How to revive a NiMH?

[Elmo]

I have some mini 6 cell NiMH packs that I use in my rc18t and in my crawler when weight is an issue. One of the packs works like new, but the other one is pretty flat and has little of its capacity left. What can I do to revive the pack without having to buy a new one? I've heard that cycling the pack will help, but I have never done it. Any recommendations?

 

[Manning]

Nope. Once a cell goes bad, that's it. Sorry.

 

[killswitch]

Do you have a charger that will discharge? If so, discharge them to .9v per cell, let them cool off and charge them again at a low rate. Do this a few times and they should come back. Once you've done this, discharge them again and charge at your normal rate. If they don't take a good charge by then, they probably aren't going to.

 

[Elmo]

My charger does discharge as well so that's a good sign. I'll give it a shot tomorrow when I get back to the shop. I think my chargers lowest charge rate is .5 amps and I hope that will be a slow enough charge. Should I expect it to false peak quite a bit and if so should I continue the charge or start to discharge the pack again?

 

[killswitch]

It may false peak, but the lower than normal charge rate should keep that at a minimum. If you tried to hit them with a lot of amps at first, it'll false peak like a mofo. If it does false peak, start the charge cycle again. Just keep tabs on cell temp. They charge best when warm, but you don't want them to get too hot.

Cycling would really be better if you had a discharge tray that would take each cell to .9v/cell, but those are almost non-existant for the smaller cells. Just make sure to set your discharge cutoff correctly based on your number of cells. I wouldn't go any lower than .9v/cell on the smaller cells.

 

[Olle P]

... my chargers lowest charge rate is .5 amps and I hope that will be a slow enough charge.

Ideally the batteries should be charged at 0.1C for reconditioning.
For a 5,000mAh battery 0.5A is low enough...