12v Battery Charger Circuit
The circuit can be used to charge 12V lead acid batteries.
Overview
Pin 1 of the LM317 IC is the control pin which is used to control the charging voltage, Pin 2 is the output at which the charging voltage appears, Pin 3 is the input to which the regulated DC supply is given.
The charging voltage and current is controlled by the transistor (Q1), resistor (R1) and POT (VR1). When the battery is first connected to the charging terminals, the current through R1 increases. This in turn increases the current and voltage from LM317. When the battery is fully charged the charger reduces the charging current and the battery will be charged in the trickle charging mode.
Schematic
Notes
- The input voltage to the circuit must be at least 3V higher than the expected output voltage. LM 317 dissipates around 3V during its operation. Here I used 18V DC as the input.
- The charging voltage can be set by using the POT (VR1).
- The LM 317 must be mounted on a heat sink.
- All capacitors must be rated at least 25V.
- You can use crocodile clips for connecting the battery to the charger.
