12v battery charger auto cut circuit

12v Battery Charger circuit with Overcharge Protection

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12v Battery Charger circuit with Overcharge Protection

This 12 battery charger circuit provides the Automatic cut-off facility when the battery gets fully charged. Before the use of this circuit, you need to adjust the Cut off voltage range for the auto cut. This adjustment is done by the moving 10k preset, and for testing of output voltage auto cut range a multimeter connected with the output terminals that go to the battery. This voltage range can be set by using any 13v or 14v DC supply which connects the terminals which go to the battery. And move the preset till the green led ON. Once the auto cut voltage is set, the circuit is ready to use. 

One terminal of Input AC power to Transformer connected through 12 V Relay. When Battery needs charge then Red Led glow, When the Charge level goes to about above 12v or 13v then the Red LED will OFF and the Green LED will Glow. And Input Power to the Transformer of charger is also Disconnected by Relay. 

12v battery charger with auto cut off circuit diagram

One 555 timer ic is used for detecting the voltage level and Relay is used to disconnect the AC input. 7808 voltage regulator is used for constant supply to the operation of the circuit to cut at a required fixed voltage.

This 12v battery charger Automatic cut circuit after a full charge and provides 6 Ampere high current and this can use for a big size Lead-acid Battery up to 100 AH. If you want to more high current then replace the transformer with 10A and use 10A10 Diode. You can use a readymade 12v  10 A Bridge Rectifier which is available in the market.

Schematic diagram 

how to make a 12v battery charger



6A8 or 6A10- 4 pc

1N4007 – 1

7808 ic – 1 pc

555 timer ic – 1 pc


1000uf 50v – 1pc

1000uf 25v – 1pc

100nf (104) – 1 pc 


10K – 1

5k – 1

470 Ω – 2 

Relay 12v 6 A – 1

Preset 10k – 1 pc

LED 1 pc – Green

LED 1 pc- RED

Transistor BC547 -1 pc

 10 amp battery charger circuit diagram

Schematic diagram 

Circuit 2

Connect positive output wire on NC through Common pin of Relay

autocut off 12v battery overcharge protection


Schematic diagram 

Circuit 3


This circuit has a maximum current capacity of 1 A only.


12v battery charger circuit diagram

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6 thoughts on “12v Battery Charger circuit with Overcharge Protection”

  1. Hi sir,

    I am designing a lead acid battery charger with autocut off feature.
    I build a circuit as mentioned in your website (upto 10A circuit).

    Currently I am using 12-0 transformer and bc 547 for auticutoff and 10k pot for to set cut off voltage.

    I set a cut off voltage at 13.5 volt but while setting 13.5v I have faced some issues due to hanging wires now it’s resolved but still 10k pot resolution is very less I can’t able to set exact value simply if I just touch the pot cut off voltage will jump 1v like that.
    For example from 13.5v cut off voltage to 13.7v I am unable to set it small rotation will go more than 14v so please let me know how you selected 150 resistor and 10k pot in the design and also let me know by changing this value I can achieve more resolution or not.

    And also I have one more query like to set cutoff voltage I am used fully charged lead acid battery is there any easy way
    Is there to set the cut off voltage
    (In some video they will connect multimeter and they set the cut off voltage but if I connect multimeter it will showing maximum voltage only so I can’t able to set cut off voltage)
    In circuit I added one switch (on/off)and one 5A diode(reverse protection)

    I am building 3A,13.5v cutoff lead acid battery charger so please help me as soon as possible.

    1. Thanks for sharing your experience and difficulties in making this.
      If many times relay not active at a fix voltage level, then adjust the pot some below or some high than 12 v
      Keep in mind The step-down transformer is of higher than 12v. you can use 14v or 15 v transformer

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