Voltage set

[Adrianablett]

Hi
What voltage cut of should I set my charge controller to if I only want to achieve 80% soc on a 4s 12v pack?

Cheers guys

 

[chrisski]

Is this lIthium batteries?

 

[Adrianablett]

Sorry
Yes

 

[upnorthandpersonal]

You can't do this purely with voltage. Assuming LiFePO4, to maximize cycle life, you should just consider to charge to 3.45V to 3.55V per cell (13.8V - 14.2V) and call it a day. Temperature will be much more important for long cycle life - make sure they're not in a hot environment.

 

[RCinFLA]

Other thing to consider is many BMS's don't balance until a cell exceeds 3.4v. Always running a lower recharge voltage will not perform much balancing. With only 100-200 mA of passive resistor dump balancing current you also need some time to balance.

With the low balancing current, setting a charging absorb voltage of 3.50 - 3.55v per cell x number of series cells is about as low as can be set to get sufficient balancing time. 14.0-14.2v charge absorb setting for 12v LFP battery.

 

[Substrate]

Assuming a hands-off setup with just an scc, set your CV voltage to no more than 13.6v.

LFP cells will not fully charge at 3.4v per cell or lower. Anything higher and they *WILL* fully charge to full capacity eventually. It happens faster at higher voltages, and much slower at lower ones, like 3.45v per cell.

It's a knife-edge setting, so generally 13.6v (3.4v / cell) - while actually charging - is the highest you'd want to go to prevent them from slowly absorbing to full capacity. That's approx 80% capacity.

If you are using a system with a bms that has balancing, I'd charge to 100% with higher voltages at least once to attempt to smooth out any *small* differences in balance. Then change your CV to the lower voltage to limit the charge to 80% with your normal operation.