Many of my readers require a High current battery charger with battery protection facility. So I am posting this circuit for charging 12 volt Lead Acid battery using Mains power. The same circuit can be connected to Solar panel also. The circuit has features like
1. High current charging
2. Voltage regulation
3. Current regulation
4. Full charge cut off
5. Battery protection
6. LED status indicators

The working of the Charger is

1. A 15-0-15 Volt 3 Amps step-down transformer reduces the 230 volt AC .

2. Diodes D3 and D4 rectifies the low volt AC to DC.

3. Capacitor C2 makes the DC ripple free. But instead of a high value capacitor, 470 uF is included to leave some ripples since “Dirty DC “ is good for battery charging.

4. Regulator IC LM7815 provides well regulated 15 volt DC for charging. 12 Volt battery requires around 15 volt DC for charging.

5. Series resistors R3 and R4 regulate charging current.

Click Image to get its enlarged view

4. Regulator IC LM7815 provides well regulated 15 volt DC for charging. 12 Volt battery requires around 15 volt DC for charging.

5. Series resistors R3 and R4 regulate charging current.

6. Comparator IC CA3140 along with medium power PNP transistor BD140 act a switch to prevent over charging of battery. IC1 is designed as a comparator to compare the input voltage and the terminal voltage of battery. The Non inverting input( pin3) of the comparator gets voltage from regulator IC through R5. The inverting input (pin2) is connected to the battery terminal. So in the charging mode, the output of comparator will be high because the inverting input remains low due to the flow of current into the battery. Diode D2 remains reverse biased. Since the base of T1 gets positive bias through R5, VR1 and R6, the transistor will be off. When the battery attains full charge, its terminal voltage rises to 13.5 volts, no more current passes into the battery ( if it is good). This increases the voltage at pin2 of the comparator and its output turns low. Diode D2 then forward biases and T1 conducts. This drains the output voltage of the regulator IC to ground. Red LED indicates the full charge status. VR1 can be used to adjust the biasing of T1. Set it to keep Red LED off in the normal charging mode.
7. A Cow bar protection circuit is also added to protect battery from excess voltage (Suitable in Solar charger) . SCR 2P4M and Zener diode ZD act like a Cow bar circuit. When the charging voltage or the battery voltage is excess than 15 volts, Zener conducts and triggers SCR. Excess voltage will be drained through SCR. Yellow LED indicates the activation of protection circuit.

8. Assemble the circuit on a good quality Common PCB for prototyping. Use a heat sink for the regulator IC. Connecting wires to the battery (Red for positive and Black for negative) should be high gauge one. 6 mm wire used for AC wiring can be used.

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High Current Charger with Cut Off

9. To test all parts are working, use a 18 volt variable power supply .Provide 13 V (Before connecting the battery) to the Test Points (TP) A and B. LEDs should be off. Increase the voltage to 16 Volts, both LEDs should light.

Note: Construction methods may vary and a number of minute errors can appear. So don’t leave the circuit. Trouble shoot carefully and if needed slightly change the values of R5 and R6. The Cow bar circuit can be avoided if not needed.


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About D.Mohankumar

D. Mohan Kumar M.Sc., M.Phil, is an Associate Professor from Trivandrum, Kerala, India. He has been guiding Post Graduate students in Animal Science research for the last 25 years in several premier institutions in Kerala, India. He is an avid electronics enthusiast and has been designing circuits for the past 20 years. In this period he has supported many electronics/electrical engineering students in their final year projects. He is a regular contributor to Electronics For You magazine which is South Asia’s largest circulating electronics magazine published from New Delhi. He is also contributing articles in and

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