Smart & Fast Battery Charger for NiCd/NiMH

The project utilizes MAX712/MAX713 fast charge controllers in order to build a smart & fast NiCd/NiMH battery charger.

 

The MAX712 is designed for NiMH batteries and the MAX713 is for NiCd batteries where the battery-fully-charged sensing method is the only difference between them. The values for some of the components included in the circuit can be chosen using the reference from Maxim. Depending on the number of cells of the battery pack intended to charge as well as the charging time, those values may vary.
The charger won’t be able to charge packs with more than six 1.2V cells if it is powered only with 12V. the MAX will get hot and the charging current won’t be what is expected from the value of the sensing resistor if something bigger than 12V would be tried. This is due to the sinking of as much current as possible from the base of the power transistor as it tries to obtained up to 250mV voltage drop on the sensing resistor.
The timer feature of MAX712/713 cannot be disabled while a high current could still be a result of the maximum possible charging time.

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