2.7 volts for a whole night

[Robbert]

Usually I don't discharge my batteries very low and have very conservative settings.

Back to grid at 50v and BMS discharge-cutoff at 2.7v (lowest cell).

Since solar is not fantastic these months and guests are arriving I do expect that my current setup will not be able to supply enough power.

I have one weak cell that might hit 2.7v before the inverter will switch to grid. Not a big deal because that is how the system is designed.
I know one can discharge to 2.5v max, so still on the safe side.

My question is how 'bad' it is to keep a cell at 2.7v for lets say a whole night and recharge it the next day. I think it will be fine, but would like to double check with the experts on the forum.

 

[740GLE]

How much load is on the battery once switched over to grid? Just the BMS?

I’d want to track voltage to see if it holds 2.7 or if it continues to drop even after switched over to grid power.

 

[Robbert]

How much load is on the battery once switched over to grid? Just the BMS?

I’d want to track voltage to see if it holds 2.7 or if it continues to drop even after switched over to grid power.

If switched to grid, no load and only bms.
If bms kicks in before inverter does, the same

 

[curiouscarbon]

LiFePO4 cells?

if so..
3.0 volts per cell is a common conservative "discharge stop" advice.

2.7 volts per cell, sitting for 12-24 hours, i cannot say how much this might affect longevity of battery storing energy. 2.5 volts per cell is my personal "hard stop" threshold

the one known as @RCinFLA might have more productive insight as to storing the cells overnight at 2.7 v

good luck

 

[RCinFLA]

Impedance of cell rises below 5% SoC so depending on load current you may want lower than 3.0v cutoff voltage.

Just should not allow cell voltage to drop below 2.0v. The 2.5v spec you see on most LFP cell specs provides some margin to the absolute limit of about 1.5vdc. A resting voltage below 1.5v runs the risk of growing lithium metal dendrite shorts.

There is not much capacity left in cell below 3.0v so with some load current the voltage on cell will drop rather quickly.

In real world, all the series cells will not be perfectly matched so one of the cell's will drop out first.