only is the lithium no longer available, it is also preventing access to that part of the cathode meaning Li that can still move has to take a longer path to reach the cathode. Lithium plating is one cause of increased cell resistance (there are others), a sign of worsening cell health.

There is no linear relationship between actual capacity loss and impedance rise. However some cell defects will also increase impedance.

Increasing cell resistance may cause a number of symptoms which may be confused with [https://earthshipbiotecture.com/a-lithium-ion-battery-primer/ High Self Discharge.]
# Elevated Peukert Losses. As more energy per amount of current through the cell is lost as heat, the cells useable capacity decreases. So the apparent capacity loss is higher than the actual capacity loss of cycleable lithium. When used in low current applications (e.g. solar energy storage) the actual and apparent decrease in capacity will be small. In high current draw applications (like EV traction packs), the Peukert loss increases proportionally, so the apparent capacity loss increases much faster than the actual capacity loss.
# Greater voltage excursion under the same load. Due to increased cell resistancethe voltage will sag further under the same load than a cell in optimal condition. The inverse is also true, the voltage will be higher for the same amount of charging current applied. The cell will then rebound to a voltage further from the loaded and charging voltages. This, obviously, can look like high self discharge but is a different phenomenon.
# Absolute maximum current decrease.
Elevated impedance causes a more complex constellation of symptoms, some of which may be easy to confuse with High Self Discharge (HSD). Ohm's law (E=I/R) holds the key to understanding here.

'''1) Elevated Peukert losses.''' Because more energy per unit of current through the cell is lost as heat, less of the cell's capacity is actually USABLE. Thus, apparent capacity loss can be significantly greater than actual capacity loss caused by the loss of cycleable Li alone. In low current applications, the two numbers will be close together. In high current applications, Peukert losses increase in proportion, so apparent loss of capacity breaks further and further away from actual capacity loss as current increases.

'''2) Greater voltage excursion under the same load.''' Elevated resistance across the cell means that voltage will sag more under the same load than it did when the cell was healthier. Conversely, voltage will rise higher with the same amount of applied charge current than it did when it was healthier. At the same time, rebound/settling voltages will be further away from loaded/charging voltages. In other words, the cell will rebound to a voltage further away from loaded voltage, all else being equal. Similarly, voltage will settle farther from the charge voltage with the same charge applied. This can give the illusion of elevated self-discharge, but the phenomenon is actually not the same thing. Again, the greater the charge and load currents, the greater the effect becomes.

'''3) Absolute max current decreases.''' Because the cell's series resistance is elevated, the maximum possible current through the cell is decreased.

Just to confuse things further, there can be many factors that lead to impedance rise. Some are related to Li plating, others are not.

=== Lithium-ion ===
Lithium-ion (Li-ion) batteries have a greater energy density than Lithium Iron Phosphate batteries, but have more challenging needs to use safely. The ideal operating range of Li-ion batteries is between +15 and +45°C. The upper limit of temperature is particularly important as Li-ion batteries experience thermal runaway - an unstoppable chain reaction that can occur in milliseconds releasing the stored energy in the cell. This can produce temperatures of 400°C and a fire that is extremely difficult to put out. Thermal runaway can start as low as 60°C and becomes much more likely at 100°C

Risk factors for thermal runaway:
* Short Circuits - either internally or externally
* Overcharging
* Excessive current draw or when charging

==== Li-ion pouch cells ====
[https://kokam.com/cell Kokam] produce high-performance Li-ion pouch cells. These combine relative ease of use and pack construction with performance close to cylindrical cells.

==== Li-ion 18650 and other cylindrical cells ====
Cylindrical cells are favoured by Tesla, and are probably the main reason why their cars achieve such excellent performance. They are light, compact, powerful and expensive. Unfortunately, cylindrical cells are difficult (and potentially dangerous) to use in DIY conversions. There are two good reasons for this: thermal management and cell configuration.

As stated above, Li-ion cells are prone to thermal runaway. So you need perfect battery and thermal management to ensure that no cell ever exceeds the critical voltage or temperature. If this happens, a cell can short-circuit internally, releasing a lot of energy - potentially explosively. Furthermore, the individual cells are small, so need to be arranged in parallel. In the case of the Tesla Model S 85kW pack, there are 74 cells in parallel. Imagine if one of those cells fails and becomes short circuited internally. You now have 73 very high power cells all feeding in to that short circuit...

In fact, you don't have to imagine: you can watch this famous video instead (courtesy of Rich Rebuilds).

<youtube>WdDi1haA71Q</youtube>

== OEM modules ==
Using an OEM module means a lot of the difficulties and safety issues associated with battery design are taken care of e.g. cooling, clamping, etc.

Here is a handy list of OEM modules:
{| class="wikitable sortable mw-collapsible"
|+
!Manufacturer
!Type
!Capacity (kWh)
!Weight (kg)
!w (mm)
!d (mm)
!h (mm)
!Gravity (kg/kWh)
!Volume (L/kWh)
!Voltage (V)
!Current (cont A)
!Current (peak A)
!Cell arrangement
!Cell type
!Chemistry
|-
|Tesla
|Model S 85kWh
|5.3
|26
|690
|315
|80
|4.9
|3.3
|22.8
|500
|750
|74p6s
|18650
|Li-ion
|-
|Tesla
|Model S 100kWh
|6.4
|28
|680
|315
|80
|4.4
|2.7
|22.8
|
|870
|86p6s
|18650
|Li-ion
|-
|Chevrolet
|Volt 2012
|4
|38
|470
|180
|280
|9.5
|5.9
|88
|140
|210
|24s
|Pouch
|Li-ion
|-
|BMW
|i3 60Ah
|2
|13
|368
|178
|102
|6.5
|3.3
|28.8
|210
|350
|8s2p
|Prismatic
|Li-ion
|-
|BMW
|i3 94Ah
|4.15
|28
|410
|310
|150
|6.7
|4.6
|45.6
|
|409
|12s
|Prismatic
|Li-ion
|-
|BMW
|i3 120Ah
|5.3
|28
|410
|310
|150
|5.3
|3.6
|45.6
|
|360
|12s
|Prismatic
|Li-ion
|-
|Mitsubishi
|Outlander
|2.4
|26
|646
|184
|130
|10.8
|6.4
|60
|
|240
|16s
|
|Li-ion
|-
|Nissan
|Leaf 24kWh
|0.5
|3.65
|300
|222
|34
|7.3
|4.5
|7.4
|130
|
|2s2p
|
|Li-ion
|-
|Nissan
|Leaf 40kWh
|1.6
|8.7
|300
|222
|68
|5.4
|2.8
|14.6
|
|
|4s2p
|
|Li-ion
|-
|Volvo
|XC90 T8
|2.01
|12.1
|300
|180
|150
|6.0
|4.0
|59.2
|170
|340
|16s
|
|Li-ion
|}

Batteries

2020-11-30T21:42:22Z

Clanger9: /* Li-ion 18650 and other cylindrical cells */

== Introduction ==
There are a wide variety of battery chemistries available for use as the main traction battery of an EV. To use each chemistry safely, and to ensure an adequate service life from the battery pack it is important to understand the requirements for the chemistry you are using. Failure to do so may lead to premature or catastrophic failure of the pack.

Good pack design will allow for a nominal amount of abuse. People make mistakes and the pack should allow a margin for safety - and for longevity!

== Battery pack specification ==
When deciding on your battery pack, here are some basic parameters to consider:

=== Capacity (kWh) ===
'''How far do you want to go?''' A standard car conversion will need around 1kWh for 3 miles of range. For a middleweight motorcycle, 1kWh should give around 9 miles. ''Your mileage may vary'', as they say.

=== Voltage (V) ===
'''How fast do you want to go?''' The pack voltage defines the maximum speed your motor can spin. Motors are usually specified with "KV" - or RPM-per-volt. Check the KV of your motor and how fast it needs to spin to get your desired top speed. e.g. if you need 3,000 RPM from a 25 KV motor then your pack voltage needs to be 3,000 / 25 = 120 V. The exact number of cells in series you need depends on the cell design, but 3.8 V for Li-ion and 3.2 V for LiFePO4 is a reasonable guess.

=== Maximum current (A) ===
'''How quickly do you want to accelerate?''' Your motor's maximum power will be specified in kW. To estimate your maximum current draw, divide the peak power by the battery voltage. e.g. a 30 kW motor with a 120 V battery pack will pull 30,000 / 120 = 250 A. The higher the current rating of the cells, the heavier they will be for a given capacity. Ideally, you want "enough" current capacity for full throttle acceleration, but no more. You can put cells in parallel to double the current rating of your pack (which of course will half the voltage).

=== Mass (kg) ===
'''Can your vehicle carry the weight?''' You'll need to keep the kerb weight within the original design limits. For a car, this could be a few hundred kg. For a motorcycle, likely less than 100 kg. This is a huge variable - and each new generation of battery tech seems to be a little lighter. For older EV or hybrid batteries, you can reckon on approximately 10 kg/kWh. Nissan Leaf batteries are relatively light (7.5 kg/kWh). With the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 5-6 kg/kWh.

=== Volume (L) ===
'''Will it fit?''' Batteries are bulky. They are getting smaller, but finding enough space my be your biggest challenge. You could be looking at over 5 L/kWh for older EV or hybrid batteries. For the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 3 kg/kWh.

There is much, much more to battery design than this (e.g. maximum charge rate, terminations, cooling, clamping), but the above should help work out which options will or won't work for your project...

== Cell chemistry ==

=== Lithium Iron Phosphate (LiFePO4) ===
Lithium Iron Phosphate (also known as LFP, or LiFePO4) batteries offer a good compromise between safety, energy density and ease of use for DIY conversions. They are available in a number of formats, commonly pouch cells, prismatic cells and cylindrical cells.

==== LiFePO4 pouch cells ====
The majority of this content is drawn from this thread: [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761&start=900 https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761] discussing the use of the A123 20Ah pouch cell. However, many of the general points apply equally to other similar pouch cells.

===== General build requirements =====
Pouch cells are vulnerable to damage from debris, and must be held in compression (see the datasheet for your battery, but 10-12 psi is recommended for the A123 pouch cells as a guide). A rigid container capable of preventing damage and providing compression is therefore required. Be aware the cells expand and contract in use, so allowance for this must be included in the structure of the case.

The pouch cells should be separated to prevent abrasion between cells, and also to avoid the development of hot spots. Prebuilt modules from A123 systems had thin foam sheets or heatsinks between each cell. Be sure to avoid any debris that could rub on the pouch surface, particularly if using recycled cells.

Mylar, '[https://www.americanmicroinc.com/fish-paper/ Fish paper]' or a [https://www.rogerscorp.com/elastomeric-material-solutions/poron-industrial-polyurethanes compliant foam] may be appropriate materials to serve this purpose. This material should not be flammable. If the material is heat insulating, it is important to address thermal management.

===== Compression =====
Compression is required to prevent premature failure of the cell. Without compression electrolyte will become unevenly distributed, causing current gradients in the cell and uneven heating. Local temperatures can become high enough to form gas formation leading to cells 'puffing up' even when the pack is otherwise held within temperature and voltage constraints. This will be exacerbated in packs with otherwise poor thermal management. Compression forces gas generated to the margins of the cell, outside of the cell stack, minimising its effect cell performance. Gas in the middle cells will create a dead space which does not store or release energy.

There is ~1% expansion through a discharge cycle. As the cell ages, the nominal cell thickness can grow by 3-5%. For A123 cells the ideal pressure is between 4 and 18psi with the ideal pressure being ~12psi. Maintaining 12psi can increase the life by 500 cycles over that of 4 or 18psi

There is some suggestion that in uses where 1C is never exceeded compression ''may'' not be required.

Highly rigid endplates with a mechanism to allow for a limited degree of expansion (e.g. steel bands) are considered an effective solution to this challenge.

It should be noted that compression is a challenge specific to pouch cells. Cylindrical cells are designed to maintain their own compression within the cell's electrode stack by their design.

This thread provides more information and experimentation relating to pack compression: <nowiki>https://endless-sphere.com/forums/viewtopic.php?f=14&t=52244</nowiki>

===== Pouch Cell Pack Design Examples =====
<nowiki>*</nowiki>placeholder*

===== Notes regarding recycled pouch cells =====
Pouch cells are somewhat fragile, and breaching the insulation is not difficult, especially in a cells removed from existing packs and repurposed. If the pouch has had their poly-layers compromised you may see a number of faults:
* Black spots around the perimeter of the cell indicate electrolyte leakage
* Voltage on the outside of the bag. Note that microvoltage between the pouch and the electrode is normal (and due to a capacitive effect).
While the majority of these cells should no longer be in the market, a significant number of faulty cells made it back into the 'greymarket' in around 2013. These cells had misaligned tabs which can also lead to isolation failures between the tab and the pack. These cells should be avoided, particularly in high demand applications.

===== Situations likely to cause pouch cell failure =====
''Taken directly from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''
# '''Overcharge'''. Any extended time above 3.8 Volts will generate enough heat and electrochemical activity to puff a cell, especially one that is improperly compressed.
# '''Overdischarge followed by charge'''. Any A123 cell that has been pulled low enough to come to rest at <300 mV should be immediately scrapped. The published number for that is 500 mV, but the real figure is closer to 300, so that's a "safety buffer" if you will. Below this Voltage, the Cu electrodes start to dissolve into the electrolyte. When charge is applied, the Cu forms dendrites that puncture the separator layer, forming an internal short in the cell. This can puff a cell in a hurry---the more charge current on tap, the worse it's prone to be.
# '''Driving a cell negative'''. I've neglected to mention this before, but it is a possibility. I don't know much about the specific mechanism at this time.
# '''Malfunctioning or misinformed electronics'''. This is the most common cause of all of the above in my experience. At this stage of the game, it is critical for YOU to understand how your BMS functions on at least a cursory level. Choose your BMS very carefully and periodically verify that it is operating properly. They're not all created equal. Make sure V sense lines are securely connected and free of corrosion. Just because your BMS says there was never a problem doesn't necessarily make it so. Avoid harnesses or ribbon cables between multiple modules if possible--they are problematic wherever they are used in any mobile electronics.
# '''Exposure to or generation of sufficient heat'''. I don't know exactly at what temperature gas formation begins in the electrolyte, but we spec a max storage temp of 80 (or 85?) degrees C and I suspect this is the reason. The hotter, the puffier--to a point. This is why soldering tabs poses a real hazard to cell health. If you feel you must solder, sink or blow the heat away from the body of the cell. Use a big iron that can make sufficient local heat quickly, before the whole mass of the cell gets hot. You might even get the cell warm enough to melt separator if not careful.
# '''No compression, not enough compression, improperly distributed compression'''. This is a pack/module design issue. Apply 10, maybe 15 psi to your cell stack end to end and then band snugly and evenly. Use hard endplates of some sort--never wrap cells directly or allow their shape to become distorted. Protect all areas of the pouch from impact damage. This obviously does not apply to cylindrical cells.

==== LiFePO4 prismatic cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cylindrical cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cell ageing ====
''Derived (barely paraphrased) from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''

Capacity loss is caused by the lithium that was available for storage becoming permanently plated on the cathode. Being unable to move within the cell it is no longer available to store energy. The impact of this plating is greater than the amount of lithium 'lost' to plating because not only is the lithium no longer available, it is also preventing access to that part of the cathode meaning Li that can still move has to take a longer path to reach the cathode. Lithium plating is one cause of increased cell resistance (there are others), a sign of worsening cell health.

There is no linear relationship between actual capacity loss and impedance rise. However some cell defects will also increase impedance.

Increasing cell resistance may cause a number of symptoms which may be confused with [https://earthshipbiotecture.com/a-lithium-ion-battery-primer/ High Self Discharge.]
# Elevated Peukert Losses. As more energy per amount of current through the cell is lost as heat, the cells useable capacity decreases. So the apparent capacity loss is higher than the actual capacity loss of cycleable lithium. When used in low current applications (e.g. solar energy storage) the actual and apparent decrease in capacity will be small. In high current draw applications (like EV traction packs), the Peukert loss increases proportionally, so the apparent capacity loss increases much faster than the actual capacity loss.
# Greater voltage excursion under the same load. Due to increased cell resistancethe voltage will sag further under the same load than a cell in optimal condition. The inverse is also true, the voltage will be higher for the same amount of charging current applied. The cell will then rebound to a voltage further from the loaded and charging voltages. This, obviously, can look like high self discharge but is a different phenomenon.
# Absolute maximum current decrease.
Elevated impedance causes a more complex constellation of symptoms, some of which may be easy to confuse with High Self Discharge (HSD). Ohm's law (E=I/R) holds the key to understanding here.

'''1) Elevated Peukert losses.''' Because more energy per unit of current through the cell is lost as heat, less of the cell's capacity is actually USABLE. Thus, apparent capacity loss can be significantly greater than actual capacity loss caused by the loss of cycleable Li alone. In low current applications, the two numbers will be close together. In high current applications, Peukert losses increase in proportion, so apparent loss of capacity breaks further and further away from actual capacity loss as current increases.

'''2) Greater voltage excursion under the same load.''' Elevated resistance across the cell means that voltage will sag more under the same load than it did when the cell was healthier. Conversely, voltage will rise higher with the same amount of applied charge current than it did when it was healthier. At the same time, rebound/settling voltages will be further away from loaded/charging voltages. In other words, the cell will rebound to a voltage further away from loaded voltage, all else being equal. Similarly, voltage will settle farther from the charge voltage with the same charge applied. This can give the illusion of elevated self-discharge, but the phenomenon is actually not the same thing. Again, the greater the charge and load currents, the greater the effect becomes.

'''3) Absolute max current decreases.''' Because the cell's series resistance is elevated, the maximum possible current through the cell is decreased.

Just to confuse things further, there can be many factors that lead to impedance rise. Some are related to Li plating, others are not.

=== Lithium-ion ===
Lithium-ion (Li-ion) batteries have a greater energy density than Lithium Iron Phosphate batteries, but have more challenging needs to use safely. The ideal operating range of Li-ion batteries is between +15 and +45°C. The upper limit of temperature is particularly important as Li-ion batteries experience thermal runaway - an unstoppable chain reaction that can occur in milliseconds releasing the stored energy in the cell. This can produce temperatures of 400°C and a fire that is extremely difficult to put out. Thermal runaway can start as low as 60°C and becomes much more likely at 100°C

Risk factors for thermal runaway:
* Short Circuits - either internally or externally
* Overcharging
* Excessive current draw or when charging

==== Li-ion pouch cells ====
[https://kokam.com/cell Kokam] produce high-performance Li-ion pouch cells. These combine relative ease of use and pack construction with performance close to cylindrical cells.

==== Li-ion 18650 and other cylindrical cells ====
Cylindrical cells are favoured by Tesla, and are probably the main reason why their cars achieve such excellent performance. They are light, compact, powerful and expensive. Unfortunately, cylindrical cells are staggeringly difficult (and dangerous) to use in DIY conversions. There are two good reasons for this: thermal management and cell configuration.

As stated above, Li-ion cells are prone to thermal runaway. So you need perfect battery and thermal management to ensure that no cell ever exceeds the critical voltage or temperature. If this happens, a cell can short-circuit internally, releasing a lot of energy - potentially explosively. Furthermore, the individual cells are small, so need to be arranged in parallel. In the case of the Tesla Model S 85kW pack, there are 74 cells in parallel. Imagine if one of those cells fails and becomes short circuited internally. You now have 73 very high power cells all feeding in to that short circuit...

In fact, you don't have to imagine: you can watch this famous video instead (courtesy of Rich Rebuilds).

<youtube>WdDi1haA71Q</youtube>

== OEM modules ==
Using an OEM module means a lot of the difficulties associated with battery design are taken care of e.g. cooling, clamping, etc. Here is a list of OEM modules.
{| class="wikitable sortable mw-collapsible"
|+
!Manufacturer
!Type
!Capacity (kWh)
!Weight (kg)
!w (mm)
!d (mm)
!h (mm)
!Gravity (kg/kWh)
!Volume (L/kWh)
!Voltage (V)
!Current (cont A)
!Current (peak A)
!Cell arrangement
!Cell type
!Chemistry
|-
|Tesla
|Model S 85kWh
|5.3
|26
|690
|315
|80
|4.9
|3.3
|22.8
|500
|750
|74p6s
|18650
|Li-ion
|-
|Tesla
|Model S 100kWh
|6.4
|28
|680
|315
|80
|4.4
|2.7
|22.8
|
|870
|86p6s
|18650
|Li-ion
|-
|Chevrolet
|Volt 2012
|4
|38
|470
|180
|280
|9.5
|5.9
|88
|140
|210
|24s
|Pouch
|Li-ion
|-
|BMW
|i3 60Ah
|2
|13
|368
|178
|102
|6.5
|3.3
|28.8
|210
|350
|8s2p
|Prismatic
|Li-ion
|-
|BMW
|i3 94Ah
|4.15
|28
|410
|310
|150
|6.7
|4.6
|45.6
|
|409
|12s
|Prismatic
|Li-ion
|-
|BMW
|i3 120Ah
|5.3
|28
|410
|310
|150
|5.3
|3.6
|45.6
|
|360
|12s
|Prismatic
|Li-ion
|-
|Mitsubishi
|Outlander
|2.4
|26
|646
|184
|130
|10.8
|6.4
|60
|
|240
|16s
|
|Li-ion
|-
|Nissan
|Leaf 24kWh
|0.5
|3.65
|300
|222
|34
|7.3
|4.5
|7.4
|130
|
|2s2p
|
|Li-ion
|-
|Nissan
|Leaf 40kWh
|1.6
|8.7
|300
|222
|68
|5.4
|2.8
|14.6
|
|
|4s2p
|
|Li-ion
|-
|Volvo
|XC90 T8
|2.01
|12.1
|300
|180
|150
|6.0
|4.0
|59.2
|170
|340
|16s
|
|Li-ion
|}

Batteries

2020-11-30T21:39:31Z

Clanger9:

== Introduction ==
There are a wide variety of battery chemistries available for use as the main traction battery of an EV. To use each chemistry safely, and to ensure an adequate service life from the battery pack it is important to understand the requirements for the chemistry you are using. Failure to do so may lead to premature or catastrophic failure of the pack.

Good pack design will allow for a nominal amount of abuse. People make mistakes and the pack should allow a margin for safety - and for longevity!

== Battery pack specification ==
When deciding on your battery pack, here are some basic parameters to consider:

=== Capacity (kWh) ===
'''How far do you want to go?''' A standard car conversion will need around 1kWh for 3 miles of range. For a middleweight motorcycle, 1kWh should give around 9 miles. ''Your mileage may vary'', as they say.

=== Voltage (V) ===
'''How fast do you want to go?''' The pack voltage defines the maximum speed your motor can spin. Motors are usually specified with "KV" - or RPM-per-volt. Check the KV of your motor and how fast it needs to spin to get your desired top speed. e.g. if you need 3,000 RPM from a 25 KV motor then your pack voltage needs to be 3,000 / 25 = 120 V. The exact number of cells in series you need depends on the cell design, but 3.8 V for Li-ion and 3.2 V for LiFePO4 is a reasonable guess.

=== Maximum current (A) ===
'''How quickly do you want to accelerate?''' Your motor's maximum power will be specified in kW. To estimate your maximum current draw, divide the peak power by the battery voltage. e.g. a 30 kW motor with a 120 V battery pack will pull 30,000 / 120 = 250 A. The higher the current rating of the cells, the heavier they will be for a given capacity. Ideally, you want "enough" current capacity for full throttle acceleration, but no more. You can put cells in parallel to double the current rating of your pack (which of course will half the voltage).

=== Mass (kg) ===
'''Can your vehicle carry the weight?''' You'll need to keep the kerb weight within the original design limits. For a car, this could be a few hundred kg. For a motorcycle, likely less than 100 kg. This is a huge variable - and each new generation of battery tech seems to be a little lighter. For older EV or hybrid batteries, you can reckon on approximately 10 kg/kWh. Nissan Leaf batteries are relatively light (7.5 kg/kWh). With the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 5-6 kg/kWh.

=== Volume (L) ===
'''Will it fit?''' Batteries are bulky. They are getting smaller, but finding enough space my be your biggest challenge. You could be looking at over 5 L/kWh for older EV or hybrid batteries. For the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 3 kg/kWh.

There is much, much more to battery design than this (e.g. maximum charge rate, terminations, cooling, clamping), but the above should help work out which options will or won't work for your project...

== Cell chemistry ==

=== Lithium Iron Phosphate (LiFePO4) ===
Lithium Iron Phosphate (also known as LFP, or LiFePO4) batteries offer a good compromise between safety, energy density and ease of use for DIY conversions. They are available in a number of formats, commonly pouch cells, prismatic cells and cylindrical cells.

==== LiFePO4 pouch cells ====
The majority of this content is drawn from this thread: [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761&start=900 https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761] discussing the use of the A123 20Ah pouch cell. However, many of the general points apply equally to other similar pouch cells.

===== General build requirements =====
Pouch cells are vulnerable to damage from debris, and must be held in compression (see the datasheet for your battery, but 10-12 psi is recommended for the A123 pouch cells as a guide). A rigid container capable of preventing damage and providing compression is therefore required. Be aware the cells expand and contract in use, so allowance for this must be included in the structure of the case.

The pouch cells should be separated to prevent abrasion between cells, and also to avoid the development of hot spots. Prebuilt modules from A123 systems had thin foam sheets or heatsinks between each cell. Be sure to avoid any debris that could rub on the pouch surface, particularly if using recycled cells.

Mylar, '[https://www.americanmicroinc.com/fish-paper/ Fish paper]' or a [https://www.rogerscorp.com/elastomeric-material-solutions/poron-industrial-polyurethanes compliant foam] may be appropriate materials to serve this purpose. This material should not be flammable. If the material is heat insulating, it is important to address thermal management.

===== Compression =====
Compression is required to prevent premature failure of the cell. Without compression electrolyte will become unevenly distributed, causing current gradients in the cell and uneven heating. Local temperatures can become high enough to form gas formation leading to cells 'puffing up' even when the pack is otherwise held within temperature and voltage constraints. This will be exacerbated in packs with otherwise poor thermal management. Compression forces gas generated to the margins of the cell, outside of the cell stack, minimising its effect cell performance. Gas in the middle cells will create a dead space which does not store or release energy.

There is ~1% expansion through a discharge cycle. As the cell ages, the nominal cell thickness can grow by 3-5%. For A123 cells the ideal pressure is between 4 and 18psi with the ideal pressure being ~12psi. Maintaining 12psi can increase the life by 500 cycles over that of 4 or 18psi

There is some suggestion that in uses where 1C is never exceeded compression ''may'' not be required.

Highly rigid endplates with a mechanism to allow for a limited degree of expansion (e.g. steel bands) are considered an effective solution to this challenge.

It should be noted that compression is a challenge specific to pouch cells. Cylindrical cells are designed to maintain their own compression within the cell's electrode stack by their design.

This thread provides more information and experimentation relating to pack compression: <nowiki>https://endless-sphere.com/forums/viewtopic.php?f=14&t=52244</nowiki>

===== Pouch Cell Pack Design Examples =====
<nowiki>*</nowiki>placeholder*

===== Notes regarding recycled pouch cells =====
Pouch cells are somewhat fragile, and breaching the insulation is not difficult, especially in a cells removed from existing packs and repurposed. If the pouch has had their poly-layers compromised you may see a number of faults:
* Black spots around the perimeter of the cell indicate electrolyte leakage
* Voltage on the outside of the bag. Note that microvoltage between the pouch and the electrode is normal (and due to a capacitive effect).
While the majority of these cells should no longer be in the market, a significant number of faulty cells made it back into the 'greymarket' in around 2013. These cells had misaligned tabs which can also lead to isolation failures between the tab and the pack. These cells should be avoided, particularly in high demand applications.

===== Situations likely to cause pouch cell failure =====
''Taken directly from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''
# '''Overcharge'''. Any extended time above 3.8 Volts will generate enough heat and electrochemical activity to puff a cell, especially one that is improperly compressed.
# '''Overdischarge followed by charge'''. Any A123 cell that has been pulled low enough to come to rest at <300 mV should be immediately scrapped. The published number for that is 500 mV, but the real figure is closer to 300, so that's a "safety buffer" if you will. Below this Voltage, the Cu electrodes start to dissolve into the electrolyte. When charge is applied, the Cu forms dendrites that puncture the separator layer, forming an internal short in the cell. This can puff a cell in a hurry---the more charge current on tap, the worse it's prone to be.
# '''Driving a cell negative'''. I've neglected to mention this before, but it is a possibility. I don't know much about the specific mechanism at this time.
# '''Malfunctioning or misinformed electronics'''. This is the most common cause of all of the above in my experience. At this stage of the game, it is critical for YOU to understand how your BMS functions on at least a cursory level. Choose your BMS very carefully and periodically verify that it is operating properly. They're not all created equal. Make sure V sense lines are securely connected and free of corrosion. Just because your BMS says there was never a problem doesn't necessarily make it so. Avoid harnesses or ribbon cables between multiple modules if possible--they are problematic wherever they are used in any mobile electronics.
# '''Exposure to or generation of sufficient heat'''. I don't know exactly at what temperature gas formation begins in the electrolyte, but we spec a max storage temp of 80 (or 85?) degrees C and I suspect this is the reason. The hotter, the puffier--to a point. This is why soldering tabs poses a real hazard to cell health. If you feel you must solder, sink or blow the heat away from the body of the cell. Use a big iron that can make sufficient local heat quickly, before the whole mass of the cell gets hot. You might even get the cell warm enough to melt separator if not careful.
# '''No compression, not enough compression, improperly distributed compression'''. This is a pack/module design issue. Apply 10, maybe 15 psi to your cell stack end to end and then band snugly and evenly. Use hard endplates of some sort--never wrap cells directly or allow their shape to become distorted. Protect all areas of the pouch from impact damage. This obviously does not apply to cylindrical cells.

