NiCd – NiMH Battery Charger

Here is the simple and low cost NiCd and NiMH battery charger circuit which can be used for various battery type and size. This battery charger use a regulator IC of LM317.

Schematic diagram:

The charge will start if a battery is connected between pins JP1-JP4 or JP2-JP4 or JP3-JP4. For example, if a battery is connected to JP1-JP4 pins then the current that flows cause a voltage drop to R1, then D1 causes a voltage drop of 0,7 volts and ?1 conducts. Then through transistor’s emitter flows a current that comes from Adjustment pin of LM317.

NiCd – NiMH Battery Charger Circuit Notes:

• I is 1/10 of the battery’s charging capacity. For example if battery has a rated capacity of 1700mA then ?=170.
• Diode D4 prevents current to flow from battery back to the charging circuit. Resistors R1,R2 and R3 adjusts the charging current and it’s value is given from : Rx=(1,25 + 0,1) / I , where x = 1,2,3.
• The input voltage must be at least 3 times the battery’s voltage. For example an input voltage of 25V can charge a 8,4V (9V) battery.
• R3 is 1/2 Watt and R1 and R2 it’s 1/4 Watt.
• Pins distribution:

Pins	Battery type
JP1 – JP4	AAA
JP2 – JP4	AA
JP3 – JP4	PP3 & 6F22

PCB top and bottom layout: