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Accu-Cycle Pro Display Problem

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Old 07-04-2008 | 05:55 PM
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Default Accu-Cycle Pro Display Problem

Greetings -
I have an Accy-Cycle Pro series charger.
I routinely check batteries as they age by cycling them twice - once to provide a full charge, and a second time to evaluate the full-charge capacity.

I recently noted that batteries I expected to be in good shape were showing very low capacities per the Accu-Cycle. A 1700 mAh NiMH 4-cell Rx pack was showing only 60 mAh capacity. Post-charging voltage is usually in the 5.5 to 5.6v range, which seems good.

When I swapped that battery out with a brand new 1700 mAh 4 cell NiMH, I saw several cycles reaching only 200 mAh at best (as indicated by the mAh display). So I did some measurements on connector and wiring resistances to see if the unit was reaching 1.05 volts per cell before the battery really got there, and this is what I found:

Measured connector and wiring resistance: 1.3 ohms (yes - not good)
Discharge Rate setting: 250 mA (assumed, from the setting; not measured)
Time to Discharge: 5.2h (actual time)
Minimum Battery Voltage (when switched to charge cycle): 4.64v at battery (measured)
Calculated capacity (assuming 250 mA for 5.2h: 1304 mAh
Voltage differential between battery and Accucycle terminals: 0.5V measured during 250 mA discharge
Indicated battery capacity at end of discharge cycle: 250 mAh indicated on the Accu-Cycle
Indicated "minutes" of discharge: 6.2 minutes indicated

This discharge cycle was recorded usign a digital multimeter on a computer at 10-second intervals.

At one point during the discharge I recall checking the Accu-Cycle LCDs and saw 360 mAh at about 80 minutes, which surprised me, because none of the completed cycles I'd run so far got past 200 mAh. But as you can see from above, at the END of the cycle, the display showed only 250 mAh, and 6.2 minutes.
There's no indication in the discharge / charge cycle data plot that indicates a stop or restart.

Granted, if I improve the wiring and connector resistances (I have many connector adapters in the charge lines), I can get the discharge cycle to get closer to the 4.2v cutout (1.05 v per cell), but that's really not the primary concern here.

Is there a roll-over in the display circuits? I pulled over 1300 mAh out of this battery, and the Accu-Cycle showed only 250 at end of cycle? It discharged for 5.2 hours (recorded), but the Accu-Cycle says 6.2 minutes. I've thrown batteries away due to this false indication.

I've attached the discharge plot. At least I think I did. The charge plot doesn't include the full 15 hour charge cycle, but I don't question that right now.

Any help you can provide would be great!
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