The circuit given here current lead acid battery charger famous variable voltage regulator IC LM 317. The charging current depends on of resistor R2 and here it's set to be 700mA. Resistor R3 and POT R4 determines the charging voltage. Transformer T1 steps down the mains voltage and bridge D1 of rectification. C1 filter capacitor. Diode D1 prevents the reverse flow of current from the battery when charger is or when mains power .
Notes.
- Assemble the circuit on a good quality PCB.
- T1 can be a 230V primary, 35V/3A secondary step down transformer.
- If 3A Bridge is not available, make one using four 1N5003 diodes.
- LM317 must be fitted with a heat sink.
- R2 = 0.85 ohm is not a standard value. You can obtain it by combining a 6.2 ohm and 1 ohm resistors in parallel.
- F1 can be a 2A fuse.
- To setup the charging voltage, power ON the charger and hook up a voltmeter across the output terminals and adjust R4 to make the voltmeter read 28V. Now the charger is ready and you can connect the batteries.
- This charger is specifically designed for two 12V/7AH/6 cell lead acid batteries in series OR a 24V/7AH/12 cell lead acid battery.
