Charge and Discharge Cell voltage limits

[rye_bread]

Hey folks
I've been working with liFePO4 cells for a minute and I'm having some issues at the bottom of my discharge when discharging at a heavy load. Under a load of like 120A, the cell voltage dips like 0.3v under what the voltage reading would be when the load is disconnected. This leads to my back bottoming out at 2.5v per cell pretty early. So that when the load is shut off due to a low cell voltage, the cells each return to like 2.8v. Would it be dangerous to decrease the minimum cell voltage in my BMS to say, 2.2v during these high load scenarios?
Thanks

 

[sunshine_eggo]

sounds like you have excessive resistance in your battery. A 0.3V drop under 120A indicates a 2.5mΩ resistance. This is about 10X the resistance of what's typical for 280Ah cells.

I assume you've already gone through the battery and confirmed all the cell/bus bar connections are properly torqued.

2.8V is a nearly empty cell, so I wouldn't consider lowering the cut off below 2.5V.

 

[HRTKD]

I've pulled close to that load from my 4s LiFePO4 battery without any issues. Are you seeing the low voltage in every cell or just one or two?

As said above, check all your connections. Clean all the contact surfaces and make sure the fasteners are good and tight.