Top balancing- power supply goes to zero then back up

[jdy2kgt]

I've searched for this specific question without luck. I have the power supply set to 3.65v and the CC is maxed out (10amps). However the voltage on the power supply is staying at 3.60 and the amps are going from 0.00 to 0.24 and anywhere in between. The cells are testing at 3.644-3.641 each (4 in parallel). So is this normal? Is it done charging or should I allow it to continue with this bouncing from 0 to .2 back to 0 for a bit more?

Video link:

 

[sunshine_eggo]

It's full. You can stop overcharging it.

 

[Rednecktek]

Yup! 3.6 is done.

 

[jdy2kgt]

Thank you for your replies. Do you know why the power supply was only showing 3.60 vs 3.64?

 

[TomC4306]

Less than perfect connections, inadequate charger to cells cabling.
There is 0 (zero) capacity up that high.
There is no practical difference between 3.60 and 3.64.

 

[sunshine_eggo]

Thank you for your replies. Do you know why the power supply was only showing 3.60 vs 3.64?

Because you're assuming any of the voltage measurements were accurate. Different meters have different accuracies, and it's rare that they all report the same value unless they are all calibrated to the same reference. A measurement difference of .04V is noise unless you're using expensive calibrated equipment.

 

[RCinFLA]

When CV/CC power supply reaches CV voltage limit setting its current output drops off.

Cheaper CV/CC power supplies can begin to drop off in output current as they get within 0.1-0.2v of the CV limit setting. You don't want too much voltage drop in battery cables between supply and cells or this voltage drop with current will cause the power supply to cut back current early before cells reach the desired charge voltage. This can greatly lengthen the charging top off time. Should always verify voltage at cell terminals with separate DVM.

Other common misunderstanding is setting power supply CV limit with no load, then seeing it drop when connecting supply to cells. This is power supply limiting current by dropping its voltage output to match present cell voltage. It is important to only adjust CV limit with no load on power supply. Adjusting CV knob when connected to cells runs the risk of over charge voltage and damaging cells when they get to fully charged state.

 

[Rednecktek]

I know mine drifts too. I've set it disconnected at 3.6 and come back hours later to see it at 3.67! Now I just set it to 3.55 and let it drift up to 3.6 if it wants too.