This battery charger circuit provides the Automatic cut off the facility when the battery gets fully charged.

Before the use of this circuit, you need to adjust the Cut off voltage range for the auto cut.

This adjustment is done by the 10k preset, and a multimeter connected with the output terminals that go to the battery.

This voltage range can be set by using any 4v to 15v DC supply which connects the terminals which go to the battery. And move the preset till the green led ON. Once the auto cut voltage is set, the circuit is ready to use.

automatic battery charger circuit

Parts List for automatic Battery Charger

  • Transistor BC547 or use any NPN transistor
  • D1 Red LED, D2 Green LED, D3 IN5408 or according to Output current, D4 IN4007
  • Resistor R1 1k, R2 10k, R3 for 3.7-volt battery 220 ohms, 6volt-470 ohms, 12V 1k
  • VR1 10k
  • Relay for 3.7-volt battery 5V, 6volt- 5V or 6V, 12V -12V

Working of Auto Cut-off Battery Charger Circuit

  • In the above circuit, whole charging is governed by BC547 transistor and relay RL1 acts as the changeover.
  • During charging the circuits takes input via a charger /bridge rectifier charger circuit shown above and through the relay’s COM and NC, the power is directly connected to the battery.
  • After the battery reaches a certain level the transistor bc547 id tuned ON and it drives a relay which in turn changes the COM pin’s link from NC to NO which is connected to the red color LED that will start glowing after relay changeover, indicating the battery charging completion.

PCB Layout For Auto cut-off battery charger circuit

12 volt battery auto-cut off battery charger