"Backward" Charge Results

[jayflash]

I've a few 7Ah, D size, NiCd cells from 2008 which seem to have self discharged too soon, so I began testing them. At a 500mA discharge rate they ranged from 3 - 6Ah of capacity right after charging with a dumb charger.

Recharging them at 1.8A from my LaCrosse BC-900 and an adapter, each cell displayed only about 1/2 the capacity indicated by discharging. This is the opposite of typical results where the charger will show a slightly higher charging capacity. I know that's due to charging losses so I ignore the inflated capacity.

Have these two year old NiCd cells deteriorated and won't accept that charge rate? I'm in the process of further testing so any suggestions are appreciated.

 

[uk_caver]

I've a few 7Ah, D size, NiCd cells from 2008 which seem to have self discharged too soon, so I began testing them. At a 500mA discharge rate they ranged from 3 - 6Ah of capacity right after charging with a dumb charger.

Recharging them at 1.8A from my LaCrosse BC-900 and an adapter, each cell displayed only about 1/2 the capacity indicated by discharging. This is the opposite of typical results where the charger will show a slightly higher charging capacity. I know that's due to charging losses so I ignore the inflated capacity.

Have these two year old NiCd cells deteriorated and won't accept that charge rate? I'm in the process of further testing so any suggestions are appreciated.

The charger manual says that the maximum capacity is 3000mAh.
That could mean that the charger will terminate after that much energy has been put in to it, even if it isn't full, and could explain a ~6aH cell only having ~3Ah in after charging
Putting the cells through a second charge cycle could get round that problem.

Is it possible that with a higher-capacity cell, the charger would terminate prematurely, due to the different shape of the voltage/time curve when charging?

 

[jayflash]

The cells are reaching ~1.66 volts or more and indicate full charge after only an hour or two at most. The internal resistance of these recharged cells is ~.04 ohms, unless I'm testing improperly. My good LSD AA cells also have about .04 ohms of resistance.

EDIT: That resistance was with a .5A load. I'll have to check again using several amps for a load.

 

[45/70]

While I've never seen my BC-900 charge a cell with 3000mAh input, as far as I know the BC-900 will "stop" at 3000mAh. The closest I've come is with Sanyo 2700 AA's. I've had them take in 2900+ mAh. I've never adapted C's or D's and tried to charge them.

So, maybe there is hope for revitalizing you NiCd D's. If what's happening is that the charger is stopping at 3000mAh, just put them on again and see what happens.

EDIT: You beat me to the post, jayflash. The 1.66 Volt does sound like the cells are at the very least, approaching full charge. It doesn't sound good, but you might try a few cycles and see if they improve.
Dave