Frozen LiFePO4 batteries

umdumchuck

New Member
I understand that you shouldn't or can't charge a LiFePO4 battery below -20 C.
Does it hurt the battery if it drops below freezing, if it's disconnected? Does it degrade the battery?
I plan on using a BMS with a temperature sensor.
My system will be in an unheated cabin, while not in use.
 

snoobler

Solar Honey Badger
Moderator
Charging below freezing causes plating of the lithium ions onto the anode. This is a permanent loss of the lithium ions used to transport charge. Causes severe capacity loss.
 

FilterGuy

What, me worry?
I understand that you shouldn't or can't charge a LiFePO4 battery below -20 C.
Actually, you should not charge below 0C

Does it hurt the battery if it drops below freezing, if it's disconnected? Does it degrade the battery?
I plan on using a BMS with a temperature sensor.
My system will be in an unheated cabin, while not in use.

I have researched this a lot and have not found a definitive answer. However, it seems that LiFePO can be stored down to about -20 C.

In my cabin, I have a well insulated storage box inside the well insulated cabin. In the battery box I have a heat pad hooked up to a 0F mechanical thermostat and and directly to a small 20W solar panel (no battery and no charge controller in the circuit) Over the winter, the cells are disconnected from everything (included the BMS)
 

umdumchuck

New Member
Thank you. I'll do the same. Since I already have a 12 volt Lead Acid 400 watt system, I'll keep it for winter use with a battery warmer. My initial plan was to set my BMS to disconnect well above the danger point. Now, I think I'll do what you do, disconnect the LiFEPO4 batteries. Thank you for your help. How big is your system and what BMS do you use?
 

FilterGuy

What, me worry?
It is a 24V 200aH 1p8s battery bank with an ANT BMS. It uses a 3000W inverter.

Edit: Corrected the Inverter size.
 
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FilterGuy

What, me worry?
Thank you. I'll do the same. Since I already have a 12 volt Lead Acid 400 watt system, I'll keep it for winter use with a battery warmer. My initial plan was to set my BMS to disconnect well above the danger point. Now, I think I'll do what you do, disconnect the LiFEPO4 batteries. Thank you for your help. How big is your system and what BMS do you use?

BTW: My installation is a little unique because my charge source is a micro-hydro generator that is shut down in the winter. Consequently, any drain on the battery over the winter could result in a sever undercharge. Since the self-discharge rate for LiFePO4 is so low, (~2%/month) I can let them set for several months without worry about undercharge. However, I have to worry about cold storage..... thus the simple heater and small solar panel.
 
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