Simple LM317 Solar Charger Circuit with Auto Cut off

The LM317 solar charger circuit with auto cut off is like a smart nanny for your batteries.

It uses sunlight to charge them up but knows exactly when to stop.

This circuit uses a clever chip called an LM317 to control the charging process, making sure the battery gets just the right amount of juice.

The best part it has a built in safety feature that automatically cuts off the charging once the battery is full, preventing damage from overcharging.

So you can relax and enjoy clean, solar powered gadget use.

Circuit Working:

Parts List:

This circuit presents a solar charger designed for recharging Lead Acid or Ni Cd batteries using solar energy.

It efficiently utilizes solar power to charge a 6V,12V or 24V rechargeable battery suitable for a variety of applications.

The charger includes features for voltage and current regulation as well as over voltage protection.

The circuit utilizes a 6V,12V or 24V solar panel along with a variable voltage regulator IC LM317.

The charging current flows through diode D1 to the LM317 voltage regulator IC.

Adjusting its adjust pin allows for the regulation of output voltage and current.

VR is positioned between the adjust pin and ground ensuring an output voltage of 9V for charging the battery.

Resistor R3 limits the charging current, while diode D2 prevents current discharge from the battery.

Transistor T1 and Zener diode act as a cut off mechanism when the battery reaches full charge.

Under normal conditions, T1 remains off allowing the battery to receive charging current.

However, when the batteries terminal voltage exceeds the zener diode voltage the zener diode conducts, supplying base current to T1.

This causes T1 to turn on grounding the output of LM317 and halting the charging process.

Formula:

Below is a basic schematic and formula for a solar charger circuit based on LM317 that has an auto cut off.

LM317 Voltage Setting:

In its configured state, the LM317 is a voltage regulator.

The output voltage V_out is calculated using the following formula:

V_out​ = V_ref​(1+R2 / R1​) + I_adj​ * R2

where:

• V_ref is the reference voltage of the LM317 around 1.25V
• R1 and R2 are the resistors in the voltage divider configuration.
• I_adj is the adjustment pin current is around 50 µA.

Note:

You should be able to start creating an LM317 solar charger circuit with auto cut off for your particular application with the aid of this basic schematic and formula overview.

Depending on your precise needs and the specifications of the components, adjustments could be required.

How to Build:

To build an LM317 Solar Charger Circuit with Auto Cut off follow these steps:

Connect the LM317:

• Insert the LM317 IC into the breadboard.
• Connect the input pin 3 to the positive terminal of the solar panel.
• Connect the output pin 2 to the positive terminal of the battery.
• Connect the adjust pin 1 to the resistor network.

Add the Resistor Network:

• Connect a 180 ohm resistor from the adjust pin 1 to the output pin 2 of the LM317.
• Connect a 1k resistor through the base of T1 to the positive terminal through zener diode

Add the Transistor and Zener Diode:

• Connect the collector of the transistor to the output pin 2 of the LM317.
• Connect the emitter of the transistor to the ground.
• Connect the base of the transistor to the zener diode.
• Connect the other end of the zener diode to the ground.

Add the Diodes:

• Connect a diode D1 1N4007 in series with the positive terminal of the solar panel to prevent reverse current flow.
• Connect another diode D2 1N4007 in series with the positive terminal of the battery to prevent reverse current flow.

Connect the Negative Terminals:

• Connect the negative terminal of the solar panel and the negative terminal of the battery to the ground.

Test the Circuit:

• Place the solar panel under sunlight and verify that the battery charges.
• Observe the transistor and zener diode to ensure they cut off the charging when the battery is full.

Finalize the Circuit:

• Once the circuit is working correctly finalize the connections on a PCB or a more permanent setup.

Note:

• Remember to take necessary precautions while working with electronics such as wearing safety glasses and avoiding short circuits.

Conclusion:

To conclude, the LM317 solar charger circuit with auto cut off is an efficient and reliable way to charge Lead Acid or Ni Cd batteries using solar energy.

By utilizing the LM317 voltage regulator IC, this circuit provides voltage and current regulation along with an auto cut off feature to prevent overcharging.

With the proper components and setup this circuit can be a cost effective and environmentally friendly solution for various applications requiring solar powered battery charging.

References:

Project Report on Solar Charger Circuit using IC LM317

Solar Based Adjustable Voltage Regulator Using IC LM317