Rechargable Battery Using a Solar Panel

This Instructible is a guide on recharging a lithium battery using a small solar panel. As a bonus I will be showing the battery connected to an Arduino to power an LED. I tried to keep the soldering in this project to a minimum, but some will be needed at certain points.

I decided to make this project to showcase how useful solar energy is here in Arizona. using solar power also helps prevent waste by encouraging the use of rechargeable batteries.

Small 5V Solar Panel: https://www.amazon.com/dp/B0FD7CYD72?ref=ppx_yo2ov_dt_b_fed_asin_title

Alligator Clips: https://a.co/d/07smkjbr

Female to Female Jumper Cables: https://a.co/d/0dFM5rBT

1N4004 Diodes: https://a.co/d/085TT9tA

Lithium Battery Charging Board: https://a.co/d/0iPwb3tW

Header Pins: https://a.co/d/0ixqgmiE

Li-ion Rechargeable Battery: Samsung 35E INR 18650 Li-ion Flat Top Battery | Battery Junction

Battery Holder: https://a.co/d/0bQZ5fns

DC-DC Boost Converter 0.9V-5V to 5V USB Module 5 Pack: https://a.co/d/06vynJ7I

Arduino Uno: https://store-usa.arduino.cc/collections/uno/products/arduino-uno-rev3

Soldering Kit: https://a.co/d/01h0EknE

The solar panel is what is charging the battery. According to this article, a 3.7V Li-Ion battery has an max charge voltage of 4.2V (±.5V). So I decided to use a 5V solar panel to charge the battery. But going beyond the recommended 4.2V could damage the battery in the long term and that's where the charging board comes in. These boards are used in many devices to ensure that batteries get the optimal voltage to charge it while keeping it from going too high and damaging the battery or causing a safety hazard.

I set a diode in between the solar panel and the charging board. The diode is there to make sure that the electrons are only flowing in one direction. If the battery is fully charged and is still being charged by the solar panel, the electrons could potentially push in the opposite direction of the circuit and damage the solar panel. The diode prevents this from happening. Just make sure that it is set up the same way as the diagram above so it actually flows in the right direction.

After connecting the circuit to the battery, the purpose of this guide is technically done. But as a bonus you can connect this circuit to a voltage booster (also known as a step-up converter) to increase the voltage output. I decided to plug my arduino to the voltage converter to show that the circuit is powerful enough light up an LED through the arduino.

I tried to make this circuit as simple to make as possible by using alligator clips and jumper cables instead of soldering everything. I would like to note that there are many ways to approach this, so it should still work fine if some of the parts you use are different from the ones used in this guide.

I clamped the positive wire of the solar panel to the diode. Make sure that the diode is set up to flow from the positive to the negative end in the circuit. If you need help with the diode, check out this article. I then connected both the positive and negatives wires on to female-to-female jumper cables to set up for the charging board.

Before we can put the charging board to into the circuit, we need to solder header pins to the board. This will make it very simple to connect the jumper cables to the charging board. If you are unfamiliar with soldering, check out this quick video to get an idea of the basics.

After soldering, you can connect the jumper cables to the board. Make sure you check which side is connected to the solar panel and which side is going to the battery. Yours might have different labeling, but my charging board has the labels OUT+ and OUT-. That side of the board should be connecting to the battery, while the opposite side (with the usb-c port) should be connecting to the jumper cables you set up earlier.

Now you have to connect the battery to the circuit. I used a battery holder that would be easy to clamp with alligator clips, but you can use a different method and it should work completly fine. Just make sure the positive and negative ends of the charging board are corresponding with the positive and negative ends of the battery.

After that, you now have a solar charged battery!

To test if your battery is charged, you should connect it to something to power it on. In my case, I decided to power my arduino. To do this, I needed to connect the battery to a boost converter (also known as a voltage booster or a step-up converter). The boost converter helps to efficiently raise the voltage in a circuit to help power higher voltage devices. This is perfect for this project because we don't want the initial voltage to be too great to damage the battery, but we also need it to be high enough to power the Arduino efficiently.

It was a similar process to set up as the charging board. Just solder the headers and clamp on the alligator clips. It was very convenient to have a USB port on the boost converter because I can directly plug my arduino into the circuit.

You can tell that the arduino is powered on by the small green light on the arduino itself, but I also decided to put a red LED on the bread board to show how bright it could light up.

I hope you found this guide helpful!