==== LiFePO4 prismatic cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cylindrical cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cell ageing ====
''Derived (barely paraphrased) from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''

Capacity loss is caused by the lithium that was available for storage becoming permanently plated on the cathode. Being unable to move within the cell it is no longer available to store energy. The impact of this plating is greater than the amount of lithium 'lost' to plating because not only is the lithium no longer available, it is also preventing access to that part of the cathode meaning Li that can still move has to take a longer path to reach the cathode. Lithium plating is one cause of increased cell resistance (there are others), a sign of worsening cell health.

There is no linear relationship between actual capacity loss and impedance rise. However some cell defects will also increase impedance.

Increasing cell resistance may cause a number of symptoms which may be confused with [https://earthshipbiotecture.com/a-lithium-ion-battery-primer/ High Self Discharge.]
# Elevated Peukert Losses. As more energy per amount of current through the cell is lost as heat, the cells useable capacity decreases. So the apparent capacity loss is higher than the actual capacity loss of cycleable lithium. When used in low current applications (e.g. solar energy storage) the actual and apparent decrease in capacity will be small. In high current draw applications (like EV traction packs), the Peukert loss increases proportionally, so the apparent capacity loss increases much faster than the actual capacity loss.
# Greater voltage excursion under the same load. Due to increased cell resistancethe voltage will sag further under the same load than a cell in optimal condition. The inverse is also true, the voltage will be higher for the same amount of charging current applied. The cell will then rebound to a voltage further from the loaded and charging voltages. This, obviously, can look like high self discharge but is a different phenomenon.
# Absolute maximum current decrease.
Elevated impedance causes a more complex constellation of symptoms, some of which may be easy to confuse with High Self Discharge (HSD). Ohm's law (E=I/R) holds the key to understanding here.

'''1) Elevated Peukert losses.''' Because more energy per unit of current through the cell is lost as heat, less of the cell's capacity is actually USABLE. Thus, apparent capacity loss can be significantly greater than actual capacity loss caused by the loss of cycleable Li alone. In low current applications, the two numbers will be close together. In high current applications, Peukert losses increase in proportion, so apparent loss of capacity breaks further and further away from actual capacity loss as current increases.

'''2) Greater voltage excursion under the same load.''' Elevated resistance across the cell means that voltage will sag more under the same load than it did when the cell was healthier. Conversely, voltage will rise higher with the same amount of applied charge current than it did when it was healthier. At the same time, rebound/settling voltages will be further away from loaded/charging voltages. In other words, the cell will rebound to a voltage further away from loaded voltage, all else being equal. Similarly, voltage will settle farther from the charge voltage with the same charge applied. This can give the illusion of elevated self-discharge, but the phenomenon is actually not the same thing. Again, the greater the charge and load currents, the greater the effect becomes.

'''3) Absolute max current decreases.''' Because the cell's series resistance is elevated, the maximum possible current through the cell is decreased.

Just to confuse things further, there can be many factors that lead to impedance rise. Some are related to Li plating, others are not.

=== Lithium-ion ===
Lithium-ion (Li-ion) batteries have a greater energy density than Lithium Iron Phosphate batteries, but have more challenging needs to use safely. The ideal operating range of Li-ion batteries is between +15 and +45°C. The upper limit of temperature is particularly important as Li-ion batteries experience thermal runaway - an unstoppable chain reaction that can occur in milliseconds releasing the stored energy in the cell. This can produce temperatures of 400°C and a fire that is extremely difficult to put out. Thermal runaway can start as low as 60°C and becomes much more likely at 100°C

Risk factors for thermal runaway:
* Short Circuits - either internally or externally
* Overcharging
* Excessive current draw or when charging

==== Li-ion pouch cells ====
[https://kokam.com/cell Kokam] produce high-performance Li-ion pouch cells. These combine relative ease of use and pack construction with performance close to cylindrical cells.

==== Li-ion 18650 and other cylindrical cells ====
Cylindrical cells are favoured by Tesla, and are probably the main reason why their cars achieve such excellent performance. They are light, compact, powerful and expensive. Unfortunately, cylindrical cells are staggeringly difficult (and dangerous) to use in DIY conversions. There are two good reasons for this: thermal management and cell configuration.

As stated above, Li-ion cells are prone to thermal runaway. So you need perfect battery and thermal management to ensure that no cell ever exceeds the critical voltage or temperature. If this happens, a cell can short-circuit internally, releasing a lot of energy - potentially explosively. Furthermore, the individual cells are small, so need to be arranged in parallel. In the case of the Tesla Model S, there are 74 cells in each parallel. Imagine if one of those cells fails and becomes short circuited internally. You now have 73 very high power cells in parallel feeding in to that short circuit...

In fact, you don't have to imagine: you can watch this famous video instead (courtesy of Rich Rebuilds).

<youtube>WdDi1haA71Q</youtube>

== OEM modules ==
Using an OEM module means a lot of the difficulties associated with battery design are taken care of e.g. cooling, clamping, etc. Here is a list of OEM modules.
{| class="wikitable sortable mw-collapsible"
|+
!Manufacturer
!Type
!Capacity (kWh)
!Weight (kg)
!w (mm)
!d (mm)
!h (mm)
!Gravity (kg/kWh)
!Volume (L/kWh)
!Voltage (V)
!Current (cont A)
!Current (peak A)
!Cell arrangement
!Cell type
!Chemistry
|-
|Tesla
|Model S 85kWh
|5.3
|26
|690
|315
|80
|4.9
|3.3
|22.8
|500
|750
|74p6s
|18650
|Li-ion
|-
|Tesla
|Model S 100kWh
|6.4
|28
|680
|315
|80
|4.4
|2.7
|22.8
|
|870
|86p6s
|18650
|Li-ion
|-
|Chevrolet
|Volt 2012
|4
|38
|470
|180
|280
|9.5
|5.9
|88
|140
|210
|24s
|Pouch
|Li-ion
|-
|BMW
|i3 60Ah
|2
|13
|368
|178
|102
|6.5
|3.3
|28.8
|210
|350
|8s2p
|Prismatic
|Li-ion
|-
|BMW
|i3 94Ah
|4.15
|28
|410
|310
|150
|6.7
|4.6
|45.6
|
|409
|12s
|Prismatic
|Li-ion
|-
|BMW
|i3 120Ah
|5.3
|28
|410
|310
|150
|5.3
|3.6
|45.6
|
|360
|12s
|Prismatic
|Li-ion
|-
|Mitsubishi
|Outlander
|2.4
|26
|646
|184
|130
|10.8
|6.4
|60
|
|240
|16s
|
|Li-ion
|-
|Nissan
|Leaf 24kWh
|0.5
|3.65
|300
|222
|34
|7.3
|4.5
|7.4
|130
|
|2s2p
|
|Li-ion
|-
|Nissan
|Leaf 40kWh
|1.6
|8.7
|300
|222
|68
|5.4
|2.8
|14.6
|
|
|4s2p
|
|Li-ion
|-
|Volvo
|XC90 T8
|2.01
|12.1
|300
|180
|150
|6.0
|4.0
|59.2
|170
|340
|16s
|
|Li-ion
|}

Batteries

2020-11-30T21:22:52Z

Clanger9: /* OEM modules */

== Introduction ==
There are a wide variety of battery chemistries available for use as the main traction battery of an EV. To use each chemistry safely, and to ensure an adequate service life from the battery pack it is important to understand the requirements for the chemistry you are using. Failure to do so may lead to premature or catastrophic failure of the pack.

Good pack design will allow for a nominal amount of abuse. People make mistakes and the pack should allow a margin for safety - and for longevity!

== Battery pack specification ==
When deciding on your battery pack, here are some basic parameters to consider:

=== Capacity (kWh) ===
'''How far do you want to go?''' A standard car conversion will need around 1kWh for 3 miles of range. For a middleweight motorcycle, 1kWh should give around 9 miles. ''Your mileage may vary'', as they say.

=== Voltage (V) ===
'''How fast do you want to go?''' The pack voltage defines the maximum speed your motor can spin. Motors are usually specified with "KV" - or RPM-per-volt. Check the KV of your motor and how fast it needs to spin to get your desired top speed. e.g. if you need 3,000 RPM from a 25 KV motor then your pack voltage needs to be 3,000 / 25 = 120 V. The exact number of cells in series you need depends on the cell design, but 3.8 V for Li-ion and 3.2 V for LiFePO4 is a reasonable guess.

=== Maximum current (A) ===
'''How quickly do you want to accelerate?''' Your motor's maximum power will be specified in kW. To estimate your maximum current draw, divide the peak power by the battery voltage. e.g. a 30 kW motor with a 120 V battery pack will pull 30,000 / 120 = 250 A. The higher the current rating of the cells, the heavier they will be for a given capacity. Ideally, you want "enough" current capacity for full throttle acceleration, but no more. You can put cells in parallel to double the current rating of your pack (which of course will half the voltage).

=== Mass (kg) ===
'''Can your vehicle carry the weight?''' You'll need to keep the kerb weight within the original design limits. For a car, this could be a few hundred kg. For a motorcycle, likely less than 100 kg. This is a huge variable - and each new generation of battery tech seems to be a little lighter. For older EV or hybrid batteries, you can reckon on approximately 10 kg/kWh. Nissan Leaf batteries are relatively light (7.5 kg/kWh). With the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 5-6 kg/kWh.

=== Volume (L) ===
'''Will it fit?''' Batteries are bulky. They are getting smaller, but finding enough space my be your biggest challenge. You could be looking at over 5 L/kWh for older EV or hybrid batteries. For the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 3 kg/kWh.

There is much, much more to battery design than this (e.g. maximum charge rate, terminations, cooling, clamping), but the above should help work out which options will or won't work for your project...

== Cell chemistry ==

=== Lithium Iron Phosphate (LiFePO4) ===
Lithium Iron Phosphate (also known as LFP, or LiFePO4) batteries offer a good compromise between safety, energy density and ease of use for DIY conversions. They are available in a number of formats, commonly pouch cells, prismatic cells and cylindrical cells.

==== LiFePO4 pouch cells ====
The majority of this content is drawn from this thread: [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761&start=900 https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761] discussing the use of the A123 20Ah pouch cell. However, many of the general points apply equally to other similar pouch cells.

===== General build requirements =====
Pouch cells are vulnerable to damage from debris, and must be held in compression (see the datasheet for your battery, but 10-12 psi is recommended for the A123 pouch cells as a guide). A rigid container capable of preventing damage and providing compression is therefore required. Be aware the cells expand and contract in use, so allowance for this must be included in the structure of the case.

The pouch cells should be separated to prevent abrasion between cells, and also to avoid the development of hot spots. Prebuilt modules from A123 systems had thin foam sheets or heatsinks between each cell. Be sure to avoid any debris that could rub on the pouch surface, particularly if using recycled cells.

Mylar, '[https://www.americanmicroinc.com/fish-paper/ Fish paper]' or a [https://www.rogerscorp.com/elastomeric-material-solutions/poron-industrial-polyurethanes compliant foam] may be appropriate materials to serve this purpose. This material should not be flammable. If the material is heat insulating, it is important to address thermal management.

===== Compression =====
Compression is required to prevent premature failure of the cell. Without compression electrolyte will become unevenly distributed, causing current gradients in the cell and uneven heating. Local temperatures can become high enough to form gas formation leading to cells 'puffing up' even when the pack is otherwise held within temperature and voltage constraints. This will be exacerbated in packs with otherwise poor thermal management. Compression forces gas generated to the margins of the cell, outside of the cell stack, minimising its effect cell performance. Gas in the middle cells will create a dead space which does not store or release energy.

There is ~1% expansion through a discharge cycle. As the cell ages, the nominal cell thickness can grow by 3-5%. For A123 cells the ideal pressure is between 4 and 18psi with the ideal pressure being ~12psi. Maintaining 12psi can increase the life by 500 cycles over that of 4 or 18psi

There is some suggestion that in uses where 1C is never exceeded compression ''may'' not be required.

Highly rigid endplates with a mechanism to allow for a limited degree of expansion (e.g. steel bands) are considered an effective solution to this challenge.

It should be noted that compression is a challenge specific to pouch cells. Cylindrical cells are designed to maintain their own compression within the cell's electrode stack by their design.

This thread provides more information and experimentation relating to pack compression: <nowiki>https://endless-sphere.com/forums/viewtopic.php?f=14&t=52244</nowiki>

===== Pouch Cell Pack Design Examples =====
<nowiki>*</nowiki>placeholder*

===== Notes regarding recycled pouch cells =====
Pouch cells are somewhat fragile, and breaching the insulation is not difficult, especially in a cells removed from existing packs and repurposed. If the pouch has had their poly-layers compromised you may see a number of faults:
* Black spots around the perimeter of the cell indicate electrolyte leakage
* Voltage on the outside of the bag. Note that microvoltage between the pouch and the electrode is normal (and due to a capacitive effect).
While the majority of these cells should no longer be in the market, a significant number of faulty cells made it back into the 'greymarket' in around 2013. These cells had misaligned tabs which can also lead to isolation failures between the tab and the pack. These cells should be avoided, particularly in high demand applications.

===== Situations likely to cause pouch cell failure =====
''Taken directly from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''
# '''Overcharge'''. Any extended time above 3.8 Volts will generate enough heat and electrochemical activity to puff a cell, especially one that is improperly compressed.
# '''Overdischarge followed by charge'''. Any A123 cell that has been pulled low enough to come to rest at <300 mV should be immediately scrapped. The published number for that is 500 mV, but the real figure is closer to 300, so that's a "safety buffer" if you will. Below this Voltage, the Cu electrodes start to dissolve into the electrolyte. When charge is applied, the Cu forms dendrites that puncture the separator layer, forming an internal short in the cell. This can puff a cell in a hurry---the more charge current on tap, the worse it's prone to be.
# '''Driving a cell negative'''. I've neglected to mention this before, but it is a possibility. I don't know much about the specific mechanism at this time.
# '''Malfunctioning or misinformed electronics'''. This is the most common cause of all of the above in my experience. At this stage of the game, it is critical for YOU to understand how your BMS functions on at least a cursory level. Choose your BMS very carefully and periodically verify that it is operating properly. They're not all created equal. Make sure V sense lines are securely connected and free of corrosion. Just because your BMS says there was never a problem doesn't necessarily make it so. Avoid harnesses or ribbon cables between multiple modules if possible--they are problematic wherever they are used in any mobile electronics.
# '''Exposure to or generation of sufficient heat'''. I don't know exactly at what temperature gas formation begins in the electrolyte, but we spec a max storage temp of 80 (or 85?) degrees C and I suspect this is the reason. The hotter, the puffier--to a point. This is why soldering tabs poses a real hazard to cell health. If you feel you must solder, sink or blow the heat away from the body of the cell. Use a big iron that can make sufficient local heat quickly, before the whole mass of the cell gets hot. You might even get the cell warm enough to melt separator if not careful.
# '''No compression, not enough compression, improperly distributed compression'''. This is a pack/module design issue. Apply 10, maybe 15 psi to your cell stack end to end and then band snugly and evenly. Use hard endplates of some sort--never wrap cells directly or allow their shape to become distorted. Protect all areas of the pouch from impact damage. This obviously does not apply to cylindrical cells.

==== LiFePO4 prismatic cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cylindrical cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cell ageing ====
''Derived (barely paraphrased) from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''

Capacity loss is caused by the lithium that was available for storage becoming permanently plated on the cathode. Being unable to move within the cell it is no longer available to store energy. The impact of this plating is greater than the amount of lithium 'lost' to plating because not only is the lithium no longer available, it is also preventing access to that part of the cathode meaning Li that can still move has to take a longer path to reach the cathode. Lithium plating is one cause of increased cell resistance (there are others), a sign of worsening cell health.

There is no linear relationship between actual capacity loss and impedance rise. However some cell defects will also increase impedance.

Increasing cell resistance may cause a number of symptoms which may be confused with [https://earthshipbiotecture.com/a-lithium-ion-battery-primer/ High Self Discharge.]
# Elevated Peukert Losses. As more energy per amount of current through the cell is lost as heat, the cells useable capacity decreases. So the apparent capacity loss is higher than the actual capacity loss of cycleable lithium. When used in low current applications (e.g. solar energy storage) the actual and apparent decrease in capacity will be small. In high current draw applications (like EV traction packs), the Peukert loss increases proportionally, so the apparent capacity loss increases much faster than the actual capacity loss.
# Greater voltage excursion under the same load. Due to increased cell resistancethe voltage will sag further under the same load than a cell in optimal condition. The inverse is also true, the voltage will be higher for the same amount of charging current applied. The cell will then rebound to a voltage further from the loaded and charging voltages. This, obviously, can look like high self discharge but is a different phenomenon.
# Absolute maximum current decrease.
Elevated impedance causes a more complex constellation of symptoms, some of which may be easy to confuse with High Self Discharge (HSD). Ohm's law (E=I/R) holds the key to understanding here.

'''1) Elevated Peukert losses.''' Because more energy per unit of current through the cell is lost as heat, less of the cell's capacity is actually USABLE. Thus, apparent capacity loss can be significantly greater than actual capacity loss caused by the loss of cycleable Li alone. In low current applications, the two numbers will be close together. In high current applications, Peukert losses increase in proportion, so apparent loss of capacity breaks further and further away from actual capacity loss as current increases.

'''2) Greater voltage excursion under the same load.''' Elevated resistance across the cell means that voltage will sag more under the same load than it did when the cell was healthier. Conversely, voltage will rise higher with the same amount of applied charge current than it did when it was healthier. At the same time, rebound/settling voltages will be further away from loaded/charging voltages. In other words, the cell will rebound to a voltage further away from loaded voltage, all else being equal. Similarly, voltage will settle farther from the charge voltage with the same charge applied. This can give the illusion of elevated self-discharge, but the phenomenon is actually not the same thing. Again, the greater the charge and load currents, the greater the effect becomes.

'''3) Absolute max current decreases.''' Because the cell's series resistance is elevated, the maximum possible current through the cell is decreased.

Just to confuse things further, there can be many factors that lead to impedance rise. Some are related to Li plating, others are not.

=== Lithium-ion ===
Lithium-ion (Li-ion) batteries have a greater energy density than Lithium Iron Phosphate batteries, but have more challenging needs to use safely. The ideal operating range of Li-ion batteries is between +15 and +45°C. The upper limit of temperature is particularly important as Li-ion batteries experience thermal runaway - an unstoppable chain reaction that can occur in milliseconds releasing the stored energy in the cell. This can produce temperatures of 400°C and a fire that is extremely difficult to put out. Thermal runaway can start as low as 60°C and becomes much more likely at 100°C

Risk factors for thermal runaway:
* Short Circuits - either internally or externally
* Overcharging
* Excessive current draw or when charging

==== Li-ion pouch cells ====
[https://kokam.com/cell Kokam] produce high-performance Li-ion pouch cells. These combine relative ease of use and pack construction with performance close to cylindrical cells.

==== Li-ion 18650 and other cylindrical cells ====
Cylindrical cells are favoured by Tesla, and are probably the main reason why their cars achieve such excellent performance. They are light, compact, powerful and expensive. Unfortunately, cylindrical cells are staggeringly difficult (and dangerous) to use in DIY conversions. There are two good reasons for this: thermal management and cell configuration.

As stated above, Li-ion cells are prone to thermal runaway. So you need perfect thermal management to ensure that no cell ever exceeds the critical temperature. If this happens, the cell will short-circuit internally, releasing a lot of energy - potentially explosively. Furthermore, the individual cells are small, so need to be arranged in parallel. In the case of the Tesla Model S, there are 74 cells in each parallel. Imagine if one of those cells fails and becomes short circuited internally. You now have 73 very high power cells in parallel feeding in to that short circuit. In fact, you don't have to imagine: you can watch this famous video instead (courtesy of Rich Rebuilds).

<youtube>WdDi1haA71Q</youtube>

== OEM modules ==
Using an OEM module means a lot of the difficulties associated with battery design are taken care of e.g. cooling, clamping, etc. Here is a list of OEM modules.
{| class="wikitable sortable mw-collapsible"
|+
!Manufacturer
!Type
!Capacity (kWh)
!Weight (kg)
!w (mm)
!d (mm)
!h (mm)
!Gravity (kg/kWh)
!Volume (L/kWh)
!Voltage (V)
!Current (cont A)
!Current (peak A)
!Cell arrangement
!Cell type
!Chemistry
|-
|Tesla
|Model S 85kWh
|5.3
|26
|690
|315
|80
|4.9
|3.3
|22.8
|500
|750
|74p6s
|18650
|Li-ion
|-
|Tesla
|Model S 100kWh
|6.4
|28
|680
|315
|80
|4.4
|2.7
|22.8
|
|870
|86p6s
|18650
|Li-ion
|-
|Chevrolet
|Volt 2012
|4
|38
|470
|180
|280
|9.5
|5.9
|88
|140
|210
|24s
|Pouch
|Li-ion
|-
|BMW
|i3 60Ah
|2
|13
|368
|178
|102
|6.5
|3.3
|28.8
|210
|350
|8s2p
|Prismatic
|Li-ion
|-
|BMW
|i3 94Ah
|4.15
|28
|410
|310
|150
|6.7
|4.6
|45.6
|
|409
|12s
|Prismatic
|Li-ion
|-
|BMW
|i3 120Ah
|5.3
|28
|410
|310
|150
|5.3
|3.6
|45.6
|
|360
|12s
|Prismatic
|Li-ion
|-
|Mitsubishi
|Outlander
|2.4
|26
|646
|184
|130
|10.8
|6.4
|60
|
|240
|16s
|
|Li-ion
|-
|Nissan
|Leaf 24kWh
|0.5
|3.65
|300
|222
|34
|7.3
|4.5
|7.4
|130
|
|2s2p
|
|Li-ion
|-
|Nissan
|Leaf 40kWh
|1.6
|8.7
|300
|222
|68
|5.4
|2.8
|14.6
|
|
|4s2p
|
|Li-ion
|-
|Volvo
|XC90 T8
|2.01
|12.1
|300
|180
|150
|6.0
|4.0
|59.2
|170
|340
|16s
|
|Li-ion
|}

Batteries

2020-11-30T21:17:00Z

Clanger9: /* OEM modules */

== Introduction ==
There are a wide variety of battery chemistries available for use as the main traction battery of an EV. To use each chemistry safely, and to ensure an adequate service life from the battery pack it is important to understand the requirements for the chemistry you are using. Failure to do so may lead to premature or catastrophic failure of the pack.

Good pack design will allow for a nominal amount of abuse. People make mistakes and the pack should allow a margin for safety - and for longevity!

== Battery pack specification ==
When deciding on your battery pack, here are some basic parameters to consider:

=== Capacity (kWh) ===
'''How far do you want to go?''' A standard car conversion will need around 1kWh for 3 miles of range. For a middleweight motorcycle, 1kWh should give around 9 miles. ''Your mileage may vary'', as they say.

=== Voltage (V) ===
'''How fast do you want to go?''' The pack voltage defines the maximum speed your motor can spin. Motors are usually specified with "KV" - or RPM-per-volt. Check the KV of your motor and how fast it needs to spin to get your desired top speed. e.g. if you need 3,000 RPM from a 25 KV motor then your pack voltage needs to be 3,000 / 25 = 120 V. The exact number of cells in series you need depends on the cell design, but 3.8 V for Li-ion and 3.2 V for LiFePO4 is a reasonable guess.

=== Maximum current (A) ===
'''How quickly do you want to accelerate?''' Your motor's maximum power will be specified in kW. To estimate your maximum current draw, divide the peak power by the battery voltage. e.g. a 30 kW motor with a 120 V battery pack will pull 30,000 / 120 = 250 A. The higher the current rating of the cells, the heavier they will be for a given capacity. Ideally, you want "enough" current capacity for full throttle acceleration, but no more. You can put cells in parallel to double the current rating of your pack (which of course will half the voltage).

=== Mass (kg) ===
'''Can your vehicle carry the weight?''' You'll need to keep the kerb weight within the original design limits. For a car, this could be a few hundred kg. For a motorcycle, likely less than 100 kg. This is a huge variable - and each new generation of battery tech seems to be a little lighter. For older EV or hybrid batteries, you can reckon on approximately 10 kg/kWh. Nissan Leaf batteries are relatively light (7.5 kg/kWh). With the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 5-6 kg/kWh.

=== Volume (L) ===
'''Will it fit?''' Batteries are bulky. They are getting smaller, but finding enough space my be your biggest challenge. You could be looking at over 5 L/kWh for older EV or hybrid batteries. For the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 3 kg/kWh.

There is much, much more to battery design than this (e.g. maximum charge rate, terminations, cooling, clamping), but the above should help work out which options will or won't work for your project...

== Cell chemistry ==

=== Lithium Iron Phosphate (LiFePO4) ===
Lithium Iron Phosphate (also known as LFP, or LiFePO4) batteries offer a good compromise between safety, energy density and ease of use for DIY conversions. They are available in a number of formats, commonly pouch cells, prismatic cells and cylindrical cells.

==== LiFePO4 pouch cells ====
The majority of this content is drawn from this thread: [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761&start=900 https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761] discussing the use of the A123 20Ah pouch cell. However, many of the general points apply equally to other similar pouch cells.

===== General build requirements =====
Pouch cells are vulnerable to damage from debris, and must be held in compression (see the datasheet for your battery, but 10-12 psi is recommended for the A123 pouch cells as a guide). A rigid container capable of preventing damage and providing compression is therefore required. Be aware the cells expand and contract in use, so allowance for this must be included in the structure of the case.

The pouch cells should be separated to prevent abrasion between cells, and also to avoid the development of hot spots. Prebuilt modules from A123 systems had thin foam sheets or heatsinks between each cell. Be sure to avoid any debris that could rub on the pouch surface, particularly if using recycled cells.

Mylar, '[https://www.americanmicroinc.com/fish-paper/ Fish paper]' or a [https://www.rogerscorp.com/elastomeric-material-solutions/poron-industrial-polyurethanes compliant foam] may be appropriate materials to serve this purpose. This material should not be flammable. If the material is heat insulating, it is important to address thermal management.

===== Compression =====
Compression is required to prevent premature failure of the cell. Without compression electrolyte will become unevenly distributed, causing current gradients in the cell and uneven heating. Local temperatures can become high enough to form gas formation leading to cells 'puffing up' even when the pack is otherwise held within temperature and voltage constraints. This will be exacerbated in packs with otherwise poor thermal management. Compression forces gas generated to the margins of the cell, outside of the cell stack, minimising its effect cell performance. Gas in the middle cells will create a dead space which does not store or release energy.

There is ~1% expansion through a discharge cycle. As the cell ages, the nominal cell thickness can grow by 3-5%. For A123 cells the ideal pressure is between 4 and 18psi with the ideal pressure being ~12psi. Maintaining 12psi can increase the life by 500 cycles over that of 4 or 18psi

There is some suggestion that in uses where 1C is never exceeded compression ''may'' not be required.

Highly rigid endplates with a mechanism to allow for a limited degree of expansion (e.g. steel bands) are considered an effective solution to this challenge.

It should be noted that compression is a challenge specific to pouch cells. Cylindrical cells are designed to maintain their own compression within the cell's electrode stack by their design.

This thread provides more information and experimentation relating to pack compression: <nowiki>https://endless-sphere.com/forums/viewtopic.php?f=14&t=52244</nowiki>

===== Pouch Cell Pack Design Examples =====
<nowiki>*</nowiki>placeholder*

===== Notes regarding recycled pouch cells =====
Pouch cells are somewhat fragile, and breaching the insulation is not difficult, especially in a cells removed from existing packs and repurposed. If the pouch has had their poly-layers compromised you may see a number of faults:
* Black spots around the perimeter of the cell indicate electrolyte leakage
* Voltage on the outside of the bag. Note that microvoltage between the pouch and the electrode is normal (and due to a capacitive effect).
While the majority of these cells should no longer be in the market, a significant number of faulty cells made it back into the 'greymarket' in around 2013. These cells had misaligned tabs which can also lead to isolation failures between the tab and the pack. These cells should be avoided, particularly in high demand applications.

