The solar battery charger circuit can be used to charge a 12 V lead-acid battery. The lead acid battery should be 1.3Ah rechargeable. The basic operating principle of a battery charger is that it should deliver a constant voltage that can be used to charge the battery. A LM317 is therefore used to regulate both the voltage and current supplied to the DC battery. The solar panel itself also acts as a current limiter, as it only delivers a specified current.
In order to protect the circuit, when there is no battery connected, a Schottky diode is added to the circuit. A 3 A diode can be used as a substitute to the Schottky diode.
The circuit can also be used to charge any other battery, with a constant voltage by adjusting the output voltage, using the variable resistor. The output voltage can be adjusted between 5V and 14 V and the maximum current that the circuit can deliver is 0.29A.
The time taken to charge the battery can be calculated by divided the amp hours of the battery by the current that the solar battery charger circuit delivers. Therefore, it will take approximately 4.4 hours to recharge a 1.3Ah battery.
- 1 x 17 V Solar panel (or 12 V Solar panel)
- 1 x LM317 Voltage regulator
- 1 x DC battery
- 1 x 1n4007 Diode
- 1 x 0.1uF Capacitor
- 1 x 3A, 50V Schottky diode
- 1 x 220 Ω Resistor
- 1 x 680 Ω Resistor
- 1 x 2 kΩ Variable resistor
Note a 12 V solar panel can also be used in this circuit. The output voltage to the battery will then be 5 – 12 V.