How to make a homemade system to charge batteries with solar energy

How to make a homemade system to charge batteries with solar energy

Extending the life of batteries is a good alternative to consume them as little as possible and to contain the generation of waste which, in the case of batteries, is highly harmful. With the sun’s energy and a bit of patience, you can build your own solar system to recharge the batteries. We explain how to shape it in just nine steps.



If you’ve taken a look at the image, you’ll already have an idea of ​​what you’ll need to build your battery charger, but we break it down below:

  • Copper charger board in the size you prefer. If you choose it big, you can expand the system in the future.
  • Battery support. If they are not included in the bracket, you will need two bolts, one for the positive and one for the negative.
  • 100 ohm resistor.
  • LEDs with a voltage of 3.2-3.6 and a current of 1400 mA. It is a high intensity light which emits a diode and which you will need to install in the circuit.
  • 1N5817 diode to keep current flowing in one direction so the battery won’t drain overnight.
  • 4 wires, one black and one red for the solar panel; one brown as a bridge and one for soldering tests.
  • Solar panel. The one you see in the picture has an output power of 3v at 150mA.

You may also need a multimeter to get useful information about panel voltage and current in different weather conditions. You’ll also probably need to use a soldering iron to make the battery charger, so if you have one and know how to use it, it’ll be fine for this project.


Step 1: Connect the cables to the solar panel.

For the wiring of the panel, the most suitable formula will be welding, although other methods are also possible. If you are going to use the panel a lot or install more than one, it may be beneficial to mount it to a piece of wood or plastic. This way it will be easier to maintain the wiring and avoid tensions in the positives.

As you can see in the photos, adhesive tape was used to secure the cables. The red rectangles in the image indicate where the contacts are. Exactly there you will have to fix the end of the cables, previously stripped.

Make sure that everything is well glued and that the contacts are perfectly clean.

Step 2: Put the battery and connect the circuit.

Place a fully charged 1.2V NiMH rechargeable battery into the battery holder. This battery will not be able to light the LED on its own, so its voltage will be combined with that of the panel to power it.

Connect the positive red wire from the panel to the negative on the battery holder. Use an extra wire to connect the positive of the holder to the longer end of the LED. This is the part that should always be connected to the positive of a circuit.

If the battery has been charged and the day is sunny, the LED should light up.

Step 3: Charge the battery.

At this point, the production of your own battery charger begins, for which it will be useful to review the scheme. As you can see the positive of the solar cell is connected via the diode to the positive of the battery. If the panel voltage drops below 1.4 volts, there will be insufficient power to charge the battery. The reason the diode is used is precisely so that current does not flow from the battery to the panel when a voltage drop occurs.

Step 4: Charge the battery II.

The complete circuit is the one you see in this image. For your better understanding, the marked red lines at the bottom of the board show how the copper tracks are aligned with the other side of the board. On the other hand, the lines marked in blue illustrate how the circuit is completed. Thus, the small silver band at the end of the diode is positioned towards the positive terminal of the battery, allowing flow to the battery, but not from it.

Step 5: Charge the battery III.

In this image of the back of the board you can see how the connections have been soldered and how they pass through the copper traces. As you can see, the blue line corresponds to the diode, while the positive and negative of the battery should be placed as in the photo.

Step 6: Additional Charger Information.

Throughout this process, it is important that you consider how many batteries you want to be able to charge at once and at what speed. With the charger mounted as before, the time you will need to recharge your batteries will be approximately 13 hours. For this reason, it may be interesting to add more panels to the system and thus improve its performance.

Step 7: What if I want more tension?

To double the voltage, you just need another panel in series. To do this you will need to connect the negative of one panel to the positive of the other. This way you will achieve 6v at 150mA, under maximum performance conditions. Do not forget that it will also be necessary to connect the batteries in series, that is to say the negative with the positive.

Step 8: Add more current.

This way you can also recharge your batteries faster. To multiply the current by two it will be necessary to connect the panels in parallel. Thus, connect the positive of one with the positive of the other, and the negative with the negative. With this you will reach 3V at 300 mA, instead of 150, although the voltage is maintained.

Step 9: Final ideas.

To make sure you don’t make a mistake when building this system, it’s important that you use a multimeter. You will also need to be careful of the current entering the battery to avoid overcharging, damage and even an explosion. With these precautions and if you have followed the steps described, you can start enjoying your own battery charging system.

Original project on Instructables.

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