In this tutorial, we are making a simple transistor based solar battery charger with auto cut off function. When the battery gets fully charged the solar panel keeps running and this can result in battery getting deep discharged which will shorten its life. Or the solar panel’s energy could be wasted. To overcome all these problems we have come up with this circuit.
It will charge a battery from a solar panel and disconnects it when it gets fully charged.
Hardware Components
| S.no | Component | Value | Qty |
|---|---|---|---|
| 1. | Solar Panel | – | 1 |
| 2. | Battery | 12V | 1 |
| 3. | Diode | 1N5823 | 1 |
| 4. | Zener diode | 9.1V | 1 |
| 5. | Transistor | 2N4401 | 3 |
| 6. | Transistor | TIP127 | 1 |
| 7. | Heatsink | – | 1 |
| 8. | LED | – | 1 |
| 9. | Resistor | 1KΩ, 10KΩ, 4.7KΩ | 3, 2, 1 |
Circuit Diagram
Working Explanation
This circuit is using four transistors and other passive components. 12V battery is connected whose input is coming from a solar panel. The transistors are used to detect when the battery gets charged. A charge indicator LED is used to indicate when the battery is getting charged and it goes off when the charging is full. This circuit can only provide up to 5A to the battery.
Circuit Adjustments
For using this circuit will have to make the following adjustments at first,
- Disconnect the battery from this circuit and replace it with an adjustable power supply with an output of 15V set into it.
- Adjust the 10K variable resistor until the LED goes off. Now your circuit is ready
Even though this circuit is adjusted for a 12V battery, you can easily adjust it to charge a battery with some different voltage by following the same procedure. For that, you need to know the full charge voltage of the battery which is usually written on the batteries on in their specifications. The above procedure for a 12V battery we set the output to 15V because a 12V SLA battery gets completely charged when it shows 15V on DMM while charging. Similarly, a 6V battery displays 7.2V when it is completely charged so you will have to set 7.2 volts on the adjustable power supply when using a 6V battery.
