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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:

CategoryComponentQuantityNotes
Resistors180Ω11/4 watt
1k11/4 watt
10Ω 1W11 watt
Preset 1k11/4 watt
SemiconductorsIC LM3171
Transistor BC5471
Zener diode (as shown in diagram)1
Diodes1N40072
Other ComponentsSolar Panel (as shown in diagram)1
Battery 6V to 24V1

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 Vout is calculated using the following formula:

Vout​ = Vref​(1+R2 / R1​) + Iadj​ * R2

where:

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:

Add the Resistor Network:

Add the Transistor and Zener Diode:

Add the Diodes:

Connect the Negative Terminals:

Test the Circuit:

Finalize the Circuit:

Note:

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

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