===== Situations likely to cause pouch cell failure =====
''Taken directly from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''
# '''Overcharge'''. Any extended time above 3.8 Volts will generate enough heat and electrochemical activity to puff a cell, especially one that is improperly compressed.
# '''Overdischarge followed by charge'''. Any A123 cell that has been pulled low enough to come to rest at <300 mV should be immediately scrapped. The published number for that is 500 mV, but the real figure is closer to 300, so that's a "safety buffer" if you will. Below this Voltage, the Cu electrodes start to dissolve into the electrolyte. When charge is applied, the Cu forms dendrites that puncture the separator layer, forming an internal short in the cell. This can puff a cell in a hurry---the more charge current on tap, the worse it's prone to be.
# '''Driving a cell negative'''. I've neglected to mention this before, but it is a possibility. I don't know much about the specific mechanism at this time.
# '''Malfunctioning or misinformed electronics'''. This is the most common cause of all of the above in my experience. At this stage of the game, it is critical for YOU to understand how your BMS functions on at least a cursory level. Choose your BMS very carefully and periodically verify that it is operating properly. They're not all created equal. Make sure V sense lines are securely connected and free of corrosion. Just because your BMS says there was never a problem doesn't necessarily make it so. Avoid harnesses or ribbon cables between multiple modules if possible--they are problematic wherever they are used in any mobile electronics.
# '''Exposure to or generation of sufficient heat'''. I don't know exactly at what temperature gas formation begins in the electrolyte, but we spec a max storage temp of 80 (or 85?) degrees C and I suspect this is the reason. The hotter, the puffier--to a point. This is why soldering tabs poses a real hazard to cell health. If you feel you must solder, sink or blow the heat away from the body of the cell. Use a big iron that can make sufficient local heat quickly, before the whole mass of the cell gets hot. You might even get the cell warm enough to melt separator if not careful.
# '''No compression, not enough compression, improperly distributed compression'''. This is a pack/module design issue. Apply 10, maybe 15 psi to your cell stack end to end and then band snugly and evenly. Use hard endplates of some sort--never wrap cells directly or allow their shape to become distorted. Protect all areas of the pouch from impact damage. This obviously does not apply to cylindrical cells.

==== LiFePO4 prismatic cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cylindrical cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cell ageing ====
''Derived (barely paraphrased) from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''

Capacity loss is caused by the lithium that was available for storage becoming permanently plated on the cathode. Being unable to move within the cell it is no longer available to store energy. The impact of this plating is greater than the amount of lithium 'lost' to plating because not only is the lithium no longer available, it is also preventing access to that part of the cathode meaning Li that can still move has to take a longer path to reach the cathode. Lithium plating is one cause of increased cell resistance (there are others), a sign of worsening cell health.

There is no linear relationship between actual capacity loss and impedance rise. However some cell defects will also increase impedance.

Increasing cell resistance may cause a number of symptoms which may be confused with [https://earthshipbiotecture.com/a-lithium-ion-battery-primer/ High Self Discharge.]
# Elevated Peukert Losses. As more energy per amount of current through the cell is lost as heat, the cells useable capacity decreases. So the apparent capacity loss is higher than the actual capacity loss of cycleable lithium. When used in low current applications (e.g. solar energy storage) the actual and apparent decrease in capacity will be small. In high current draw applications (like EV traction packs), the Peukert loss increases proportionally, so the apparent capacity loss increases much faster than the actual capacity loss.
# Greater voltage excursion under the same load. Due to increased cell resistancethe voltage will sag further under the same load than a cell in optimal condition. The inverse is also true, the voltage will be higher for the same amount of charging current applied. The cell will then rebound to a voltage further from the loaded and charging voltages. This, obviously, can look like high self discharge but is a different phenomenon.
# Absolute maximum current decrease.
Elevated impedance causes a more complex constellation of symptoms, some of which may be easy to confuse with High Self Discharge (HSD). Ohm's law (E=I/R) holds the key to understanding here.

'''1) Elevated Peukert losses.''' Because more energy per unit of current through the cell is lost as heat, less of the cell's capacity is actually USABLE. Thus, apparent capacity loss can be significantly greater than actual capacity loss caused by the loss of cycleable Li alone. In low current applications, the two numbers will be close together. In high current applications, Peukert losses increase in proportion, so apparent loss of capacity breaks further and further away from actual capacity loss as current increases.

'''2) Greater voltage excursion under the same load.''' Elevated resistance across the cell means that voltage will sag more under the same load than it did when the cell was healthier. Conversely, voltage will rise higher with the same amount of applied charge current than it did when it was healthier. At the same time, rebound/settling voltages will be further away from loaded/charging voltages. In other words, the cell will rebound to a voltage further away from loaded voltage, all else being equal. Similarly, voltage will settle farther from the charge voltage with the same charge applied. This can give the illusion of elevated self-discharge, but the phenomenon is actually not the same thing. Again, the greater the charge and load currents, the greater the effect becomes.

'''3) Absolute max current decreases.''' Because the cell's series resistance is elevated, the maximum possible current through the cell is decreased.

Just to confuse things further, there can be many factors that lead to impedance rise. Some are related to Li plating, others are not.

=== Lithium-ion ===
Lithium-ion (Li-ion) batteries have a greater energy density than Lithium Iron Phosphate batteries, but have more challenging needs to use safely. The ideal operating range of Li-ion batteries is between +15 and +45°C. The upper limit of temperature is particularly important as Li-ion batteries experience thermal runaway - an unstoppable chain reaction that can occur in milliseconds releasing the stored energy in the cell. This can produce temperatures of 400°C and a fire that is extremely difficult to put out. Thermal runaway can start as low as 60°C and becomes much more likely at 100°C

Risk factors for thermal runaway:
* Short Circuits - either internally or externally
* Overcharging
* Excessive current draw or when charging

==== Li-ion pouch cells ====
[https://kokam.com/cell Kokam] produce high-performance Li-ion pouch cells. These combine relative ease of use and pack construction with performance close to cylindrical cells.

==== Li-ion 18650 and other cylindrical cells ====
Cylindrical cells are favoured by Tesla, and are probably the main reason why their cars achieve such excellent performance. They are light, compact, powerful and expensive. Unfortunately, cylindrical cells are staggeringly difficult (and dangerous) to use in DIY conversions. There are two good reasons for this: thermal management and cell configuration.

As stated above, Li-ion cells are prone to thermal runaway. So you need perfect thermal management to ensure that no cell ever exceeds the critical temperature. If this happens, the cell will short-circuit internally, releasing a lot of energy - potentially explosively. Furthermore, the individual cells are small, so need to be arranged in parallel. In the case of the Tesla Model S, there are 74 cells in each parallel. Imagine if one of those cells fails and becomes short circuited internally. You now have 73 very high power cells in parallel feeding in to that short circuit. In fact, you don't have to imagine: you can watch this famous video instead (courtesy of Rich Rebuilds).

<youtube>WdDi1haA71Q</youtube>

== OEM modules ==
Using an OEM module means a lot of the difficulties associated with battery design are taken care of e.g. cooling, clamping, etc. Here is a list of OEM modules.
{| class="wikitable sortable mw-collapsible"
|+
!Manufacturer
!Type
!Capacity (kWh)
!Weight (kg)
!w (mm)
!d (mm)
!h (mm)
!Gravity (kg/kWh)
!Volume (L/kWh)
!Voltage (V)
!Current (cont A)
!Current (peak A)
!Cell arrangement
!Cell type
!Chemistry
|-
|Tesla
|Model S 85kWh
|5.3
|26
|690
|315
|80
|4.9
|3.3
|22.8
|500
|750
|74p6s
|18650
|Li-ion
|-
|Tesla
|Model S 100kWh
|6.4
|28
|680
|315
|80
|4.4
|2.7
|22.8
|
|870
|86p6s
|18650
|Li-ion
|-
|Chevrolet
|Volt 2012
|4
|38
|470
|180
|280
|9.5
|5.9
|88
|140
|210
|24s
|Pouch
|Li-ion
|-
|BMW
|i3 60Ah
|2
|13
|368
|178
|102
|6.5
|3.3
|28.8
|210
|350
|8s2p
|Prismatic
|Li-ion
|-
|BMW
|i3 94Ah
|4.15
|28
|410
|310
|150
|6.7
|4.6
|45.6
|
|409
|12s
|Prismatic
|Li-ion
|-
|BMW
|i3 120Ah
|5.3
|28
|410
|310
|150
|5.3
|3.6
|45.6
|
|360
|12s
|Prismatic
|Li-ion
|-
|Mitsubishi
|Outlander
|2.4
|26
|646
|184
|130
|10.8
|6.4
|60
|
|240
|16s
|
|Li-ion
|-
|Nissan
|Leaf 24kWh
|0.5
|3.65
|300
|222
|34
|7.3
|4.5
|7.4
|130
|
|2s2p
|
|Li-ion
|-
|Nissan
|Leaf 40kWh
|1.6
|8.7
|300
|222
|68
|5.4
|2.8
|14.6
|
|
|4s2p
|
|Li-ion
|}

Batteries

2020-11-30T21:06:03Z

Clanger9: /* OEM modules */

== Introduction ==
There are a wide variety of battery chemistries available for use as the main traction battery of an EV. To use each chemistry safely, and to ensure an adequate service life from the battery pack it is important to understand the requirements for the chemistry you are using. Failure to do so may lead to premature or catastrophic failure of the pack.

Good pack design will allow for a nominal amount of abuse. People make mistakes and the pack should allow a margin for safety - and for longevity!

== Battery pack specification ==
When deciding on your battery pack, here are some basic parameters to consider:

=== Capacity (kWh) ===
'''How far do you want to go?''' A standard car conversion will need around 1kWh for 3 miles of range. For a middleweight motorcycle, 1kWh should give around 9 miles. ''Your mileage may vary'', as they say.

=== Voltage (V) ===
'''How fast do you want to go?''' The pack voltage defines the maximum speed your motor can spin. Motors are usually specified with "KV" - or RPM-per-volt. Check the KV of your motor and how fast it needs to spin to get your desired top speed. e.g. if you need 3,000 RPM from a 25 KV motor then your pack voltage needs to be 3,000 / 25 = 120 V. The exact number of cells in series you need depends on the cell design, but 3.8 V for Li-ion and 3.2 V for LiFePO4 is a reasonable guess.

=== Maximum current (A) ===
'''How quickly do you want to accelerate?''' Your motor's maximum power will be specified in kW. To estimate your maximum current draw, divide the peak power by the battery voltage. e.g. a 30 kW motor with a 120 V battery pack will pull 30,000 / 120 = 250 A. The higher the current rating of the cells, the heavier they will be for a given capacity. Ideally, you want "enough" current capacity for full throttle acceleration, but no more. You can put cells in parallel to double the current rating of your pack (which of course will half the voltage).

=== Mass (kg) ===
'''Can your vehicle carry the weight?''' You'll need to keep the kerb weight within the original design limits. For a car, this could be a few hundred kg. For a motorcycle, likely less than 100 kg. This is a huge variable - and each new generation of battery tech seems to be a little lighter. For older EV or hybrid batteries, you can reckon on 10-15 kg/kWh. Nissan Leaf batteries are relatively light (7.5 kg/kWh). With the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 5-6 kg/kWh.

=== Volume (L) ===
'''Will it fit?''' Batteries are bulky. They are getting smaller, but finding enough space my be your biggest challenge. You can reckon on 5-10 L/kWh for older EV or hybrid batteries. For the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 3-3.5 kg/kWh.

There is much, much more to battery design than this (e.g. maximum charge rate, terminations, cooling, clamping), but the above should help work out which options will or won't work for your project...

== Cell chemistry ==

=== Lithium Iron Phosphate (LiFePO4) ===
Lithium Iron Phosphate (also known as LFP, or LiFePO4) batteries offer a good compromise between safety, energy density and ease of use for DIY conversions. They are available in a number of formats, commonly pouch cells, prismatic cells and cylindrical cells.

==== LiFePO4 pouch cells ====
The majority of this content is drawn from this thread: [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761&start=900 https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761] discussing the use of the A123 20Ah pouch cell. However, many of the general points apply equally to other similar pouch cells.

===== General build requirements =====
Pouch cells are vulnerable to damage from debris, and must be held in compression (see the datasheet for your battery, but 10-12 psi is recommended for the A123 pouch cells as a guide). A rigid container capable of preventing damage and providing compression is therefore required. Be aware the cells expand and contract in use, so allowance for this must be included in the structure of the case.

The pouch cells should be separated to prevent abrasion between cells, and also to avoid the development of hot spots. Prebuilt modules from A123 systems had thin foam sheets or heatsinks between each cell. Be sure to avoid any debris that could rub on the pouch surface, particularly if using recycled cells.

Mylar, '[https://www.americanmicroinc.com/fish-paper/ Fish paper]' or a [https://www.rogerscorp.com/elastomeric-material-solutions/poron-industrial-polyurethanes compliant foam] may be appropriate materials to serve this purpose. This material should not be flammable. If the material is heat insulating, it is important to address thermal management.

===== Compression =====
Compression is required to prevent premature failure of the cell. Without compression electrolyte will become unevenly distributed, causing current gradients in the cell and uneven heating. Local temperatures can become high enough to form gas formation leading to cells 'puffing up' even when the pack is otherwise held within temperature and voltage constraints. This will be exacerbated in packs with otherwise poor thermal management. Compression forces gas generated to the margins of the cell, outside of the cell stack, minimising its effect cell performance. Gas in the middle cells will create a dead space which does not store or release energy.

There is ~1% expansion through a discharge cycle. As the cell ages, the nominal cell thickness can grow by 3-5%. For A123 cells the ideal pressure is between 4 and 18psi with the ideal pressure being ~12psi. Maintaining 12psi can increase the life by 500 cycles over that of 4 or 18psi

There is some suggestion that in uses where 1C is never exceeded compression ''may'' not be required.

Highly rigid endplates with a mechanism to allow for a limited degree of expansion (e.g. steel bands) are considered an effective solution to this challenge.

It should be noted that compression is a challenge specific to pouch cells. Cylindrical cells are designed to maintain their own compression within the cell's electrode stack by their design.

This thread provides more information and experimentation relating to pack compression: <nowiki>https://endless-sphere.com/forums/viewtopic.php?f=14&t=52244</nowiki>

===== Pouch Cell Pack Design Examples =====
<nowiki>*</nowiki>placeholder*

===== Notes regarding recycled pouch cells =====
Pouch cells are somewhat fragile, and breaching the insulation is not difficult, especially in a cells removed from existing packs and repurposed. If the pouch has had their poly-layers compromised you may see a number of faults:
* Black spots around the perimeter of the cell indicate electrolyte leakage
* Voltage on the outside of the bag. Note that microvoltage between the pouch and the electrode is normal (and due to a capacitive effect).
While the majority of these cells should no longer be in the market, a significant number of faulty cells made it back into the 'greymarket' in around 2013. These cells had misaligned tabs which can also lead to isolation failures between the tab and the pack. These cells should be avoided, particularly in high demand applications.

===== Situations likely to cause pouch cell failure =====
''Taken directly from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''
# '''Overcharge'''. Any extended time above 3.8 Volts will generate enough heat and electrochemical activity to puff a cell, especially one that is improperly compressed.
# '''Overdischarge followed by charge'''. Any A123 cell that has been pulled low enough to come to rest at <300 mV should be immediately scrapped. The published number for that is 500 mV, but the real figure is closer to 300, so that's a "safety buffer" if you will. Below this Voltage, the Cu electrodes start to dissolve into the electrolyte. When charge is applied, the Cu forms dendrites that puncture the separator layer, forming an internal short in the cell. This can puff a cell in a hurry---the more charge current on tap, the worse it's prone to be.
# '''Driving a cell negative'''. I've neglected to mention this before, but it is a possibility. I don't know much about the specific mechanism at this time.
# '''Malfunctioning or misinformed electronics'''. This is the most common cause of all of the above in my experience. At this stage of the game, it is critical for YOU to understand how your BMS functions on at least a cursory level. Choose your BMS very carefully and periodically verify that it is operating properly. They're not all created equal. Make sure V sense lines are securely connected and free of corrosion. Just because your BMS says there was never a problem doesn't necessarily make it so. Avoid harnesses or ribbon cables between multiple modules if possible--they are problematic wherever they are used in any mobile electronics.
# '''Exposure to or generation of sufficient heat'''. I don't know exactly at what temperature gas formation begins in the electrolyte, but we spec a max storage temp of 80 (or 85?) degrees C and I suspect this is the reason. The hotter, the puffier--to a point. This is why soldering tabs poses a real hazard to cell health. If you feel you must solder, sink or blow the heat away from the body of the cell. Use a big iron that can make sufficient local heat quickly, before the whole mass of the cell gets hot. You might even get the cell warm enough to melt separator if not careful.
# '''No compression, not enough compression, improperly distributed compression'''. This is a pack/module design issue. Apply 10, maybe 15 psi to your cell stack end to end and then band snugly and evenly. Use hard endplates of some sort--never wrap cells directly or allow their shape to become distorted. Protect all areas of the pouch from impact damage. This obviously does not apply to cylindrical cells.

==== LiFePO4 prismatic cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cylindrical cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cell ageing ====
''Derived (barely paraphrased) from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''

Capacity loss is caused by the lithium that was available for storage becoming permanently plated on the cathode. Being unable to move within the cell it is no longer available to store energy. The impact of this plating is greater than the amount of lithium 'lost' to plating because not only is the lithium no longer available, it is also preventing access to that part of the cathode meaning Li that can still move has to take a longer path to reach the cathode. Lithium plating is one cause of increased cell resistance (there are others), a sign of worsening cell health.

There is no linear relationship between actual capacity loss and impedance rise. However some cell defects will also increase impedance.

Increasing cell resistance may cause a number of symptoms which may be confused with [https://earthshipbiotecture.com/a-lithium-ion-battery-primer/ High Self Discharge.]
# Elevated Peukert Losses. As more energy per amount of current through the cell is lost as heat, the cells useable capacity decreases. So the apparent capacity loss is higher than the actual capacity loss of cycleable lithium. When used in low current applications (e.g. solar energy storage) the actual and apparent decrease in capacity will be small. In high current draw applications (like EV traction packs), the Peukert loss increases proportionally, so the apparent capacity loss increases much faster than the actual capacity loss.
# Greater voltage excursion under the same load. Due to increased cell resistancethe voltage will sag further under the same load than a cell in optimal condition. The inverse is also true, the voltage will be higher for the same amount of charging current applied. The cell will then rebound to a voltage further from the loaded and charging voltages. This, obviously, can look like high self discharge but is a different phenomenon.
# Absolute maximum current decrease.
Elevated impedance causes a more complex constellation of symptoms, some of which may be easy to confuse with High Self Discharge (HSD). Ohm's law (E=I/R) holds the key to understanding here.

'''1) Elevated Peukert losses.''' Because more energy per unit of current through the cell is lost as heat, less of the cell's capacity is actually USABLE. Thus, apparent capacity loss can be significantly greater than actual capacity loss caused by the loss of cycleable Li alone. In low current applications, the two numbers will be close together. In high current applications, Peukert losses increase in proportion, so apparent loss of capacity breaks further and further away from actual capacity loss as current increases.

'''2) Greater voltage excursion under the same load.''' Elevated resistance across the cell means that voltage will sag more under the same load than it did when the cell was healthier. Conversely, voltage will rise higher with the same amount of applied charge current than it did when it was healthier. At the same time, rebound/settling voltages will be further away from loaded/charging voltages. In other words, the cell will rebound to a voltage further away from loaded voltage, all else being equal. Similarly, voltage will settle farther from the charge voltage with the same charge applied. This can give the illusion of elevated self-discharge, but the phenomenon is actually not the same thing. Again, the greater the charge and load currents, the greater the effect becomes.

'''3) Absolute max current decreases.''' Because the cell's series resistance is elevated, the maximum possible current through the cell is decreased.

Just to confuse things further, there can be many factors that lead to impedance rise. Some are related to Li plating, others are not.

=== Lithium-ion ===
Lithium-ion (Li-ion) batteries have a greater energy density than Lithium Iron Phosphate batteries, but have more challenging needs to use safely. The ideal operating range of Li-ion batteries is between +15 and +45°C. The upper limit of temperature is particularly important as Li-ion batteries experience thermal runaway - an unstoppable chain reaction that can occur in milliseconds releasing the stored energy in the cell. This can produce temperatures of 400°C and a fire that is extremely difficult to put out. Thermal runaway can start as low as 60°C and becomes much more likely at 100°C

Risk factors for thermal runaway:
* Short Circuits - either internally or externally
* Overcharging
* Excessive current draw or when charging

==== Li-ion pouch cells ====
[https://kokam.com/cell Kokam] produce high-performance Li-ion pouch cells. These combine relative ease of use and pack construction with performance close to cylindrical cells.

==== Li-ion 18650 and other cylindrical cells ====
Cylindrical cells are favoured by Tesla, and are probably the main reason why their cars achieve such excellent performance. They are light, compact, powerful and expensive. Unfortunately, cylindrical cells are staggeringly difficult (and dangerous) to use in DIY conversions. There are two good reasons for this: thermal management and cell configuration.

As stated above, Li-ion cells are prone to thermal runaway. So you need perfect thermal management to ensure that no cell ever exceeds the critical temperature. If this happens, the cell will short-circuit internally, releasing a lot of energy - potentially explosively. Furthermore, the individual cells are small, so need to be arranged in parallel. In the case of the Tesla Model S, there are 74 cells in each parallel. Imagine if one of those cells fails and becomes short circuited internally. You now have 73 very high power cells in parallel feeding in to that short circuit. In fact, you don't have to imagine: you can watch this famous video instead (courtesy of Rich Rebuilds).

<youtube>WdDi1haA71Q</youtube>

== OEM modules ==
Using an OEM module means a lot of the difficulties associated with battery design are taken care of e.g. cooling, clamping, etc. Here is a list of OEM modules.
{| class="wikitable sortable mw-collapsible"
|+
!Manufacturer
!Type
!Capacity (kWh)
!Weight (kg)
!w (mm)
!d (mm)
!h (mm)
!Gravity (kg/kWh)
!Volume (L/kWh)
!Voltage (V)
!Current (cont A)
!Current (peak A)
!Cell arrangement
!Cell type
!Chemistry
|-
|Tesla
|Model S 85kWh
|5.3
|26
|690
|315
|80
|4.9
|3.3
|22.8
|500
|750
|74p6s
|18650
|Li-ion
|-
|Tesla
|Model S 100kWh
|6.4
|28
|680
|315
|80
|4.4
|2.7
|22.8
|
|870
|86p6s
|18650
|Li-ion
|-
|Chevrolet
|Volt 2012
|4
|38
|470
|180
|280
|9.5
|5.9
|88
|140
|210
|24s
|Pouch
|Li-ion
|-
|BMW
|i3 60Ah
|2
|13
|368
|178
|102
|6.5
|3.3
|28.8
|210
|350
|8s2p
|Prismatic
|Li-ion
|-
|BMW
|i3 94Ah
|4.15
|28
|410
|310
|150
|6.7
|4.6
|45.6
|
|409
|12s
|Prismatic
|Li-ion
|-
|BMW
|i3 120Ah
|5.3
|28
|410
|310
|150
|5.3
|3.6
|45.6
|
|360
|12s
|Prismatic
|Li-ion
|-
|Mitsubishi
|Outlander
|2.4
|26
|646
|184
|130
|10.8
|6.4
|60
|
|240
|16s
|
|Li-ion
|-
|Nissan
|Leaf 24kWh
|0.5
|3.65
|300
|222
|34
|7.3
|4.5
|7.4
|
|
|2s2p
|
|Li-ion
|}

Batteries

2020-11-30T21:01:42Z

Clanger9: /* OEM modules */

== Introduction ==
There are a wide variety of battery chemistries available for use as the main traction battery of an EV. To use each chemistry safely, and to ensure an adequate service life from the battery pack it is important to understand the requirements for the chemistry you are using. Failure to do so may lead to premature or catastrophic failure of the pack.

Good pack design will allow for a nominal amount of abuse. People make mistakes and the pack should allow a margin for safety - and for longevity!

== Battery pack specification ==
When deciding on your battery pack, here are some basic parameters to consider:

=== Capacity (kWh) ===
'''How far do you want to go?''' A standard car conversion will need around 1kWh for 3 miles of range. For a middleweight motorcycle, 1kWh should give around 9 miles. ''Your mileage may vary'', as they say.

=== Voltage (V) ===
'''How fast do you want to go?''' The pack voltage defines the maximum speed your motor can spin. Motors are usually specified with "KV" - or RPM-per-volt. Check the KV of your motor and how fast it needs to spin to get your desired top speed. e.g. if you need 3,000 RPM from a 25 KV motor then your pack voltage needs to be 3,000 / 25 = 120 V. The exact number of cells in series you need depends on the cell design, but 3.8 V for Li-ion and 3.2 V for LiFePO4 is a reasonable guess.

=== Maximum current (A) ===
'''How quickly do you want to accelerate?''' Your motor's maximum power will be specified in kW. To estimate your maximum current draw, divide the peak power by the battery voltage. e.g. a 30 kW motor with a 120 V battery pack will pull 30,000 / 120 = 250 A. The higher the current rating of the cells, the heavier they will be for a given capacity. Ideally, you want "enough" current capacity for full throttle acceleration, but no more. You can put cells in parallel to double the current rating of your pack (which of course will half the voltage).

=== Mass (kg) ===
'''Can your vehicle carry the weight?''' You'll need to keep the kerb weight within the original design limits. For a car, this could be a few hundred kg. For a motorcycle, likely less than 100 kg. This is a huge variable - and each new generation of battery tech seems to be a little lighter. For older EV or hybrid batteries, you can reckon on 10-15 kg/kWh. Nissan Leaf batteries are relatively light (7.5 kg/kWh). With the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 5-6 kg/kWh.

=== Volume (L) ===
'''Will it fit?''' Batteries are bulky. They are getting smaller, but finding enough space my be your biggest challenge. You can reckon on 5-10 L/kWh for older EV or hybrid batteries. For the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 3-3.5 kg/kWh.

There is much, much more to battery design than this (e.g. maximum charge rate, terminations, cooling, clamping), but the above should help work out which options will or won't work for your project...

== Cell chemistry ==

=== Lithium Iron Phosphate (LiFePO4) ===
Lithium Iron Phosphate (also known as LFP, or LiFePO4) batteries offer a good compromise between safety, energy density and ease of use for DIY conversions. They are available in a number of formats, commonly pouch cells, prismatic cells and cylindrical cells.

==== LiFePO4 pouch cells ====
The majority of this content is drawn from this thread: [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761&start=900 https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761] discussing the use of the A123 20Ah pouch cell. However, many of the general points apply equally to other similar pouch cells.

===== General build requirements =====
Pouch cells are vulnerable to damage from debris, and must be held in compression (see the datasheet for your battery, but 10-12 psi is recommended for the A123 pouch cells as a guide). A rigid container capable of preventing damage and providing compression is therefore required. Be aware the cells expand and contract in use, so allowance for this must be included in the structure of the case.

The pouch cells should be separated to prevent abrasion between cells, and also to avoid the development of hot spots. Prebuilt modules from A123 systems had thin foam sheets or heatsinks between each cell. Be sure to avoid any debris that could rub on the pouch surface, particularly if using recycled cells.

Mylar, '[https://www.americanmicroinc.com/fish-paper/ Fish paper]' or a [https://www.rogerscorp.com/elastomeric-material-solutions/poron-industrial-polyurethanes compliant foam] may be appropriate materials to serve this purpose. This material should not be flammable. If the material is heat insulating, it is important to address thermal management.

===== Compression =====
Compression is required to prevent premature failure of the cell. Without compression electrolyte will become unevenly distributed, causing current gradients in the cell and uneven heating. Local temperatures can become high enough to form gas formation leading to cells 'puffing up' even when the pack is otherwise held within temperature and voltage constraints. This will be exacerbated in packs with otherwise poor thermal management. Compression forces gas generated to the margins of the cell, outside of the cell stack, minimising its effect cell performance. Gas in the middle cells will create a dead space which does not store or release energy.

There is ~1% expansion through a discharge cycle. As the cell ages, the nominal cell thickness can grow by 3-5%. For A123 cells the ideal pressure is between 4 and 18psi with the ideal pressure being ~12psi. Maintaining 12psi can increase the life by 500 cycles over that of 4 or 18psi

There is some suggestion that in uses where 1C is never exceeded compression ''may'' not be required.

Highly rigid endplates with a mechanism to allow for a limited degree of expansion (e.g. steel bands) are considered an effective solution to this challenge.

It should be noted that compression is a challenge specific to pouch cells. Cylindrical cells are designed to maintain their own compression within the cell's electrode stack by their design.

This thread provides more information and experimentation relating to pack compression: <nowiki>https://endless-sphere.com/forums/viewtopic.php?f=14&t=52244</nowiki>

===== Pouch Cell Pack Design Examples =====
<nowiki>*</nowiki>placeholder*

===== Notes regarding recycled pouch cells =====
Pouch cells are somewhat fragile, and breaching the insulation is not difficult, especially in a cells removed from existing packs and repurposed. If the pouch has had their poly-layers compromised you may see a number of faults:
* Black spots around the perimeter of the cell indicate electrolyte leakage
* Voltage on the outside of the bag. Note that microvoltage between the pouch and the electrode is normal (and due to a capacitive effect).
While the majority of these cells should no longer be in the market, a significant number of faulty cells made it back into the 'greymarket' in around 2013. These cells had misaligned tabs which can also lead to isolation failures between the tab and the pack. These cells should be avoided, particularly in high demand applications.

