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Large voltage drops in cold weather.

wntrhwk

New Member
Joined
Jan 8, 2020
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91
Hello, just installed a SOK 12v 100amph LIFEPO4 battery in my trailer. when I left yesterday (storage lot) the battery was around 13.5v. I went this morning to do some work on the trailer, temp was 26 degrees, battery voltage was 12.6v. No loads, just the 25-30ma that the Victron 100|20 takes. Once the trailer warmed up, the voltage went back to around 13.3v, I disabled the controller, wanted to see if the voltage would jump back on it's own. I also know that charging a cold LIFEPO4 is super bad, I have the temp cutoff at 5 degrees C. My question, is the low voltage normal when it is this cold, with no loads?
 
When the battery BMS shuts down the charge path, ( in this case due to low temperature), and no significant current is being drawn from the battery, the voltage at the terminals will drop by a diode volt drop, around 0.6 volts. Internally the 4 cells in series remain at the actual battery voltage, the drop is across the BMS.
Once a significant load is applied, 1 to 2 amps, the BMS electronics restores the actual series cell volts to the battery terminals.

Mike
 
Mike, great information, and very good explanation. I was hoping I was not doing damage. I appreciate your help.
 
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