Introduction
In today’s world, batteries are an essential part of our everyday lives. From mobile phones to remote controls, we heavily rely on batteries to power our devices. However, recharging batteries can sometimes be a cumbersome task, especially if you forget to unplug the charger after it’s fully charged. To overcome this issue, we have a solution for you – a 6V auto cutoff battery charger!
The 6V auto cutoff battery charger is a DIY homemade circuit that automatically cuts off power to the battery once it reaches its full charge, preventing overcharging and extending the battery’s lifespan. In this article, we will guide you on how to assemble this circuit using commonly available components such as the 555 timer IC, BC547 transistors, 7805 voltage regulator IC, and a 6V relay.
Understanding the Major Components:
Before we start building the circuit, let’s take a brief look at the components we will be using:
555 Timer IC:
The 555 timer IC is a highly versatile and widely used integrated circuit. It can be configured in various ways to perform numerous tasks, including timing, oscillation, and pulse generation. In our battery charger circuit, we will use the 555 timer IC in astable mode.
BC547 Transistor:
The BC547 is a general-purpose NPN transistor commonly used in electronic circuits. It can handle moderate currents and voltages, making it suitable for our battery charger application. We will use BC547 transistors as switches in our circuit.
7805 Voltage Regulator IC:
The 7805 is a popular positive voltage regulator IC that provides a constant regulated output of +5V. We will use the 7805 in our circuit to get a stable 5V supply, which will be essential for driving the 555 timer IC and other components.
6V Relay:
A relay is an electromagnetic switch that can be controlled by a small electric current. In our circuit, the 6V relay will act as the cutoff mechanism, disconnecting the battery from the charging source once it reaches its full charge.

Circuit Diagram of Auto Cutoff Battery Charger
This project can be designed using a few basic components. The circuit diagram of this project is shown below.
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Components List of Auto Cutoff Battery Charger
Following is the list of all components used in this project:
- 1- 1X 555 timer ic
- 2- 1XBC547 transistors
- 3- 1X 7805 voltage regulator ic
- 4- 1X 6v relay
- 5- 3X 10K ohm resistors (1/4 watt)
- 6- 2X 470 ohm resistors (1/4 watt)
- 7- 1X 10K variable resistor
- 8- 1X 1N4007 diode
- 9- 1X 100uf 50V capacitors (electrolytic)
- 10- 1X 47uf 50V capacitors (electrolytic)
- 11- 1X 0.1uf non-polar capacitors
- 12- 1X red led
- 13-1X green led
- 14- 1X 2pin terminal blocks
- 15- 1X 3pin terminal block
- 16- 1X 5mm dc female jack
- 17- vero board
- 18- jumper wires
- 19- Crocodile clip wires
Downloadable Project Files:
Gerber files:
Proteus file:
PCB layouts: Rear
PCB Layout Font:
Circuit Schematic:
Building the Circuit of Auto Cutoff Battery Charger
Now that we have a basic understanding of the components involved, let’s move on to assembling the 6V auto cutoff battery charger circuit:
- First insert a DC Jack on a vero board then insert a 7805 regulator IC and connect its pin-1 to positive and pin-2 to negative terminals of the jack.
- Connect 0.1uf capacitor’s one pin to pin-2 and the other pin to pin-3 of 7805 regulator ic.
- Connect a 47uf capacitor’s positive pin to pin-3 and its negative pin to pin-2 of 7805 regulator ic.
- Next insert a 555 Timer IC and join its pin-4, pin-6 and pin-8 together and connect them to pin-3 of 7805 regulator ic. Also connect pin-1 of 555 timer ic to ground.
- Connect a 10k resister’s one side to pin-5 and the side to pin-1 of the 555 timer ic .
- Connect a 10k Trimpot’s pin-2 to pin-2 and pin-3 to pin-1 of the 555 timer ic.
- Next insert a 12v relay and a 3-pin terminal block together on vero board. Connect terminal block’s pin-1 to Normally Closed pin, pin-2 to Common pin and pin-3 to the Normally Open pin of the relay.
- Connect a 1n4007 diode’s Anode to coil pin-1 and cathode to coil pin-2 of the relay. Also join coil pin-2 with common pin of the relay.
- Now insert a BC547 transistor and connect its pin-1 to anode of 1n4007 diode and pin-3 to negative supply.
- Connect a 10k resister between pin-3 of 555 timer ic and pin-2 of BC547 transistor.
- Connect an LED’s anode to pin-6 of the 555 timer ic. Also connect a 470 ohms resister to pin-3 of 555 timer ic. Now connect the remaining of 470 ohms resister to cathode of the LED.
- Connect another LED’s cathode to negative supply. Aslso connect another 470 resister to pin-3 of 555 timer ic. Now connect the remaining pin of 470 ohms resister to anode of the LED.
- Connect a 100uf capacitor’s positive pin in-1 and negative pin to pin-2 of 7805 regulator ic.
- Connect a 10k resister’s one side to pin-1 of 10 trimpot and the other side to Normally Open pin the relay.
- Insert a 2 pin terminal block and connect its pins to pin-2 of 7805 regulator ic. Also make a connection between Common pin of the relay and the positive pin of the power supply jack.
- For battery connections, connect red wire to pin-3 of terminal block which is connected to Normally Open pin of the relay. And then connect black wire to 2-pin terminal block for negative connection.
- For adjustments, connect multi meter with the battery connection then provide 6v power supply to jack and adjust the voltage to 7.2v with trimpot for 6v battery charging.
Conclusion of Auto Cutoff Battery Charger
By following the step-by-step instructions provided in this article, you can successfully build a 6V auto cutoff battery charger using easily accessible components such as the 555 timer IC, BC547 transistors, 7805 voltage regulator IC, and a 6V relay. This homemade circuit will not only charge your batteries efficiently but also protect them from overcharging, ensuring a longer lifespan.
Remember to exercise caution while working with high power electricity.
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For more project and circuit diagrams, you can go through the Schematics in the main menu where you can find many interesting projects and circuit diagrams like audio amplifier circuits, voltage booster circuit, battery charger circuit and timer circuits etc., which are all beginner circuit projects. Feel free to check them out!
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