LiFePO4 voltage drop question

Question for the experts. I have a 15S/30P configuration of lithium iron phosphate (LiFePo4) cells. These are cylindrical K2 cells which I have connected with a spot welder. I carefully checked the voltage of each cell before spot welding and all cells were within an acceptable voltage range of each other. Nominal voltage for the pack is 48V and maximum voltage is 54V. There is very little variation between the voltages of the 15 parallel groups of cells within the pack. Basically the individual cell groups are within 30 mV of each other. I have not fully discharged the pack yet but I noticed that after charging the pack it up to 54V, the pack eventually settles back down to about 50V or 51 V. Is this common for new cells that have yet to be discharged? Thanks for any suggestions you may have.

All of the LFP cells I have used fall to about 3.45 VPC plus or minus, soon after charging. Whether charged to 3.5, 3.55 or 3.6VPC, the results are the same.

I have never had that happen with my Headway's, but other LiFePo4 owners have said that their Lifepo4 does settle.

It could also be your BMS working on the cells.

How long do you leave them on the charger?

e-beach said:

How long do you leave them on the charger?

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Basically I just waited until the packet 54 V. At that point the cells were properly top balanced so I turned off the charger. Really appreciate your response. :thumb:

BVH said:

All of the LFP cells I have used fall to about 3.45 VPC plus or minus, soon after charging. Whether charged to 3.5, 3.55 or 3.6VPC, the results are the same.

Click to expand...

Excellent info. Thanks for the response