LFP during winter

[jorgemiguel4]

Hi, I bought 4 REPT 100Ah cells to play a bit. I'm planing to charge them only with solar surplus and discharge at night with my network equipment that works mostly at 12v.
I'm now concerned about keep the cells at low SOC during winter, is that a problem?
I already have a charge controller made by me with an Arduino, I can keep track of current, voltages and coloumb couting . So I can limit lower and upper limits of any of those things. What is the best strategy to not kill the cells prematurely?

 

[DIYrich]

"keeping" is not the problem. You will damage the battery if you try to charge (not discharge) when the battery temp is below freezing (-20c for discharging).

 

[chrisski]

Same Strategies you would use with a BMS. The actual numbers should be found on the battery spec sheet.

-A low temp cutoff for charge. 33° volts may work with a 35° cutin. This is a little harder to judge since your temp probe would not be on the battery cells, but outside. This could lead to early cutoff with a higher internal temp, and an earlier cutin where the internal temp has not caught up to outside temp.
-A low battery voltage cutoff for discharge. 48 volts could work with a 50 volt cutin.
-THere is also a low discharge cutoff temp, but in sunny AZ, I never reach that temp.

I would not worry about a battery cycled every day to 20% with the battery spec limitations met, as long as it was cycled full daily. May be some less cycles reached. I would also not worry about a couple of BMS trips for low voltage throughout its life.

 

[jorgemiguel4]

Freezing temperatures are not a problem here, the room where the batteries are will probably never reach less 10ºC(50ºF) probably.
My current settings are
Charge to 3.5V at 12A with a termination current of 4A then float at 3.35V. Trying to keep them a little bellow full.
Discharge -80Ah( keep approximately 20% SoC as reserve in case of power outage ).

My main concern is keep them that low for weeks at time when the sun won't shine, don't know if it's a problem or not.

 

[kommando]

don't know if it's a problem or not.

Its not, just make sure when the sun comes back in spring that on the first good charge you allow time for a full balance of the cells.