===== Situations likely to cause pouch cell failure =====
''Taken directly from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''
# '''Overcharge'''. Any extended time above 3.8 Volts will generate enough heat and electrochemical activity to puff a cell, especially one that is improperly compressed.
# '''Overdischarge followed by charge'''. Any A123 cell that has been pulled low enough to come to rest at <300 mV should be immediately scrapped. The published number for that is 500 mV, but the real figure is closer to 300, so that's a "safety buffer" if you will. Below this Voltage, the Cu electrodes start to dissolve into the electrolyte. When charge is applied, the Cu forms dendrites that puncture the separator layer, forming an internal short in the cell. This can puff a cell in a hurry---the more charge current on tap, the worse it's prone to be.
# '''Driving a cell negative'''. I've neglected to mention this before, but it is a possibility. I don't know much about the specific mechanism at this time.
# '''Malfunctioning or misinformed electronics'''. This is the most common cause of all of the above in my experience. At this stage of the game, it is critical for YOU to understand how your BMS functions on at least a cursory level. Choose your BMS very carefully and periodically verify that it is operating properly. They're not all created equal. Make sure V sense lines are securely connected and free of corrosion. Just because your BMS says there was never a problem doesn't necessarily make it so. Avoid harnesses or ribbon cables between multiple modules if possible--they are problematic wherever they are used in any mobile electronics.
# '''Exposure to or generation of sufficient heat'''. I don't know exactly at what temperature gas formation begins in the electrolyte, but we spec a max storage temp of 80 (or 85?) degrees C and I suspect this is the reason. The hotter, the puffier--to a point. This is why soldering tabs poses a real hazard to cell health. If you feel you must solder, sink or blow the heat away from the body of the cell. Use a big iron that can make sufficient local heat quickly, before the whole mass of the cell gets hot. You might even get the cell warm enough to melt separator if not careful.
# '''No compression, not enough compression, improperly distributed compression'''. This is a pack/module design issue. Apply 10, maybe 15 psi to your cell stack end to end and then band snugly and evenly. Use hard endplates of some sort--never wrap cells directly or allow their shape to become distorted. Protect all areas of the pouch from impact damage. This obviously does not apply to cylindrical cells.

==== LiFePO4 prismatic cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cylindrical cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cell ageing ====
''Derived (barely paraphrased) from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''

Capacity loss is caused by the lithium that was available for storage becoming permanently plated on the cathode. Being unable to move within the cell it is no longer available to store energy. The impact of this plating is greater than the amount of lithium 'lost' to plating because not only is the lithium no longer available, it is also preventing access to that part of the cathode meaning Li that can still move has to take a longer path to reach the cathode. Lithium plating is one cause of increased cell resistance (there are others), a sign of worsening cell health.

There is no linear relationship between actual capacity loss and impedance rise. However some cell defects will also increase impedance.

Increasing cell resistance may cause a number of symptoms which may be confused with [https://earthshipbiotecture.com/a-lithium-ion-battery-primer/ High Self Discharge.]
# Elevated Peukert Losses. As more energy per amount of current through the cell is lost as heat, the cells useable capacity decreases. So the apparent capacity loss is higher than the actual capacity loss of cycleable lithium. When used in low current applications (e.g. solar energy storage) the actual and apparent decrease in capacity will be small. In high current draw applications (like EV traction packs), the Peukert loss increases proportionally, so the apparent capacity loss increases much faster than the actual capacity loss.
# Greater voltage excursion under the same load. Due to increased cell resistancethe voltage will sag further under the same load than a cell in optimal condition. The inverse is also true, the voltage will be higher for the same amount of charging current applied. The cell will then rebound to a voltage further from the loaded and charging voltages. This, obviously, can look like high self discharge but is a different phenomenon.
# Absolute maximum current decrease.
Elevated impedance causes a more complex constellation of symptoms, some of which may be easy to confuse with High Self Discharge (HSD). Ohm's law (E=I/R) holds the key to understanding here.

'''1) Elevated Peukert losses.''' Because more energy per unit of current through the cell is lost as heat, less of the cell's capacity is actually USABLE. Thus, apparent capacity loss can be significantly greater than actual capacity loss caused by the loss of cycleable Li alone. In low current applications, the two numbers will be close together. In high current applications, Peukert losses increase in proportion, so apparent loss of capacity breaks further and further away from actual capacity loss as current increases.

'''2) Greater voltage excursion under the same load.''' Elevated resistance across the cell means that voltage will sag more under the same load than it did when the cell was healthier. Conversely, voltage will rise higher with the same amount of applied charge current than it did when it was healthier. At the same time, rebound/settling voltages will be further away from loaded/charging voltages. In other words, the cell will rebound to a voltage further away from loaded voltage, all else being equal. Similarly, voltage will settle farther from the charge voltage with the same charge applied. This can give the illusion of elevated self-discharge, but the phenomenon is actually not the same thing. Again, the greater the charge and load currents, the greater the effect becomes.

'''3) Absolute max current decreases.''' Because the cell's series resistance is elevated, the maximum possible current through the cell is decreased.

Just to confuse things further, there can be many factors that lead to impedance rise. Some are related to Li plating, others are not.

=== Lithium-ion ===
Lithium-ion (Li-ion) batteries have a greater energy density than Lithium Iron Phosphate batteries, but have more challenging needs to use safely. The ideal operating range of Li-ion batteries is between +15 and +45°C. The upper limit of temperature is particularly important as Li-ion batteries experience thermal runaway - an unstoppable chain reaction that can occur in milliseconds releasing the stored energy in the cell. This can produce temperatures of 400°C and a fire that is extremely difficult to put out. Thermal runaway can start as low as 60°C and becomes much more likely at 100°C

Risk factors for thermal runaway:
* Short Circuits - either internally or externally
* Overcharging
* Excessive current draw or when charging

==== Li-ion pouch cells ====
[https://kokam.com/cell Kokam] produce high-performance Li-ion pouch cells. These combine relative ease of use and pack construction with performance close to cylindrical cells.

==== Li-ion 18650 and other cylindrical cells ====
Cylindrical cells are favoured by Tesla, and are probably the main reason why their cars achieve such excellent performance. They are light, compact, powerful and expensive. Unfortunately, cylindrical cells are staggeringly difficult (and dangerous) to use in DIY conversions. There are two good reasons for this: thermal management and cell configuration.

As stated above, Li-ion cells are prone to thermal runaway. So you need perfect thermal management to ensure that no cell ever exceeds the critical temperature. If this happens, the cell will short-circuit internally, releasing a lot of energy - potentially explosively. Furthermore, the individual cells are small, so need to be arranged in parallel. In the case of the Tesla Model S, there are 74 cells in each parallel. Imagine if one of those cells fails and becomes short circuited internally. You now have 73 very high power cells in parallel feeding in to that short circuit. In fact, you don't have to imagine: you can watch this famous video instead (courtesy of Rich Rebuilds).

<youtube>WdDi1haA71Q</youtube>

== OEM modules ==
Using an OEM module means a lot of the difficulties associated with battery design are taken care of e.g. cooling, clamping, etc. Here is a list of OEM modules.
{| class="wikitable sortable mw-collapsible"
|+
!Manufacturer
!Type
!Capacity (kWh)
!Weight (kg)
!w (mm)
!d (mm)
!h (mm)
!Gravity (kg/kWh)
!Volume (L/kWh)
!Voltage (V)
!Current (cont A)
!Current (peak A)
!Cell arrangement
!Cell type
!Chemistry
|-
|Tesla
|Model S
|5.3
|25
|666
|303
|79
|4.7
|3.0
|22.8
|500
|750
|74p6s
|18650
|Li-ion
|-
|Chevrolet
|Volt 2012
|4
|38
|470
|180
|280
|9.5
|5.9
|88
|140
|210
|24s
|Pouch
|Li-ion
|-
|BMW
|i3 60Ah
|2
|13
|368
|178
|102
|6.5
|3.3
|28.8
|210
|350
|8s2p
|Prismatic
|Li-ion
|-
|BMW
|i3 94Ah
|4.15
|28
|410
|310
|150
|6.7
|4.6
|45.6
|
|409
|12s
|Prismatic
|Li-ion
|-
|BMW
|i3 120Ah
|5.3
|28
|410
|310
|150
|5.3
|3.6
|45.6
|
|360
|12s
|Prismatic
|Li-ion
|-
|Mitsubishi
|Outlander
|2.4
|26
|646
|184
|130
|10.8
|6.4
|60
|
|240
|16s
|
|Li-ion
|-
|Nissan
|Leaf 24kWh
|0.5
|3.65
|300
|222
|34
|7.3
|4.5
|7.4
|
|
|2s2p
|
|Li-ion
|}

Batteries

2020-11-30T20:46:02Z

Clanger9: /* OEM modules */

== Introduction ==
There are a wide variety of battery chemistries available for use as the main traction battery of an EV. To use each chemistry safely, and to ensure an adequate service life from the battery pack it is important to understand the requirements for the chemistry you are using. Failure to do so may lead to premature or catastrophic failure of the pack.

Good pack design will allow for a nominal amount of abuse. People make mistakes and the pack should allow a margin for safety - and for longevity!

== Battery pack specification ==
When deciding on your battery pack, here are some basic parameters to consider:

=== Capacity (kWh) ===
'''How far do you want to go?''' A standard car conversion will need around 1kWh for 3 miles of range. For a middleweight motorcycle, 1kWh should give around 9 miles. ''Your mileage may vary'', as they say.

=== Voltage (V) ===
'''How fast do you want to go?''' The pack voltage defines the maximum speed your motor can spin. Motors are usually specified with "KV" - or RPM-per-volt. Check the KV of your motor and how fast it needs to spin to get your desired top speed. e.g. if you need 3,000 RPM from a 25 KV motor then your pack voltage needs to be 3,000 / 25 = 120 V. The exact number of cells in series you need depends on the cell design, but 3.8 V for Li-ion and 3.2 V for LiFePO4 is a reasonable guess.

=== Maximum current (A) ===
'''How quickly do you want to accelerate?''' Your motor's maximum power will be specified in kW. To estimate your maximum current draw, divide the peak power by the battery voltage. e.g. a 30 kW motor with a 120 V battery pack will pull 30,000 / 120 = 250 A. The higher the current rating of the cells, the heavier they will be for a given capacity. Ideally, you want "enough" current capacity for full throttle acceleration, but no more. You can put cells in parallel to double the current rating of your pack (which of course will half the voltage).

=== Mass (kg) ===
'''Can your vehicle carry the weight?''' You'll need to keep the kerb weight within the original design limits. For a car, this could be a few hundred kg. For a motorcycle, likely less than 100 kg. This is a huge variable - and each new generation of battery tech seems to be a little lighter. For older EV or hybrid batteries, you can reckon on 10-15 kg/kWh. Nissan Leaf batteries are relatively light (7.5 kg/kWh). With the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 5-6 kg/kWh.

=== Volume (L) ===
'''Will it fit?''' Batteries are bulky. They are getting smaller, but finding enough space my be your biggest challenge. You can reckon on 5-10 L/kWh for older EV or hybrid batteries. For the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 3-3.5 kg/kWh.

There is much, much more to battery design than this (e.g. maximum charge rate, terminations, cooling, clamping), but the above should help work out which options will or won't work for your project...

== Cell chemistry ==

=== Lithium Iron Phosphate (LiFePO4) ===
Lithium Iron Phosphate (also known as LFP, or LiFePO4) batteries offer a good compromise between safety, energy density and ease of use for DIY conversions. They are available in a number of formats, commonly pouch cells, prismatic cells and cylindrical cells.

==== LiFePO4 pouch cells ====
The majority of this content is drawn from this thread: [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761&start=900 https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761] discussing the use of the A123 20Ah pouch cell. However, many of the general points apply equally to other similar pouch cells.

===== General build requirements =====
Pouch cells are vulnerable to damage from debris, and must be held in compression (see the datasheet for your battery, but 10-12 psi is recommended for the A123 pouch cells as a guide). A rigid container capable of preventing damage and providing compression is therefore required. Be aware the cells expand and contract in use, so allowance for this must be included in the structure of the case.

The pouch cells should be separated to prevent abrasion between cells, and also to avoid the development of hot spots. Prebuilt modules from A123 systems had thin foam sheets or heatsinks between each cell. Be sure to avoid any debris that could rub on the pouch surface, particularly if using recycled cells.

Mylar, '[https://www.americanmicroinc.com/fish-paper/ Fish paper]' or a [https://www.rogerscorp.com/elastomeric-material-solutions/poron-industrial-polyurethanes compliant foam] may be appropriate materials to serve this purpose. This material should not be flammable. If the material is heat insulating, it is important to address thermal management.

===== Compression =====
Compression is required to prevent premature failure of the cell. Without compression electrolyte will become unevenly distributed, causing current gradients in the cell and uneven heating. Local temperatures can become high enough to form gas formation leading to cells 'puffing up' even when the pack is otherwise held within temperature and voltage constraints. This will be exacerbated in packs with otherwise poor thermal management. Compression forces gas generated to the margins of the cell, outside of the cell stack, minimising its effect cell performance. Gas in the middle cells will create a dead space which does not store or release energy.

There is ~1% expansion through a discharge cycle. As the cell ages, the nominal cell thickness can grow by 3-5%. For A123 cells the ideal pressure is between 4 and 18psi with the ideal pressure being ~12psi. Maintaining 12psi can increase the life by 500 cycles over that of 4 or 18psi

There is some suggestion that in uses where 1C is never exceeded compression ''may'' not be required.

Highly rigid endplates with a mechanism to allow for a limited degree of expansion (e.g. steel bands) are considered an effective solution to this challenge.

It should be noted that compression is a challenge specific to pouch cells. Cylindrical cells are designed to maintain their own compression within the cell's electrode stack by their design.

This thread provides more information and experimentation relating to pack compression: <nowiki>https://endless-sphere.com/forums/viewtopic.php?f=14&t=52244</nowiki>

===== Pouch Cell Pack Design Examples =====
<nowiki>*</nowiki>placeholder*

===== Notes regarding recycled pouch cells =====
Pouch cells are somewhat fragile, and breaching the insulation is not difficult, especially in a cells removed from existing packs and repurposed. If the pouch has had their poly-layers compromised you may see a number of faults:
* Black spots around the perimeter of the cell indicate electrolyte leakage
* Voltage on the outside of the bag. Note that microvoltage between the pouch and the electrode is normal (and due to a capacitive effect).
While the majority of these cells should no longer be in the market, a significant number of faulty cells made it back into the 'greymarket' in around 2013. These cells had misaligned tabs which can also lead to isolation failures between the tab and the pack. These cells should be avoided, particularly in high demand applications.

===== Situations likely to cause pouch cell failure =====
''Taken directly from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''
# '''Overcharge'''. Any extended time above 3.8 Volts will generate enough heat and electrochemical activity to puff a cell, especially one that is improperly compressed.
# '''Overdischarge followed by charge'''. Any A123 cell that has been pulled low enough to come to rest at <300 mV should be immediately scrapped. The published number for that is 500 mV, but the real figure is closer to 300, so that's a "safety buffer" if you will. Below this Voltage, the Cu electrodes start to dissolve into the electrolyte. When charge is applied, the Cu forms dendrites that puncture the separator layer, forming an internal short in the cell. This can puff a cell in a hurry---the more charge current on tap, the worse it's prone to be.
# '''Driving a cell negative'''. I've neglected to mention this before, but it is a possibility. I don't know much about the specific mechanism at this time.
# '''Malfunctioning or misinformed electronics'''. This is the most common cause of all of the above in my experience. At this stage of the game, it is critical for YOU to understand how your BMS functions on at least a cursory level. Choose your BMS very carefully and periodically verify that it is operating properly. They're not all created equal. Make sure V sense lines are securely connected and free of corrosion. Just because your BMS says there was never a problem doesn't necessarily make it so. Avoid harnesses or ribbon cables between multiple modules if possible--they are problematic wherever they are used in any mobile electronics.
# '''Exposure to or generation of sufficient heat'''. I don't know exactly at what temperature gas formation begins in the electrolyte, but we spec a max storage temp of 80 (or 85?) degrees C and I suspect this is the reason. The hotter, the puffier--to a point. This is why soldering tabs poses a real hazard to cell health. If you feel you must solder, sink or blow the heat away from the body of the cell. Use a big iron that can make sufficient local heat quickly, before the whole mass of the cell gets hot. You might even get the cell warm enough to melt separator if not careful.
# '''No compression, not enough compression, improperly distributed compression'''. This is a pack/module design issue. Apply 10, maybe 15 psi to your cell stack end to end and then band snugly and evenly. Use hard endplates of some sort--never wrap cells directly or allow their shape to become distorted. Protect all areas of the pouch from impact damage. This obviously does not apply to cylindrical cells.

==== LiFePO4 prismatic cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cylindrical cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cell ageing ====
''Derived (barely paraphrased) from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''

Capacity loss is caused by the lithium that was available for storage becoming permanently plated on the cathode. Being unable to move within the cell it is no longer available to store energy. The impact of this plating is greater than the amount of lithium 'lost' to plating because not only is the lithium no longer available, it is also preventing access to that part of the cathode meaning Li that can still move has to take a longer path to reach the cathode. Lithium plating is one cause of increased cell resistance (there are others), a sign of worsening cell health.

There is no linear relationship between actual capacity loss and impedance rise. However some cell defects will also increase impedance.

Increasing cell resistance may cause a number of symptoms which may be confused with [https://earthshipbiotecture.com/a-lithium-ion-battery-primer/ High Self Discharge.]
# Elevated Peukert Losses. As more energy per amount of current through the cell is lost as heat, the cells useable capacity decreases. So the apparent capacity loss is higher than the actual capacity loss of cycleable lithium. When used in low current applications (e.g. solar energy storage) the actual and apparent decrease in capacity will be small. In high current draw applications (like EV traction packs), the Peukert loss increases proportionally, so the apparent capacity loss increases much faster than the actual capacity loss.
# Greater voltage excursion under the same load. Due to increased cell resistancethe voltage will sag further under the same load than a cell in optimal condition. The inverse is also true, the voltage will be higher for the same amount of charging current applied. The cell will then rebound to a voltage further from the loaded and charging voltages. This, obviously, can look like high self discharge but is a different phenomenon.
# Absolute maximum current decrease.
Elevated impedance causes a more complex constellation of symptoms, some of which may be easy to confuse with High Self Discharge (HSD). Ohm's law (E=I/R) holds the key to understanding here.

'''1) Elevated Peukert losses.''' Because more energy per unit of current through the cell is lost as heat, less of the cell's capacity is actually USABLE. Thus, apparent capacity loss can be significantly greater than actual capacity loss caused by the loss of cycleable Li alone. In low current applications, the two numbers will be close together. In high current applications, Peukert losses increase in proportion, so apparent loss of capacity breaks further and further away from actual capacity loss as current increases.

'''2) Greater voltage excursion under the same load.''' Elevated resistance across the cell means that voltage will sag more under the same load than it did when the cell was healthier. Conversely, voltage will rise higher with the same amount of applied charge current than it did when it was healthier. At the same time, rebound/settling voltages will be further away from loaded/charging voltages. In other words, the cell will rebound to a voltage further away from loaded voltage, all else being equal. Similarly, voltage will settle farther from the charge voltage with the same charge applied. This can give the illusion of elevated self-discharge, but the phenomenon is actually not the same thing. Again, the greater the charge and load currents, the greater the effect becomes.

'''3) Absolute max current decreases.''' Because the cell's series resistance is elevated, the maximum possible current through the cell is decreased.

Just to confuse things further, there can be many factors that lead to impedance rise. Some are related to Li plating, others are not.

=== Lithium-ion ===
Lithium-ion (Li-ion) batteries have a greater energy density than Lithium Iron Phosphate batteries, but have more challenging needs to use safely. The ideal operating range of Li-ion batteries is between +15 and +45°C. The upper limit of temperature is particularly important as Li-ion batteries experience thermal runaway - an unstoppable chain reaction that can occur in milliseconds releasing the stored energy in the cell. This can produce temperatures of 400°C and a fire that is extremely difficult to put out. Thermal runaway can start as low as 60°C and becomes much more likely at 100°C

Risk factors for thermal runaway:
* Short Circuits - either internally or externally
* Overcharging
* Excessive current draw or when charging

==== Li-ion pouch cells ====
[https://kokam.com/cell Kokam] produce high-performance Li-ion pouch cells. These combine relative ease of use and pack construction with performance close to cylindrical cells.

==== Li-ion 18650 and other cylindrical cells ====
Cylindrical cells are favoured by Tesla, and are probably the main reason why their cars achieve such excellent performance. They are light, compact, powerful and expensive. Unfortunately, cylindrical cells are staggeringly difficult (and dangerous) to use in DIY conversions. There are two good reasons for this: thermal management and cell configuration.

As stated above, Li-ion cells are prone to thermal runaway. So you need perfect thermal management to ensure that no cell ever exceeds the critical temperature. If this happens, the cell will short-circuit internally, releasing a lot of energy - potentially explosively. Furthermore, the individual cells are small, so need to be arranged in parallel. In the case of the Tesla Model S, there are 74 cells in each parallel. Imagine if one of those cells fails and becomes short circuited internally. You now have 73 very high power cells in parallel feeding in to that short circuit. In fact, you don't have to imagine: you can watch this famous video instead (courtesy of Rich Rebuilds).

<youtube>WdDi1haA71Q</youtube>

== OEM modules ==
Using an OEM module means a lot of the difficulties associated with battery design are taken care of e.g. cooling, clamping, etc. Here is a list of OEM modules.
{| class="wikitable sortable mw-collapsible"
|+
!Manufacturer
!Type
!Capacity (kWh)
!Weight (kg)
!w (mm)
!d (mm)
!h (mm)
!Gravity (kg/kWh)
!Volume (L/kWh)
!Voltage (V)
!Current (cont A)
!Current (peak A)
!Cell arrangement
!Cell type
!Chemistry
|-
|Tesla
|Model S
|5.3
|25
|666
|303
|79
|4.7
|3.0
|22.8
|500
|750
|74p6s
|18650
|Li-ion
|-
|Chevrolet
|Volt
|2
|20.5
|241
|241
|267
|10.2
|7.8
|48
|240
|350
|3p12s
|Pouch
|Li-ion
|-
|BMW
|i3 60Ah
|2
|13
|368
|178
|102
|6.5
|3.3
|28.8
|210
|350
|8s2p
|Prismatic
|Li-ion
|-
|BMW
|i3 94Ah
|4.15
|28
|410
|310
|150
|6.7
|4.6
|45
|
|280
|12s1p
|Prismatic
|Li-ion
|}

Batteries

2020-11-30T20:29:42Z

Clanger9:

== Introduction ==
There are a wide variety of battery chemistries available for use as the main traction battery of an EV. To use each chemistry safely, and to ensure an adequate service life from the battery pack it is important to understand the requirements for the chemistry you are using. Failure to do so may lead to premature or catastrophic failure of the pack.

Good pack design will allow for a nominal amount of abuse. People make mistakes and the pack should allow a margin for safety - and for longevity!

== Battery pack specification ==
When deciding on your battery pack, here are some basic parameters to consider:

=== Capacity (kWh) ===
'''How far do you want to go?''' A standard car conversion will need around 1kWh for 3 miles of range. For a middleweight motorcycle, 1kWh should give around 9 miles. ''Your mileage may vary'', as they say.

=== Voltage (V) ===
'''How fast do you want to go?''' The pack voltage defines the maximum speed your motor can spin. Motors are usually specified with "KV" - or RPM-per-volt. Check the KV of your motor and how fast it needs to spin to get your desired top speed. e.g. if you need 3,000 RPM from a 25 KV motor then your pack voltage needs to be 3,000 / 25 = 120 V. The exact number of cells in series you need depends on the cell design, but 3.8 V for Li-ion and 3.2 V for LiFePO4 is a reasonable guess.

=== Maximum current (A) ===
'''How quickly do you want to accelerate?''' Your motor's maximum power will be specified in kW. To estimate your maximum current draw, divide the peak power by the battery voltage. e.g. a 30 kW motor with a 120 V battery pack will pull 30,000 / 120 = 250 A. The higher the current rating of the cells, the heavier they will be for a given capacity. Ideally, you want "enough" current capacity for full throttle acceleration, but no more. You can put cells in parallel to double the current rating of your pack (which of course will half the voltage).

=== Mass (kg) ===
'''Can your vehicle carry the weight?''' You'll need to keep the kerb weight within the original design limits. For a car, this could be a few hundred kg. For a motorcycle, likely less than 100 kg. This is a huge variable - and each new generation of battery tech seems to be a little lighter. For older EV or hybrid batteries, you can reckon on 10-15 kg/kWh. Nissan Leaf batteries are relatively light (7.5 kg/kWh). With the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 5-6 kg/kWh.

=== Volume (L) ===
'''Will it fit?''' Batteries are bulky. They are getting smaller, but finding enough space my be your biggest challenge. You can reckon on 5-10 L/kWh for older EV or hybrid batteries. For the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 3-3.5 kg/kWh.

There is much, much more to battery design than this (e.g. maximum charge rate, terminations, cooling, clamping), but the above should help work out which options will or won't work for your project...

== Cell chemistry ==

=== Lithium Iron Phosphate (LiFePO4) ===
Lithium Iron Phosphate (also known as LFP, or LiFePO4) batteries offer a good compromise between safety, energy density and ease of use for DIY conversions. They are available in a number of formats, commonly pouch cells, prismatic cells and cylindrical cells.

==== LiFePO4 pouch cells ====
The majority of this content is drawn from this thread: [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761&start=900 https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761] discussing the use of the A123 20Ah pouch cell. However, many of the general points apply equally to other similar pouch cells.

===== General build requirements =====
Pouch cells are vulnerable to damage from debris, and must be held in compression (see the datasheet for your battery, but 10-12 psi is recommended for the A123 pouch cells as a guide). A rigid container capable of preventing damage and providing compression is therefore required. Be aware the cells expand and contract in use, so allowance for this must be included in the structure of the case.

The pouch cells should be separated to prevent abrasion between cells, and also to avoid the development of hot spots. Prebuilt modules from A123 systems had thin foam sheets or heatsinks between each cell. Be sure to avoid any debris that could rub on the pouch surface, particularly if using recycled cells.

Mylar, '[https://www.americanmicroinc.com/fish-paper/ Fish paper]' or a [https://www.rogerscorp.com/elastomeric-material-solutions/poron-industrial-polyurethanes compliant foam] may be appropriate materials to serve this purpose. This material should not be flammable. If the material is heat insulating, it is important to address thermal management.

===== Compression =====
Compression is required to prevent premature failure of the cell. Without compression electrolyte will become unevenly distributed, causing current gradients in the cell and uneven heating. Local temperatures can become high enough to form gas formation leading to cells 'puffing up' even when the pack is otherwise held within temperature and voltage constraints. This will be exacerbated in packs with otherwise poor thermal management. Compression forces gas generated to the margins of the cell, outside of the cell stack, minimising its effect cell performance. Gas in the middle cells will create a dead space which does not store or release energy.

There is ~1% expansion through a discharge cycle. As the cell ages, the nominal cell thickness can grow by 3-5%. For A123 cells the ideal pressure is between 4 and 18psi with the ideal pressure being ~12psi. Maintaining 12psi can increase the life by 500 cycles over that of 4 or 18psi

There is some suggestion that in uses where 1C is never exceeded compression ''may'' not be required.

Highly rigid endplates with a mechanism to allow for a limited degree of expansion (e.g. steel bands) are considered an effective solution to this challenge.

It should be noted that compression is a challenge specific to pouch cells. Cylindrical cells are designed to maintain their own compression within the cell's electrode stack by their design.

This thread provides more information and experimentation relating to pack compression: <nowiki>https://endless-sphere.com/forums/viewtopic.php?f=14&t=52244</nowiki>

===== Pouch Cell Pack Design Examples =====
<nowiki>*</nowiki>placeholder*

===== Notes regarding recycled pouch cells =====
Pouch cells are somewhat fragile, and breaching the insulation is not difficult, especially in a cells removed from existing packs and repurposed. If the pouch has had their poly-layers compromised you may see a number of faults:
* Black spots around the perimeter of the cell indicate electrolyte leakage
* Voltage on the outside of the bag. Note that microvoltage between the pouch and the electrode is normal (and due to a capacitive effect).
While the majority of these cells should no longer be in the market, a significant number of faulty cells made it back into the 'greymarket' in around 2013. These cells had misaligned tabs which can also lead to isolation failures between the tab and the pack. These cells should be avoided, particularly in high demand applications.

===== Situations likely to cause pouch cell failure =====
''Taken directly from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''
# '''Overcharge'''. Any extended time above 3.8 Volts will generate enough heat and electrochemical activity to puff a cell, especially one that is improperly compressed.
# '''Overdischarge followed by charge'''. Any A123 cell that has been pulled low enough to come to rest at <300 mV should be immediately scrapped. The published number for that is 500 mV, but the real figure is closer to 300, so that's a "safety buffer" if you will. Below this Voltage, the Cu electrodes start to dissolve into the electrolyte. When charge is applied, the Cu forms dendrites that puncture the separator layer, forming an internal short in the cell. This can puff a cell in a hurry---the more charge current on tap, the worse it's prone to be.
# '''Driving a cell negative'''. I've neglected to mention this before, but it is a possibility. I don't know much about the specific mechanism at this time.
# '''Malfunctioning or misinformed electronics'''. This is the most common cause of all of the above in my experience. At this stage of the game, it is critical for YOU to understand how your BMS functions on at least a cursory level. Choose your BMS very carefully and periodically verify that it is operating properly. They're not all created equal. Make sure V sense lines are securely connected and free of corrosion. Just because your BMS says there was never a problem doesn't necessarily make it so. Avoid harnesses or ribbon cables between multiple modules if possible--they are problematic wherever they are used in any mobile electronics.
# '''Exposure to or generation of sufficient heat'''. I don't know exactly at what temperature gas formation begins in the electrolyte, but we spec a max storage temp of 80 (or 85?) degrees C and I suspect this is the reason. The hotter, the puffier--to a point. This is why soldering tabs poses a real hazard to cell health. If you feel you must solder, sink or blow the heat away from the body of the cell. Use a big iron that can make sufficient local heat quickly, before the whole mass of the cell gets hot. You might even get the cell warm enough to melt separator if not careful.
# '''No compression, not enough compression, improperly distributed compression'''. This is a pack/module design issue. Apply 10, maybe 15 psi to your cell stack end to end and then band snugly and evenly. Use hard endplates of some sort--never wrap cells directly or allow their shape to become distorted. Protect all areas of the pouch from impact damage. This obviously does not apply to cylindrical cells.

