12V Lead Acid Battery Charging Circuit with Auto Cut-Off. DIY PB Battery Charger

This circuit is intended for charging lead acid batteries up to a maximum of 7000Mah (7A / h) 12V PB. Charging is terminated when the battery reaches the set voltage when it is charged. The full voltage of such batteries is approximately 13.8 Volts. In order to achieve this value, the voltage measured on the battery during charging should reach approximately 14.4 volts. (It is 14.8V for full occupancy but it is better to stay a little under security.)

14.4V is the voltage value of the load during charging. When we disconnect the charging connection, the voltage becomes 13.8 and rapidly decreases to approximately 13.5 volts. This is a natural condition. When PB batteries fall below 11.8V, they should not be used. This may damage the battery. Continue to use after recharging.

WARNING: This circuit is for hobby purposes. Its work has been tested, but no long-term repeated tests have been performed. Charging has inherent risks. Use of this circuit is at your own risk.

Necessary materials:

5 * 1N5408 Diode
4 * 1N4007 Diode
1 * 6.8K 1 / 4W Resistor
1 * 100R 1 / 4W Resistor
1 * 1K 1 / 4W Resistor
1 * 0.85R 3W or 2W Resistor. If you can’t find 0R85, you can also use 1R. As the current will drop, the charge slows down a little but it works.
1 * 10K Trimpot
1 * 4.3V 1W Zener Diode (also can be 4.7V)
1 * 3300uF 25V Capacitor (can also be 4700uF 35V)
1 * 10uF 35V Capacitor
1 * BD139 Transistor
1 * 12V Relay
1 * 5mm LED Red
1 * 5mm LED Green
1 * 12V Buzzer
1 * 1A Insurance
1 * PCB Terminal Block
1 * 12V Min 16VA Transformer