Make this Solar Battery Charger Circuit using IC 7812

Here we talk about a simple solar charger circuit. It takes power from a 20V, 1A solar panel and then charges a 12V battery. We are using a 7812 voltage regulator IC, three 1N4007 diodes, and a 2.2kΩ resistor to make sure the charging happens safely. Now let’s go step by step.

Circuit Diagram

Solar Panel Power

First our solar panel gives us 20V DC at 1A when the sun is bright. But a 12V battery cannot take direct 20V, so we need to regulate this voltage, otherwise the battery can get damaged.

Voltage Regulation with 7812

Now we put a 7812 voltage regulator IC in between. This IC normally gives 12V output. But wait, 12V is not enough for charging a 12V lead-acid battery, because a 12V battery actually needs around 14V to charge fully. So we need to tweak the 7812 output a little.

Voltage Boost using Diodes (1N4007 x 3)

Here we add three 1N4007 diodes in series with the ground pin of the 7812 IC. Why? Because each 1N4007 drops about 0.7V so three of them together drop around 2.1V. Now this tricks the 7812 IC into thinking its ground is at 2.1V higher, so instead of 12V it now gives 14.1V output. This is perfect for charging our 12V battery.

The 2.2kΩ Resistor

Then we connect a 2.2kΩ (2k2) 1/4-watt resistor from the output of 7812 to the battery. This is not for limiting charging current but to give proper biasing for the 3 diodes so that they conduct optimally and enable proper 7812 regulation

Battery Charging Process

Now our circuit is ready. When sunlight is there, then solar panel gives power, the 7812 regulates it to 14.1V and then this voltage charges the 12V battery. The diodes also act as a one-way valve stopping the battery from sending power back to the solar panel at night.

Some Things to Improve

Heat Problem: The 7812 IC gets hot so we should attach a heatsink, ok?

Better Efficiency: Instead of the 7812 we can use a buck converter (switching regulator) because it wastes less power.

Diode Drop Issue: If we use Schottky diodes (like 1N5822) instead of 1N4007, the voltage drop will be lower, making the circuit a little more efficient.

So basically this circuit is cheap, simple, and works fine... but if we want better efficiency, we can use better diodes and a buck converter.

Construction Tips – How We Build This

Ok, now we know how this circuit works but how do we build it properly? Let us go step by step and do it the right way.

1. Choosing the Right Heat Sink for 7812

First thing, 7812 gets hot, very hot if the solar panel gives full 20V at 1A. So we must fix a metal heat sink on its back. If the heat is too much, we can also add a small cooling fan powered from the battery itself. No heat sink = IC burns out fast.

2. Proper Diode Placement (1N4007 x 3)

Now the three 1N4007 diodes should be soldered in series properly. Wrong direction = no output voltage. The banded side (cathode) of the first diode goes to the ground of 7812 and the last diode’s unbanded side (anode) goes to the main ground (battery negative and solar panel negative). Solder them neatly, no loose joints or they might stop working after some time.

3. Wiring and Connections

Use thick wires (at least 18 AWG) from the solar panel to the circuit because thin wires will drop voltage and cause low charging.

Battery wires should be even thicker (14 AWG or 12 AWG) because charging current can be high.

Solder all joints properly. Bad solder joints = bad charging.

4. Resistor Connection (2.2kΩ, 1/4W)

The 2.2kΩ resistor is small so it does not heat up, but still it is better to keep it slightly away from the IC so it doesn’t pick up unnecessary heat.

5. Securing Components and Waterproofing

If using this outside then don’t leave the circuit open. Put everything inside a plastic or metal box with small air vents.

For outdoor use, seal the box edges with silicone or rubber seal so rainwater does not go inside.

The solar panel should be placed at an angle facing the sun to get maximum power.

6. Testing Before Connecting to Battery

Ok, before we connect the battery, let us test the circuit:

Use a multimeter to check the output voltage from the 7812. It should be around 14V to 14.2V.

If voltage is too low, then maybe the diodes are in the wrong direction or the solar panel is not getting enough sunlight.

If the voltage is correct then we can connect the battery and start charging.

So that is how we build this properly, ok? If we follow these tips then our solar charger will last long and work smoothly without problems!