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Batteries dead suddenly

alexcl

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Nov 21, 2021
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I have 2 206 Ah SOK batteries that I installed (wired in parallel) in my campervan last week. At first the electrical system was working flawlessly - I hooked up a victron inverter, a sterling b2b charger, and numerous outlets. All working. I changed a few things and at some point everything went belly side up. Now one battery reads 2.4V and the other reads 9V.

Does anyone have any idea how I could diagnose or fix the problem?

In case it makes a difference, here are the things that changed since I last confirmed everything was working:

1. Added a temperature sensor to one of the negative battery terminals (connected to the inverter)
2. Built wooden frames around the batteries, added furniture pads to the outside battery case, and installed them in the frames. With the furniture pads, there is a fair amount of pressure on the battery case.
3. It has gotten colder outside (down to high 20s at night).
 
If SOKs have built in low temperature cut off on the BMS that could be what caused the 1 with 2.4 volts to disconnect. Were the batteries allowed to go to 0 C. ? If not could be they weren’t charging because of low temperature.
 
Yes it did go down to 0C. Could this have caused the 9V one as well? These batteries do have a "Low Temperature Charging Cut-off" but I don't see a way to reset it. Shouldn't the battery function normally once temperatures warm up again? @acdoctor Any advice on how to proceed if this is the case?
 
If temperature recovered and BMS is still open l would think that they are off on low voltage disconnect. Do they have internal heat? If so it could have contributed to running them down.
 
If off on low voltage charging should wake them up. The b2b charge is the only source of charge? What amperage is it capable of? Do you have cables large enough to support the amps? How long and often have you been charging?
 
depending on the BMS they can have BOTH charge, and discharge fets; and they could just cut off the current flow in both directions; it is all dependent on your BMS.
here is a copy of the specs for an eve 280ah battery and you can see it has temp limits for both charging and discharging.

to get the BMS to reset the fets when it hits a temperature limit,well, the temp probes just need to warm up ;-)

1637539523874.png
 
@acdoctor thanks for the advice

The batteries do not have internal heat

Shore power and b2b is capable of 60 amps (using 4 AWG cables) are the only permanently installed mode of charging, but I can hook up a car charger to the batteries at low amperage (2 amps)

I have not been actively charging (or really discharging aside from tests) in the last week - my build is still underway. There probably was some charging from the b2b (I let the van run weekly so the alternator probably did some charging)
 
What method do you use to determine approximate SOC? The system could have been lower than you think it was.
Last week I looked at the voltage and then compared to the voltage after charging via the alternator (12.8 or 12.9). Tonight I just looked at the voltage of the individual batteries to see that they were not working.
 
put the battery in a warm room for a few hours and if it is just a temperature cut-off event, it will turn itself back on with no dmg ;-)
Unfortunately it was 62 F (16.5 C) today when I was testing and the batteries weren't working. I can take them out and bring them inside if you thin it will make a difference - they are a bit of a pain to get out of their frame which is why I haven't done so already.
 
Last week I looked at the voltage and then compared to the voltage after charging via the alternator (12.8 or 12.9)
Keep in mind that 12.8-12.9V is only about 25% SOC for LiFePO4 batteries.
 
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