NiMH Battery Chargers

USB Powered NiMH Battery Charger

Widely available AA NiMH battery chargers are in the market, even those already in a single package that can be used to charge other battery types such as NiCd, NiCad, and other types.

Battery charger in this project is designed for two AA NiMH or NiCd cells of any capacity (as long as they are the same) at approximately 470 mA which will use the USB port as power.

This battery charger will charge 700mAh NiCds in about 1.5 hours, 1500mAh NiMHs in about 3.5 hours, and 2500mAh NiMHs in about 5.5 hours. Charger incorporates the automatic bill cut-off circuit based on cell temperature, and the cells can be left in the charger indefinitely after the cut-off. The NiMH Battery charger schematic can be viewed as follows:

As important to know that any USB port can supply 5V up to 500mA. USB standard specifies that the device cannot use more than 100mA until it has negotiated the right to use the 500mA, but apparently no USB ports enforce that requirement. This makes the USB port is a convenient source of power for devices like this charger.

PCB Artwork

Maybe you are interesting with my other guide about the LM317 Circuit and Alkaline Charger.