Battery Temperature Management

Batteries, Chargers, and Battery Management Systems.
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ninepointeight   1 W

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Battery Temperature Management

Post by ninepointeight » Oct 19 2019 1:37pm

Hello all, having past through my quarter life crisis, I am embarking on another build and to address previous shortcomings. I am planning likely 20s36p pack of Panasonic's NCR18650pf, these still seem to be the best cell for a long lasting chemistry + high discharge(I haven't seen anything that looks like a direct upgrade). The datasheet says you can store these at up to 50C and discharge up to 60C. Obviously these are not the best conditions for a long lasting battery, but just how bad are they? I can't find any data about the cycle life impact other than that the cells have a bit more capacity at 30C than 20C which is to be expected.

Heating the pack is pretty simple with a few resistive pads, the problem is cooling.

The implication of living in Texas is that temperatures are regularly 35C-40C outdoors, and can easily reach 50C inside a garage, and we all know that a ebike spends the majority of its life not moving. The easiest solution to this was to make the battery removable, so I plan to have 2 packs 10s36p that are fairly easy to remove for long term storage/charging inside. This isn't exactly convenient though. The next question is, what if I park my black ebike outside on a hot sunny day, I doubt it would have much trouble reaching garage temperatures in a semi enclosed battery compartment. I thought about forced air cooling through past the 2 packs that could keep the enclosure at least just above air temperature. This seems like the most practical option.

I don't know how much heat these cells put out under load, and could probably write a thesis on it, but I don't think these cells will really see more than a continuous 0.5 C-rate on them so it shouldn't be an issue.

Then I found some neat little compressor units for small refrigerator systems:
https://www.rigidhvac.com/mini-compressor
This combined with a small evaporator in the battery enclosure area and condenser out of it should have no problem maintaining ideal battery temperature in even the worst conditions, and would enable me to just leave it on the charger to run the AC. I am building a custom frame for this bike so it could easily be integrated (only a few pounds).

I'm curious to hear what you all think of this problem and if I am over engineering a solution, and what are electric motorcycle doing about this problem? I think most electric cars have battery cooling systems, is this something worth it for large ebikes? I am pretty much looking for a no compromises solution when compared to gas bikes (except maybe price), I just don't know how negatively these cells are impacting by spending time out in the heat.

john61ct   1 MW

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Re: Battery Temperature Management

Post by john61ct » Oct 19 2019 2:16pm

The cost and complexity of active cooling will not be worth the trouble, unless you enjoy the science project.

Designing portability, easy swapping to bring into the aircon, yes go for it.

Otherwise just accept shorter lifespan, more frequent replacement,

too may variables to give hard numbers

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fechter   100 GW

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Re: Battery Temperature Management

Post by fechter » Oct 19 2019 2:42pm

A nice reflective bike cover would help keep the battery cool when parked in the sun. I agree that an active cooling system would likely not be worth the effort.
"One test is worth a thousand opinions"

John in CR   100 GW

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Re: Battery Temperature Management

Post by John in CR » Oct 19 2019 5:24pm

Park the cars outside, or just get rid of them, and then your garage won't get so hot. If that or moving to somewhere with a better climate isn't an option, I certainly wouldn't make that size pack removable. Long before that hassle my bike would get an indoor parking, or it's own space in the garage with walls along an interior wall and tie it in to the central air with some simple duct work. I prefer my solution, which is living where it's in the 70's during the day and 60's at night almost every day of the year, so my bikes get to live in the gated car port with shade and a fresh breeze while the car that's only been used once in 2.5yrs roasts in the tropical sun. Of course it's A123 amp20 starter pack lives in comfort on a shelf in the carport. :mrgreen:

ninepointeight   1 W

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Re: Battery Temperature Management

Post by ninepointeight » Oct 19 2019 6:24pm

Thanks for all the good advice, unfortunately I don't have much of a say of what else goes in the garage, but I like the idea of having a cooled setup for storage in the garage, it will be a workout moving a pack like this. Less things to break on the bike as well, good to keep the moving parts count down to the suspension and a few bearings.

I guess I will start my own testing with a few of my leftover NCR18650pf, because so far for me data on the temperature impacts on specific cells is hard to find at best, and at worst obfuscated in vape and flashlight forums :confused: .

John in CR   100 GW

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Re: Battery Temperature Management

Post by John in CR » Oct 19 2019 7:34pm

ninepointeight wrote:
Oct 19 2019 6:24pm
...it will be a workout moving a pack like this. Less things to break on the bike as well, good to keep the moving parts count down to the suspension and a few bearings...
Exactly, on both counts. Major risk of something bad happening to the most expensive part of your ebike, the battery. I mount mine quite securely, and hardwire everything to prevent failures, so removal is a significant project. No rattling around even on major bumps, and 100% crash and getting knocked over survival so far is my benefit.

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