Discharging problems

[Erik Aa]

I discharged my brand new Nosram VTEC SC4100UVH cells today after having charged them about 2000mAh 3 weeks ago (I'm trying to store them until the winter season starts). I first discharded them using a light bulb. When I afterwards put them on the LRP discharge tray to equalize them at 1.0 volts, one of the cells immediately started venting (sizzling sound and a small amount of liquid leaked out of the cell). I took them off the tray right away. Is this a common problem (that these cells vent when put on a discharge tray)? Is the cell damaged now? I later charged the pack and everything seems ok. How to avoid this problem? Thanks.

[sosidge]

Originally Posted by Erik Aa

I discharged my brand new Nosram VTEC SC4100UVH cells today after having charged them about 2000mAh 3 weeks ago (I'm trying to store them until the winter season starts). I first discharded them using a light bulb. When I afterwards put them on the LRP discharge tray to equalize them at 1.0 volts, one of the cells immediately started venting (sizzling sound and a small amount of liquid leaked out of the cell). I took them off the tray right away. Is this a common problem (that these cells vent when put on a discharge tray)? Is the cell damaged now? I later charged the pack and everything seems ok. How to avoid this problem? Thanks.

Does your light bulb have a voltage cutoff? Probably not. You should never discharge NiMH cells down to 0V, all decent dischargers have a cutoff in the region of 0.9V per cell.

A loss of electrolyte when venting will have decreased the performance of the cell, although it sounds like it has survived, it will not be at the same level as a new cell, or the rest of the pack.

It is very important to check the voltage of NiMH cells regularly, ideally before each charge, they self-discharge very rapidly and this causes a lot of problems.

[Erik Aa]

The cells wee in the 1,2 volt range when I put them on the tray. After having charged them again (after the vent) with around 2000 mAh (remember I'm only charing them for storage), all cells were in the 1,4 + volt range.

[sosidge]

Originally Posted by Erik Aa

The cells wee in the 1,2 volt range when I put them on the tray. After having charged them again (after the vent) with around 2000 mAh (remember I'm only charing them for storage), all cells were in the 1,4 + volt range.

Cells are always in the 1.2V range when resting, it is their nominal voltage. Since it seems your don't have a cutoff on your lightbulb, it sounds like you have over-discharged the cells and that has started your problems.

[Erik Aa]

I measured them with a multimeter.

[Erik Aa]

I just noticed that the cell that vented has actually expanded on the minus pole. It is bulging out approx half a mm. Doesn't look good. The cell still appears to be working well though. Any advice/comments regarding this? Thanks.