FilterGuy
Solar Engineering Consultant - EG4 and Consumers
Looking at the specs of LiFePO4 cells, the short term storage usually goes down to -10deg C. However, the discharge temp is often specified down to -27deg C. They may be counting on internal heating during discharge. The other possibility is that a discharge current prevents whatever chemical reaction damages the battery at cold temps. If so, how small can the current be? If a tiny discharge can prevent damage, it could offer a great way to help prevent low temp damage without a large drain on the battery. Does anyone know about this?
Either way, this made me realize that if I am using the batteries to drive a heat pad, I get two heat sources: The heat pad and the battery. I guess I can use the internal resistance of the cell times the current^2 to calculate the battery heating effect in each cell (P=I^2R).
Edited to clarify that one possibility is that the discharge current prevents whatever chemical reaction damages the battery at cold temps. (I had previously assumed the damage was due to formation of Lithium. That is true for charging at cold temps, but I don't know what the damage is for cold storage)
Either way, this made me realize that if I am using the batteries to drive a heat pad, I get two heat sources: The heat pad and the battery. I guess I can use the internal resistance of the cell times the current^2 to calculate the battery heating effect in each cell (P=I^2R).
Edited to clarify that one possibility is that the discharge current prevents whatever chemical reaction damages the battery at cold temps. (I had previously assumed the damage was due to formation of Lithium. That is true for charging at cold temps, but I don't know what the damage is for cold storage)
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