How to build a circuit to charge a 12v battery with a solar panel?

How to build a circuit to charge a 12v battery with a solar panel

In recent times, more people are using solar panels to generate electricity. Also, you can store that electricity in batteries for after use. People mostly use 12v batteries to store solar power energy.

Before storing solar power in a 12v battery, we need to figure out how to properly make this circuit. Charging a 12v battery using a solar panel is a simple task.

To make this circuit we need,

  • 12v solar panel
  • Charge controller
  • wires

First, we need to select a suitable 12v solar panel and charge controller. After you connect the solar panel to the battery by wire. you should connect the charge controller between the solar panel and battery. When you connect these items by wires make sure to connect the positive terminal to the positive terminal negative terminal to the negative terminal.

Why do you need a charge controller?

A charge controller is a device that can protect the batteries from overcharging and continue the cycle of charging on/off.

Even if you use the best battery for your system. you still need a charge controller. Because normally a 12v solar panel generates a higher voltage around 14v to 20v. and higher voltage can harm your batteries. That’s why you need to attach a solar charge controller to your system.

Why do you need to use a 12v solar panel?

It depends on the voltage of the battery you use.

You are using a 12v battery, so you need a 12v solar panel. It should always be equal to the voltage of the battery you use. If the voltage on your solar panel is higher than the voltage on your battery, it will directly damage your battery. Also, if the voltage on your solar panel is less than the voltage of the battery, your battery will never charge.

So always choose a solar panel with a voltage that matches the voltage of your battery.

How to choose the most suitable WATT (W) value for your solar panel?

You can use solar panels with any WATT value.

The Watt value of the solar panel does not affect the system operation. It only affects the time required to fully charge the battery.

How does the Watt (W) value of the solar panel affect the charging time?

This depends on the voltage and the amperes of the battery you want to charge. To understand the above statement you should know a simple theory.

The theory is power or watt value equals the voltage multiplied by the ampere value.

So according to this theory, you can find out the power of the electricity that you would need to charge your battery. Then you have to check the Watt (W) value of your solar panel and then you can calculate the time it will require to fully charge the battery.


To fully charge a 12v 7Ah (amperes) battery you need an 84W power supply. we can find a commercially available solar panel with 2W,5W,10W,20W,50W,100W e.t.c.

if you use a 100W solar panel you can fully charge the battery in less than 1 hour as the solar panel gives 100 Watt per hour. But if you use a 50W solar panel it will take more than 1 hour (twice as 100W solar panel) As it gives 50W per hour.

What is the best battery for this circuit?

There are 3 popular batteries to use for your solar system. But you have to select the right one for your system. Because batteries are an integral part of your solar system and you have to spend a fair amount of money to buy them. Here is a quick review to select a suitable battery for your solar system.

  • Flooded Lead-Acid Batteries (FLA)
  • Sealed Lead-Acid Batteries
  • Lithium Batteries

Flooded Lead Acid Battery

The flooded lead-acid battery is the cheapest battery for the solar system. And it’s widely used for a solar off-grid system. A flooded lead-acid battery can be used for a long time and the cell inside the battery is full of acid and it should be checked at least once in three months.

This battery is cheap but if you find it difficult to check from time to time that, then your next option is the Sealed Lead-Acid battery.

Sealed Lead-Acid Battery

The sealed Lead-Acid battery does not need to check from time to time. These batteries are currently used for solar systems and have a lower lifespan than other batteries. This battery is relatively inexpensive and that’s why people mostly use this battery. If you need a cheap battery and can’t check your battery regularly, this battery is a good choice.

Lithium Battery

These batteries are the best as solar batteries. This is due to the lack of maintenance, large storage capacity, long battery life, and efficient use. It is also the most expensive battery. Currently, lithium batteries are used in mobile phones and laptops. The lithium battery is the best battery you can use for this solar system.

Can you use a couple of batteries as a 12v battery?

Yes, you can. But in this case, you have to make sure that the batteries you are using have the same voltage.

For example, you can use three 4v batteries or four 3v batteries instead of a 12v battery.

You can use other voltages too (2v,6v). but you have to make sure all the batteries have the same voltage as we mentioned before.

How do connect these batteries?

There are two main ways to connect batteries.

  1. Parallel
  2. Series

If we connect the batteries in a parallel way, it does not affect the final voltage. It only increases the ampere value. As our target is to get a higher voltage by combining lower voltage batteries, this way is not effective.

But if we connect batteries in series we get the sum of the voltages of all the batteries as output voltage. So this is an effective way to accomplish our target. So by simply connecting three 4v batteries in series, we can get 12v output voltage. We can use this combination of batteries instead of a 12v battery.

Why can not we use different voltage batteries?

If we combine different voltage batteries to get higher voltage it can damage both batteries. The reason for this is, always the higher voltage battery tries to keep the lower battery fully charge. If this happens continuously both batteries will be damaged before their expected lifetime. So it’s important to use batteries with the same voltage.

Can you use a couple of solar panels as a 12v solar panel?

Yes, we can.

When combining the solar panels you have to use solar panels with the same voltage. You can use any number of lower voltage solar panels to get a higher output voltage.

For example, you can use either three 4v solar panels or four 3v solar panels instead of a 12v solar panel.

How should we combine these solar panels?

Same as batteries, solar panels also can be connected in either parallel or series. But if we connected in parallel, the voltage remains the same. As we want to increase our voltage we should connect solar panels in series.

For example instead of 12v solar panels we can use three 4v solar panels combine in series.

Make sure to connect the positive terminal to the positive terminal and the negative terminal to the negative terminal.

Combining solar panels with different voltages to get a higher voltage can result in a loss of stability of the circuit. So the use of solar panels with the same voltage is very important.

Do you have to maintain the system?

Normally the solar panel system does not malfunction. But with time problems can arise in your battery, connecting wires, or terminal of the solar panel. The main problem associated with the terminals of the solar panel is corrosion.

With time, the battery will gradually lose its capacity. Also, the length of time we can power up any product using the battery will decrease. These problems are irreversible so the only solution is replacing the battery.


If you are charging a 12V battery using a solar panel. Try to use a 12v solar panel for that. Also, select the best battery that fits your budget and system. If you are using multiple panels to generate 12 volts, use solar panels with the same voltage. Also, if you use multiple batteries to make 12 volts, use batteries with the same voltage.

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