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bobhuck asked

Lithium Battery Heater Test

Two Victron 330ah Lithium batteries with heaters are installed (parallel 12 VDC) in our camper van. I ran a battery heater (BH) test. Overnight low was -11 ℃, battery 1 (B1) = 4 ℃, battery 2 (B2) = 1 ℃, and both had under temperature alarm A-SL22. The batteries were at 83% State of Charge (SoC). Turned the BH switch on. Drawing an additional 55 watts of power. Checked 2 hours later B1/B2 = 11 ℃; both in ready state. Turned on the generator for 30 minutes, 86% SoC. All good! Left the switch on. Overnight low = -11 ℃. Next day B1 = 12 ℃, B2 = 6 ℃; both in ready state. Short charging test AOK. Overnight low -6.7 ℃. B1 = 6 ℃, ready; B2 =4 ℃, A-SL22; 70% SoC. Later B2 = 5 ℃ still A-SL22. Overnight low 0 ℃. B1 = 7 ℃, ready, B2 = 5 ℃, A-SL22. Four hours later, B1 = 8 ℃, B2 = 6 ℃; both ready. Van temperature = 8.9 ℃. Batteries can be charged.

Questions:

At what temperature should the battery heater turn on?

At what temperature should the battery heater turn off?

How many watts should a battery heater draw when on?

Why aren't the battery heaters working?

Lithium Battery
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matt1309 avatar image matt1309 commented ·
If they're LiFePo4 you dont want to charge them below 0 degrees (Celcius). However manufacturer specs may vary.


1.I have mine turn on at 1 degree, but might want to add a slightly bigger buffer.

2. Turn off temp again will vary, worse case scenario it'll just turn on/off more frequently if not high enough/insulation isnt great. I set mine at 5-6.

3. This will vary massively on the battery/heat pad side etc. You manufacturer specs will likely state what they expect to draw.

4. Not sure sorry... I would confirm it gets warm, and warms in line with spec manufacturer quote. And then check insulation? ie is heater being overpowered by a cold draft for example

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ejrossouw answered ·

@bobhuck "The temperature range over which the Victron batteries can be charged is 5°C to 50°C." and is why you get alarms below 5°C and the BMS will prevent charging. Don't forget heat has to transfer through casing to the cells which in very cold conditions can take some doing and may in part explain your findings. Probably a good idea to experiment with always keeping the battery temp slightly above the 5°C or even higher regardless of the ambient temperature.

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