This project shows about a Low Cost 1.2V AA Ni-MH Solar Battery Charger Circuit.
It works with small cheap solar panel as it charges the battery safely in sunlight.
It uses only solar panel, diode, resistors and two transistors.
And these parts are few which are easy to find.
The circuit protects battery from too much charge.
It is good for DIY and small electronics projects.
Circuit Working:
Parts List:
| Parts | Value | Quantity |
|---|---|---|
| Resistors (All resistors are 0.25W unless specified) | 27Ω | 1 |
| 3.3k | 1 | |
| 330Ω | 1 | |
| 4.7Ω 1W | 1 | |
| Semiconductors | Solar Cell 6 watts 12V 0.5A | 1 |
| Transistor BC547 NPN | 1 | |
| Transistor BD140 PNP | 1 | |
| LED any 5mm | 1 | |
| Diode 1N4007 0.7V | 1 | |
| Battery Ni-MH 2.4V or 2 × 1.2V AA | 1 |
Solar cell gives around 5V to 6V sunlight voltage.
D1 1N4007 diode stops reverse current at night.
R4 limits charging current to the battery.
Q2 transistor controls charging when battery becomes full.
LED lights when battery is charging.
Q1 works like a sensor transistor.
When battery voltage becomes high around 2.8V then Q1 turns ON.
Q1 turning ON will activate Q2 and reduce charging current.
This protects battery from too much charging.
Formulas:
Formulas for charging current approx = (Solar voltage – Battery voltage – Diode drop) / R4
Take example: solar voltage = 6V
Battery = 2.4V
Diode drop = 0.7V
So current = (6 – 2.4 – 0.7) / 4.7
Current = 2.9 / 4.7
Current approx = 0.6A max in full sunlight
Actual current is lower because we used small solar cell.
Transistor Q1 starts working near battery voltage about 0.6V + 0.6V = 1.2V + offset
So battery full threshold is around 2.7V to 2.8V.
How to Build:
To build a Low Cost 1.2V AA Ni-MH Solar Battery Charger Circuit follow the below steps for connction:
- Take all the parts as shown in circuit diagram.
- Place diode D1 in series with solar positive.
- R4 goes after diode to battery positive.
- Battery negative goes to ground.
- Q2 BD140 Emitter goes to solar positive after R4.
- Collector goes to battery positive.
- Base goes between resistor R3 and LED.
- R3 also connects to collector of Q1.
- Q1 BC547 transistor emitter goes to ground.
- Collector goes to R3.
- Base connects between R2 and R1.
- R1 connects to battery positive.
- R2 connects to ground.
Conclusion:
This small project for Low Cost 1.2V AA Ni-MH Solar Battery Charger Circuit is cheap and easy.
It is good for charging one AA Ni-MH cell slowly.
Transistor control gives simple overcharge protection.
The circuit works well for small solar devices and for outdoor use.