The circuit diagram of lead acid battery charger has been described here. The core part of this circuit is the IC LM 317. The function of this IC in this circuit is to provide the correct charging voltage for the battery. One of the most important criteria is followed in the design of this circuit that is the battery must be charged with one tenth of its Ah value.
The operation of this charger circuit is determined mainly by the transistor Q1 (BC 548) and the resistors R1 (0.5 ohm), R4 (100 ohm) and R5 (1K). The current through R1 increases as the battery gets charged. The conduction state of transistor Q1 changes due to this. The adjust pin of IC 317 is connected to the collector of Q1 so that the output voltage changes accordingly. The circuit reduces charging current when the battery is fully charged this mode is called trickle charging mode.
- Use a good quality PCB to assemble this circuit.
- Adequate heat sink should be provided for IC LM 317.
- Potentiometer R5 is used to set the charging current.
- In order to get 12 V for charging the battery, the input to the IC must be minimum 15V.