Automatic Car Battery Charger

This 5 Amps charger automatically stops charging when the terminal voltage of battery rises to 13.7 V thus preventing over charging. If the battery voltage drops below 11 V, Charger turns on and starts charging. Check it……….

Components required

1K ½ watt – 5
22 K 1 watt -1
1 Ohm 10 watts -1
1N 4007 -3
5.1V 1 watt Zener diode -1
7815 Voltage regulator -1
BD 139 Medium power NPN transistor-1
100 K Potentiometer -1
LEDs – Red, Green, Yellow, Blue
12 V Relay -1
Fuse carrier with 5 amps fuse -1
Terminal blocks -1

Assemble the circuit as shown in the diagram

Remove Fuse and connect a variable power supply to the test points.
Increase voltage to 13.8 Volts.

Adjust Pot till Relay turns on and Blue LED lights. This is cut off point.

Connect a 12 V bulb as load and do the same procedure. At 13.8 V, bulb turns off.

Insert Fuse and connect the input of circuit to a 15 V 5 Amps transformer power supply. Green LED indicates Power on.

Connect output to the battery. Yellow LED turns on indicating that the battery is connected.
Red LED indicates charging.

When the terminal voltage of battery increases to 13.8 Volts, relay turns on and breaks charging current. Blue LED indicates full charge. Red LED turns off.