Differing voltages on never-used Eneloop batteries?

[dmenezes]

@SammysHP

The Gyrfalcon uses constant current with the option to reduce the current at the end to compensate for the rebound.

Thanks for chiming in @SammysHP!

By “reducing current at the end”, you mean using the “DISCHARGE REDUCE” setting, so that when the charger reaches “TARGET VOLTAGE”, it then enters constant voltage charging and therefore starts reducing current to keep the battery at that voltage, until the current being supplied goes down to the “DISCHARGE REDUCE” value, correct?

What I’ve been doing with NiMH batteries is to set “DISCHARGE REDUCE” to exactly the same value as “DISCHARGE CURRENT”, therefore effectively disabling the constant voltage charging phase at the end. This is aligned with the recommendation indicated in the “NiMH Eneloop AA” tab of the excellent MC3000_Program_Guide_v1.0 by @SYZYGY and with what I determined to be consensus in multiple forums/subreddits conversations.

Do you suggest I set it to something else instead in order to enable the constant voltage charging phase at the end? If yes, to how much?

BTW, in case it’s important or you’re just curious, here’s the complete program configuration I’m now using for the current C>D cycle testing:

{[...]'battery_type': 'ni-mh/cd', 'task': 'cycle', 'cycle_mode': 'cd', 'cycle_counts': '10', 
'capacity': '2400', 'current_pre': '50', 'current_charge': '750',  'voltage_target': '1650', 
'deltapeak': '3', 'voltage_pre': '1000', 'time_pre_cut': '180', 'time_charge': '460', 
'voltage_discharge_cut': '1000', 'current_discharge': '750', 'current_discharge_reduce': '750', 
'time_cut': '540', 'charge_resting': '15', 'discharge_resting': '15', [...]}

Please feel free to suggest any changes.

TIA!

[dmenezes]

@dmenezes

So, moving ahead, […] I will just program a dozen charge/discharge cycles at 0.5A/0.5A respectively on all 4 slots, and leave the S8000 to it, with my telemetry capturing everything (except IR, which the S8000 current firmware unfortunately only updates when a battery is inserted or its slot program is changed). I will then disconnect and reconnect each battery to get a final IR measurement and will publish the results here.

Thanks everyone for following me so far and for your comments and suggestions, and please stay tuned.

Ran into an unexpected problem: with the charging current set to 0.5A, all 4 batteries were unable to terminate with the -3dV DELTA PEAK setting (which I use instead of 0dV to make sure the batteries are getting fully topped off) and so the phase charge aborted with MaxCap error right in the first cycle, after getting the configured maximum capacity of 2400mAh pumped into them:

To be absolutely sure they were not just a little way to being topped off, I briefly disconnected and reconnected each one (to reset the error) and tried again with 0.5A charging current: exactly the same thing happened. In my experience this happens when the charging current is too low to cause the necessary voltage drop at the end that the charger needs to detect the topped-off state by the configured DELTA PEAK.

So I set the charging current 0.75A (and just for consistency’s sake, did the same to the discharge current) and tried a 3rd time, and that was the charm: things are now proceeding normally and 2 full charge-discharge cycles have already gone through.

Should have a final result in a couple more days, will then post the results here. Thanks everyone again for your comments and suggestions, and please stay tuned.

[SammysHP]

I usually charge my regular Eneloops AA at 1A.

[dmenezes]

@SammysHP

I usually charge my regular Eneloops AA at 1A.

That’s also what I was doing initially. But decided to try and reduce it to 0.5A because (a) it’s closer(ish) to the 200mA (!) that Panasonic recommends for capacity measuring on this particular battery, and (b) because I had a suspicion that the divergence I was starting to see among the cells that were initially almost exactly matched, perhaps were being caused by using too high a current.

But if I charge with 0.5A, delta-peak detection at 3mV (which I consider essential to be sure the cell is fully charged) won’t work, so this rules it out. I’m now proceeding at 0.75A and it seems to be working, it’s at cycle #3 now and so far no problems.

And what about DISCHARGE REDUCE (not sure if you saw my post here), do you set it when charging AA Eneloops? And if yes, what value do you set it to?