ElectricMotorcycleForum.com
General Category => General Discussion => Topic started by: NEW2elec on December 14, 2018, 12:59:56 AM
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I know you can't get more work out than you put in and those basic concepts.
What I'm wondering is can you use your EV's battery as an electric resistance heating system to heat a cold weather battery with overall increased range versus the normal non heated battery?
My understanding is the cold limits the chemical process within the cells limiting your range in the real world.
In a quick fictional example: If you had a 10kWh battery with 100 mile range in 80F heat but at -10F you range is down to 70 miles. In that example losing 3kWhs of effective battery use leaving you at 7kWhs of usable power.
If your battery had a heating blanket or internally wired heating system that used 1kwh of battery power warming it back up to a battery temp closer to 80F could you then have more than 7kWhs of usable battery power giving you more real world range?
In ICE terms it seems like the cold puts a lock on a gas can and if you get it heated up it would unlock letting you use it as if it were still warm outside.
Now I know my numbers aren't even close to correct but hopefully they can describe the theory question.
I know Brian T Rice was working on an insulating cover for the battery which I can see would at least help but could active heating achieve better results?
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Tesla has a charging mode that delays charging until a drive is planned so that the last phase of charging's heat production helps pre-warm the battery so it performs better once you set out on the road.
I've done this with a J-plug, warming a battery up from an overnight outdoor storage session (at 0.6C or so, where the low overnight was probably 37F) just before travel (but after some initial warmup by local transit to the charging station). It seemed to work, but it's hard to measure with lots of confounding factors like rain, etc, that accompany cold weather days.
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It's worth noting that cooling from travel happens differentially from the outside, so there's a temperature gradient, and this contributes to a single lowest cell reducing range for the entire pack.
Heating from current (while driving or charging) seems to happen more evenly across the pack, so it's enough to have a very light insulator around the pack to reduce the temperature gradient. Heat still needs to escape, especially once temperatures rise above say 55F.
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I'd say yes, it might make some sense to use a little of the battery's energy to heat the battery itself before a ride, but it would depend very specifically on the exact numbers. It's certainly theoretically possible that using 5% of the battery's energy to warm the battery up might increase the amount of energy you can get out of the battery by 20%, in which case you've gained 15%. But again, very specific information about the battery's performance would have to be known.
I've got a good friend who used to live in Chicago, and on very cold days the battery on his car wouldn't have enough oomph to crank the engine over, even with winter-grade oil in the crankcase. But he'd turn the headlights on for a few minutes, and the headlight current flowing through the battery's own internal resistance would warm it up enough that it could then start the car.
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Thanks for the replies guys.
I was thinking of the poor unfortunate souls in the cold and some of their issues. ;)
Their range loss making some trips out of the question and the even bigger issue of no ability to charge below freezing.
A heater to warm the battery controlled by the MBB and BMS sourced from the onboard charge cord maybe.
Not really a problem for garage charging or even charging stations if you have been riding and the battery was warmer from it's own use but street parking and outdoor storage assistance.
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In case of daily commuting this isn't an issue in the morning. Even if not heated, the garage is less cold than outside. And you may add a little electric fan heater near the bike, with a timer to switch it on 30 minutes before riding or so.
Issue will more be in the evening, if thebike was parked outside, with less than 100% remaining and no socket to plug charger or heater. The battery having been frozen by the whole day.
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My ‘13 S 12.5 battery will not turn on the bike if the pack is 45F or lower. This is much higher than Zero claims and a real PITA. I park it in the sun for about 20 min. and that usually works.
I live in California and even here winter mornings are usually this low. Unheated shop does not help at all.
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Tesla has a charging mode that delays charging until a drive is planned so that the last phase of charging's heat production helps pre-warm the battery so it performs better once you set out on the road.
On a very cold day (Reno cold--not Auburn cold) my Tesla display on a cold morning will say "Regeneration reduced". And then it coasts a lot better. The default in the Tesla is to slow down the car so much from regen that it's rare to need any braking, espcally at city speeds. In the Tesla, the brake lights come on NOT by a brake light switch, but by how fast the car is decelerating.
So when you see a Tesla's brake lights coming on a lot while going down a hill on curves, the odds are the brake pedal was not even touched. But it really is slowing down.
-Don- Auburn, CA
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Maybe try a seedling heater? I'd get one with a thermostat...
https://smile.amazon.com/s?k=seedling+heater&ref=nb_sb_noss