SilverFox
Flashaholic
CPF member Bones sent me a couple of Eneloop cells to check out. One of them is a dud, and has been a dud since originally purchased. I have a few tricks up my sleeve, but this seems to be a bad cell. The problem is that it has higher internal resistance, which results in capacities in the 1650 - 1700 mAh range. This puts it in the well worn category, but not in the "crap" category.
At any rate, I have been running cycles and Break-In's on these two cells in the C9000. Normally I don't leave cells in the charger, but rather than writing down the value from the good cell, I just left it in the charger, discharged, and would compare the results back and forth with the problem cell.
About a week later... I noticed that the voltage of the discharged cell was increasing...
I decided to run a test on this.
I charged both cells up and let them top off overnight. I then ran a discharge at 100 mA. The good cell came in at 2016 mAh, and the problem cell came in at 1625 mAh. This is interesting because it seems that this cells capacity is falling off rapidly. About 10 cycles ago the problem cells capacity was over 1650 mAh.
I left the cells in the charger, discharged, for a few (I think it was 3 or 4) days. At this time the voltage had increased to 1.30 volts. I then ran another discharge at 100 mA and recorded 180 mAh from the good cell and 153 mAh from the problem cell.
Normally, when you discharge at a low rate there is very little capacity observed during a second discharge. I would have expected less than 10 mAh. To further test this, I removed the cells from the charger and let them sit for 24 hours. I then ran another discharge and recorded 10 mAh from the good cell and 0 mAh from the problem cell.
I have two C9000 chargers, and these results were observed on my oldest unit. I happen to be breaking in some GP2700 mAh cells for testing on my other unit, so I decided to see what happened with them.
After the Break-In cycle, I discharged them, then charged them at 1500 mAh. I only let them top off for a short period of time (about 1 hour I think), then discharged them at 500 mA. Capacities were 2331, 2336, 2368, 2360 mAh. I left them in the discharged condition for 2 days, and then repeated the 500 mA discharge. During this time the cell voltages recovered to 1.25 volts. Capacities this time were 81, 61, 70, and 74 mAh.
Next I charged the cells and once again discharged them at 500 mA. When they finished the discharge I removed them from the charger and let them sit for 24 hours. I then discharged them again at 500 mA and capacities were 17, 14, 13, and 18 mAh. This time the cell voltage only recovered to 1.18 volts.
Given the higher discharge rate, and the higher capacity cells, this last observation seems more normal to me. The question is Why does leaving the cells in the charger result in almost 5X more capacity...?
Does the C9000 switch into trickle charge mode after discharging...?
Tom
At any rate, I have been running cycles and Break-In's on these two cells in the C9000. Normally I don't leave cells in the charger, but rather than writing down the value from the good cell, I just left it in the charger, discharged, and would compare the results back and forth with the problem cell.
About a week later... I noticed that the voltage of the discharged cell was increasing...
I decided to run a test on this.
I charged both cells up and let them top off overnight. I then ran a discharge at 100 mA. The good cell came in at 2016 mAh, and the problem cell came in at 1625 mAh. This is interesting because it seems that this cells capacity is falling off rapidly. About 10 cycles ago the problem cells capacity was over 1650 mAh.
I left the cells in the charger, discharged, for a few (I think it was 3 or 4) days. At this time the voltage had increased to 1.30 volts. I then ran another discharge at 100 mA and recorded 180 mAh from the good cell and 153 mAh from the problem cell.
Normally, when you discharge at a low rate there is very little capacity observed during a second discharge. I would have expected less than 10 mAh. To further test this, I removed the cells from the charger and let them sit for 24 hours. I then ran another discharge and recorded 10 mAh from the good cell and 0 mAh from the problem cell.
I have two C9000 chargers, and these results were observed on my oldest unit. I happen to be breaking in some GP2700 mAh cells for testing on my other unit, so I decided to see what happened with them.
After the Break-In cycle, I discharged them, then charged them at 1500 mAh. I only let them top off for a short period of time (about 1 hour I think), then discharged them at 500 mA. Capacities were 2331, 2336, 2368, 2360 mAh. I left them in the discharged condition for 2 days, and then repeated the 500 mA discharge. During this time the cell voltages recovered to 1.25 volts. Capacities this time were 81, 61, 70, and 74 mAh.
Next I charged the cells and once again discharged them at 500 mA. When they finished the discharge I removed them from the charger and let them sit for 24 hours. I then discharged them again at 500 mA and capacities were 17, 14, 13, and 18 mAh. This time the cell voltage only recovered to 1.18 volts.
Given the higher discharge rate, and the higher capacity cells, this last observation seems more normal to me. The question is Why does leaving the cells in the charger result in almost 5X more capacity...?
Does the C9000 switch into trickle charge mode after discharging...?
Tom
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:twothumbs :buddies: :twothumbs 
