nimh charging

rondoolaa · #1 24-11-2012

hi,

i have some nimh 3300 batteries that havnt been used for a while and my son wishes to use them tomorrow in his b4,

i have tried charging them but they are peaking way to early and not getting a full charge,

i was thinking of putting them on my other chargers and cycling them, ie: discharge then charge,

what is this the best thing to do to get them to properly charge ?

any help appreciated as he wants to use these tomorrow, am charging 12 lipo's while waiting for replies about this, lol

thanks,

neiloliver · #2 24-11-2012

You are seeing premature charge termination due to the long term storage of the cells. The active materials have reverted to an inactive state and electrolyte has migrated from the electrodes... in other words they need waking up. It might be that the storage at low potentials has lead to internal short circuits and this may mean the cells are at end of life

I suggest you charge the pack at 0.5A (500mA) for maybe ten minutes.. then stop charging and measure the cell voltages - they should all be similar and all above 1.15V. If any are lower then the cells are suspect and you should consider throwing the battery away.

Assuming the voltages are OK then charge the battery at 1A in the normal method. Dont charge at anything higher than this for the first charge. Assuming everything works our OK you can later start charging at 3300mA but never higher than this.

Neil

rondoolaa · #3 24-11-2012

firstly, thankyou for the reply and info,

when the first battery said charged i just started it again and a third time, now its charging at the 3.3a but after reading your reply i have just stopped the charge and set it to charge at 1.1 amp, a third of its norm, i will continue to charge them at 1.1a and keep restarting the charge process if this sounds ok

neiloliver · #4 24-11-2012

The reason for reducing the charge current is two fold: first it reduces the chance of getting a false peak, and second it is safer.

n

adon30 · #5 24-11-2012

It's the same with new Nimh cell you charge at c/10. So in your case 0.3A.
Exactly what Neil has put is correct with the false peaking. Best thing to do is to charge them as softly as possible. So 0.3a for 10 hours. Use a timed charger if possible.
If you can access them measure each cell individually. If you have any duff ones it will help you find it now rather than later.

Charging at a higher rate can increase the risk of overheating and damage. Once the cells have been recovered and cycled you should be able to charge at a higher rate.

It's really complicated this Nimh charging

lipos are so much easier nowadays