diy solar

diy solar

Does a LiFePo4's charge rating lower as capacity degrades over time?

forscience

New Member
Joined
Dec 13, 2021
Messages
30
I see that most LiFepo4 cells have a charge rating of 0.5C which means for a 100ah cell, you can charge it at a max of 100ah * 0.5C = 50 amps. Since after a certain amount of cycles, the battery cells will degrade to only 80% of its original capacity, does the max allowable charging amps(50a in this example) also become lower? I'm asking because I'm interested in this 40a "smart" Charger and I'm afraid that it could overload my cells if they are at reduced capacities.
 
I'm interested in this 40a "smart" Charger
It perhaps not that smart for a 30 to 40 amp charger. For long service life, if possible charge, at less than 0.5C. However most cells specify there number of charge cycled, offer in excess of 2000 cycles based on this charge rate so natural aging will perhaps end the service life before charge and discharge cycles.
With a lithium battery charger a voltage lower than 14.6 volts may/will be less stress full and prevent BMS shutdown due to cell over volts. Victron for example recommend 14,2 volts and it can be shown that voltages as low as 13.8 volts can charge to 'nearly full' without a significant increase in charge time.
The charger does not specify the float voltage or the mechanism that will determine 'full charge'.
I would not worry too much about the effect of charging when the batteries are near end of practical life. If you treat the batteries with a correct and low stress charge regime, any loss of capacity will be well into the future.
However if you charge and discharge at high currents and/or keep the battery at high charge voltages for extended time periods, and/or use and store the battery at high temperatures, then the service life could be less that two years.
For slightly more money , the Victron 30 A would in my view offer a better solution. Has the ability to fully programme, via the Bluetooth app, all charge parameters, has a last 40 charge cycle log and has a 5 year warranty

Mike
 
As cells age their internal impedance rises. This will mean more cell internal self heating for moderate amount of current, either charging or discharging.

It's not the 80% capacity degradation that really hurts. It is the inability to support moderate current loads without significant slump in battery voltage, which in turn, causes inverter to draw more battery current for equivalent AC output load.
 
Back
Top