==== LiFePO4 prismatic cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cylindrical cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cell ageing ====
''Derived (barely paraphrased) from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''

Capacity loss is caused by the lithium that was available for storage becoming permanently plated on the cathode. Being unable to move within the cell it is no longer available to store energy. The impact of this plating is greater than the amount of lithium 'lost' to plating because not only is the lithium no longer available, it is also preventing access to that part of the cathode meaning Li that can still move has to take a longer path to reach the cathode. Lithium plating is one cause of increased cell resistance (there are others), a sign of worsening cell health.

There is no linear relationship between actual capacity loss and impedance rise. However some cell defects will also increase impedance.

Increasing cell resistance may cause a number of symptoms which may be confused with [https://earthshipbiotecture.com/a-lithium-ion-battery-primer/ High Self Discharge.]
# Elevated Peukert Losses. As more energy per amount of current through the cell is lost as heat, the cells useable capacity decreases. So the apparent capacity loss is higher than the actual capacity loss of cycleable lithium. When used in low current applications (e.g. solar energy storage) the actual and apparent decrease in capacity will be small. In high current draw applications (like EV traction packs), the Peukert loss increases proportionally, so the apparent capacity loss increases much faster than the actual capacity loss.
# Greater voltage excursion under the same load. Due to increased cell resistancethe voltage will sag further under the same load than a cell in optimal condition. The inverse is also true, the voltage will be higher for the same amount of charging current applied. The cell will then rebound to a voltage further from the loaded and charging voltages. This, obviously, can look like high self discharge but is a different phenomenon.
# Absolute maximum current decrease.
Elevated impedance causes a more complex constellation of symptoms, some of which may be easy to confuse with High Self Discharge (HSD). Ohm's law (E=I/R) holds the key to understanding here.

'''1) Elevated Peukert losses.''' Because more energy per unit of current through the cell is lost as heat, less of the cell's capacity is actually USABLE. Thus, apparent capacity loss can be significantly greater than actual capacity loss caused by the loss of cycleable Li alone. In low current applications, the two numbers will be close together. In high current applications, Peukert losses increase in proportion, so apparent loss of capacity breaks further and further away from actual capacity loss as current increases.

'''2) Greater voltage excursion under the same load.''' Elevated resistance across the cell means that voltage will sag more under the same load than it did when the cell was healthier. Conversely, voltage will rise higher with the same amount of applied charge current than it did when it was healthier. At the same time, rebound/settling voltages will be further away from loaded/charging voltages. In other words, the cell will rebound to a voltage further away from loaded voltage, all else being equal. Similarly, voltage will settle farther from the charge voltage with the same charge applied. This can give the illusion of elevated self-discharge, but the phenomenon is actually not the same thing. Again, the greater the charge and load currents, the greater the effect becomes.

'''3) Absolute max current decreases.''' Because the cell's series resistance is elevated, the maximum possible current through the cell is decreased.

Just to confuse things further, there can be many factors that lead to impedance rise. Some are related to Li plating, others are not.

=== Lithium-ion ===
Lithium-ion (Li-ion) batteries have a greater energy density than Lithium Iron Phosphate batteries, but have more challenging needs to use safely. The ideal operating range of Li-ion batteries is between +15 and +45°C. The upper limit of temperature is particularly important as Li-ion batteries experience thermal runaway - an unstoppable chain reaction that can occur in milliseconds releasing the stored energy in the cell. This can produce temperatures of 400°C and a fire that is extremely difficult to put out. Thermal runaway can start as low as 60°C and becomes much more likely at 100°C

Risk factors for thermal runaway:
* Short Circuits - either internally or externally
* Overcharging
* Excessive current draw or when charging

==== Li-ion pouch cells ====
[https://kokam.com/cell Kokam] produce high-performance Li-ion pouch cells. These combine relative ease of use and pack construction with performance close to cylindrical cells.

==== Li-ion 18650 and other cylindrical cells ====
Cylindrical cells are favoured by Tesla, and are probably the main reason why their cars achieve such excellent performance. They are light, compact, powerful and expensive. Unfortunately, cylindrical cells are staggeringly difficult (and dangerous) to use in DIY conversions. There are two good reasons for this: thermal management and cell configuration.

As stated above, Li-ion cells are prone to thermal runaway. So you need perfect thermal management to ensure that no cell ever exceeds the critical temperature. If this happens, the cell will short-circuit internally, releasing a lot of energy - potentially explosively. Furthermore, the individual cells are small, so need to be arranged in parallel. In the case of the Tesla Model S, there are 74 cells in each parallel. Imagine if one of those cells fails and becomes short circuited internally. You now have 73 very high power cells in parallel feeding in to that short circuit. In fact, you don't have to imagine: you can watch this famous video instead (courtesy of Rich Rebuilds).

<youtube>WdDi1haA71Q</youtube>

== OEM modules ==
Using an OEM module means a lot of the difficulties associated with battery design are taken care of e.g. cooling, clamping, etc. Here is a list of OEM modules.
{| class="wikitable sortable mw-collapsible"
|+
!Manufacturer
!Type
!Capacity (kWh)
!Weight (kg)
!w (mm)
!d (mm)
!h (mm)
!Gravity (kg/kWh)
!Volume (L/kWh)
!Voltage (V)
!Current (cont A)
!Current (peak A)
!Cell arrangement
!Cell type
!Chemistry
|-
|Tesla
|Model S
|5.3
|25
|666
|303
|79
|4.7
|3.0
|22.8
|500
|750
|74p6s
|18650
|Li-ion
|-
|Chevrolet
|Volt
|2
|20.5
|241
|241
|267
|10.2
|7.8
|48
|240
|350
|3p12s
|Pouch
|Li-ion
|-
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|}

Batteries

2020-11-30T20:28:50Z

Clanger9: Add OEM module table

== Introduction ==
There are a wide variety of battery chemistries available for use as the main traction battery of an EV. To use each chemistry safely, and to ensure an adequate service life from the battery pack it is important to understand the requirements for the chemistry you are using. Failure to do so may lead to premature or catastrophic failure of the pack.

Good pack design will allow for a nominal amount of abuse. People make mistakes and the pack should allow a margin for safety - and for longevity!

== Battery pack specification ==
When deciding on your battery pack, here are some basic parameters to consider:

=== Capacity (kWh) ===
'''How far do you want to go?''' A standard car conversion will need around 1kWh for 3 miles of range. For a middleweight motorcycle, 1kWh should give around 9 miles. ''Your mileage may vary'', as they say.

=== Voltage (V) ===
'''How fast do you want to go?''' The pack voltage defines the maximum speed your motor can spin. Motors are usually specified with "KV" - or RPM-per-volt. Check the KV of your motor and how fast it needs to spin to get your desired top speed. e.g. if you need 3,000 RPM from a 25 KV motor then your pack voltage needs to be 3,000 / 25 = 120 V. The exact number of cells in series you need depends on the cell design, but 3.8 V for Li-ion and 3.2 V for LiFePO4 is a reasonable guess.

=== Maximum current (A) ===
'''How quickly do you want to accelerate?''' Your motor's maximum power will be specified in kW. To estimate your maximum current draw, divide the peak power by the battery voltage. e.g. a 30 kW motor with a 120 V battery pack will pull 30,000 / 120 = 250 A. The higher the current rating of the cells, the heavier they will be for a given capacity. Ideally, you want "enough" current capacity for full throttle acceleration, but no more. You can put cells in parallel to double the current rating of your pack (which of course will half the voltage).

=== Mass (kg) ===
'''Can your vehicle carry the weight?''' You'll need to keep the kerb weight within the original design limits. For a car, this could be a few hundred kg. For a motorcycle, likely less than 100 kg. This is a huge variable - and each new generation of battery tech seems to be a little lighter. For older EV or hybrid batteries, you can reckon on 10-15 kg/kWh. Nissan Leaf batteries are relatively light (7.5 kg/kWh). With the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 5-6 kg/kWh.

=== Volume (L) ===
'''Will it fit?''' Batteries are bulky. They are getting smaller, but finding enough space my be your biggest challenge. You can reckon on 5-10 L/kWh for older EV or hybrid batteries. For the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 3-3.5 kg/kWh.

There is much, much more to battery design than this (e.g. maximum charge rate, terminations, cooling, clamping), but the above should help work out which options will or won't work for your project...

== Cell chemistry ==

=== Lithium Iron Phosphate (LiFePO4) ===
Lithium Iron Phosphate (also known as LFP, or LiFePO4) batteries offer a good compromise between safety, energy density and ease of use for DIY conversions. They are available in a number of formats, commonly pouch cells, prismatic cells and cylindrical cells.

==== LiFePO4 pouch cells ====
The majority of this content is drawn from this thread: [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761&start=900 https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761] discussing the use of the A123 20Ah pouch cell. However, many of the general points apply equally to other similar pouch cells.

===== General build requirements =====
Pouch cells are vulnerable to damage from debris, and must be held in compression (see the datasheet for your battery, but 10-12 psi is recommended for the A123 pouch cells as a guide). A rigid container capable of preventing damage and providing compression is therefore required. Be aware the cells expand and contract in use, so allowance for this must be included in the structure of the case.

The pouch cells should be separated to prevent abrasion between cells, and also to avoid the development of hot spots. Prebuilt modules from A123 systems had thin foam sheets or heatsinks between each cell. Be sure to avoid any debris that could rub on the pouch surface, particularly if using recycled cells.

Mylar, '[https://www.americanmicroinc.com/fish-paper/ Fish paper]' or a [https://www.rogerscorp.com/elastomeric-material-solutions/poron-industrial-polyurethanes compliant foam] may be appropriate materials to serve this purpose. This material should not be flammable. If the material is heat insulating, it is important to address thermal management.

===== Compression =====
Compression is required to prevent premature failure of the cell. Without compression electrolyte will become unevenly distributed, causing current gradients in the cell and uneven heating. Local temperatures can become high enough to form gas formation leading to cells 'puffing up' even when the pack is otherwise held within temperature and voltage constraints. This will be exacerbated in packs with otherwise poor thermal management. Compression forces gas generated to the margins of the cell, outside of the cell stack, minimising its effect cell performance. Gas in the middle cells will create a dead space which does not store or release energy.

There is ~1% expansion through a discharge cycle. As the cell ages, the nominal cell thickness can grow by 3-5%. For A123 cells the ideal pressure is between 4 and 18psi with the ideal pressure being ~12psi. Maintaining 12psi can increase the life by 500 cycles over that of 4 or 18psi

There is some suggestion that in uses where 1C is never exceeded compression ''may'' not be required.

Highly rigid endplates with a mechanism to allow for a limited degree of expansion (e.g. steel bands) are considered an effective solution to this challenge.

It should be noted that compression is a challenge specific to pouch cells. Cylindrical cells are designed to maintain their own compression within the cell's electrode stack by their design.

This thread provides more information and experimentation relating to pack compression: <nowiki>https://endless-sphere.com/forums/viewtopic.php?f=14&t=52244</nowiki>

===== Pouch Cell Pack Design Examples =====
<nowiki>*</nowiki>placeholder*

===== Notes regarding recycled pouch cells =====
Pouch cells are somewhat fragile, and breaching the insulation is not difficult, especially in a cells removed from existing packs and repurposed. If the pouch has had their poly-layers compromised you may see a number of faults:
* Black spots around the perimeter of the cell indicate electrolyte leakage
* Voltage on the outside of the bag. Note that microvoltage between the pouch and the electrode is normal (and due to a capacitive effect).
While the majority of these cells should no longer be in the market, a significant number of faulty cells made it back into the 'greymarket' in around 2013. These cells had misaligned tabs which can also lead to isolation failures between the tab and the pack. These cells should be avoided, particularly in high demand applications.

===== Situations likely to cause pouch cell failure =====
''Taken directly from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''
# '''Overcharge'''. Any extended time above 3.8 Volts will generate enough heat and electrochemical activity to puff a cell, especially one that is improperly compressed.
# '''Overdischarge followed by charge'''. Any A123 cell that has been pulled low enough to come to rest at <300 mV should be immediately scrapped. The published number for that is 500 mV, but the real figure is closer to 300, so that's a "safety buffer" if you will. Below this Voltage, the Cu electrodes start to dissolve into the electrolyte. When charge is applied, the Cu forms dendrites that puncture the separator layer, forming an internal short in the cell. This can puff a cell in a hurry---the more charge current on tap, the worse it's prone to be.
# '''Driving a cell negative'''. I've neglected to mention this before, but it is a possibility. I don't know much about the specific mechanism at this time.
# '''Malfunctioning or misinformed electronics'''. This is the most common cause of all of the above in my experience. At this stage of the game, it is critical for YOU to understand how your BMS functions on at least a cursory level. Choose your BMS very carefully and periodically verify that it is operating properly. They're not all created equal. Make sure V sense lines are securely connected and free of corrosion. Just because your BMS says there was never a problem doesn't necessarily make it so. Avoid harnesses or ribbon cables between multiple modules if possible--they are problematic wherever they are used in any mobile electronics.
# '''Exposure to or generation of sufficient heat'''. I don't know exactly at what temperature gas formation begins in the electrolyte, but we spec a max storage temp of 80 (or 85?) degrees C and I suspect this is the reason. The hotter, the puffier--to a point. This is why soldering tabs poses a real hazard to cell health. If you feel you must solder, sink or blow the heat away from the body of the cell. Use a big iron that can make sufficient local heat quickly, before the whole mass of the cell gets hot. You might even get the cell warm enough to melt separator if not careful.
# '''No compression, not enough compression, improperly distributed compression'''. This is a pack/module design issue. Apply 10, maybe 15 psi to your cell stack end to end and then band snugly and evenly. Use hard endplates of some sort--never wrap cells directly or allow their shape to become distorted. Protect all areas of the pouch from impact damage. This obviously does not apply to cylindrical cells.

==== LiFePO4 prismatic cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cylindrical cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cell ageing ====
''Derived (barely paraphrased) from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''

Capacity loss is caused by the lithium that was available for storage becoming permanently plated on the cathode. Being unable to move within the cell it is no longer available to store energy. The impact of this plating is greater than the amount of lithium 'lost' to plating because not only is the lithium no longer available, it is also preventing access to that part of the cathode meaning Li that can still move has to take a longer path to reach the cathode. Lithium plating is one cause of increased cell resistance (there are others), a sign of worsening cell health.

There is no linear relationship between actual capacity loss and impedance rise. However some cell defects will also increase impedance.

Increasing cell resistance may cause a number of symptoms which may be confused with [https://earthshipbiotecture.com/a-lithium-ion-battery-primer/ High Self Discharge.]
# Elevated Peukert Losses. As more energy per amount of current through the cell is lost as heat, the cells useable capacity decreases. So the apparent capacity loss is higher than the actual capacity loss of cycleable lithium. When used in low current applications (e.g. solar energy storage) the actual and apparent decrease in capacity will be small. In high current draw applications (like EV traction packs), the Peukert loss increases proportionally, so the apparent capacity loss increases much faster than the actual capacity loss.
# Greater voltage excursion under the same load. Due to increased cell resistancethe voltage will sag further under the same load than a cell in optimal condition. The inverse is also true, the voltage will be higher for the same amount of charging current applied. The cell will then rebound to a voltage further from the loaded and charging voltages. This, obviously, can look like high self discharge but is a different phenomenon.
# Absolute maximum current decrease.
Elevated impedance causes a more complex constellation of symptoms, some of which may be easy to confuse with High Self Discharge (HSD). Ohm's law (E=I/R) holds the key to understanding here.

'''1) Elevated Peukert losses.''' Because more energy per unit of current through the cell is lost as heat, less of the cell's capacity is actually USABLE. Thus, apparent capacity loss can be significantly greater than actual capacity loss caused by the loss of cycleable Li alone. In low current applications, the two numbers will be close together. In high current applications, Peukert losses increase in proportion, so apparent loss of capacity breaks further and further away from actual capacity loss as current increases.

'''2) Greater voltage excursion under the same load.''' Elevated resistance across the cell means that voltage will sag more under the same load than it did when the cell was healthier. Conversely, voltage will rise higher with the same amount of applied charge current than it did when it was healthier. At the same time, rebound/settling voltages will be further away from loaded/charging voltages. In other words, the cell will rebound to a voltage further away from loaded voltage, all else being equal. Similarly, voltage will settle farther from the charge voltage with the same charge applied. This can give the illusion of elevated self-discharge, but the phenomenon is actually not the same thing. Again, the greater the charge and load currents, the greater the effect becomes.

'''3) Absolute max current decreases.''' Because the cell's series resistance is elevated, the maximum possible current through the cell is decreased.

Just to confuse things further, there can be many factors that lead to impedance rise. Some are related to Li plating, others are not.

=== Lithium-ion ===
Lithium-ion (Li-ion) batteries have a greater energy density than Lithium Iron Phosphate batteries, but have more challenging needs to use safely. The ideal operating range of Li-ion batteries is between +15 and +45°C. The upper limit of temperature is particularly important as Li-ion batteries experience thermal runaway - an unstoppable chain reaction that can occur in milliseconds releasing the stored energy in the cell. This can produce temperatures of 400°C and a fire that is extremely difficult to put out. Thermal runaway can start as low as 60°C and becomes much more likely at 100°C

Risk factors for thermal runaway:
* Short Circuits - either internally or externally
* Overcharging
* Excessive current draw or when charging

==== Li-ion pouch cells ====
[https://kokam.com/cell Kokam] produce high-performance Li-ion pouch cells. These combine relative ease of use and pack construction with performance close to cylindrical cells.

==== Li-ion 18650 and other cylindrical cells ====
Cylindrical cells are favoured by Tesla, and are probably the main reason why their cars achieve such excellent performance. They are light, compact, powerful and expensive. Unfortunately, cylindrical cells are staggeringly difficult (and dangerous) to use in DIY conversions. There are two good reasons for this: thermal management and cell configuration.

As stated above, Li-ion cells are prone to thermal runaway. So you need perfect thermal management to ensure that no cell ever exceeds the critical temperature. If this happens, the cell will short-circuit internally, releasing a lot of energy - potentially explosively. Furthermore, the individual cells are small, so need to be arranged in parallel. In the case of the Tesla Model S, there are 74 cells in each parallel. Imagine if one of those cells fails and becomes short circuited internally. You now have 73 very high power cells in parallel feeding in to that short circuit. In fact, you don't have to imagine: you can watch this famous video instead (courtesy of Rich Rebuilds).

== OEM modules ==
Using an OEM module means a lot of the difficulties associated with battery design are taken care of e.g. cooling, clamping, etc. Here is a list of OEM modules.
{| class="wikitable sortable mw-collapsible"
|+
!Manufacturer
!Type
!Capacity (kWh)
!Weight (kg)
!w (mm)
!d (mm)
!h (mm)
!Gravity (kg/kWh)
!Volume (L/kWh)
!Voltage (V)
!Current (cont A)
!Current (peak A)
!Cell arrangement
!Cell type
!Chemistry
|-
|Tesla
|Model S
|5.3
|25
|666
|303
|79
|4.7
|3.0
|22.8
|500
|750
|74p6s
|18650
|Li-ion
|-
|Chevrolet
|Volt
|2
|20.5
|241
|241
|267
|10.2
|7.8
|48
|240
|350
|3p12s
|Pouch
|Li-ion
|-
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|}
<youtube>WdDi1haA71Q</youtube>

Batteries

2020-11-30T19:53:22Z

Clanger9:

== Introduction ==
There are a wide variety of battery chemistries available for use as the main traction battery of an EV. To use each chemistry safely, and to ensure an adequate service life from the battery pack it is important to understand the requirements for the chemistry you are using. Failure to do so may lead to premature or catastrophic failure of the pack.

Good pack design will allow for a nominal amount of abuse. People make mistakes and the pack should allow a margin for safety - and for longevity!

== Battery pack specification ==
When deciding on your battery pack, here are some basic parameters to consider:

=== Capacity (kWh) ===
'''How far do you want to go?''' A standard car conversion will need around 1kWh for 3 miles of range. For a middleweight motorcycle, 1kWh should give around 9 miles. ''Your mileage may vary'', as they say.

=== Voltage (V) ===
'''How fast do you want to go?''' The pack voltage defines the maximum speed your motor can spin. Motors are usually specified with "KV" - or RPM-per-volt. Check the KV of your motor and how fast it needs to spin to get your desired top speed. e.g. if you need 3,000 RPM from a 25 KV motor then your pack voltage needs to be 3,000 / 25 = 120 V. The exact number of cells in series you need depends on the cell design, but 3.8 V for Li-ion and 3.2 V for LiFePO4 is a reasonable guess.

=== Maximum current (A) ===
'''How quickly do you want to accelerate?''' Your motor's maximum power will be specified in kW. To estimate your maximum current draw, divide the peak power by the battery voltage. e.g. a 30 kW motor with a 120 V battery pack will pull 30,000 / 120 = 250 A. The higher the current rating of the cells, the heavier they will be for a given capacity. Ideally, you want "enough" current capacity for full throttle acceleration, but no more. You can put cells in parallel to double the current rating of your pack (which of course will half the voltage).

=== Mass (kg) ===
'''Can your vehicle carry the weight?''' You'll need to keep the kerb weight within the original design limits. For a car, this could be a few hundred kg. For a motorcycle, likely less than 100 kg. This is a huge variable - and each new generation of battery tech seems to be a little lighter. For older EV or hybrid batteries, you can reckon on 10-15 kg/kWh. Nissan Leaf batteries are relatively light (7.5 kg/kWh). With the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 5-6 kg/kWh.

=== Volume (L) ===
'''Will it fit?''' Batteries are bulky. They are getting smaller, but finding enough space my be your biggest challenge. You can reckon on 5-10 L/kWh for older EV or hybrid batteries. For the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 3-3.5 kg/kWh.

There is much, much more to battery design than this (e.g. maximum charge rate, terminations, cooling, clamping), but the above should help work out which options will or won't work for your project...

== Cell chemistry ==

=== Lithium Iron Phosphate (LiFePO4) ===
Lithium Iron Phosphate (also known as LFP, or LiFePO4) batteries offer a good compromise between safety, energy density and ease of use for DIY conversions. They are available in a number of formats, commonly pouch cells, prismatic cells and cylindrical cells.

==== LiFePO4 pouch cells ====
The majority of this content is drawn from this thread: [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761&start=900 https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761] discussing the use of the A123 20Ah pouch cell. However, many of the general points apply equally to other similar pouch cells.

===== General build requirements =====
Pouch cells are vulnerable to damage from debris, and must be held in compression (see the datasheet for your battery, but 10-12 psi is recommended for the A123 pouch cells as a guide). A rigid container capable of preventing damage and providing compression is therefore required. Be aware the cells expand and contract in use, so allowance for this must be included in the structure of the case.

The pouch cells should be separated to prevent abrasion between cells, and also to avoid the development of hot spots. Prebuilt modules from A123 systems had thin foam sheets or heatsinks between each cell. Be sure to avoid any debris that could rub on the pouch surface, particularly if using recycled cells.

Mylar, '[https://www.americanmicroinc.com/fish-paper/ Fish paper]' or a [https://www.rogerscorp.com/elastomeric-material-solutions/poron-industrial-polyurethanes compliant foam] may be appropriate materials to serve this purpose. This material should not be flammable. If the material is heat insulating, it is important to address thermal management.

===== Compression =====
Compression is required to prevent premature failure of the cell. Without compression electrolyte will become unevenly distributed, causing current gradients in the cell and uneven heating. Local temperatures can become high enough to form gas formation leading to cells 'puffing up' even when the pack is otherwise held within temperature and voltage constraints. This will be exacerbated in packs with otherwise poor thermal management. Compression forces gas generated to the margins of the cell, outside of the cell stack, minimising its effect cell performance. Gas in the middle cells will create a dead space which does not store or release energy.

There is ~1% expansion through a discharge cycle. As the cell ages, the nominal cell thickness can grow by 3-5%. For A123 cells the ideal pressure is between 4 and 18psi with the ideal pressure being ~12psi. Maintaining 12psi can increase the life by 500 cycles over that of 4 or 18psi

There is some suggestion that in uses where 1C is never exceeded compression ''may'' not be required.

Highly rigid endplates with a mechanism to allow for a limited degree of expansion (e.g. steel bands) are considered an effective solution to this challenge.

It should be noted that compression is a challenge specific to pouch cells. Cylindrical cells are designed to maintain their own compression within the cell's electrode stack by their design.

This thread provides more information and experimentation relating to pack compression: <nowiki>https://endless-sphere.com/forums/viewtopic.php?f=14&t=52244</nowiki>

===== Pouch Cell Pack Design Examples =====
<nowiki>*</nowiki>placeholder*

===== Notes regarding recycled pouch cells =====
Pouch cells are somewhat fragile, and breaching the insulation is not difficult, especially in a cells removed from existing packs and repurposed. If the pouch has had their poly-layers compromised you may see a number of faults:
* Black spots around the perimeter of the cell indicate electrolyte leakage
* Voltage on the outside of the bag. Note that microvoltage between the pouch and the electrode is normal (and due to a capacitive effect).
While the majority of these cells should no longer be in the market, a significant number of faulty cells made it back into the 'greymarket' in around 2013. These cells had misaligned tabs which can also lead to isolation failures between the tab and the pack. These cells should be avoided, particularly in high demand applications.

===== Situations likely to cause pouch cell failure =====
''Taken directly from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''
# '''Overcharge'''. Any extended time above 3.8 Volts will generate enough heat and electrochemical activity to puff a cell, especially one that is improperly compressed.
# '''Overdischarge followed by charge'''. Any A123 cell that has been pulled low enough to come to rest at <300 mV should be immediately scrapped. The published number for that is 500 mV, but the real figure is closer to 300, so that's a "safety buffer" if you will. Below this Voltage, the Cu electrodes start to dissolve into the electrolyte. When charge is applied, the Cu forms dendrites that puncture the separator layer, forming an internal short in the cell. This can puff a cell in a hurry---the more charge current on tap, the worse it's prone to be.
# '''Driving a cell negative'''. I've neglected to mention this before, but it is a possibility. I don't know much about the specific mechanism at this time.
# '''Malfunctioning or misinformed electronics'''. This is the most common cause of all of the above in my experience. At this stage of the game, it is critical for YOU to understand how your BMS functions on at least a cursory level. Choose your BMS very carefully and periodically verify that it is operating properly. They're not all created equal. Make sure V sense lines are securely connected and free of corrosion. Just because your BMS says there was never a problem doesn't necessarily make it so. Avoid harnesses or ribbon cables between multiple modules if possible--they are problematic wherever they are used in any mobile electronics.
# '''Exposure to or generation of sufficient heat'''. I don't know exactly at what temperature gas formation begins in the electrolyte, but we spec a max storage temp of 80 (or 85?) degrees C and I suspect this is the reason. The hotter, the puffier--to a point. This is why soldering tabs poses a real hazard to cell health. If you feel you must solder, sink or blow the heat away from the body of the cell. Use a big iron that can make sufficient local heat quickly, before the whole mass of the cell gets hot. You might even get the cell warm enough to melt separator if not careful.
# '''No compression, not enough compression, improperly distributed compression'''. This is a pack/module design issue. Apply 10, maybe 15 psi to your cell stack end to end and then band snugly and evenly. Use hard endplates of some sort--never wrap cells directly or allow their shape to become distorted. Protect all areas of the pouch from impact damage. This obviously does not apply to cylindrical cells.

==== LiFePO4 prismatic cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cylindrical cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cell ageing ====
''Derived (barely paraphrased) from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''

Capacity loss is caused by the lithium that was available for storage becoming permanently plated on the cathode. Being unable to move within the cell it is no longer available to store energy. The impact of this plating is greater than the amount of lithium 'lost' to plating because not only is the lithium no longer available, it is also preventing access to that part of the cathode meaning Li that can still move has to take a longer path to reach the cathode. Lithium plating is one cause of increased cell resistance (there are others), a sign of worsening cell health.

There is no linear relationship between actual capacity loss and impedance rise. However some cell defects will also increase impedance.

