I fabricated a 48 volt 16S LiFePO4 battery pack for my golf cart using Coslight 150 AH cells. I carefully top balanced the cells before final assembly using the parallel method and bringing them all slowly up to 3.65 volts [all 16 cells at the same time]. I actually did this twice; once after receiving the cells and again after a short discharge test. I stopped the top balance when the total bank current had dropped below 1 amp.
After the top balance I noticed that the cells had varying self discharge rates and within a few days or so the highest/lowest cells were 50 mV or more apart - some were still over 3.500 volts and some were in the 3.450 or less range.
During a normal charge they do not stay together - the highest cell will reach 3.55 volts [my BMS over voltage trip point] with other cells still in the 3.46 volt range [charging at about 0.1C].
During normal discharge in the golf cart they will quickly "come together", and when they are below 3.4 volts per cell or so they are all within less than 10 mV of each other. They will remain this close together even when the cart has not been used for a day or more.
Working with these cells is new to me, but my thoughts on this are that it might be normal for these cells to charge and self-discharge at vastly different rates when near the top of charge curve, and since the stored energy above 3.4 volts or so is minimal there isn't really anything to be worried about here.
I would appreciate hearing from others with experience with these types of cells on this.
After the top balance I noticed that the cells had varying self discharge rates and within a few days or so the highest/lowest cells were 50 mV or more apart - some were still over 3.500 volts and some were in the 3.450 or less range.
During a normal charge they do not stay together - the highest cell will reach 3.55 volts [my BMS over voltage trip point] with other cells still in the 3.46 volt range [charging at about 0.1C].
During normal discharge in the golf cart they will quickly "come together", and when they are below 3.4 volts per cell or so they are all within less than 10 mV of each other. They will remain this close together even when the cart has not been used for a day or more.
Working with these cells is new to me, but my thoughts on this are that it might be normal for these cells to charge and self-discharge at vastly different rates when near the top of charge curve, and since the stored energy above 3.4 volts or so is minimal there isn't really anything to be worried about here.
I would appreciate hearing from others with experience with these types of cells on this.