Is scavenging inverter/motor heat safe during winter?

[0tik]

I suspect that OEM solution of turning on coolant pump only when set temperature limits are reached is most likely done to prolong pump's life. But what if motor and inverters have their optimal working temperature above 0°C and deteriorate faster when working against below-freezing temperature of a coldplate? I hope there is someone here who has some kind of knowledge on that subject because i really, really want to use this heat to preheat air inside cabin but I'm afraid this might break my motor and inverter a lot sooner

[jrbe]

Batteries, oil, and grease don't like the cold. Keeping them in their temperature window helps them do their job well.

Electronic components do like the cold. Look at any mosfet / ight datasheet and look how much they derate the current at higher temps. This goes for every component I can think of except some laser components that need a narrow temp range to operate - not something in an inverter..

[snelly]

Hi I run a bypass valve to stop water going thro the radiator and a heat exchanger off the cabin diesel water heater system.

works great pre heats battery and motor before driving and i don't lose any range at low outdoor temps.

[0tik]

@snelly

That's great but it's the opposite of my question.

@jrbe

I don't think i-miev motor has coolant anywhere close to oil and grease.

[MattsAwesomeStuff]

a heat exchanger off the cabin diesel water heater system.

What diesel heater do you use?

[arber333]

Batteries, oil, and grease don't like the cold. Keeping them in their temperature window helps them do their job well.

Electronic components do like the cold. Look at any mosfet / ight datasheet and look how much they derate the current at higher temps. This goes for every component I can think of except some laser components that need a narrow temp range to operate - not something in an inverter..

Electroncs parts have their limits too. Transistors need control elements. Commercial parts patience ends near 0degC, industrial automotive parts at -40degC and military at -55degC.

[jrbe]

I don't think the question was to push the temp down anywhere near -40. Good antifreeze can freeze around there depending on the mix.

My answer was trying to be generic about different areas. The oil and grease might be in the motor or differential. It isn't always possible to easily separate the cooling from these different areas and why I mentioned them. But basically the inverter will be fine with any reasonable cold temperature you plan to keep it at and will not shorten life past extra energy to overcome extra drag of cold mechanical components / fluids.

-40 is far below freezing and not reasonable for preheating air.
Synthetic oil / grease should do ok kept around freezing temps but will add some extra drag if that applies to your setup.

[arber333]

I don't think the question was to push the temp down anywhere near -40. Good antifreeze can freeze around there depending on the mix.
....

I will rant a bit...
Dont get me wrong. Industrial grade components are really tough. However if we dont respect standards and include some of the easily accessible commercial components we can have a problem.
Granted even those chips may work fine around 0degC, but their operation may be failing, signals may be inaccurate or different uncontroled anomalies may happen during powering up theese systems.

I remember my first DIY builds of OI. Inverter would operate really good at most of the year. But in winter i would regularly start to get annoying failures until total failure of IGBT forced me to rebuild inverter. This stoped as soon as i started to use automotive inverter units (Chevy Volt, Nissan Leaf etc...)

I see the title at the top is about how reasonable would be to use motor waste heat in winter to heat up the cabin...
Answer would be: Not very... from the efficiency standpoint, not so much safety...
Elaborated: BLDC Motors today are about 90% efficient <ACIM motors about 86%. Lets take that for good measure.
This leaves us with 14% of invested energy.
If we use 5kW to drive the road at 50km/h we waste only about 700W. Granted even that is something, however you need to consider you have to heat up coolant to a reasonable temperature to be effective inside the heater matrix. I would say you need about 50DegC coolant with 0degC outside temperature you would feel warmth. Remember this is constant power and as you go through hils and valleys motor drops or raises power required according to terrain.

Water heating works like this: P*t = (4.2 × V × dT )
P-power, t-time, V- volume, dT - temp difference... i have about 4l in my coolant loop
We keep power and want to calculate time required to reach 10deg to 50deg = 40deg difference. Say my car is keept in a garage...
So we get t = (4.2 × V × dT ) / P; t = 17min for perfect energy transfer.
However entropy leaves us with a lot to be desired especially with temperatures under 0degC!

I would say it can be done for mild climates, provided you insulate your coolant hoses any totaly bypass any radiators so as much coolant would transfer heat to heater matrix...

Real life experience differs a lot from ideal model since you have to run the air to keep windshield from misting and that also removes heat from coolant faster than it can be brought up. I would say you can keep your loop, but add additional inline heater so it can quickly raise temp to your level and then use it to only keep with demand.... Outlander CAN bus heater is great for this as you get free temperature reports from it which allows you to run your control loop with.

[0tik]

Well... Given that lithium batteries stop working below ~ -20°C I'm not worried about such low temperatures. Here in Poland it's mostly -5°C in winter.
Judging by the posts so far it looks like I'm going to post some pictures of this modification sooner or later

@Arber333
Thank you for a detailed calculations but as I said in OP, it's just for PRE-heating. As a bonus I could remove OEM front radiator if the cabin radiator manages to keep temps down in summer. I'll use air-to-air parking heater for the actual winter heating. And it will be installed in a way that won't overheat cabin radiator connected to the inverter/motor.

[arber333]

Well... Given that lithium batteries stop working below ~ -20°C I'm not worried about such low temperatures. Here in Poland it's mostly -5°C in winter.
Judging by the posts so far it looks like I'm going to post some pictures of this modification sooner or later

@Arber333
Thank you for a detailed calculations but as I said in OP, it's just for PRE-heating. As a bonus I could remove OEM front radiator if the cabin radiator manages to keep temps down in summer. I'll use air-to-air parking heater for the actual winter heating.

You could stil use your radiator, but install a 3 way valve for winter operation to bypass flow into your heater directly.
https://www.diyelectriccar.com/threads/ ... ve.199131/

You must be careful though, inverters and regulators have upper limit of about 90degC.

[snelly]

this is the parts i used

over size radiator for summer temps passive no fan, 3 way bypast and heated in winter.
temp controlled using a PLC

[arber333]

this is the parts i used

over size radiator for summer temps passive no fan, 3 way bypast and heated in winter.
temp controlled using a PLC

Nicely done!

I would recommend you use Fiat 500 Siecento radiator. It is much smaller in height and size and is plentiful for summer.
I recognized the greatest source of heat is actually charger when car is stationary. This is the only reason to keep a cooling fan.
https://mazdamx3ev.wordpress.com/2023/1 ... ng-piping/

[snelly]

thanks I understand, so far only seen a plus 2deg rise over summer outside temps, but only using granny charger :-]

[snelly]

thanks I understand, so far only seen a plus 2deg rise over summer outside temps, but only using granny charger