Increasing cell resistance may cause a number of symptoms which may be confused with [https://earthshipbiotecture.com/a-lithium-ion-battery-primer/ High Self Discharge.]
# Elevated Peukert Losses. As more energy per amount of current through the cell is lost as heat, the cells useable capacity decreases. So the apparent capacity loss is higher than the actual capacity loss of cycleable lithium. When used in low current applications (e.g. solar energy storage) the actual and apparent decrease in capacity will be small. In high current draw applications (like EV traction packs), the Peukert loss increases proportionally, so the apparent capacity loss increases much faster than the actual capacity loss.
# Greater voltage excursion under the same load. Due to increased cell resistancethe voltage will sag further under the same load than a cell in optimal condition. The inverse is also true, the voltage will be higher for the same amount of charging current applied. The cell will then rebound to a voltage further from the loaded and charging voltages. This, obviously, can look like high self discharge but is a different phenomenon.
# Absolute maximum current decrease.
Elevated impedance causes a more complex constellation of symptoms, some of which may be easy to confuse with High Self Discharge (HSD). Ohm's law (E=I/R) holds the key to understanding here.

'''1) Elevated Peukert losses.''' Because more energy per unit of current through the cell is lost as heat, less of the cell's capacity is actually USABLE. Thus, apparent capacity loss can be significantly greater than actual capacity loss caused by the loss of cycleable Li alone. In low current applications, the two numbers will be close together. In high current applications, Peukert losses increase in proportion, so apparent loss of capacity breaks further and further away from actual capacity loss as current increases.

'''2) Greater voltage excursion under the same load.''' Elevated resistance across the cell means that voltage will sag more under the same load than it did when the cell was healthier. Conversely, voltage will rise higher with the same amount of applied charge current than it did when it was healthier. At the same time, rebound/settling voltages will be further away from loaded/charging voltages. In other words, the cell will rebound to a voltage further away from loaded voltage, all else being equal. Similarly, voltage will settle farther from the charge voltage with the same charge applied. This can give the illusion of elevated self-discharge, but the phenomenon is actually not the same thing. Again, the greater the charge and load currents, the greater the effect becomes.

'''3) Absolute max current decreases.''' Because the cell's series resistance is elevated, the maximum possible current through the cell is decreased.

Just to confuse things further, there can be many factors that lead to impedance rise. Some are related to Li plating, others are not.

=== Lithium-ion ===
Lithium-ion (Li-ion) batteries have a greater energy density than Lithium Iron Phosphate batteries, but have more challenging needs to use safely. The ideal operating range of Li-ion batteries is between +15 and +45°C. The upper limit of temperature is particularly important as Li-ion batteries experience thermal runaway - an unstoppable chain reaction that can occur in milliseconds releasing the stored energy in the cell. This can produce temperatures of 400°C and a fire that is extremely difficult to put out. Thermal runaway can start as low as 60°C and becomes much more likely at 100°C

Risk factors for thermal runaway:
* Short Circuits - either internally or externally
* Overcharging
* Excessive current draw or when charging

==== Li-ion pouch cells ====
[https://kokam.com/cell Kokam] produce high-performance Li-ion pouch cells. These combine relative ease of use and pack construction with performance close to cylindrical cells.

==== Li-ion 18650 and other cylindrical cells ====
Cylindrical cells are favoured by Tesla, and are probably the main reason why their cars achieve such excellent performance. They are light, compact, powerful and expensive. Unfortunately, cylindrical cells are staggeringly difficult (and dangerous) to use in DIY conversions. There are two good reasons for this: thermal management and cell configuration.

As stated above, Li-ion cells are prone to thermal runaway. So you need perfect thermal management to ensure that no cell ever exceeds the critical temperature. If this happens, the cell will short-circuit internally, releasing a lot of energy - potentially explosively. Furthermore, the individual cells are small, so need to be arranged in parallel. In the case of the Tesla Model S, there are 74 cells in each parallel. Imagine if one of those cells fails and becomes short circuited internally. You now have 73 very high power cells in parallel feeding in to that short circuit. In fact, you don't have to imagine: you can watch this famous video instead (courtesy of Rich Rebuilds).

<youtube>WdDi1haA71Q</youtube>

Batteries

2020-11-30T19:52:56Z

Clanger9:

== Introduction ==
There are a wide variety of battery chemistries available for use as the main traction battery of an EV. To use each chemistry safely, and to ensure an adequate service life from the battery pack it is important to understand the requirements for the chemistry you are using. Failure to do so may lead to premature or catastrophic failure of the pack.

Good pack design will allow for a nominal amount of abuse. People make mistakes and the pack should allow a margin for safety - and for longevity!

== Battery pack specification ==
When deciding on your battery pack, here are some basic parameters to consider:

=== Capacity (kWh) ===
'''How far do you want to go?''' A standard car conversion will need around 1kWh for 3 miles of range. For a middleweight motorcycle, 1kWh should give around 9 miles. ''Your mileage may vary'', as they say.

=== Voltage (V) ===
'''How fast do you want to go?''' The pack voltage defines the maximum speed your motor can spin. Motors are usually specified with "KV" - or RPM-per-volt. Check the KV of your motor and how fast it needs to spin to get your desired top speed. e.g. if you need 3,000 RPM from a 25 KV motor then your pack voltage needs to be 3,000 / 25 = 120 V. The exact number of cells in series you need depends on the cell design, but 3.8 V for Li-ion and 3.2 V for LiFePO4 is a reasonable guess.

=== Maximum current (A) ===
'''How quickly do you want to accelerate?''' Your motor's maximum power will be specified in kW. To estimate your maximum current draw, divide the peak power by the battery voltage. e.g. a 30 kW motor with a 120 V battery pack will pull 30,000 / 120 = 250 A. The higher the current rating of the cells, the heavier they will be for a given capacity. Ideally, you want "enough" current capacity for full throttle acceleration, but no more. You can put cells in parallel to double the current rating of your pack (which of course will half the voltage).

=== Mass (kg) ===
'''Can your vehicle carry the weight?''' You'll need to keep the kerb weight within the original design limits. For a car, this could be a few hundred kg. For a motorcycle, likely less than 100 kg. This is a huge variable - and each new generation of battery tech seems to be a little lighter. For older EV or hybrid batteries, you can reckon on 10-15 kg/kWh. Nissan Leaf batteries are relatively light (7.5 kg/kWh). With the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 5-6 kg/kWh.

=== Volume (L) ===
'''Will it fit?''' Batteries are bulky. They are getting smaller, but finding enough space my be your biggest challenge. You can reckon on 5-10 L/kWh for older EV or hybrid batteries. For the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 3-3.5 kg/kWh.

There is much, much more to battery design than this (e.g. maximum charge rate, terminations, cooling, clamping), but the above should help work out which options will or won't work for your project...

== Cell chemistry ==

=== Lithium Iron Phosphate (LiFePO4) ===
Lithium Iron Phosphate (also known as LFP, or LiFePO4) batteries offer a good compromise between safety, energy density and ease of use for DIY conversions. They are available in a number of formats, commonly pouch cells, prismatic cells and cylindrical cells.

==== LiFePO4 pouch cells ====
The majority of this content is drawn from this thread: [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761&start=900 https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761] discussing the use of the A123 20Ah pouch cell. However, many of the general points apply equally to other similar pouch cells.

===== General build requirements =====
Pouch cells are vulnerable to damage from debris, and must be held in compression (see the datasheet for your battery, but 10-12 psi is recommended for the A123 pouch cells as a guide). A rigid container capable of preventing damage and providing compression is therefore required. Be aware the cells expand and contract in use, so allowance for this must be included in the structure of the case.

The pouch cells should be separated to prevent abrasion between cells, and also to avoid the development of hot spots. Prebuilt modules from A123 systems had thin foam sheets or heatsinks between each cell. Be sure to avoid any debris that could rub on the pouch surface, particularly if using recycled cells.

Mylar, '[https://www.americanmicroinc.com/fish-paper/ Fish paper]' or a [https://www.rogerscorp.com/elastomeric-material-solutions/poron-industrial-polyurethanes compliant foam] may be appropriate materials to serve this purpose. This material should not be flammable. If the material is heat insulating, it is important to address thermal management.

===== Compression =====
Compression is required to prevent premature failure of the cell. Without compression electrolyte will become unevenly distributed, causing current gradients in the cell and uneven heating. Local temperatures can become high enough to form gas formation leading to cells 'puffing up' even when the pack is otherwise held within temperature and voltage constraints. This will be exacerbated in packs with otherwise poor thermal management. Compression forces gas generated to the margins of the cell, outside of the cell stack, minimising its effect cell performance. Gas in the middle cells will create a dead space which does not store or release energy.

There is ~1% expansion through a discharge cycle. As the cell ages, the nominal cell thickness can grow by 3-5%. For A123 cells the ideal pressure is between 4 and 18psi with the ideal pressure being ~12psi. Maintaining 12psi can increase the life by 500 cycles over that of 4 or 18psi

There is some suggestion that in uses where 1C is never exceeded compression ''may'' not be required.

Highly rigid endplates with a mechanism to allow for a limited degree of expansion (e.g. steel bands) are considered an effective solution to this challenge.

It should be noted that compression is a challenge specific to pouch cells. Cylindrical cells are designed to maintain their own compression within the cell's electrode stack by their design.

This thread provides more information and experimentation relating to pack compression: <nowiki>https://endless-sphere.com/forums/viewtopic.php?f=14&t=52244</nowiki>

===== Pouch Cell Pack Design Examples =====
<nowiki>*</nowiki>placeholder*

===== Notes regarding recycled pouch cells =====
Pouch cells are somewhat fragile, and breaching the insulation is not difficult, especially in a cells removed from existing packs and repurposed. If the pouch has had their poly-layers compromised you may see a number of faults:
* Black spots around the perimeter of the cell indicate electrolyte leakage
* Voltage on the outside of the bag. Note that microvoltage between the pouch and the electrode is normal (and due to a capacitive effect).
While the majority of these cells should no longer be in the market, a significant number of faulty cells made it back into the 'greymarket' in around 2013. These cells had misaligned tabs which can also lead to isolation failures between the tab and the pack. These cells should be avoided, particularly in high demand applications.

===== Situations likely to cause pouch cell failure =====
''Taken directly from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''
# '''Overcharge'''. Any extended time above 3.8 Volts will generate enough heat and electrochemical activity to puff a cell, especially one that is improperly compressed.
# '''Overdischarge followed by charge'''. Any A123 cell that has been pulled low enough to come to rest at <300 mV should be immediately scrapped. The published number for that is 500 mV, but the real figure is closer to 300, so that's a "safety buffer" if you will. Below this Voltage, the Cu electrodes start to dissolve into the electrolyte. When charge is applied, the Cu forms dendrites that puncture the separator layer, forming an internal short in the cell. This can puff a cell in a hurry---the more charge current on tap, the worse it's prone to be.
# '''Driving a cell negative'''. I've neglected to mention this before, but it is a possibility. I don't know much about the specific mechanism at this time.
# '''Malfunctioning or misinformed electronics'''. This is the most common cause of all of the above in my experience. At this stage of the game, it is critical for YOU to understand how your BMS functions on at least a cursory level. Choose your BMS very carefully and periodically verify that it is operating properly. They're not all created equal. Make sure V sense lines are securely connected and free of corrosion. Just because your BMS says there was never a problem doesn't necessarily make it so. Avoid harnesses or ribbon cables between multiple modules if possible--they are problematic wherever they are used in any mobile electronics.
# '''Exposure to or generation of sufficient heat'''. I don't know exactly at what temperature gas formation begins in the electrolyte, but we spec a max storage temp of 80 (or 85?) degrees C and I suspect this is the reason. The hotter, the puffier--to a point. This is why soldering tabs poses a real hazard to cell health. If you feel you must solder, sink or blow the heat away from the body of the cell. Use a big iron that can make sufficient local heat quickly, before the whole mass of the cell gets hot. You might even get the cell warm enough to melt separator if not careful.
# '''No compression, not enough compression, improperly distributed compression'''. This is a pack/module design issue. Apply 10, maybe 15 psi to your cell stack end to end and then band snugly and evenly. Use hard endplates of some sort--never wrap cells directly or allow their shape to become distorted. Protect all areas of the pouch from impact damage. This obviously does not apply to cylindrical cells.

==== LiFePO4 prismatic cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cylindrical cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cell ageing ====
''Derived (barely paraphrased) from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''

Capacity loss is caused by the lithium that was available for storage becoming permanently plated on the cathode. Being unable to move within the cell it is no longer available to store energy. The impact of this plating is greater than the amount of lithium 'lost' to plating because not only is the lithium no longer available, it is also preventing access to that part of the cathode meaning Li that can still move has to take a longer path to reach the cathode. Lithium plating is one cause of increased cell resistance (there are others), a sign of worsening cell health.

There is no linear relationship between actual capacity loss and impedance rise. However some cell defects will also increase impedance.

Increasing cell resistance may cause a number of symptoms which may be confused with [https://earthshipbiotecture.com/a-lithium-ion-battery-primer/ High Self Discharge.]
# Elevated Peukert Losses. As more energy per amount of current through the cell is lost as heat, the cells useable capacity decreases. So the apparent capacity loss is higher than the actual capacity loss of cycleable lithium. When used in low current applications (e.g. solar energy storage) the actual and apparent decrease in capacity will be small. In high current draw applications (like EV traction packs), the Peukert loss increases proportionally, so the apparent capacity loss increases much faster than the actual capacity loss.
# Greater voltage excursion under the same load. Due to increased cell resistancethe voltage will sag further under the same load than a cell in optimal condition. The inverse is also true, the voltage will be higher for the same amount of charging current applied. The cell will then rebound to a voltage further from the loaded and charging voltages. This, obviously, can look like high self discharge but is a different phenomenon.
# Absolute maximum current decrease.
Elevated impedance causes a more complex constellation of symptoms, some of which may be easy to confuse with High Self Discharge (HSD). Ohm's law (E=I/R) holds the key to understanding here.

'''1) Elevated Peukert losses.''' Because more energy per unit of current through the cell is lost as heat, less of the cell's capacity is actually USABLE. Thus, apparent capacity loss can be significantly greater than actual capacity loss caused by the loss of cycleable Li alone. In low current applications, the two numbers will be close together. In high current applications, Peukert losses increase in proportion, so apparent loss of capacity breaks further and further away from actual capacity loss as current increases.

'''2) Greater voltage excursion under the same load.''' Elevated resistance across the cell means that voltage will sag more under the same load than it did when the cell was healthier. Conversely, voltage will rise higher with the same amount of applied charge current than it did when it was healthier. At the same time, rebound/settling voltages will be further away from loaded/charging voltages. In other words, the cell will rebound to a voltage further away from loaded voltage, all else being equal. Similarly, voltage will settle farther from the charge voltage with the same charge applied. This can give the illusion of elevated self-discharge, but the phenomenon is actually not the same thing. Again, the greater the charge and load currents, the greater the effect becomes.

'''3) Absolute max current decreases.''' Because the cell's series resistance is elevated, the maximum possible current through the cell is decreased.

Just to confuse things further, there can be many factors that lead to impedance rise. Some are related to Li plating, others are not.

=== Lithium-ion ===
Lithium-ion (Li-ion) batteries have a greater energy density than Lithium Iron Phosphate batteries, but have more challenging needs to use safely. The ideal operating range of Li-ion batteries is between +15 and +45°C. The upper limit of temperature is particularly important as Li-ion batteries experience thermal runaway - an unstoppable chain reaction that can occur in milliseconds releasing the stored energy in the cell. This can produce temperatures of 400°C and a fire that is extremely difficult to put out. Thermal runaway can start as low as 60°C and becomes much more likely at 100°C

Risk factors for thermal runaway:
* Short Circuits - either internally or externally
* Overcharging
* Excessive current draw or when charging

==== Li-ion pouch cells ====
[https://kokam.com/cell Kokam] produce high-performance Li-ion pouch cells. These combine relative ease of use and pack construction with performance close to cylindrical cells.

==== Li-ion 18650 and other cylindrical cells ====
Cylindrical cells are favoured by Tesla, and are probably the main reason why their cars achieve such excellent performance. They are light, compact, powerful and expensive. Unfortunately, cylindrical cells are staggeringly difficult (and dangerous) to use in DIY conversions. There are two good reasons for this: thermal management and cell configuration.

As stated above, Li-ion cells are prone to thermal runaway. So you need perfect thermal management to ensure that no cell ever exceeds the critical temperature. If this happens, the cell will short-circuit internally, releasing a lot of energy - potentially explosively. Furthermore, the individual cells are small, so need to be arranged in parallel. In the case of the Tesla Model S, there are 74 cells in each parallel. Imagine if one of those cells fails and becomes short circuited internally. You now have 73 very high power cells in parallel feeding in to that short circuit. In fact, you don't have to imagine: you can watch this famous video instead (courtesy of Rich Rebuilds).

<nowiki><youtube>WdDi1haA71Q</youtube></nowiki>

Batteries

2020-11-30T19:50:56Z

Clanger9: /* Voltage (V) */ Add Li-ion content

== Introduction ==
There are a wide variety of battery chemistries available for use as the main traction battery of an EV. To use each chemistry safely, and to ensure an adequate service life from the battery pack it is important to understand the requirements for the chemistry you are using. Failure to do so may lead to premature or catastrophic failure of the pack.

Good pack design will allow for a nominal amount of abuse. People make mistakes and the pack should allow a margin for safety - and for longevity!

== Battery pack specification ==
When deciding on your battery pack, here are some basic parameters to consider:

=== Capacity (kWh) ===
'''How far do you want to go?''' A standard car conversion will need around 1kWh for 3 miles of range. For a middleweight motorcycle, 1kWh should give around 9 miles. ''Your mileage may vary'', as they say.

=== Voltage (V) ===
'''How fast do you want to go?''' The pack voltage defines the maximum speed your motor can spin. Motors are usually specified with "KV" - or RPM-per-volt. Check the KV of your motor and how fast it needs to spin to get your desired top speed. e.g. if you need 3,000 RPM from a 25 KV motor then your pack voltage needs to be 3,000 / 25 = 120 V. The exact number of cells in series you need depends on the cell design, but 3.8 V for Li-ion and 3.2 V for LiFePO4 is a reasonable guess.

=== Maximum current (A) ===
'''How quickly do you want to accelerate?''' Your motor's maximum power will be specified in kW. To estimate your maximum current draw, divide the peak power by the battery voltage. e.g. a 30 kW motor with a 120 V battery pack will pull 30,000 / 120 = 250 A. The higher the current rating of the cells, the heavier they will be for a given capacity. Ideally, you want "enough" current capacity for full throttle acceleration, but no more. You can put cells in parallel to double the current rating of your pack (which of course will half the voltage).

=== Mass (kg) ===
'''Can your vehicle carry the weight?''' You'll need to keep the kerb weight within the original design limits. For a car, this could be a few hundred kg. For a motorcycle, likely less than 100 kg. This is a huge variable - and each new generation of battery tech seems to be a little lighter. For older EV or hybrid batteries, you can reckon on 10-15 kg/kWh. Nissan Leaf batteries are relatively light (7.5 kg/kWh). With the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 5-6 kg/kWh.

=== Volume (L) ===
'''Will it fit?''' Batteries are bulky. They are getting smaller, but finding enough space my be your biggest challenge. You can reckon on 5-10 L/kWh for older EV or hybrid batteries. For the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 3-3.5 kg/kWh.

There is much, much more to battery design than this (e.g. maximum charge rate, terminations, cooling, clamping), but the above should help work out which options will or won't work for your project...

== Cell chemistry ==

=== Lithium Iron Phosphate (LiFePO4) ===
Lithium Iron Phosphate (also known as LFP, or LiFePO4) batteries offer a good compromise between safety, energy density and ease of use for DIY conversions. They are available in a number of formats, commonly pouch cells, prismatic cells and cylindrical cells.

==== LiFePO4 pouch cells ====
The majority of this content is drawn from this thread: [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761&start=900 https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761] discussing the use of the A123 20Ah pouch cell. However, many of the general points apply equally to other similar pouch cells.

===== General build requirements =====
Pouch cells are vulnerable to damage from debris, and must be held in compression (see the datasheet for your battery, but 10-12 psi is recommended for the A123 pouch cells as a guide). A rigid container capable of preventing damage and providing compression is therefore required. Be aware the cells expand and contract in use, so allowance for this must be included in the structure of the case.

The pouch cells should be separated to prevent abrasion between cells, and also to avoid the development of hot spots. Prebuilt modules from A123 systems had thin foam sheets or heatsinks between each cell. Be sure to avoid any debris that could rub on the pouch surface, particularly if using recycled cells.

Mylar, '[https://www.americanmicroinc.com/fish-paper/ Fish paper]' or a [https://www.rogerscorp.com/elastomeric-material-solutions/poron-industrial-polyurethanes compliant foam] may be appropriate materials to serve this purpose. This material should not be flammable. If the material is heat insulating, it is important to address thermal management.

===== Compression =====
Compression is required to prevent premature failure of the cell. Without compression electrolyte will become unevenly distributed, causing current gradients in the cell and uneven heating. Local temperatures can become high enough to form gas formation leading to cells 'puffing up' even when the pack is otherwise held within temperature and voltage constraints. This will be exacerbated in packs with otherwise poor thermal management. Compression forces gas generated to the margins of the cell, outside of the cell stack, minimising its effect cell performance. Gas in the middle cells will create a dead space which does not store or release energy.

There is ~1% expansion through a discharge cycle. As the cell ages, the nominal cell thickness can grow by 3-5%. For A123 cells the ideal pressure is between 4 and 18psi with the ideal pressure being ~12psi. Maintaining 12psi can increase the life by 500 cycles over that of 4 or 18psi

There is some suggestion that in uses where 1C is never exceeded compression ''may'' not be required.

Highly rigid endplates with a mechanism to allow for a limited degree of expansion (e.g. steel bands) are considered an effective solution to this challenge.

It should be noted that compression is a challenge specific to pouch cells. Cylindrical cells are designed to maintain their own compression within the cell's electrode stack by their design.

This thread provides more information and experimentation relating to pack compression: <nowiki>https://endless-sphere.com/forums/viewtopic.php?f=14&t=52244</nowiki>

===== Pouch Cell Pack Design Examples =====
<nowiki>*</nowiki>placeholder*

===== Notes regarding recycled pouch cells =====
Pouch cells are somewhat fragile, and breaching the insulation is not difficult, especially in a cells removed from existing packs and repurposed. If the pouch has had their poly-layers compromised you may see a number of faults:
* Black spots around the perimeter of the cell indicate electrolyte leakage
* Voltage on the outside of the bag. Note that microvoltage between the pouch and the electrode is normal (and due to a capacitive effect).
While the majority of these cells should no longer be in the market, a significant number of faulty cells made it back into the 'greymarket' in around 2013. These cells had misaligned tabs which can also lead to isolation failures between the tab and the pack. These cells should be avoided, particularly in high demand applications.

===== Situations likely to cause pouch cell failure =====
''Taken directly from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''
# '''Overcharge'''. Any extended time above 3.8 Volts will generate enough heat and electrochemical activity to puff a cell, especially one that is improperly compressed.
# '''Overdischarge followed by charge'''. Any A123 cell that has been pulled low enough to come to rest at <300 mV should be immediately scrapped. The published number for that is 500 mV, but the real figure is closer to 300, so that's a "safety buffer" if you will. Below this Voltage, the Cu electrodes start to dissolve into the electrolyte. When charge is applied, the Cu forms dendrites that puncture the separator layer, forming an internal short in the cell. This can puff a cell in a hurry---the more charge current on tap, the worse it's prone to be.
# '''Driving a cell negative'''. I've neglected to mention this before, but it is a possibility. I don't know much about the specific mechanism at this time.
# '''Malfunctioning or misinformed electronics'''. This is the most common cause of all of the above in my experience. At this stage of the game, it is critical for YOU to understand how your BMS functions on at least a cursory level. Choose your BMS very carefully and periodically verify that it is operating properly. They're not all created equal. Make sure V sense lines are securely connected and free of corrosion. Just because your BMS says there was never a problem doesn't necessarily make it so. Avoid harnesses or ribbon cables between multiple modules if possible--they are problematic wherever they are used in any mobile electronics.
# '''Exposure to or generation of sufficient heat'''. I don't know exactly at what temperature gas formation begins in the electrolyte, but we spec a max storage temp of 80 (or 85?) degrees C and I suspect this is the reason. The hotter, the puffier--to a point. This is why soldering tabs poses a real hazard to cell health. If you feel you must solder, sink or blow the heat away from the body of the cell. Use a big iron that can make sufficient local heat quickly, before the whole mass of the cell gets hot. You might even get the cell warm enough to melt separator if not careful.
# '''No compression, not enough compression, improperly distributed compression'''. This is a pack/module design issue. Apply 10, maybe 15 psi to your cell stack end to end and then band snugly and evenly. Use hard endplates of some sort--never wrap cells directly or allow their shape to become distorted. Protect all areas of the pouch from impact damage. This obviously does not apply to cylindrical cells.

==== LiFePO4 prismatic cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cylindrical cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cell ageing ====
''Derived (barely paraphrased) from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''

Capacity loss is caused by the lithium that was available for storage becoming permanently plated on the cathode. Being unable to move within the cell it is no longer available to store energy. The impact of this plating is greater than the amount of lithium 'lost' to plating because not only is the lithium no longer available, it is also preventing access to that part of the cathode meaning Li that can still move has to take a longer path to reach the cathode. Lithium plating is one cause of increased cell resistance (there are others), a sign of worsening cell health.

There is no linear relationship between actual capacity loss and impedance rise. However some cell defects will also increase impedance.

Increasing cell resistance may cause a number of symptoms which may be confused with [https://earthshipbiotecture.com/a-lithium-ion-battery-primer/ High Self Discharge.]
# Elevated Peukert Losses. As more energy per amount of current through the cell is lost as heat, the cells useable capacity decreases. So the apparent capacity loss is higher than the actual capacity loss of cycleable lithium. When used in low current applications (e.g. solar energy storage) the actual and apparent decrease in capacity will be small. In high current draw applications (like EV traction packs), the Peukert loss increases proportionally, so the apparent capacity loss increases much faster than the actual capacity loss.
# Greater voltage excursion under the same load. Due to increased cell resistancethe voltage will sag further under the same load than a cell in optimal condition. The inverse is also true, the voltage will be higher for the same amount of charging current applied. The cell will then rebound to a voltage further from the loaded and charging voltages. This, obviously, can look like high self discharge but is a different phenomenon.
# Absolute maximum current decrease.
Elevated impedance causes a more complex constellation of symptoms, some of which may be easy to confuse with High Self Discharge (HSD). Ohm's law (E=I/R) holds the key to understanding here.

'''1) Elevated Peukert losses.''' Because more energy per unit of current through the cell is lost as heat, less of the cell's capacity is actually USABLE. Thus, apparent capacity loss can be significantly greater than actual capacity loss caused by the loss of cycleable Li alone. In low current applications, the two numbers will be close together. In high current applications, Peukert losses increase in proportion, so apparent loss of capacity breaks further and further away from actual capacity loss as current increases.

'''2) Greater voltage excursion under the same load.''' Elevated resistance across the cell means that voltage will sag more under the same load than it did when the cell was healthier. Conversely, voltage will rise higher with the same amount of applied charge current than it did when it was healthier. At the same time, rebound/settling voltages will be further away from loaded/charging voltages. In other words, the cell will rebound to a voltage further away from loaded voltage, all else being equal. Similarly, voltage will settle farther from the charge voltage with the same charge applied. This can give the illusion of elevated self-discharge, but the phenomenon is actually not the same thing. Again, the greater the charge and load currents, the greater the effect becomes.

'''3) Absolute max current decreases.''' Because the cell's series resistance is elevated, the maximum possible current through the cell is decreased.

Just to confuse things further, there can be many factors that lead to impedance rise. Some are related to Li plating, others are not.

=== Lithium-ion ===
Lithium-ion (Li-ion) batteries have a greater energy density than Lithium Iron Phosphate batteries, but have more challenging needs to use safely. The ideal operating range of Li-ion batteries is between +15 and +45°C. The upper limit of temperature is particularly important as Li-ion batteries experience thermal runaway - an unstoppable chain reaction that can occur in milliseconds releasing the stored energy in the cell. This can produce temperatures of 400°C and a fire that is extremely difficult to put out. Thermal runaway can start as low as 60°C and becomes much more likely at 100°C

Risk factors for thermal runaway:
* Short Circuits - either internally or externally
* Overcharging
* Excessive current draw or when charging

=== Li-ion pouch cells ===
[https://kokam.com/cell Kokam] produce high-performance Li-ion pouch cells. These combine relative ease of use and pack construction with performance close to cylindrical cells.

=== Li-ion 18650 and other cylindrical cells ===
Cylindrical cells are favoured by Tesla, and are probably the main reason why their cars achieve such excellent performance. They are light, compact, powerful and expensive. Unfortunately, cylindrical cells are staggeringly difficult (and dangerous) to use in DIY conversions. There are two good reasons for this: thermal management and cell configuration.

As stated above, Li-ion cells are prone to thermal runaway. So you need perfect thermal management to ensure that no cell ever exceeds the critical temperature. If this happens, the cell will short-circuit internally, releasing a lot of energy - potentially explosively. Furthermore, the individual cells are small, so need to be arranged in parallel. In the case of the Tesla Model S, there are 74 cells in each parallel. Imagine if one of those cells fails and becomes short circuited internally. You now have 73 very high power cells in parallel feeding in to that short circuit. In fact, you don't have to imaging. You can watch this famous video instead (courtesy of Rich Rebuilds).

