Tesla Large Drive Unit Support Thread

[Mowza]

Now that I am all set for my circuit protection for the 120v test (thank you muehlpower!) I wanted to ask ahead of time about the current draw that can be expected during the full voltage test which is my next step. Is it still below 30A on the unloaded motor or do I need to step up the circuit protection amperage rating?

To elaborate a bit I have zero intentions of spinning the motor at any significant RPM specifically to avoid running into a scenario where the fuse might blow while the motor is spun up.

That brings me to a second question, is higher RPM bench testing at 120volts and then full voltage even a requirement before proceeding with installing the unit in a car or is a low speed test sufficient proof of functionality?

[Jack Bauer]

I have two quick questions for folks putting low value fuses in the hv feed to Tesla drive units :

1)What do you imagine will happen if/when the fuse blows and the motor is running at high rpm?

2)Have you ever seen me do that in a video or do I use some other method?

Please , please, please THINK and use the search function.

[Golf_mkIII_E]

I have two quick questions for folks putting low value fuses in the hv feed to Tesla drive units :

1)What do you imagine will happen if/when the fuse blows and the motor is running at high rpm?

2)Have you ever seen me do that in a video or do I use some other method?

Please , please, please THINK and use the search function.

I'm currently building using the Sport LDU (performance, red PCB), and I am just questioning the exact same thing. Dropping a contactor or blowing a fuse will almost certainly destroy your LDU, which makes me quite anxious about my fuse choice. Finding a HV DC fuse with a higher than 630A rating seems a bit challenging, so I was thinking about getting 2 400/500A fuses and put them in parallel.

[johu]

Keep in mind a 500A fuse will need to see 500A (180 kW at typical EV voltage) for minutes worth of time before it melts. For it to blow instantly it requires 5-10x the rated current.

[muehlpower]

Wouldn't a 430V TVS solve the problem with the destroyed drive units better than installing fuses that are too large?

[johu]

They do consume very short transient spikes at high power but they don't absorb a whole lot of energy, for obvious reasons. When they break they either disintegrate leaving you with an open circuit again or become a short circuit.
So far we have only seen very small fuses trip in action, no appropriately rated ones.

[Golf_mkIII_E]

So far we have only seen very small fuses trip in action, no appropriately rated ones.

What kind of ratings were the fuses which were too small?

The 500A Bussmann fuse can do 1500A for 4 seconds before blowing. The Sport LDU can pull 1400A peak. The small margin for error scares me a little bit.

[johu]

What kind of ratings were the fuses which were too small?

I remember someone using a 5A breaker on the bench and others used some tens of amps fuses and reported inverter failure on the bench. I assume that happened under regen as only regen moves energy from the motor into the inverter. If a fuse blows under acceleration the bus caps will bleed in no time leaving no energy to build up a rotor magnetic field. I'd be surprised if the stray magnetization of the rotor could create any significant voltage.

[jon volk]

The 500A Bussmann fuse can do 1500A for 4 seconds before blowing. The Sport LDU can pull 1400A peak. The small margin for error scares me a little bit.

The concern is perhaps not unwarranted. I have blown up a Bussmann FWH-400A under WOT. I was lucky and did not experience an inverter failure. There wasnt a short or anything of that nature in the system. Its always tough with a data point of one, but my best guess is that repeated exposure to maximums in current caused the fuse to degrade over time. I would argue that I am more abusive to my LDU than many and by repeated exposure, I mean literal hundreds of WOT pulls. Since this happened, I switched a newer Model S 2000a rated pyro fuse and have not had any issues. Im not saying a 400-500a fuse will not work, as there are plenty in use, but based on my singular experience I will continue to run the larger Tesla part.

[Mowza]

I am planning on using a fuse rated at 30A 450V for the 120v and 380 volt low speed tests. I have the frequency maxed at 100Hz and I had no intentions of moving it much farther than that. I am certainly not going to be introducing regen on the bench if I don't have to.

I see people doing high RPM no load bench testing but I am wondering if it is something that is highly recommended or even necessary before installing the LDU into the vehicle, or is it just something people do to have a bit of fun? I would like to avoid it if possible as I don't wish to be frying anything that has a large price tag on it.

