Current oscillations during top balancing

[BoatBumm]

I’m a LiFePO4 newbie. I’m doing my first top balancing of a new SOK 206Ah 12 volt marine battery. After charging with a Victron charger, I carefully opened the battery (surprisingly easy to do!), disconnected the BMS, installed 10 gauge jumper cables to convert the cells to parallel configuration. Started charging at 3.65 volts, confirmed by a separate voltmeter. The initial current was about 1.5 amps, and with time, as expected, the current slowly declined. BUT I’ve noticed that the current, while overalll slowly declining, periodically jumps back up again. It got down to about 0.2 amps, then up to 0.5, then back down to 0.3 amps, then up to 0.7 amps. Is this normal/expected?

It’s now down to 0.1 amps. Current Cell voltages are 1) 3.362, 2) 3.361, 3) 3.361, 4) 3.433. Original voltage spread was 0.217 volts

Any help/information will be greatly appreciated

Thanks!

 

[RCinFLA]

Cells do not normally react like this. Most likely cause is power supply stability. A cheap power supply may have some output variance due to AC supply variations or temperature variation causing some variability in its output regulation.

A dirty power supply adjustment potentiometer is also common cause. They have a metal contact wiper to the resistive element of the potentiometer. Lightly tap on the end of the CC and CV adjustment knobs to see if things change.

 

[BoatBumm]

Thanks! I’ll check that.

 

[BoatBumm]

And I didn’t think that was normal for the cells

 

[mikefitz]

If the cells are connected in parallel why do the voltages differ? Something is wrong if there is a 0.2 delta at rest, bad cell?
You should not have to top balance a ready built battery, any small Inbalance is usually rectified by charging at a lower voltage with a long absorbtion period.
Mike

 

[BoatBumm]

I agree that the voltage spread should not have been that much. And that was before I started the top balancing, when they were hooked up to the BMS, in series, not parallel. It’s an absolutely brand new quality SOK battery. That’s why I’m doing the top balance. The voltages are equalizing, except for one cell running consistantly a bit higher than the other three. Still puzzled about the current oscillation. This morning I moved the power supply clip leads to different +/- connections. Unexpectedly the current jumped to 3.3 amps at 3.65 volts. Still watching what happens.

 

[sollap]

Those alligator clips could be the problem. If you replace them with ring terminals you'll get more consistent results.

 

[BoatBumm]

I’ll try that. Thanks

 

[HRTKD]

Make sure the connecting surfaces of your ring terminals and cells are clean and verify the fastener is tight. I had a similar problem when I top balanced. Seven cells all looked great and then I got to the eighth which was lower. Tightened everything back up and restarted the top balancing and they all came out correct.

 

[BoatBumm]

Will do. I’m making new charging cords with ring connectors right now. Thanks.