<nowiki><youtube>WdDi1haA71Q</youtube></nowiki>

Batteries

2020-11-30T19:32:33Z

Clanger9: /* Lithium Iron Phosphate (LiFePO4) Batteries */ minor restructure

== Introduction ==
There are a wide variety of battery chemistries available for use as the main traction battery of an EV. To use each chemistry safely, and to ensure an adequate service life from the battery pack it is important to understand the requirements for the chemistry you are using. Failure to do so may lead to premature or catastrophic failure of the pack.

Good pack design will allow for a nominal amount of abuse. People make mistakes and the pack should allow a margin for safety - and for longevity!

== Battery pack specification ==
When deciding on your battery pack, here are some basic parameters to consider:

=== Capacity (kWh) ===
'''How far do you want to go?''' A standard car conversion will need around 1kWh for 3 miles of range. For a middleweight motorcycle, 1kWh should give around 9 miles. ''Your mileage may vary'', as they say.

=== Voltage (V) ===
'''How fast do you want to go?''' The pack voltage defines the maximum speed your motor can spin. Motors are usually specified with "KV" - or RPM-per-volt. Check the KV of your motor and how fast it needs to spin to get your desired top speed. e.g. if you need 3,000 RPM from a 25 KV motor then your pack voltage needs to be 3,000 / 25 = 120 V. The exact number of cells in series you need depends on the cell chemistry, but 3.8 V is a reasonable guess.

=== Maximum current (A) ===
'''How quickly do you want to accelerate?''' Your motor's maximum power will be specified in kW. To estimate your maximum current draw, divide the peak power by the battery voltage. e.g. a 30 kW motor with a 120 V battery pack will pull 30,000 / 120 = 250 A. The higher the current rating of the cells, the heavier they will be for a given capacity. Ideally, you want "enough" current capacity for full throttle acceleration, but no more. You can put cells in parallel to double the current rating of your pack (which of course will half the voltage).

=== Mass (kg) ===
'''Can your vehicle carry the weight?''' You'll need to keep the kerb weight within the original design limits. For a car, this could be a few hundred kg. For a motorcycle, likely less than 100 kg. This is a huge variable - and each new generation of battery tech seems to be a little lighter. For older EV or hybrid batteries, you can reckon on 10-15 kg/kWh. Nissan Leaf batteries are relatively light (7.5 kg/kWh). With the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 5-6 kg/kWh.

=== Volume (L) ===
'''Will it fit?''' Batteries are bulky. They are getting smaller, but finding enough space my be your biggest challenge. You can reckon on 5-10 L/kWh for older EV or hybrid batteries. For the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 3-3.5 kg/kWh.

There is much, much more to battery design than this (e.g. maximum charge rate, terminations, cooling, clamping), but the above should help work out which options will or won't work for your project...

== Cell chemistry ==

=== Lithium Iron Phosphate (LiFePO4) ===
Lithium Iron Phosphate (also known as LFP, or LiFePO4) batteries offer a good compromise between safety, energy density and ease of use for DIY conversions. They are available in a number of formats, commonly pouch cells, prismatic cells and cylindrical cells.

==== LiFePO4 pouch cells ====
The majority of this content is drawn from this thread: [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761&start=900 https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761] discussing the use of the A123 20Ah pouch cell. However, many of the general points apply equally to other similar pouch cells.

===== General build requirements =====
Pouch cells are vulnerable to damage from debris, and must be held in compression (see the datasheet for your battery, but 10-12 psi is recommended for the A123 pouch cells as a guide). A rigid container capable of preventing damage and providing compression is therefore required. Be aware the cells expand and contract in use, so allowance for this must be included in the structure of the case.

The pouch cells should be separated to prevent abrasion between cells, and also to avoid the development of hot spots. Prebuilt modules from A123 systems had thin foam sheets or heatsinks between each cell. Be sure to avoid any debris that could rub on the pouch surface, particularly if using recycled cells.

Mylar, '[https://www.americanmicroinc.com/fish-paper/ Fish paper]' or a [https://www.rogerscorp.com/elastomeric-material-solutions/poron-industrial-polyurethanes compliant foam] may be appropriate materials to serve this purpose. This material should not be flammable. If the material is heat insulating, it is important to address thermal management.

===== Compression =====
Compression is required to prevent premature failure of the cell. Without compression electrolyte will become unevenly distributed, causing current gradients in the cell and uneven heating. Local temperatures can become high enough to form gas formation leading to cells 'puffing up' even when the pack is otherwise held within temperature and voltage constraints. This will be exacerbated in packs with otherwise poor thermal management. Compression forces gas generated to the margins of the cell, outside of the cell stack, minimising its effect cell performance. Gas in the middle cells will create a dead space which does not store or release energy.

There is ~1% expansion through a discharge cycle. As the cell ages, the nominal cell thickness can grow by 3-5%. For A123 cells the ideal pressure is between 4 and 18psi with the ideal pressure being ~12psi. Maintaining 12psi can increase the life by 500 cycles over that of 4 or 18psi

There is some suggestion that in uses where 1C is never exceeded compression ''may'' not be required.

Highly rigid endplates with a mechanism to allow for a limited degree of expansion (e.g. steel bands) are considered an effective solution to this challenge.

It should be noted that compression is a challenge specific to pouch cells. Cylindrical cells are designed to maintain their own compression within the cell's electrode stack by their design.

This thread provides more information and experimentation relating to pack compression: <nowiki>https://endless-sphere.com/forums/viewtopic.php?f=14&t=52244</nowiki>

===== Pouch Cell Pack Design Examples =====
<nowiki>*</nowiki>placeholder*

===== Notes regarding recycled pouch cells =====
Pouch cells are somewhat fragile, and breaching the insulation is not difficult, especially in a cells removed from existing packs and repurposed. If the pouch has had their poly-layers compromised you may see a number of faults:
* Black spots around the perimeter of the cell indicate electrolyte leakage
* Voltage on the outside of the bag. Note that microvoltage between the pouch and the electrode is normal (and due to a capacitive effect).
While the majority of these cells should no longer be in the market, a significant number of faulty cells made it back into the 'greymarket' in around 2013. These cells had misaligned tabs which can also lead to isolation failures between the tab and the pack. These cells should be avoided, particularly in high demand applications.

===== Situations likely to cause pouch cell failure =====
''Taken directly from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''
# '''Overcharge'''. Any extended time above 3.8 Volts will generate enough heat and electrochemical activity to puff a cell, especially one that is improperly compressed.
# '''Overdischarge followed by charge'''. Any A123 cell that has been pulled low enough to come to rest at <300 mV should be immediately scrapped. The published number for that is 500 mV, but the real figure is closer to 300, so that's a "safety buffer" if you will. Below this Voltage, the Cu electrodes start to dissolve into the electrolyte. When charge is applied, the Cu forms dendrites that puncture the separator layer, forming an internal short in the cell. This can puff a cell in a hurry---the more charge current on tap, the worse it's prone to be.
# '''Driving a cell negative'''. I've neglected to mention this before, but it is a possibility. I don't know much about the specific mechanism at this time.
# '''Malfunctioning or misinformed electronics'''. This is the most common cause of all of the above in my experience. At this stage of the game, it is critical for YOU to understand how your BMS functions on at least a cursory level. Choose your BMS very carefully and periodically verify that it is operating properly. They're not all created equal. Make sure V sense lines are securely connected and free of corrosion. Just because your BMS says there was never a problem doesn't necessarily make it so. Avoid harnesses or ribbon cables between multiple modules if possible--they are problematic wherever they are used in any mobile electronics.
# '''Exposure to or generation of sufficient heat'''. I don't know exactly at what temperature gas formation begins in the electrolyte, but we spec a max storage temp of 80 (or 85?) degrees C and I suspect this is the reason. The hotter, the puffier--to a point. This is why soldering tabs poses a real hazard to cell health. If you feel you must solder, sink or blow the heat away from the body of the cell. Use a big iron that can make sufficient local heat quickly, before the whole mass of the cell gets hot. You might even get the cell warm enough to melt separator if not careful.
# '''No compression, not enough compression, improperly distributed compression'''. This is a pack/module design issue. Apply 10, maybe 15 psi to your cell stack end to end and then band snugly and evenly. Use hard endplates of some sort--never wrap cells directly or allow their shape to become distorted. Protect all areas of the pouch from impact damage. This obviously does not apply to cylindrical cells.

==== LiFePO4 prismatic cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cylindrical cells ====
<nowiki>*</nowiki>placeholder*

==== LiFePO4 cell ageing ====
''Derived (barely paraphrased) from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''

Capacity loss is caused by the lithium that was available for storage becoming permanently plated on the cathode. Being unable to move within the cell it is no longer available to store energy. The impact of this plating is greater than the amount of lithium 'lost' to plating because not only is the lithium no longer available, it is also preventing access to that part of the cathode meaning Li that can still move has to take a longer path to reach the cathode. Lithium plating is one cause of increased cell resistance (there are others), a sign of worsening cell health.

There is no linear relationship between actual capacity loss and impedance rise. However some cell defects will also increase impedance.

Increasing cell resistance may cause a number of symptoms which may be confused with [https://earthshipbiotecture.com/a-lithium-ion-battery-primer/ High Self Discharge.]
# Elevated Peukert Losses. As more energy per amount of current through the cell is lost as heat, the cells useable capacity decreases. So the apparent capacity loss is higher than the actual capacity loss of cycleable lithium. When used in low current applications (e.g. solar energy storage) the actual and apparent decrease in capacity will be small. In high current draw applications (like EV traction packs), the Peukert loss increases proportionally, so the apparent capacity loss increases much faster than the actual capacity loss.
# Greater voltage excursion under the same load. Due to increased cell resistancethe voltage will sag further under the same load than a cell in optimal condition. The inverse is also true, the voltage will be higher for the same amount of charging current applied. The cell will then rebound to a voltage further from the loaded and charging voltages. This, obviously, can look like high self discharge but is a different phenomenon.
# Absolute maximum current decrease.
Elevated impedance causes a more complex constellation of symptoms, some of which may be easy to confuse with High Self Discharge (HSD). Ohm's law (E=I/R) holds the key to understanding here.

'''1) Elevated Peukert losses.''' Because more energy per unit of current through the cell is lost as heat, less of the cell's capacity is actually USABLE. Thus, apparent capacity loss can be significantly greater than actual capacity loss caused by the loss of cycleable Li alone. In low current applications, the two numbers will be close together. In high current applications, Peukert losses increase in proportion, so apparent loss of capacity breaks further and further away from actual capacity loss as current increases.

'''2) Greater voltage excursion under the same load.''' Elevated resistance across the cell means that voltage will sag more under the same load than it did when the cell was healthier. Conversely, voltage will rise higher with the same amount of applied charge current than it did when it was healthier. At the same time, rebound/settling voltages will be further away from loaded/charging voltages. In other words, the cell will rebound to a voltage further away from loaded voltage, all else being equal. Similarly, voltage will settle farther from the charge voltage with the same charge applied. This can give the illusion of elevated self-discharge, but the phenomenon is actually not the same thing. Again, the greater the charge and load currents, the greater the effect becomes.

'''3) Absolute max current decreases.''' Because the cell's series resistance is elevated, the maximum possible current through the cell is decreased.

Just to confuse things further, there can be many factors that lead to impedance rise. Some are related to Li plating, others are not.

=== Lithium-ion ===
Lithium-ion (Li-ion) batteries have a greater energy density than Lithium Iron Phosphate batteries, but have more challenging needs to use safely. The ideal operating range of Li-ion batteries is between +15 and +45°C. The upper limit of temperature is particularly important as Li-ion batteries experience thermal runaway - an unstoppable chain reaction that can occur in milliseconds releasing the stored energy in the cell. This can produce temperatures of 400°C and a fire that is extremely difficult to put out. Thermal runaway can start as low as 60°C and becomes much more likely at 100°C

Risk factors for thermal runaway:
* Short Circuits - either internally or externally
* Overcharging
* Excessive current draw or when charging

=== Li-ion pouch cells ===
Placeholder

=== Li-ion 18650 and other cylindrical cells ===
Placeholder

Batteries

2020-11-30T19:17:32Z

Clanger9: /* Maximum current (A) */

== Introduction ==
There are a wide variety of battery chemistries available for use as the main traction battery of an EV. To use each chemistry safely, and to ensure an adequate service life from the battery pack it is important to understand the requirements for the chemistry you are using. Failure to do so may lead to premature or catastrophic failure of the pack.

Good pack design will allow for a nominal amount of abuse. People make mistakes and the pack should allow a margin for safety - and for longevity!

== Battery pack specification ==
When deciding on your battery pack, here are some basic parameters to consider:

=== Capacity (kWh) ===
'''How far do you want to go?''' A standard car conversion will need around 1kWh for 3 miles of range. For a middleweight motorcycle, 1kWh should give around 9 miles. ''Your mileage may vary'', as they say.

=== Voltage (V) ===
'''How fast do you want to go?''' The pack voltage defines the maximum speed your motor can spin. Motors are usually specified with "KV" - or RPM-per-volt. Check the KV of your motor and how fast it needs to spin to get your desired top speed. e.g. if you need 3,000 RPM from a 25 KV motor then your pack voltage needs to be 3,000 / 25 = 120 V. The exact number of cells in series you need depends on the cell chemistry, but 3.8 V is a reasonable guess for Li-ion.

=== Maximum current (A) ===
'''How quickly do you want to accelerate?''' Your motor's maximum power will be specified in kW. To estimate your maximum current draw, divide the peak power by the battery voltage. e.g. a 30 kW motor with a 120 V battery pack will pull 30,000 / 120 = 250 A. The higher the current rating of the cells, the heavier they will be for a given capacity. Ideally, you want "enough" current capacity for full throttle acceleration, but no more. You can put cells in parallel to double the current rating of your pack (which of course will half the voltage).

=== Mass (kg) ===
'''Can your vehicle carry the weight?''' You'll need to keep the kerb weight within the original design limits. For a car, this could be a few hundred kg. For a motorcycle, likely less than 100 kg. This is a huge variable - and each new generation of battery tech seems to be a little lighter. For older EV or hybrid batteries, you can reckon on 10-15 kg/kWh. Nissan Leaf batteries are relatively light (7.5 kq/kWh). With the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 5-6 kg/kWh.

=== Volume (L) ===
'''Will it fit?''' Batteries are bulky. They are getting smaller, but finding enough space my be your biggest challenge. You can reckon on 5-10 L/kWh for older EV or hybrid batteries. For the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 3-3.5 kg/kWh.

There is much, much more to battery design than this (e.g. maximum charge rate, terminations, cooling, clamping), but the above should help work out which options will or won't work for your project...

== Lithium Iron Phosphate (LiFePO4) Batteries ==
Lithium Iron Phosphate (also known as LFP, or LiFePO4) batteries offer a good compromise between safety, energy density and ease of use for DIY conversions. They are available in a number of formats, commonly pouch cells and cylindrical cells.

=== LiFePO4 Pouch cells ===
The majority of this content is drawn from this thread: [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761&start=900 https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761] discussing the use of the A123 20Ah pouch cell. However, many of the general points apply equally to other similar pouch cells.

==== General build requirements ====
Pouch cells are vulnerable to damage from debris, and must be held in compression (see the datasheet for your battery, but 10-12 psi is recommended for the A123 pouch cells as a guide). A rigid container capable of preventing damage and providing compression is therefore required. Be aware the cells expand and contract in use, so allowance for this must be included in the structure of the case.

The pouch cells should be separated to prevent abrasion between cells, and also to avoid the development of hot spots. Prebuilt modules from A123 systems had thin foam sheets or heatsinks between each cell. Be sure to avoid any debris that could rub on the pouch surface, particularly if using recycled cells.

Mylar, '[https://www.americanmicroinc.com/fish-paper/ Fish paper]' or a [https://www.rogerscorp.com/elastomeric-material-solutions/poron-industrial-polyurethanes compliant foam] may be appropriate materials to serve this purpose. This material should not be flammable. If the material is heat insulating, it is important to address thermal management.

==== Compression ====
Compression is required to prevent premature failure of the cell. Without compression electrolyte will become unevenly distributed, causing current gradients in the cell and uneven heating. Local temperatures can become high enough to form gas formation leading to cells 'puffing up' even when the pack is otherwise held within temperature and voltage constraints. This will be exacerbated in packs with otherwise poor thermal management. Compression forces gas generated to the margins of the cell, outside of the cell stack, minimising its effect cell performance. Gas in the middle cells will create a dead space which does not store or release energy.

There is ~1% expansion through a discharge cycle. As the cell ages, the nominal cell thickness can grow by 3-5%. For A123 cells the ideal pressure is between 4 and 18psi with the ideal pressure being ~12psi. Maintaining 12psi can increase the life by 500 cycles over that of 4 or 18psi

There is some suggestion that in uses where 1C is never exceeded compression ''may'' not be required.

Highly rigid endplates with a mechanism to allow for a limited degree of expansion (e.g. steel bands) are considered an effective solution to this challenge.

It should be noted that compression is a challenge specific to pouch cells. Cylindrical cells are designed to maintain their own compression within the cell's electrode stack by their design.

This thread provides more information and experimentation relating to pack compression: <nowiki>https://endless-sphere.com/forums/viewtopic.php?f=14&t=52244</nowiki>

==== Pouch Cell Pack Design Examples ====
Placeholder

==== Notes regarding recycled pouch cells ====
Pouch cells are somewhat fragile, and breaching the insulation is not difficult, especially in a cells removed from existing packs and repurposed. If the pouch has had their poly-layers compromised you may see a number of faults:
* Black spots around the perimeter of the cell indicate electrolyte leakage
* Voltage on the outside of the bag. Note that microvoltage between the pouch and the electrode is normal (and due to a capacitive effect).
While the majority of these cells should no longer be in the market, a significant number of faulty cells made it back into the 'greymarket' in around 2013. These cells had misaligned tabs which can also lead to isolation failures between the tab and the pack. These cells should be avoided, particularly in high demand applications.

=== Cylindrical cells ===
Placeholder

==== Situations likely to cause cell failure ====
''Taken directly from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''
# '''Overcharge'''. Any extended time above 3.8 Volts will generate enough heat and electrochemical activity to puff a cell, especially one that is improperly compressed.
# '''Overdischarge followed by charge'''. Any A123 cell that has been pulled low enough to come to rest at <300 mV should be immediately scrapped. The published number for that is 500 mV, but the real figure is closer to 300, so that's a "safety buffer" if you will. Below this Voltage, the Cu electrodes start to dissolve into the electrolyte. When charge is applied, the Cu forms dendrites that puncture the separator layer, forming an internal short in the cell. This can puff a cell in a hurry---the more charge current on tap, the worse it's prone to be.
# '''Driving a cell negative'''. I've neglected to mention this before, but it is a possibility. I don't know much about the specific mechanism at this time.
# '''Malfunctioning or misinformed electronics'''. This is the most common cause of all of the above in my experience. At this stage of the game, it is critical for YOU to understand how your BMS functions on at least a cursory level. Choose your BMS very carefully and periodically verify that it is operating properly. They're not all created equal. Make sure V sense lines are securely connected and free of corrosion. Just because your BMS says there was never a problem doesn't necessarily make it so. Avoid harnesses or ribbon cables between multiple modules if possible--they are problematic wherever they are used in any mobile electronics.
# '''Exposure to or generation of sufficient heat'''. I don't know exactly at what temperature gas formation begins in the electrolyte, but we spec a max storage temp of 80 (or 85?) degrees C and I suspect this is the reason. The hotter, the puffier--to a point. This is why soldering tabs poses a real hazard to cell health. If you feel you must solder, sink or blow the heat away from the body of the cell. Use a big iron that can make sufficient local heat quickly, before the whole mass of the cell gets hot. You might even get the cell warm enough to melt separator if not careful.
# '''No compression, not enough compression, improperly distributed compression'''. This is a pack/module design issue. Apply 10, maybe 15 psi to your cell stack end to end and then band snugly and evenly. Use hard endplates of some sort--never wrap cells directly or allow their shape to become distorted. Protect all areas of the pouch from impact damage. This obviously does not apply to cylindrical cells.

==== Cell aging for LiIoPO4 cells ====
''Derived (barely paraphrased) from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''

Capacity loss is caused by the Lithium that was available for storage becoming permanently plated on the cathode. Being unable to move within the cell it is no longer available to store energy. The impact of this plating is greater than the amount of lithium 'lost' to plating because not only is the lithium no longer available, it is also preventing access to that part of the cathode meaning Li that can still move has to take a longer path to reach the cathode. Lithium plating is one cause of increased cell resistance (there are others), a sign of worsening cell health.

There is no linear relationship between actual capacity loss and impedance rise. However some cell defects will also increase impedance.

Increasing cell resistance may cause a number of symptoms which may be confused with [https://earthshipbiotecture.com/a-lithium-ion-battery-primer/ High Self Discharge.]
# Elevated Peukert Losses. As more energy per amount of current through the cell is lost as heat, the cells useable capacity decreases. So the apparent capacity loss is higher than the actual capacity loss of cycleable lithium. When used in low current applications (e.g. solar energy storage) the actual and apparent decrease in capacity will be small. In high current draw applications (like EV traction packs), the Peukert loss increases proportionally, so the apparent capacity loss increases much faster than the actual capacity loss.
# Greater voltage excursion under the same load. Due to increased cell resistancethe voltage will sag further under the same load than a cell in optimal condition. The inverse is also true, the voltage will be higher for the same amount of charging current applied. The cell will then rebound to a voltage further from the loaded and charging voltages. This, obviously, can look like high self discharge but is a different phenomenon.
# Absolute maximum current decrease.
Elevated impedance causes a more complex constellation of symptoms, some of which may be easy to confuse with High Self Discharge (HSD). Ohm's law (E=I/R) holds the key to understanding here.

'''1) Elevated Peukert losses.''' Because more energy per unit of current through the cell is lost as heat, less of the cell's capacity is actually USABLE. Thus, apparent capacity loss can be significantly greater than actual capacity loss caused by the loss of cycleable Li alone. In low current applications, the two numbers will be close together. In high current applications, Peukert losses increase in proportion, so apparent loss of capacity breaks further and further away from actual capacity loss as current increases.

'''2) Greater voltage excursion under the same load.''' Elevated resistance across the cell means that voltage will sag more under the same load than it did when the cell was healthier. Conversely, voltage will rise higher with the same amount of applied charge current than it did when it was healthier. At the same time, rebound/settling voltages will be further away from loaded/charging voltages. In other words, the cell will rebound to a voltage further away from loaded voltage, all else being equal. Similarly, voltage will settle farther from the charge voltage with the same charge applied. This can give the illusion of elevated self-discharge, but the phenomenon is actually not the same thing. Again, the greater the charge and load currents, the greater the effect becomes.

'''3) Absolute max current decreases.''' Because the cell's series resistance is elevated, the maximum possible current through the cell is decreased.

Just to confuse things further, there can be many factors that lead to impedance rise. Some are related to Li plating, others are not.

== Lithium Ion Batteries ==
Lithium Ion (LiIon) batteries have a greater energy density than Lithium Iron Phosphate batteries, but have more challenging needs to use safely. The ideal operating range of LiIon batteries is between +15 and +45°C. The upper limit of temperature is particularly important as LiIon batteries experience thermal runaway - an unstoppable chain reaction that can occur in milliseconds releasing the stored energy in the cell. This can produce temperatures of 400°C and a fire that is extremely difficult to put out. Thermal runaway can start as low as 60°C and becomes much more likely at 100°C

Risk factors for thermal runaway:
* Short Circuits - either internally or externally
* Overcharging
* Excessive current draw or when charging

=== LiIon Pouch cells ===
Placeholder

=== 18650 and other cylindrical cells ===
Placeholder

Batteries

2020-11-30T19:14:42Z

Clanger9: /* Capacity (kWh) */

== Introduction ==
There are a wide variety of battery chemistries available for use as the main traction battery of an EV. To use each chemistry safely, and to ensure an adequate service life from the battery pack it is important to understand the requirements for the chemistry you are using. Failure to do so may lead to premature or catastrophic failure of the pack.

Good pack design will allow for a nominal amount of abuse. People make mistakes and the pack should allow a margin for safety - and for longevity!

== Battery pack specification ==
When deciding on your battery pack, here are some basic parameters to consider:

=== Capacity (kWh) ===
'''How far do you want to go?''' A standard car conversion will need around 1kWh for 3 miles of range. For a middleweight motorcycle, 1kWh should give around 9 miles. ''Your mileage may vary'', as they say.

=== Voltage (V) ===
'''How fast do you want to go?''' The pack voltage defines the maximum speed your motor can spin. Motors are usually specified with "KV" - or RPM-per-volt. Check the KV of your motor and how fast it needs to spin to get your desired top speed. e.g. if you need 3,000 RPM from a 25 KV motor then your pack voltage needs to be 3,000 / 25 = 120 V. The exact number of cells in series you need depends on the cell chemistry, but 3.8 V is a reasonable guess for Li-ion.

=== Maximum current (A) ===
'''How quickly do you want to accelerate?''' Your motor's maximum power will be specified in kW. To estimate your maximum current draw, divide the peak power by the battery voltage. e.g. a 30 kW motor with a 120 V battery pack will pull 30,000 / 120 = 250 A. The higher the current rating of the cells, the heavier they will be for a given capacity. Put cells in parallel to increase the current rating of your pack.

=== Mass (kg) ===
'''Can your vehicle carry the weight?''' You'll need to keep the kerb weight within the original design limits. For a car, this could be a few hundred kg. For a motorcycle, likely less than 100 kg. This is a huge variable - and each new generation of battery tech seems to be a little lighter. For older EV or hybrid batteries, you can reckon on 10-15 kg/kWh. Nissan Leaf batteries are relatively light (7.5 kq/kWh). With the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 5-6 kg/kWh.

=== Volume (L) ===
'''Will it fit?''' Batteries are bulky. They are getting smaller, but finding enough space my be your biggest challenge. You can reckon on 5-10 L/kWh for older EV or hybrid batteries. For the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 3-3.5 kg/kWh.

There is much, much more to battery design than this (e.g. maximum charge rate, terminations, cooling, clamping), but the above should help work out which options will or won't work for your project...

== Lithium Iron Phosphate (LiFePO4) Batteries ==
Lithium Iron Phosphate (also known as LFP, or LiFePO4) batteries offer a good compromise between safety, energy density and ease of use for DIY conversions. They are available in a number of formats, commonly pouch cells and cylindrical cells.

=== LiFePO4 Pouch cells ===
The majority of this content is drawn from this thread: [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761&start=900 https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761] discussing the use of the A123 20Ah pouch cell. However, many of the general points apply equally to other similar pouch cells.

==== General build requirements ====
Pouch cells are vulnerable to damage from debris, and must be held in compression (see the datasheet for your battery, but 10-12 psi is recommended for the A123 pouch cells as a guide). A rigid container capable of preventing damage and providing compression is therefore required. Be aware the cells expand and contract in use, so allowance for this must be included in the structure of the case.

The pouch cells should be separated to prevent abrasion between cells, and also to avoid the development of hot spots. Prebuilt modules from A123 systems had thin foam sheets or heatsinks between each cell. Be sure to avoid any debris that could rub on the pouch surface, particularly if using recycled cells.

Mylar, '[https://www.americanmicroinc.com/fish-paper/ Fish paper]' or a [https://www.rogerscorp.com/elastomeric-material-solutions/poron-industrial-polyurethanes compliant foam] may be appropriate materials to serve this purpose. This material should not be flammable. If the material is heat insulating, it is important to address thermal management.

==== Compression ====
Compression is required to prevent premature failure of the cell. Without compression electrolyte will become unevenly distributed, causing current gradients in the cell and uneven heating. Local temperatures can become high enough to form gas formation leading to cells 'puffing up' even when the pack is otherwise held within temperature and voltage constraints. This will be exacerbated in packs with otherwise poor thermal management. Compression forces gas generated to the margins of the cell, outside of the cell stack, minimising its effect cell performance. Gas in the middle cells will create a dead space which does not store or release energy.

There is ~1% expansion through a discharge cycle. As the cell ages, the nominal cell thickness can grow by 3-5%. For A123 cells the ideal pressure is between 4 and 18psi with the ideal pressure being ~12psi. Maintaining 12psi can increase the life by 500 cycles over that of 4 or 18psi

There is some suggestion that in uses where 1C is never exceeded compression ''may'' not be required.

Highly rigid endplates with a mechanism to allow for a limited degree of expansion (e.g. steel bands) are considered an effective solution to this challenge.

It should be noted that compression is a challenge specific to pouch cells. Cylindrical cells are designed to maintain their own compression within the cell's electrode stack by their design.

This thread provides more information and experimentation relating to pack compression: <nowiki>https://endless-sphere.com/forums/viewtopic.php?f=14&t=52244</nowiki>

==== Pouch Cell Pack Design Examples ====
Placeholder

==== Notes regarding recycled pouch cells ====
Pouch cells are somewhat fragile, and breaching the insulation is not difficult, especially in a cells removed from existing packs and repurposed. If the pouch has had their poly-layers compromised you may see a number of faults:
* Black spots around the perimeter of the cell indicate electrolyte leakage
* Voltage on the outside of the bag. Note that microvoltage between the pouch and the electrode is normal (and due to a capacitive effect).
While the majority of these cells should no longer be in the market, a significant number of faulty cells made it back into the 'greymarket' in around 2013. These cells had misaligned tabs which can also lead to isolation failures between the tab and the pack. These cells should be avoided, particularly in high demand applications.