[johu]

I am planning on using a fuse rated at 30A 450V for the 120v and 380 volt low speed tests. I have the frequency maxed at 100Hz and I had no intentions of moving it much farther than that. I am certainly not going to be introducing regen on the bench if I don't have to.

Has this not been clear?

others used some tens of amps fuses and reported inverter failure on the bench

One little glitch and your inverter is toast. Use a cooker element (or any high power resistor) like Damien or a fuse for a couple of 100A, even for bench tests.

[muehlpower]

What role do the other HV devices play in these considerations. After opening the contactors or if the main fuse breaks, they remain connected to the motor. Can this absorb energy? For bench tests, usually only the motor is connected. The audi AC compressor seems to have a 486V TVS!

[Golf_mkIII_E]

I am planning on using a fuse rated at 30A 450V for the 120v and 380 volt low speed tests. I have the frequency maxed at 100Hz and I had no intentions of moving it much farther than that. I am certainly not going to be introducing regen on the bench if I don't have to.

I see people doing high RPM no load bench testing but I am wondering if it is something that is highly recommended or even necessary before installing the LDU into the vehicle, or is it just something people do to have a bit of fun? I would like to avoid it if possible as I don't wish to be frying anything that has a large price tag on it.

I've had a amp clamp meter on my DC HV wiring when I was no-load testing the LDU at 60v. When applying the smallest amount of throttle, spinning up the motor to low RPM immediately drew about 40-50A. Keeping it at low RPM (400-500) only draws about 2-3A, but increasing the RPM draws a lot more current. I wouldn't use a 30A fuse if I were you.

I haven't done any high RPM testing myself. For the low RPM testing I used my amp clamp meter, 70mm2 cabling with a 10cm 6mm2 extension with some cutters next to it. There was a second person present, constantly monitoring the amp meter and temperature of the extension. If anything would have gone sideways, he was able to cut the 6mm2 extension.

The 500A Bussmann fuse can do 1500A for 4 seconds before blowing. The Sport LDU can pull 1400A peak. The small margin for error scares me a little bit.

The concern is perhaps not unwarranted. I have blown up a Bussmann FWH-400A under WOT. I was lucky and did not experience an inverter failure. There wasnt a short or anything of that nature in the system. Its always tough with a data point of one, but my best guess is that repeated exposure to maximums in current caused the fuse to degrade over time. I would argue that I am more abusive to my LDU than many and by repeated exposure, I mean literal hundreds of WOT pulls. Since this happened, I switched a newer Model S 2000a rated pyro fuse and have not had any issues. Im not saying a 400-500a fuse will not work, as there are plenty in use, but based on my singular experience I will continue to run the larger Tesla part.

Wasn't there an user who destroyed their LDU because the pyro fuse went off without any reason to?
I've indeed heard stories about fuses degrading when their capacity was chosen to marginal. For the moment, I think I'm gonna stick with the plan for 2 paralleled fuses.

[Golf_mkIII_E]

What kind of ratings were the fuses which were too small?

I remember someone using a 5A breaker on the bench and others used some tens of amps fuses and reported inverter failure on the bench. I assume that happened under regen as only regen moves energy from the motor into the inverter. If a fuse blows under acceleration the bus caps will bleed in no time leaving no energy to build up a rotor magnetic field. I'd be surprised if the stray magnetization of the rotor could create any significant voltage.

When testing my LDU with the amp clamp meter on the HV DC wiring, I haven't seen any regen when pulling my foot of the throttle. Isn't it disabled by default? I don't think people would enable regenerative functions for testing purposes, would they?

[Golf_mkIII_E]

What role do the other HV devices play in these considerations. After opening the contactors or if the main fuse breaks, they remain connected to the motor. Can this absorb energy? For bench tests, usually only the motor is connected. The audi AC compressor seems to have a 486V TVS!

That is also a good consideration. On the other hand, all other HV DC hardware can only draw what? Heater, DC/DC and A/C combined, about 10kW max? The LDU can regenerate about 75kW peak.


