Why does individual cell voltage fluctuate so much when charging?

[pralinebuckets]

Hi all,
I'm in the process of setting up my 16s Eve280 battery. Charging it for the first time to get it up to an easy state to top balance. I notice that for short periods of time, individual cells will have voltage spikes for >10 mins before decreasing significantly in voltage. Why does this happen? I would expect that once a cell is at a given voltage while charging, it would only go up from there?

For example, when I first started charging my battery, cell 8 showed 3.65+ volts for a good 10 minutes before going down to the average of ~3.44v, with cell 2 now being the peak at ~3.6v. What is happening chemically here?

This is with a Daly BMS.

 

[mikefitz]

Perhaps the BMS is balancing the cells by removing charge from the high cell. It's also possible the cell volts over 3.65 is causing protection, and shutting down the charge path.

 

[pralinebuckets]

I’m pretty sure that the Daly doesn’t balance without purchasing a separate active balancer. The app has a balancing section, where status is always “Balancing = No”.

No charge path shutdowns - nothing over the threshold there.

 

[RCinFLA]

A good LFP cell does not 'jump' around in voltage with a constant charging current.

Any jumping around of cell voltage is likely due to charger changing the amount of charging current.

A poor connection could also be the cause.

 

[pralinebuckets]

A good LFP cell does not 'jump' around in voltage with a constant charging current.

Any jumping around of cell voltage is likely due to charger changing the amount of charging current.

That is my understanding too - that this shouldn’t happen. But how is it even possible in a series setup? I assume the BMS is accurately measuring cell voltage…