Efficient Car Battery Charger

It charges 12 V Lead Acid battery with 5 Amps current and Automatically stops charging when the battery voltage increases above 13.8 V to prevent over charging. Charger starts charging when the battery voltage is below 11.8 V and stops charging at 13.8 V.

Power Supply
14-0-14 V 5 Amps transformer – 1
10 Amps Rectifier diodes – 2
1000 uF 25 V Electrolytic capacitor – 1
AC cord – 1
Charger case – 1

Circuit components
Resistors. All ½ watts
1K -4
Electrolytic capacitor
100 uF 25 V – 3
1N 4007 – 3
Voltage regulator IC
LM 7815 – 1
Variable Resistor
10 K Pot – 1
Zener diode
9V 1 W – 1
5 mm Red – 1
5 mm Yellow – 1
5 mm Green – 1
12 V Cube relay

Assemble the circuit on a Perf board. Connect circuit to a fully charged battery having 13.8 V or to a Variable power supply set at 13.8 V. Slowly adjust Preset till Relay turns on and Green LED lights. This is the cutoff point. Remove circuit and connect to the discharged battery. Red LED lights indicating the charging process. Check the output voltage between NC contact of relay and ground. It will be around 15 V DC.

Relay remains de energized during charging. When the battery voltage increases above 13.8 V, relay turns on and breaks the charging current from the common pin of Relay. This stops charging. Yellow LED lights when the circuit is connected to battery. This helps to see whether the battery clips are properly connected to the battery or not.