openinverter forum

I have been thinking about how to thermally manage the BMW batteries (or similar) and was wondering on the general consensus within the forum, as there seems to be quite a variation on what extent to go to. I am currently just trying to sort out a plan for when I'm ready.
My plan is probably going to be an electric mx5 so weight is going to be critical..and as always it's going to be done on a shoe string

At one end of the spectrum is OEM level such as zero ev's (or similar) cooling plates and all of the complexity of actively cooling and heating the batteries

Or the other end Damien's 10mm heatsink and just monitor what temp the batteries are. (I know this is not the most extreme but it's as far as I would go wilst keeping it safe)

My thoughts are sort of a middle ground ... And keep it as simple as I can .... Controling with an Arduino and relays etc

1. Use a sheet a aluminium as a heatsink to dissipate the heat to the battery box (also aluminium)
2. Bolting a some ntc heaters to the heatsink that would only heat when the batteries are cold (less than 5 Deg) and when plugged in.
3. Possibly bolting a couple of 240x40mm (AliExpress) water block to the heatsink and just flow the exhaust water from the Inverter and motor when the batteries are below let say 15 deg.
4. Set alarm and shutdown temps (34/50).

What's everyones thoughts?

rstevens81 wrote: ↑Sun Jul 12, 2020 7:08 pm What's everyones thoughts?

Do we have any real world test data from a battery in use? If not, then I'd begin by testing a single module so that we know what we are dealing with.

You could use alu panel as a heat/cold distribution plate under the module, which is what BMW uses in original.
Then under that plate you could sandwich some isolation material and refrigirator heat exchanger. That black tube mesh that is in the back of the fridge. It does have tiny passages, but you could paralell exchangers to a single fluid pump. Then you could also use a thermo valve (household) set to +10deg which would supply warm coolant from your cabin heater system in case of temp drop...
Such system would be automated in such a way that if you would need warmth so would your batteries.

What are the battery out in the cold experiences from the rest of you? My car is in the garage and there were not many times i had to left it in sub zero for the night. Also battery mass keeps it from going sub zero for quite some time.
The worst experience was when i had to leave the car in the airport for 4 days. Battery was like 60% SOC but there was sub zero cold for 2 nughts in a row. I didnt have battery heated in any way at the time. When i arrived back and picked up the car i started down the ramp to accelerate on the road. Pack voltage just plummeted (to about 3V per cell) and i had to drive really carefully for like 20Km. I guess then batteries heated up enough for me to drive on the highway.
I dont know if battery heating would be of any help in that situation, because you still have to heat up the battery mass and it takes some time...

My point is, do you see an actual need for active battery heating? How would you do it and results if you have please.

tnx

A

I actually ended up buying VW Passat modules instead as the price for BMW ones went bonkers, plus I get a chiller plate with the VW ones.
Originally I was thinking about preserving the for maximum life, now I am more thinking heating to 10 Deg c when plugged in, and a cooling circuit if they get a little to warm (say greater then 35 Deg c).
With the rate of increase in ev production I expect in 5 years there will be a lot of cheaper better batteries (and drivetrains).