View Full Version : Charging NiMH batteries.

04-02-2005, 06:20 PM

I have some NiMH batteries rated at 2300, charge it at 16hr at 220mA.

My battery charger is a Ni-Cd Battery Charger (as it says on the unit). Output is 180mA (with 20mA for 9 volt).

1. Can I use this charger for MiMH batteries or is this only for Ni-Cd batteries?

2. How long should I charge it for? Do I roughtly est. the length of time for the suggested mA by the battery then adjust it to the output mA given provided by the charger? Should I read the instuctions per battery or do I ahere to the suggestions with my battery charger which says no more than 5-8hr for AAs.


04-02-2005, 06:57 PM
Really, the older fixed current type chargers like that should be binned, with 2300 mAh NiMh batteries you will do them no favours.

But the figures you quote suggest 1.5 times the rated capacity for charging.
16 hours at 220 mA gives 3520 mAh.
3520 / 180 gives 19.5 hours.

The problem is, that when fully charged the proper "dv/dt" sensing of the correct charger will stop the main charge and provide a maintenance charge only to prevent damage to the battery. Your one will not.

The "180 mA" is not very precise either, when I checked one it was a lot more.
The instructions on the charger probably have no meaning for those batteries (which were not around when the charger was made). Unless they relate to the rating for the charger itself, which may overheat at the 19 hours suggested by the maths?

The older chargers of that type were sold off a year or so ago at Mitre 10 for $3 each.
I would not use one for those cells, apart from in an emergency.

Graham L
05-02-2005, 02:59 PM
Those older NiCd chargers use the rule "10% of C for 14 hours". So that one was meant for 1800 mAh cells.

That 10% rate was said to be safe for long term trickle charge of NiCds. It's not good for NiMH. (It wasn't very good for NiCDs either, when taken to extremes).

If the cells are flat, charging them for 16 hours or so will "nearly" charge them. If you then remove the cells, you won't have hurt them. The harm is done when they are left on (over)charge for long periods.