Solar Battery Charger Circuit

Solar concept is not new for us. We all know the importance of solar energy. Solar gadgets are increasing day by day. As non-renewable energy sources are decreasing, usage of solar energy is increased. This solar energy is not only used on the Earth but also used in space stations where no electrical power is available.

Here is the simple circuit to charge 6V, 4.5Ah rechargeable Lead-acid battery from the solar panel. This solar charger has current and voltage regulation and also has over voltage cut off facilities. This circuit may also be used to charge any battery at constant voltage because output voltage is adjustable. (We have already seen the circuit diagram of 9v battery charger circuit using LM311 and SCR in the earlier post.)

Solar Battery Charger Circuit Principle:

Here the solar panel produces 12V DC. The charging current passes to LM317 voltage regulator through the diode D1. The output voltage and current are regulated by adjusting the adjust pin of LM317 voltage regulator.

Solar Battery Charger Circuit Diagram:

Solar Battery Charger Circuit Diagram

Circuit Components:

• Solar panel – 12V
• LM317 voltage regulator
• DC battery
• Diode – 1n4007
• Capacitor – 0.1uF
• Schottky diode – 3A, 50V
• Resistors – 220, 680 ohms
• Pot – 2K
• Connecting wires

Do you know about the concept – How an Automatic Battery Charger Circuit Works?

Solar Battery Charger Circuit Design:

The circuit uses a 12V solar panel and an adjustable voltage regulator LM317. Solar panel consists of 1.2V rated solar cells. Pot RV1 is used to set the output voltage to the battery. Diode D2 prevents the discharge of battery.

For 6V Application:

• Output voltage: set for 7v
• Input voltage:
  • Battery discharged (6v): 8.75V@1.5mA
  • Battery charged (7V): 9V min @10mA

For 12V Application:

• Output voltage: set for 14v
• Input voltage:
  • Battery discharged (12v): 14.75V min @ 1.5mA ( available from solar panel characterized for 12V operation).
  • Battery charged (14V): 16V min @ 10mA.

Power Dissipation:

In this project, power is limited because of the thermal resistance of LM317 voltage regulator and the heat sink. To keep the temperature below 125 degree Celsius, the power must be limited to 10W. LM317 voltage regulator internally has temperature limiting circuit so that if it gets too hot, it shuts down automatically.

When battery is charging, heat sink becomes warm. When completing the charging at maximum voltage, heat sink runs hot. This heat is because of excess power that not needed in the process of charging a battery.

Current Limiting:

As the solar panel provides constant current, it acts as a current limiter. Therefore the circuit does not need any current limiting.

Solar Charger Protection:

In this circuit, capacitor C1 protects from the static discharge. Diode D1 protects from the reverse polarity. And voltage regulator IC provides voltage and current regulation.

Solar Charger Specifications:

• Solar panel rating: 20W (12V) or 10W (6V)
• Vout range: 5 to 14V
• Maximum power dissipation: 10W (includes power dissipation of schottky diode)
• Typical drop out value: 2 to 2.75V (depends on load current)
• Max current: 1.5A (internally it limited to 2.2A)
• Voltage regulation: +/- 100mV

How to Operate this Solar Battery Charger Circuit?

1. Give the connections according to the circuit diagram.
2. Place the solar panel in sunlight.
3. Now set the output voltage by adjusting pot RV1
4. Check the battery voltage using digital multi meter.

Solar Battery Charger Circuit Advantages:

• Adjustable output voltage
• Circuit is simple and inexpensive.
• Circuit uses commonly available components.
• Zero battery discharge when no sunlight on the solar panel.

Solar Battery Charger Circuit Applications:

• This circuit is used to charge Lead-Acid or Ni-Cd batteries using solar energy. (You may get an idea about How a Lead Acid Battery Charger Circuit Works by reading the earlier posts.)

Limitations of this Circuit:

1. In this project current is limited to 1.5A.
2. The circuit requires high drop-out voltage.

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