Charging in subzero

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janosch
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Charging in subzero

Post by janosch »

Hello,

what do you guys do for charging in winter? I just checked the BMS and it gave 40kWh charge rate & 125kW discharge rate for 40kWh Leaf cells.
It is -2 Deg outside.

This article here is not consistent:
https://batteryuniversity.com/article/b ... mperatures

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consumer-grade lithium-ion batteries cannot be charged below 0°C (32°F)
and

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According to research papers, the allowable charge rate at –30°C (–22°F) is 0.02C. At this low current, the charge time would stretch to over 50 hours, a time that is deemed impractical.
I charged briefly at 5A which would be 0.04C and 28 Deg warmer than in the article there. Also realised regen should be temperature adjusted for a complete build really.

I guess I am mister careful again, but not keen on degrading £10k worth of batteries.

What are you guys doing for cold days? Anyone been closely observing their OEM vehicle behaviour to give some guidelines?
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Re: Charging in subzero

Post by Mojave »

Modern OEM vehicles will condition the batteries before allowing them to charge when it gets really cold. This may take the form of heating the batteries while charging at a very low rate and increasing the charge rate as the pack temp increases, or in extreme cases it may practically withhold charging altogether and run the heater before allowing it to start.
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Re: Charging in subzero

Post by Bigpie »

I've disabled regen at the moment, but have charged at a lower rate below 0.

At 4A charging my pack still didn't get above 0°C. As far as I'm aware, the leaf has no battery heating in the UK? and I don't think the VW GTE that I've got modules from also doesn't have a battery heater. I searched forums, and apparently the GTE still does regen up to 30kw down to -10°C so maybe I'm overcautious here too.
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Re: Charging in subzero

Post by arber333 »

Bigpie wrote: Fri Dec 16, 2022 4:32 pm I've disabled regen at the moment, but have charged at a lower rate below 0.

At 4A charging my pack still didn't get above 0°C. As far as I'm aware, the leaf has no battery heating in the UK? and I don't think the VW GTE that I've got modules from also doesn't have a battery heater. I searched forums, and apparently the GTE still does regen up to 30kw down to -10°C so maybe I'm overcautious here too.
I have Passat GTE cells at home and they have liquid cooling and persumably heating too. It would be foollish not to have both with that cooling plate.
Passat GTE is using the same kind of PTC heater as Golf EV.

I wouldnt keep cells below 0. Maybe you could remedy that by using 12V camper heater foil under the cells. I have that for now but i keep the car inside and cells never went below 3deg. I charge them at 8kw rate from AC.

I find the mass of the cells is slow to heatup and also slow to cool down. But really dont let them cool down too much.

I am thinking of adding a plate between two stacks of 8s cells but cell terminals make it difficult to connect silicon hose and secure it to the tube. Have to find a solution...
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Re: Charging in subzero

Post by celeron55 »

It heavily depends on the cells. Leafs activate battery heating only at something like -17°C and the batteries last just fine here in Finland, where half of the year is freezing.

You need to research the exact vehicle you took the cells from, or find a datasheet for the cells.
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Re: Charging in subzero

Post by Bigpie »

The GTE doesn't appear to have any way to heat the battery, other than using waste heat from the charger/inverter.
Screenshot_20221217-100018_Chrome.jpg
If operating limits are found the wiki should be updated
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Re: Charging in subzero

Post by Ev8 »

My front battery modules sit on top of a pair of heated seat mats but the thermal mass is so great it takes about 40 mins to add a degree of temperature to them in -4 conditions, so pretty useless! if I ever take it apart I will add another layer
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Re: Charging in subzero

Post by celeron55 »

In my experience you need at least a watt of power per kg of batteries you're trying to heat. Preferably 5W/kg. Of course depending on how much temperature you need to add and how much time you have.
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Re: Charging in subzero

Post by Bigpie »



A modern leaf allows a 4kw charge at -20 degrees C / -5F on the display
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Re: Charging in subzero

Post by johu »

Just did the experiment myself with the e-soul 64 kWh. It's currently -8°C and the car was stationary for 2 days and sitting at 67%. First tried AC charging and that started at 8 kW and quickly maxed out at 11 kW. Next I tried the DC charger which started at 14 kW and then reached 19 kW. Video coming
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Re: Charging in subzero

Post by johu »

Early forum release

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Re: Charging in subzero

Post by MattsAwesomeStuff »

johu wrote: Sun Jan 08, 2023 11:19 amJust did the experiment myself with the e-soul 64 kWh.
So, do you know if it was actually adding energy to the battery, or, was it perhaps gobbling up all that energy into battery heaters, so that it could eventually charge the battery?
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Re: Charging in subzero

Post by johu »

MattsAwesomeStuff wrote: Sun Jan 08, 2023 9:54 pm So, do you know if it was actually adding energy to the battery, or, was it perhaps gobbling up all that energy into battery heaters, so that it could eventually charge the battery?
Good question. So the charger delivered 21 kWh in the longer charge session and brought the battery from 71 to 98%. Assuming the nominal 64 kWh this would be 17 kWh. So looks like 4 kWh might have been used for heating and general charge losses.
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