Can NiCad chargers be also used for NiMH batteries? If not what precautins should be taken? Most chargers cut off around 1.4 Volt which is ok for both kinds of batteries.
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Yes and no.
It's not a good idea if the charger is a fast charger (>2C for example ).
Good quality fast chargers for this type of cell use a technique called Delta V cut-off. This relies on the fact that (when charged by a constant current source) NiCad and NiMH cells have a characteristic voltage "peak" and subsequent slight _reduction_ in voltage when nearly full. The reduction in voltage is small and filtering must be employed to remove noise. The peak is smaller for NiMH than it is for NiCad cells.
This means that NiCad chargers can look for an absolute fall in voltage, whereas NiMH chargers have to be more sensitive and usually look for the gradient changing from +ve to -ve. If you use a NiCad fast charger on NiMH cells, there is a danger that the peak won't be big enough to trip the end of charge detector leading to a possible overcharge. However most chargers of this type use a timer or temperature sensor as a safety backup or similar.
At least Maxim MAX713 can charge both NiCd and NiMH batteries. I built one charger with that IC for my kids RC car. It is very simple and also seems to charge the battires well. No I'm going to build another charger with the same IC for NiMH batteries. If you know how to solder, I suggest you should check that IC. It needs only few additional components and is very simple to get it work.
TSa
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