=== Cylindrical cells ===
Placeholder

==== Situations likely to cause cell failure ====
''Taken directly from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''
# '''Overcharge'''. Any extended time above 3.8 Volts will generate enough heat and electrochemical activity to puff a cell, especially one that is improperly compressed.
# '''Overdischarge followed by charge'''. Any A123 cell that has been pulled low enough to come to rest at <300 mV should be immediately scrapped. The published number for that is 500 mV, but the real figure is closer to 300, so that's a "safety buffer" if you will. Below this Voltage, the Cu electrodes start to dissolve into the electrolyte. When charge is applied, the Cu forms dendrites that puncture the separator layer, forming an internal short in the cell. This can puff a cell in a hurry---the more charge current on tap, the worse it's prone to be.
# '''Driving a cell negative'''. I've neglected to mention this before, but it is a possibility. I don't know much about the specific mechanism at this time.
# '''Malfunctioning or misinformed electronics'''. This is the most common cause of all of the above in my experience. At this stage of the game, it is critical for YOU to understand how your BMS functions on at least a cursory level. Choose your BMS very carefully and periodically verify that it is operating properly. They're not all created equal. Make sure V sense lines are securely connected and free of corrosion. Just because your BMS says there was never a problem doesn't necessarily make it so. Avoid harnesses or ribbon cables between multiple modules if possible--they are problematic wherever they are used in any mobile electronics.
# '''Exposure to or generation of sufficient heat'''. I don't know exactly at what temperature gas formation begins in the electrolyte, but we spec a max storage temp of 80 (or 85?) degrees C and I suspect this is the reason. The hotter, the puffier--to a point. This is why soldering tabs poses a real hazard to cell health. If you feel you must solder, sink or blow the heat away from the body of the cell. Use a big iron that can make sufficient local heat quickly, before the whole mass of the cell gets hot. You might even get the cell warm enough to melt separator if not careful.
# '''No compression, not enough compression, improperly distributed compression'''. This is a pack/module design issue. Apply 10, maybe 15 psi to your cell stack end to end and then band snugly and evenly. Use hard endplates of some sort--never wrap cells directly or allow their shape to become distorted. Protect all areas of the pouch from impact damage. This obviously does not apply to cylindrical cells.

==== Cell aging for LiIoPO4 cells ====
''Derived (barely paraphrased) from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''

Capacity loss is caused by the Lithium that was available for storage becoming permanently plated on the cathode. Being unable to move within the cell it is no longer available to store energy. The impact of this plating is greater than the amount of lithium 'lost' to plating because not only is the lithium no longer available, it is also preventing access to that part of the cathode meaning Li that can still move has to take a longer path to reach the cathode. Lithium plating is one cause of increased cell resistance (there are others), a sign of worsening cell health.

There is no linear relationship between actual capacity loss and impedance rise. However some cell defects will also increase impedance.

Increasing cell resistance may cause a number of symptoms which may be confused with [https://earthshipbiotecture.com/a-lithium-ion-battery-primer/ High Self Discharge.]
# Elevated Peukert Losses. As more energy per amount of current through the cell is lost as heat, the cells useable capacity decreases. So the apparent capacity loss is higher than the actual capacity loss of cycleable lithium. When used in low current applications (e.g. solar energy storage) the actual and apparent decrease in capacity will be small. In high current draw applications (like EV traction packs), the Peukert loss increases proportionally, so the apparent capacity loss increases much faster than the actual capacity loss.
# Greater voltage excursion under the same load. Due to increased cell resistancethe voltage will sag further under the same load than a cell in optimal condition. The inverse is also true, the voltage will be higher for the same amount of charging current applied. The cell will then rebound to a voltage further from the loaded and charging voltages. This, obviously, can look like high self discharge but is a different phenomenon.
# Absolute maximum current decrease.
Elevated impedance causes a more complex constellation of symptoms, some of which may be easy to confuse with High Self Discharge (HSD). Ohm's law (E=I/R) holds the key to understanding here.

'''1) Elevated Peukert losses.''' Because more energy per unit of current through the cell is lost as heat, less of the cell's capacity is actually USABLE. Thus, apparent capacity loss can be significantly greater than actual capacity loss caused by the loss of cycleable Li alone. In low current applications, the two numbers will be close together. In high current applications, Peukert losses increase in proportion, so apparent loss of capacity breaks further and further away from actual capacity loss as current increases.

'''2) Greater voltage excursion under the same load.''' Elevated resistance across the cell means that voltage will sag more under the same load than it did when the cell was healthier. Conversely, voltage will rise higher with the same amount of applied charge current than it did when it was healthier. At the same time, rebound/settling voltages will be further away from loaded/charging voltages. In other words, the cell will rebound to a voltage further away from loaded voltage, all else being equal. Similarly, voltage will settle farther from the charge voltage with the same charge applied. This can give the illusion of elevated self-discharge, but the phenomenon is actually not the same thing. Again, the greater the charge and load currents, the greater the effect becomes.

'''3) Absolute max current decreases.''' Because the cell's series resistance is elevated, the maximum possible current through the cell is decreased.

Just to confuse things further, there can be many factors that lead to impedance rise. Some are related to Li plating, others are not.

== Lithium Ion Batteries ==
Lithium Ion (LiIon) batteries have a greater energy density than Lithium Iron Phosphate batteries, but have more challenging needs to use safely. The ideal operating range of LiIon batteries is between +15 and +45°C. The upper limit of temperature is particularly important as LiIon batteries experience thermal runaway - an unstoppable chain reaction that can occur in milliseconds releasing the stored energy in the cell. This can produce temperatures of 400°C and a fire that is extremely difficult to put out. Thermal runaway can start as low as 60°C and becomes much more likely at 100°C

Risk factors for thermal runaway:
* Short Circuits - either internally or externally
* Overcharging
* Excessive current draw or when charging

=== LiIon Pouch cells ===
Placeholder

=== 18650 and other cylindrical cells ===
Placeholder

Batteries

2020-11-30T19:13:10Z

Clanger9: /* Mass (kg) */

== Introduction ==
There are a wide variety of battery chemistries available for use as the main traction battery of an EV. To use each chemistry safely, and to ensure an adequate service life from the battery pack it is important to understand the requirements for the chemistry you are using. Failure to do so may lead to premature or catastrophic failure of the pack.

Good pack design will allow for a nominal amount of abuse. People make mistakes and the pack should allow a margin for safety - and for longevity!

== Battery pack specification ==
When deciding on your battery pack, here are some basic parameters to consider:

=== Capacity (kWh) ===
How far do you want to go? A standard car conversion will need around 1kWh for 3 miles of range. For a middleweight motorcycle, 1kWh should give around 9 miles. ''Your mileage may vary'', as they say.

=== Voltage (V) ===
How fast do you want to go? The pack voltage defines the maximum speed your motor can spin. Motors are usually specified with "KV" - or RPM-per-volt. Check the KV of your motor and how fast it needs to spin to get your desired top speed. e.g. if you need 3,000 RPM from a 25 KV motor then your pack voltage needs to be 3,000 / 25 = 120 V. The exact number of cells in series you need depends on the cell chemistry, but 3.8 V is a reasonable guess for Li-ion.

=== Maximum current (A) ===
How quickly do you want to accelerate? Your motor's maximum power will be specified in kW. To estimate your maximum current draw, divide the peak power by the battery voltage. e.g. a 30 kW motor with a 120 V battery pack will pull 30,000 / 120 = 250 A. The higher the current rating of the cells, the heavier they will be for a given capacity. Put cells in parallel to increase the current rating of your pack.

=== Mass (kg) ===
Can my vehicle carry the weight? You'll need to keep the kerb weight within the original design limits. For a car, this could be a few hundred kg. For a motorcycle, likely less than 100 kg. This is a huge variable - and each new generation of battery tech seems to be a little lighter. For older EV or hybrid batteries, you can reckon on 10-15 kg/kWh. Nissan Leaf batteries are relatively light (7.5 kq/kWh). With the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 5-6 kg/kWh.

=== Volume (L) ===
Will it fit? Batteries are '''big'''. They are getting smaller, but finding enough space is often the biggest challenge. You can reckon on 5-10 L/kWh for older EV or hybrid batteries. For the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 3-3.5 kg/kWh.

There is much, much more to battery design than this (e.g. maximum charge rate, terminations, cooling, clamping), but the above should help work out which options will or won't work for your project...

== Lithium Iron Phosphate (LiFePO4) Batteries ==
Lithium Iron Phosphate (also known as LFP, or LiFePO4) batteries offer a good compromise between safety, energy density and ease of use for DIY conversions. They are available in a number of formats, commonly pouch cells and cylindrical cells.

=== LiFePO4 Pouch cells ===
The majority of this content is drawn from this thread: [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761&start=900 https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761] discussing the use of the A123 20Ah pouch cell. However, many of the general points apply equally to other similar pouch cells.

==== General build requirements ====
Pouch cells are vulnerable to damage from debris, and must be held in compression (see the datasheet for your battery, but 10-12 psi is recommended for the A123 pouch cells as a guide). A rigid container capable of preventing damage and providing compression is therefore required. Be aware the cells expand and contract in use, so allowance for this must be included in the structure of the case.

The pouch cells should be separated to prevent abrasion between cells, and also to avoid the development of hot spots. Prebuilt modules from A123 systems had thin foam sheets or heatsinks between each cell. Be sure to avoid any debris that could rub on the pouch surface, particularly if using recycled cells.

Mylar, '[https://www.americanmicroinc.com/fish-paper/ Fish paper]' or a [https://www.rogerscorp.com/elastomeric-material-solutions/poron-industrial-polyurethanes compliant foam] may be appropriate materials to serve this purpose. This material should not be flammable. If the material is heat insulating, it is important to address thermal management.

==== Compression ====
Compression is required to prevent premature failure of the cell. Without compression electrolyte will become unevenly distributed, causing current gradients in the cell and uneven heating. Local temperatures can become high enough to form gas formation leading to cells 'puffing up' even when the pack is otherwise held within temperature and voltage constraints. This will be exacerbated in packs with otherwise poor thermal management. Compression forces gas generated to the margins of the cell, outside of the cell stack, minimising its effect cell performance. Gas in the middle cells will create a dead space which does not store or release energy.

There is ~1% expansion through a discharge cycle. As the cell ages, the nominal cell thickness can grow by 3-5%. For A123 cells the ideal pressure is between 4 and 18psi with the ideal pressure being ~12psi. Maintaining 12psi can increase the life by 500 cycles over that of 4 or 18psi

There is some suggestion that in uses where 1C is never exceeded compression ''may'' not be required.

Highly rigid endplates with a mechanism to allow for a limited degree of expansion (e.g. steel bands) are considered an effective solution to this challenge.

It should be noted that compression is a challenge specific to pouch cells. Cylindrical cells are designed to maintain their own compression within the cell's electrode stack by their design.

This thread provides more information and experimentation relating to pack compression: <nowiki>https://endless-sphere.com/forums/viewtopic.php?f=14&t=52244</nowiki>

==== Pouch Cell Pack Design Examples ====
Placeholder

==== Notes regarding recycled pouch cells ====
Pouch cells are somewhat fragile, and breaching the insulation is not difficult, especially in a cells removed from existing packs and repurposed. If the pouch has had their poly-layers compromised you may see a number of faults:
* Black spots around the perimeter of the cell indicate electrolyte leakage
* Voltage on the outside of the bag. Note that microvoltage between the pouch and the electrode is normal (and due to a capacitive effect).
While the majority of these cells should no longer be in the market, a significant number of faulty cells made it back into the 'greymarket' in around 2013. These cells had misaligned tabs which can also lead to isolation failures between the tab and the pack. These cells should be avoided, particularly in high demand applications.

=== Cylindrical cells ===
Placeholder

==== Situations likely to cause cell failure ====
''Taken directly from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''
# '''Overcharge'''. Any extended time above 3.8 Volts will generate enough heat and electrochemical activity to puff a cell, especially one that is improperly compressed.
# '''Overdischarge followed by charge'''. Any A123 cell that has been pulled low enough to come to rest at <300 mV should be immediately scrapped. The published number for that is 500 mV, but the real figure is closer to 300, so that's a "safety buffer" if you will. Below this Voltage, the Cu electrodes start to dissolve into the electrolyte. When charge is applied, the Cu forms dendrites that puncture the separator layer, forming an internal short in the cell. This can puff a cell in a hurry---the more charge current on tap, the worse it's prone to be.
# '''Driving a cell negative'''. I've neglected to mention this before, but it is a possibility. I don't know much about the specific mechanism at this time.
# '''Malfunctioning or misinformed electronics'''. This is the most common cause of all of the above in my experience. At this stage of the game, it is critical for YOU to understand how your BMS functions on at least a cursory level. Choose your BMS very carefully and periodically verify that it is operating properly. They're not all created equal. Make sure V sense lines are securely connected and free of corrosion. Just because your BMS says there was never a problem doesn't necessarily make it so. Avoid harnesses or ribbon cables between multiple modules if possible--they are problematic wherever they are used in any mobile electronics.
# '''Exposure to or generation of sufficient heat'''. I don't know exactly at what temperature gas formation begins in the electrolyte, but we spec a max storage temp of 80 (or 85?) degrees C and I suspect this is the reason. The hotter, the puffier--to a point. This is why soldering tabs poses a real hazard to cell health. If you feel you must solder, sink or blow the heat away from the body of the cell. Use a big iron that can make sufficient local heat quickly, before the whole mass of the cell gets hot. You might even get the cell warm enough to melt separator if not careful.
# '''No compression, not enough compression, improperly distributed compression'''. This is a pack/module design issue. Apply 10, maybe 15 psi to your cell stack end to end and then band snugly and evenly. Use hard endplates of some sort--never wrap cells directly or allow their shape to become distorted. Protect all areas of the pouch from impact damage. This obviously does not apply to cylindrical cells.

==== Cell aging for LiIoPO4 cells ====
''Derived (barely paraphrased) from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''

Capacity loss is caused by the Lithium that was available for storage becoming permanently plated on the cathode. Being unable to move within the cell it is no longer available to store energy. The impact of this plating is greater than the amount of lithium 'lost' to plating because not only is the lithium no longer available, it is also preventing access to that part of the cathode meaning Li that can still move has to take a longer path to reach the cathode. Lithium plating is one cause of increased cell resistance (there are others), a sign of worsening cell health.

There is no linear relationship between actual capacity loss and impedance rise. However some cell defects will also increase impedance.

Increasing cell resistance may cause a number of symptoms which may be confused with [https://earthshipbiotecture.com/a-lithium-ion-battery-primer/ High Self Discharge.]
# Elevated Peukert Losses. As more energy per amount of current through the cell is lost as heat, the cells useable capacity decreases. So the apparent capacity loss is higher than the actual capacity loss of cycleable lithium. When used in low current applications (e.g. solar energy storage) the actual and apparent decrease in capacity will be small. In high current draw applications (like EV traction packs), the Peukert loss increases proportionally, so the apparent capacity loss increases much faster than the actual capacity loss.
# Greater voltage excursion under the same load. Due to increased cell resistancethe voltage will sag further under the same load than a cell in optimal condition. The inverse is also true, the voltage will be higher for the same amount of charging current applied. The cell will then rebound to a voltage further from the loaded and charging voltages. This, obviously, can look like high self discharge but is a different phenomenon.
# Absolute maximum current decrease.
Elevated impedance causes a more complex constellation of symptoms, some of which may be easy to confuse with High Self Discharge (HSD). Ohm's law (E=I/R) holds the key to understanding here.

'''1) Elevated Peukert losses.''' Because more energy per unit of current through the cell is lost as heat, less of the cell's capacity is actually USABLE. Thus, apparent capacity loss can be significantly greater than actual capacity loss caused by the loss of cycleable Li alone. In low current applications, the two numbers will be close together. In high current applications, Peukert losses increase in proportion, so apparent loss of capacity breaks further and further away from actual capacity loss as current increases.

'''2) Greater voltage excursion under the same load.''' Elevated resistance across the cell means that voltage will sag more under the same load than it did when the cell was healthier. Conversely, voltage will rise higher with the same amount of applied charge current than it did when it was healthier. At the same time, rebound/settling voltages will be further away from loaded/charging voltages. In other words, the cell will rebound to a voltage further away from loaded voltage, all else being equal. Similarly, voltage will settle farther from the charge voltage with the same charge applied. This can give the illusion of elevated self-discharge, but the phenomenon is actually not the same thing. Again, the greater the charge and load currents, the greater the effect becomes.

'''3) Absolute max current decreases.''' Because the cell's series resistance is elevated, the maximum possible current through the cell is decreased.

Just to confuse things further, there can be many factors that lead to impedance rise. Some are related to Li plating, others are not.

== Lithium Ion Batteries ==
Lithium Ion (LiIon) batteries have a greater energy density than Lithium Iron Phosphate batteries, but have more challenging needs to use safely. The ideal operating range of LiIon batteries is between +15 and +45°C. The upper limit of temperature is particularly important as LiIon batteries experience thermal runaway - an unstoppable chain reaction that can occur in milliseconds releasing the stored energy in the cell. This can produce temperatures of 400°C and a fire that is extremely difficult to put out. Thermal runaway can start as low as 60°C and becomes much more likely at 100°C

Risk factors for thermal runaway:
* Short Circuits - either internally or externally
* Overcharging
* Excessive current draw or when charging

=== LiIon Pouch cells ===
Placeholder

=== 18650 and other cylindrical cells ===
Placeholder

Batteries

2020-11-30T19:09:04Z

Clanger9: Add battery pack spec section

== Introduction ==
There are a wide variety of battery chemistries available for use as the main traction battery of an EV. To use each chemistry safely, and to ensure an adequate service life from the battery pack it is important to understand the requirements for the chemistry you are using. Failure to do so may lead to premature or catastrophic failure of the pack.

Good pack design will allow for a nominal amount of abuse. People make mistakes and the pack should allow a margin for safety - and for longevity!

== Battery pack specification ==
When deciding on your battery pack, here are some basic parameters to consider:

=== Capacity (kWh) ===
How far do you want to go? A standard car conversion will need around 1kWh for 3 miles of range. For a middleweight motorcycle, 1kWh should give around 9 miles. ''Your mileage may vary'', as they say.

=== Voltage (V) ===
How fast do you want to go? The pack voltage defines the maximum speed your motor can spin. Motors are usually specified with "KV" - or RPM-per-volt. Check the KV of your motor and how fast it needs to spin to get your desired top speed. e.g. if you need 3,000RPM from a 25KV motor then your pack voltage needs to be 3,000 / 25 = 120V. The exact number of cells in series you need depends on the cell chemistry, but 3.8V is a reasonable guess for Li-ion.

=== Maximum current (A) ===
How quickly do you want to accelerate? Your motor's maximum power will be specified in kW. To estimate your maximum current draw, divide the peak power by the battery voltage. e.g. a 30kW motor with a 120V battery pack will pull 30,000 / 120 = 250A. The higher the current rating of the cells, the heavier they will be for a given capacity. Put cells in parallel to increase the current rating of your pack.

=== Mass (kg) ===
Can my vehicle carry the weight? You'll need to keep the kerb weight within the original design. For a car, this will be a few hundred kg (max). For a motorcycle, likely less than 100kg. This is a huge variable and is improving with each new generation of battery tech. For older EV or hybrid batteries, you can reckon on 10-15kg/kWh. Nissan Leaf batteries are relatively light (7.5kq/kWh). For the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 5-6kg/kWh.

=== Volume (L) ===
Will it fit? Batteries are '''big'''. They are getting smaller, but finding enough space is often the biggest challenge. You can reckon on 5-10L/kWh for older EV or hybrid batteries. For the latest technology (e.g. Kokam pouch cells or 18650s), you can get this down to 3-3.5kg/kWh.

There is much, much more to battery design than this (e.g. maximum charge rate, terminations, cooling, clamping), but the above should help consider what options will or won't work for your project...

== Lithium Iron Phosphate (LiFePO4) Batteries ==
Lithium Iron Phosphate (also known as LFP, or LiFePO4) batteries offer a good compromise between safety, energy density and ease of use for DIY conversions. They are available in a number of formats, commonly pouch cells and cylindrical cells.

=== LiFePO4 Pouch cells ===
The majority of this content is drawn from this thread: [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761&start=900 https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761] discussing the use of the A123 20Ah pouch cell. However, many of the general points apply equally to other similar pouch cells.

==== General build requirements ====
Pouch cells are vulnerable to damage from debris, and must be held in compression (see the datasheet for your battery, but 10-12 psi is recommended for the A123 pouch cells as a guide). A rigid container capable of preventing damage and providing compression is therefore required. Be aware the cells expand and contract in use, so allowance for this must be included in the structure of the case.

The pouch cells should be separated to prevent abrasion between cells, and also to avoid the development of hot spots. Prebuilt modules from A123 systems had thin foam sheets or heatsinks between each cell. Be sure to avoid any debris that could rub on the pouch surface, particularly if using recycled cells.

Mylar, '[https://www.americanmicroinc.com/fish-paper/ Fish paper]' or a [https://www.rogerscorp.com/elastomeric-material-solutions/poron-industrial-polyurethanes compliant foam] may be appropriate materials to serve this purpose. This material should not be flammable. If the material is heat insulating, it is important to address thermal management.

==== Compression ====
Compression is required to prevent premature failure of the cell. Without compression electrolyte will become unevenly distributed, causing current gradients in the cell and uneven heating. Local temperatures can become high enough to form gas formation leading to cells 'puffing up' even when the pack is otherwise held within temperature and voltage constraints. This will be exacerbated in packs with otherwise poor thermal management. Compression forces gas generated to the margins of the cell, outside of the cell stack, minimising its effect cell performance. Gas in the middle cells will create a dead space which does not store or release energy.

There is ~1% expansion through a discharge cycle. As the cell ages, the nominal cell thickness can grow by 3-5%. For A123 cells the ideal pressure is between 4 and 18psi with the ideal pressure being ~12psi. Maintaining 12psi can increase the life by 500 cycles over that of 4 or 18psi

There is some suggestion that in uses where 1C is never exceeded compression ''may'' not be required.

Highly rigid endplates with a mechanism to allow for a limited degree of expansion (e.g. steel bands) are considered an effective solution to this challenge.

It should be noted that compression is a challenge specific to pouch cells. Cylindrical cells are designed to maintain their own compression within the cell's electrode stack by their design.

This thread provides more information and experimentation relating to pack compression: <nowiki>https://endless-sphere.com/forums/viewtopic.php?f=14&t=52244</nowiki>

==== Pouch Cell Pack Design Examples ====
Placeholder

==== Notes regarding recycled pouch cells ====
Pouch cells are somewhat fragile, and breaching the insulation is not difficult, especially in a cells removed from existing packs and repurposed. If the pouch has had their poly-layers compromised you may see a number of faults:
* Black spots around the perimeter of the cell indicate electrolyte leakage
* Voltage on the outside of the bag. Note that microvoltage between the pouch and the electrode is normal (and due to a capacitive effect).
While the majority of these cells should no longer be in the market, a significant number of faulty cells made it back into the 'greymarket' in around 2013. These cells had misaligned tabs which can also lead to isolation failures between the tab and the pack. These cells should be avoided, particularly in high demand applications.

=== Cylindrical cells ===
Placeholder

==== Situations likely to cause cell failure ====
''Taken directly from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''
# '''Overcharge'''. Any extended time above 3.8 Volts will generate enough heat and electrochemical activity to puff a cell, especially one that is improperly compressed.
# '''Overdischarge followed by charge'''. Any A123 cell that has been pulled low enough to come to rest at <300 mV should be immediately scrapped. The published number for that is 500 mV, but the real figure is closer to 300, so that's a "safety buffer" if you will. Below this Voltage, the Cu electrodes start to dissolve into the electrolyte. When charge is applied, the Cu forms dendrites that puncture the separator layer, forming an internal short in the cell. This can puff a cell in a hurry---the more charge current on tap, the worse it's prone to be.
# '''Driving a cell negative'''. I've neglected to mention this before, but it is a possibility. I don't know much about the specific mechanism at this time.
# '''Malfunctioning or misinformed electronics'''. This is the most common cause of all of the above in my experience. At this stage of the game, it is critical for YOU to understand how your BMS functions on at least a cursory level. Choose your BMS very carefully and periodically verify that it is operating properly. They're not all created equal. Make sure V sense lines are securely connected and free of corrosion. Just because your BMS says there was never a problem doesn't necessarily make it so. Avoid harnesses or ribbon cables between multiple modules if possible--they are problematic wherever they are used in any mobile electronics.
# '''Exposure to or generation of sufficient heat'''. I don't know exactly at what temperature gas formation begins in the electrolyte, but we spec a max storage temp of 80 (or 85?) degrees C and I suspect this is the reason. The hotter, the puffier--to a point. This is why soldering tabs poses a real hazard to cell health. If you feel you must solder, sink or blow the heat away from the body of the cell. Use a big iron that can make sufficient local heat quickly, before the whole mass of the cell gets hot. You might even get the cell warm enough to melt separator if not careful.
# '''No compression, not enough compression, improperly distributed compression'''. This is a pack/module design issue. Apply 10, maybe 15 psi to your cell stack end to end and then band snugly and evenly. Use hard endplates of some sort--never wrap cells directly or allow their shape to become distorted. Protect all areas of the pouch from impact damage. This obviously does not apply to cylindrical cells.

==== Cell aging for LiIoPO4 cells ====
''Derived (barely paraphrased) from [https://endless-sphere.com/forums/memberlist.php?mode=viewprofile&u=33107 wb9k]'s post on endless sphere in the [https://endless-sphere.com/forums/viewtopic.php?f=14&t=38761 A123 thread]''

Capacity loss is caused by the Lithium that was available for storage becoming permanently plated on the cathode. Being unable to move within the cell it is no longer available to store energy. The impact of this plating is greater than the amount of lithium 'lost' to plating because not only is the lithium no longer available, it is also preventing access to that part of the cathode meaning Li that can still move has to take a longer path to reach the cathode. Lithium plating is one cause of increased cell resistance (there are others), a sign of worsening cell health.

There is no linear relationship between actual capacity loss and impedance rise. However some cell defects will also increase impedance.

Increasing cell resistance may cause a number of symptoms which may be confused with [https://earthshipbiotecture.com/a-lithium-ion-battery-primer/ High Self Discharge.]
# Elevated Peukert Losses. As more energy per amount of current through the cell is lost as heat, the cells useable capacity decreases. So the apparent capacity loss is higher than the actual capacity loss of cycleable lithium. When used in low current applications (e.g. solar energy storage) the actual and apparent decrease in capacity will be small. In high current draw applications (like EV traction packs), the Peukert loss increases proportionally, so the apparent capacity loss increases much faster than the actual capacity loss.
# Greater voltage excursion under the same load. Due to increased cell resistancethe voltage will sag further under the same load than a cell in optimal condition. The inverse is also true, the voltage will be higher for the same amount of charging current applied. The cell will then rebound to a voltage further from the loaded and charging voltages. This, obviously, can look like high self discharge but is a different phenomenon.
# Absolute maximum current decrease.
Elevated impedance causes a more complex constellation of symptoms, some of which may be easy to confuse with High Self Discharge (HSD). Ohm's law (E=I/R) holds the key to understanding here.

'''1) Elevated Peukert losses.''' Because more energy per unit of current through the cell is lost as heat, less of the cell's capacity is actually USABLE. Thus, apparent capacity loss can be significantly greater than actual capacity loss caused by the loss of cycleable Li alone. In low current applications, the two numbers will be close together. In high current applications, Peukert losses increase in proportion, so apparent loss of capacity breaks further and further away from actual capacity loss as current increases.

'''2) Greater voltage excursion under the same load.''' Elevated resistance across the cell means that voltage will sag more under the same load than it did when the cell was healthier. Conversely, voltage will rise higher with the same amount of applied charge current than it did when it was healthier. At the same time, rebound/settling voltages will be further away from loaded/charging voltages. In other words, the cell will rebound to a voltage further away from loaded voltage, all else being equal. Similarly, voltage will settle farther from the charge voltage with the same charge applied. This can give the illusion of elevated self-discharge, but the phenomenon is actually not the same thing. Again, the greater the charge and load currents, the greater the effect becomes.

'''3) Absolute max current decreases.''' Because the cell's series resistance is elevated, the maximum possible current through the cell is decreased.

Just to confuse things further, there can be many factors that lead to impedance rise. Some are related to Li plating, others are not.

== Lithium Ion Batteries ==
Lithium Ion (LiIon) batteries have a greater energy density than Lithium Iron Phosphate batteries, but have more challenging needs to use safely. The ideal operating range of LiIon batteries is between +15 and +45°C. The upper limit of temperature is particularly important as LiIon batteries experience thermal runaway - an unstoppable chain reaction that can occur in milliseconds releasing the stored energy in the cell. This can produce temperatures of 400°C and a fire that is extremely difficult to put out. Thermal runaway can start as low as 60°C and becomes much more likely at 100°C

Risk factors for thermal runaway:
* Short Circuits - either internally or externally
* Overcharging
* Excessive current draw or when charging

=== LiIon Pouch cells ===
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=== 18650 and other cylindrical cells ===
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