Battery heater in cold weather

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The problem with using the 12 volt to power the heaters, is it is grossly inefficient. You are using 12 volts that you invert to 120 then using 360 volts to keep the 12 volt supplying the inverter. All to keep the HV pack warm, you end up with less range then if you didn't do anything at all.
I can see the advantage if the heaters are plugged into the house power grid, but not if running off the cars stored power.
 
The problem with using the 12 volt to power the heaters, is it is grossly inefficient. You are using 12 volts that you invert to 120 then using 360 volts to keep the 12 volt supplying the inverter. All to keep the HV pack warm, you end up with less range then if you didn't do anything at all.
I can see the advantage if the heaters are plugged into the house power grid, but not if running off the cars stored power.
Also, if considering 300 w at 12 v, that requires 25 amps continuously to the heating pad. Using 120 VAC at 2.5 amps would be much easier if there's a spare circuit available.
 
How you install/use it ?
Do you have some photos?
Thank you
RV water/wastewater tank heaters are available in 12v and 120v (also 240 for the rest of the world). They are a stick on self insulated pad. We’d probably have to run several of them and either add a thermostat or switch them on and off ourselves. Generally they have a thermostat that turns on just above freezing and shuts off about 10C 50f so probably a bit warm for the battery.
 
It would indeed be better to use 12v heaters. 3d printer heating pads (presumably 120 v) are just one possibility. I like the RV water tank heater pads.

Personally my goal is not exactly to extend the range, but to prevent wear/damage on the cells when charging them under freezing temperatures, also possible wear/damage when using lots of power under freezing temperatures, and finally and mostly to prevent the sudden loss of SoC I've been experiencing on my last three battery packs while driving on "Hill of Despair". At some point it's covered by the warranty but I reckon there's a limit to what lithium batteries can deliver when they're cold. And two warranty claims is enough for me 😉

From what I gather, if we could keep the pack above 5 C when charging and driving, we'd be golden.
 
It would indeed be better to use 12v heaters. 3d printer heating pads (presumably 120 v) are just one possibility. I like the RV water tank heater pads.

Personally my goal is not exactly to extend the range, but to prevent wear/damage on the cells when charging them under freezing temperatures, also possible wear/damage when using lots of power under freezing temperatures, and finally and mostly to prevent the sudden loss of SoC I've been experiencing on my last three battery packs while driving on "Hill of Despair". At some point it's covered by the warranty but I reckon there's a limit to what lithium batteries can deliver when they're cold. And two warranty claims is enough for me 😉

From what I gather, if we could keep the pack above 5 C when charging and driving, we'd be golden.
Don't forget this will be a fairly inefficient process.

You are trying to heat a large mass, about 300kg of cells with some convected air.
The heat pads will heat the metal outer case which is un-insulated.
The heat will warm the metal case & start to heat the air inside which will convect up towards the large battery mass.

Some heat will escape from the outer case back to atmosphere, so perhaps 2/3 will be useful unless you insulate the outer battery case.
The heat inside the battery case will start to warm the outer skin of the cells by convection, the outer skin of the cells then will conduct heat towards the centre of the cells vvveeerrryyy slowly.

Convected air continues to rise to the outer metal skin of the battery case which will heat the air above & probably start to warm the cars metal floor which could slightly warm the cars interior.

I'm guessing that about 1/3 of the heat energy actually gets into the cells.
This of course assumes the car is stationary in a garage with few drafts.

According to Mr Google :-
The specific heat capacity of a material is the amount of energy required to raise the temperature of 1 kilogram of that material by 1°C. For example, water has a specific heat capacity of 4,200 joules per kilogram per degree Celsius.

I would assume lithium cells would be denser than water but use water for the calculation.
So 300kg would require 4200 x 300 = 1,260,000 Joules.

Mr Google also says that :-
How to calculate joules to kWh?

A watt is one joule per second; a kilowatt is 1000 joules per second; a kilowatt-hour (kWh) is 1000 joules per second times 1 hour times 3600 seconds per hour, which equals 3,600,000 joules. To convert joules to kWh, divide the number of joules by 3,600,000.

1260000/3600000 = 0.35 kwh which ties in nicely with the 300w heat pads, but as only 1/3 ( guess ) of the heat gets to the cells it would need the heater to be on for 3 hours to heat the cells by 1 degree C.

Could be that Mr Google has thrown me duff information, but thought i'd just add my 2 peneth ( cents ) of working out.
I expect there are other more knowledgeable folk out there who can add to or correct this.
 
The way I see it: let's assume it could take 10 hours at 300W to bring a pack from -10 C to 5 C. That's 3 kWh at 0.10$/kWh = 30¢

Worth it. Even at 10 times the cost. Still worth it.

Would I sacrifice 3 kWh on the traction battery pack to have it warm up? Absolutely. 6? Yes.

10 hours and 300 W sound reasonable to me. They may be orders of magnitude off. I'm just guessing ;)
 
The way I see it: let's assume it could take 10 hours at 300W to bring a pack from -10 C to 5 C. That's 3 kWh at 0.10$/kWh = 30¢

Worth it. Even at 10 times the cost. Still worth it.

Would I sacrifice 3 kWh on the traction battery pack to have it warm up? Absolutely. 6? Yes.

10 hours and 300 W sound reasonable to me. They may be orders of magnitude off. I'm just guessing ;)
Oh, I agree, as long as your running off the grid and not power in the batteries themselves.
 
I was thinking about @knightmb 's setup for like 1000w. 300w should be easy right?

https://mynissanleaf.com/threads/15...r-1500-watt-ac-inverter-use.31914/post-599344
My old setup from 2021 has evolved into this now. 😉
The high power quick connects work even better than the stove plug from before, especially for ease of use and power efficiency.
oSlG69M.jpeg
 
My old setup from 2021 has evolved into this now. 😉
The high power quick connects work even better than the stove plug from before, especially for ease of use and power efficiency.
oSlG69M.jpeg
I dig this very much 😁 have you tried to power the inverter other than when the car is on? Like when its climate control comes on from timers?
 
Someone put a temp. isolation between battery pack and the plastic cover , winter mode ? :)
 
I stumbled upon this thread where apparently this has been done, and it's working reasonably well:

https://mynissanleaf.com/threads/battery-pack-heat-pads-installation.15673/

It was -25 C this morning. Leaf Spy reported -15 C on the battery pack, and it climbed to -6 C when at destination and I had to charge L2 @ 6.4 kW. I was sweating bullets on the "Hill of Despair", but it went fine this time.

TIL the Bolt EV tries to keep its battery pack above 0 C. It that right? I can't figure why the LEAF let its pack go down to -15 C even though it could heat it, from the EVSE. That's just... I don't know. Counterintuitive?

I'll eventually install these pads. Even if it could only raise the pack temperature by 5 C in 2 hours, I still think it's worth it. I reckon 12 V pads would be difficult to install properly, and TBH I don't mind the extra 120 V connection for the pads that much if it means more reliable and simple installation.
 
-29 C this morning, but I had the car sleep in the garage. Small garage, lots of stuff to move around, can open only one door, high risk of dents and scratches... Anyways, the pack was at -0.5C. I drove it to work and it was light night and day. The delta reading on the battery pack was significantly less and a lot more stable, even at sustained high torque. Just like in summer.

So I'll stop the experiments here, and I'll try to report some data when the pads are installed. Don't know when though.
 
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