openinverter forum

cajamatt wrote: ↑Fri May 30, 2025 2:00 am
The equation Q=w*c*dT where Q us heat transfer, w is mass flow rate, and c is specific heat of air is used.
- mass flow rate is found from 200LFM and the open cross sectional area of the heatsink.
- dT is 42C (max battery temp from the other thread) - 27C (hot summer day) = 15C
- gives 450W of heat transfer out of the whole pack. This is not a conservative estimate and I plan to adjust the variables as i find better info for them, but 500W compared to the 129W targeted tells me there is margin for this type of forced air cooling directly on the packs!

Oops! This is not the performance of the heatsink, this is the amount of energy the air would absorb if the air changed by 15C.

The heatsink performance is:

q=h*A*(Ts-Ta) where R=1/(H*A). rearranged to: Q=(Ts-Ta)/R

Ts= 42C (max battery temp)
Ta= 27C
R=0.8C/W

Q=18.75W for a single slab of the heatsink.
Q=225W for the whole pack (12 individual slabs)

The surface won't actually reach 42C when the internals do. There is a gradient, and then another gradient through the thermal paste. So if the surface is actually 35C:

Q=120W per pack.

Hmmmmmmm...

One thing to consider before committing to aircooling - liquid cooling gives you the option to provide battery heating as well. I've had issues with my car even in the mild North Carolina winters because even above freezing is cold enough to affect my pack. I've got the cooling half plumbed but need to finish the job so that I can add heating.

P.S.Mangelsdorf wrote: ↑Fri May 30, 2025 12:04 pm One thing to consider before committing to aircooling - liquid cooling gives you the option to provide battery heating as well. I've had issues with my car even in the mild North Carolina winters because even above freezing is cold enough to affect my pack. I've got the cooling half plumbed but need to finish the job so that I can add heating.

I was wondering about this! you're currently switching from air cooling to liquid cooling? what is the heating device that you're adding? have you considered adding heating elements to your pack without liquid cooling? i was wondering about embedding something like a seat heater coil to the heatsink sandwich below my packs and adding a insulating cover around the packs for the winter season.

I have searched around a bit and haven't found a solid answer, has anyone experienced a hiccup with the cooling system when the PDM is oriented on either side? I might have a hard time fitting it in upright.

cajamatt wrote: ↑Sun Jun 01, 2025 1:41 pm I was wondering about this! you're currently switching from air cooling to liquid cooling? what is the heating device that you're adding? have you considered adding heating elements to your pack without liquid cooling? i was wondering about embedding something like a seat heater coil to the heatsink sandwich below my packs and adding a insulating cover around the packs for the winter season.

The Volt batteries originally were liquid cooled/heated and had a HV heating element in the head end of the pack. I've been running them without cooling (beyond whatever airflow they might get) and haven't seen issues with heat, just with cold. I see range degradation when they are below 70 degrees F (20ish C). The plan will be to use the OEM heating element, but I'm working on where I fill fit it, and how I'll control the power to it.

I couldn't get the PDM to fit in CAD so i went and tried to fit it in the drivers side front corner in real life and it didn't fit. So i chopped off some random little brackets and it kinda fit, but not with the giant radiator in. Next to do: see if i can get back with like a half size radiator for cooling a 2013 leaf stack with the 80kw inverter. Then going to consider rotating the motor and inverter about the transmission center to make more room for the PDM. That's what's shown below, and the most promising orientation for the PDM is fully upside down. After viewing Johannes' teardown and noticing the cooling channels are all planar i'm not concerned about air bubbles or anything regarding orientation of the PDM. It also looks like both the bottom and top covers of the PDM are oversized and maybe i'll consider making smaller custom covers for the PDM to do a honey-i-shrunk-the-PDM!

P.S.Mangelsdorf wrote: ↑Sun Jun 01, 2025 11:46 pm The Volt batteries originally were liquid cooled/heated and had a HV heating element in the head end of the pack. I've been running them without cooling (beyond whatever airflow they might get) and haven't seen issues with heat, just with cold. I see range degradation when they are below 70 degrees F (20ish C). The plan will be to use the OEM heating element, but I'm working on where I fill fit it, and how I'll control the power to it.

I'll be sure to follow along with your findings on this!

I also had a hard time getting the PDM to fit in my build. But final solution looks like it was always meant to be there now.
I rotated 90 horizontally and ran the coolant flow through backwards and has all worked fine for me so far - 300 miles of testing so far.

I did consider a custom lid, but concluded it didn’t save very much. If you hunt through my build page you’ll see a link to Flying Tools YouTube where he briefly shows a custom lid in case it helps your thoughts.

The most important space saving I found for my particular constraints was how the cables exited the PDM. Once I’d sorted that, it worked out ok for me.

Sell the pdm and get an outlander obc, or Tesla pcs