This Dual Power Source battery charger can utilize two power sources like Solar energy as well as electrical energy to charge a Lead Acid battery. Its charging is voltage and current controlled and can be used as a portable charger in places where AC is not accessible. It also has an LED indicator to show the full charge state of the battery.
AC charger section uses a 0-14 volt 500 mA step down transformer with 1 amps bridge module for rectification and a capacitor C1 for smoothing. This rectified DC passes through Switch S1 to the Variable voltage regulator IC LM317. Its output voltage can be set using the preset VR1.Output from IC1 passes through diode D3 to the gate of SCR 2P4M. When the gate of SCR gets firing pulse from IC1, it triggers and current flows through its cathode for charging the battery. Red LED indicates the power On status.
An LED indicator is also provided to show the Full charge state of the battery. Transistor T1 is used as a switch to light the Green LED when the battery attains full charge. When the battery voltage is less than 11 volts, Zener ZD remains non conducting to keep T1 off. When the battery attains full charge, no more current passes into it and the voltage through R3 rises which causes the breakdown of Zener and T1 conducts. Green LED then lights to indicate the full charge state of the battery.
A 12 volt 150 mA Solar panel is used to charge the battery using solar energy. In bright sunlight, the solar panel generates voltage and current which passes through switch S2. The charging process is similar to the charging using AC.
To set the charge indicator, connect the circuit to a variable power supply or a fully charged battery to give 13.8 volts. Slowly adjust VR2 till Green LED turns on. Use crocodile clips to connect with the battery.