Sorry, I've seem to be quoting rather than editing

[muehlpower]

That is also a good consideration. On the other hand, all other HV DC hardware can only draw what? Heater, DC/DC and A/C combined, about 10kW max? The LDU can regenerate about 75kW peak.


Sorry, I've seem to be quoting myself rather than editing

That is correct, but the question remains why the fuse fails. Johu says if the fuse breaks when accelerating, the energy is quickly dissipated by the motor, while recuperation only generates currents of up to 250A, which a 400A fuse can easily do. Jon destroyed his fuse while accelerating, the inverter was undamaged. The case you quoted with the pyrofuse was after accelerating when removing the gas with very little recuperation and led to the destruction!

A completely different approach that only Johu can answer. In the inverter there are transistors for + and - with a rise and fall time. Can it happen if the processor stalls, there is an overlap and high currents arise that destroy the transistors and finally break any fuse?

[EV_Builder]

The big fuses inside consist of many smaller ones in parallel. When you reuse a fuse the risk is valid that the fuse isn't as original spec.

I tested with a 250amp fuse. More then enough. For a bit of bench testing.

[jon volk]

Here's an internal shot after I cut apart the failed fuse.

[johu]

A completely different approach that only Johu can answer. In the inverter there are transistors for + and - with a rise and fall time. Can it happen if the processor stalls, there is an overlap and high currents arise that destroy the transistors and finally break any fuse?

It is super unlikely, as the gate signals are generated by software-independent hardware. If the clock fails for some reason 3 random gate signals would remain on, probably triggering an over current condition and then the hardware comparator would shut down all gate signals asynchronously, i.e. no clock is required to shut down. For that very reason I disabled saving to flash in run mode as that essentially stalls the processor for a while.
As a last resort there is the gate drivers desat detection but it seems Tesla didn't implement that too well.

[Clanarn]

So after a week of troubleshooting, I found the issue. Not the same I inverter/pcb with overcurrent and blown fuses that I described here a month ago. Anyway, this pcb was purchased fully assembled and tested.
I had it on the bench fully working in February this year. But when test running it now it threw OVERCURRENT and HIRESOFS. First I thought it was software related. Then I measured around on current sensing related TP and components and when holding the probe against a leg of IC11, That bastard moved! Turns out IC11 had only been soldered on one of leg. Looked hand soldered. So I soldered it and now it works.

[johu]

Please contact me for some compensation (I assume you bought from me?). Not sure how this would have slipped through as I measure the analog voltage signal on the test points while feeding the clock signal to the input.

[Golf_mkIII_E]

Today, I've had the opportunity to lay my hands on a new Mercedes fuse.



It's a 700A rated fuse, with quite promising characteristics.



I think it will be perfect for the LDU.
Also, it is pretty big.

[johu]

So after a week of troubleshooting, I found the issue. Not the same I inverter/pcb with overcurrent and blown fuses that I described here a month ago. Anyway, this pcb was purchased fully assembled and tested.
I had it on the bench fully working in February this year. But when test running it now it threw OVERCURRENT and HIRESOFS. First I thought it was software related. Then I measured around on current sensing related TP and components and when holding the probe against a leg of IC11, That bastard moved! Turns out IC11 had only been soldered on one of leg. Looked hand soldered. So I soldered it and now it works.

Ok, Clanarn contacted me and the board was not sourced from the openinverter shop - always buy original

[Maverick441]

First LDU test, question on Regen.

I am putting together a bench setup to test the LDU board with the mother and contactor / fuse box (following the wiring diagram on github). I have 6 LG Chem batteries but I am only using 2 in series (~120V) for the first test. With 12V input from a power supply set at 3A, I can ping to the Inverter board interface. I browse the parameter set and found the Regen section. I want to disable the Regen function as I don't have an extra fuse or a load in series with the motor. I don't want the Regen current to go back to the battery stack. I don't plan to rev to high RPM, just to test all my connections. I look through the wiki and search the forum but I didn't find how or what to set. I don't have a break paddle installed.

The parameter set for Regen seems to be all on brake paddle.

I saw a thread that the Regen can be disable but there's no detail.

thanks,

[johu]

Without brake pedal just set brkmax=0 . I should make it an FAQ item...