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Simple LM317 Solar Charger Circuit with Auto Cut off

LM317 solar charger circuit works like smart nanny for a battery.

It takes sunlight and charge battery but stop at right time.

Inside it have one smart chip called LM317 which control charging and gives battery only needed power which is not too much.

Best thing is it also have safety part inside like when battery is full it cut off the charging by itself so the battery is not overcharge or damage.

One should just sit back, relax and enjoy solar power for its own use.

Circuit Working:

Parts List:

CategoryComponentQuantity
Resistors (All resistors are 1/4 watt unless specified)180Ω1
1k1
10Ω 1W1
Preset 1k1
SemiconductorsIC LM3171
Transistor BC5471
Zener diode (as shown in diagram)1
Diodes 1N40072
Solar Panel (as shown in diagram)1
Battery 6V to 24V1

This circuit makes solar charger to charge Lead Acid or Ni-Cd battery using sun power.

It uses solar energy smartly to charge 6V, 12V or 24V battery which are good for many things.

Charger have voltage and current control which also protect from too much voltage.

It uses solar panel for 6V, 12V or 24V and one adjustable chip called LM317.

Charging current go through diode D1 into LM317 chip.

We can change output voltage and current by adjusting adjust pin of LM317.

One variable resistor VR is put between adjust pin and ground that makes output around 9V to charge battery.

Resistor R3 stop too much current and diode D2 stop battery from losing power backward.

One transistor T1 and Zener diode work together to stop charging when battery is full.

Normally T1 stay OFF so battery keep getting charge.

But when battery voltage go more than Zener diode value then Zener start working and send current to T1.

Then T1 turns ON and connect LM317 output to ground and so the charging stops.

Formula:

Below is simple diagram and formula for LM317 solar charger with auto cut off.

LM317 Voltage Setup:

LM317 work as voltage controller when setup like this.

Output voltage (Vout) can be found by this formula:

Vout = Vref × (1 + R2 / R1) + Iadj × R2

where:

Note:

With this simple diagram and formula one can start building its own LM317 solar charger with auto cut off which is based on what battery or setup is needed.

One just need to change the values as per its use.

How to Build:

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

Put LM317 on Breadboard:

Add Resistor Setup:

Add Transistor and Zener Diode:

Add the Diodes:

Connect the Grounds:

Test the Circuit:

Finish the Circuit:

Note:

Conclusion:

Simple LM317 Solar Charger Circuit with Auto Cut off is smart and easy way to charge Lead Acid or Ni-Cd batteries using sunlight.

It use LM317 chip to control voltage and current and also stop charging when battery is full so there wont be any overcharge.

With right parts and setup this circuit is cheap and good for environment.

One can use it in many solar charging projects.

References:

Project Report on Solar Charger Circuit using IC LM317

Solar Based Adjustable Voltage Regulator Using IC LM317

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