I have four new (never powered up) 2000mah NIMH batteries in series (4.8v) that I am putting in my drill. The drill used to have 4 x NiCD. I have a charger that is 6V 500 mah. Do I need to drop the current to 200mah for these batteries and if so, how can I do that, or, do you have a charger that will do the job I can purchase? Thanks, Mark
This will do the job. You configure that battery pack as 4 x NiMH and it takes care of the rest. It will also look after all your other battery charging requirements. Overkill for your current task, but well worth it in the longer run.
Modifying a NiCad charger for NiMH is probably not feasible, as you need to consider the charge sensing circuitry as well as the charge current in order to ensure proper operation.
Thanks for the reply. What would be the result/issues with using the 6v 500mah charger?
Assume the 6V 500mAh charger you have is for the original NiCD cells.
Using a NiCD charger to charge NiMH can result in low life of the NiMH. The battery chemistry is very different between NiCD & NiMH.
The link goes into a lot of detail but for me the relevant part is :-
NiMH dislikes overcharge, and the trickle charge is set to around 0.05C. NiCd is better at absorbing overcharge and the original NiCd chargers had a trickle charge of 0.1C. The differences in trickle charge current and the need for more sensitive full-charge detection render the original NiCd charger unsuitable for NiMH batteries. A NiMH in a NiCd charger would overheat, but a NiCd in a NiMH charger functions well. Modern chargers accommodate both battery systems.
The product linked by Jeff is an excellent device, I have a similar older one thats suits what I need.
Alternatively you could use a cheaper charger like this, but it does not come with a 12VDC plug pack. When you add that the cost is about the same. Also you would need to remove the cells from the drill to charge them.
Suggest you don’t use the 6V 500mAh charger to charge the NiMH, it would shorten the life of the cells and could be a safety issue when they overheat.