Introduction: Solar Battery Charging

This instructable will show you how to make your own solar battery charger from very simple components. It is taken from my documentation provided with a kit I supply - you should easily be able to source the same components yourself of course.

If you have any comments on how to improve the documentation then please do not hesitate to say :)

Step 1: The Components Needed

The items shown in the image are contained in your kit. This page explains their uses. Your kit may have a smaller/larger copper stripboard than this and may contain extra wire - I try to beef up the kit as time goes on.

The Copper Stripboard contains rows of copper tracks. Each track is electrically separate from its neighbour. It contains holes for your components. The boards I supply are larger than needed, this will allow you to expand the system at some future date.

The Batter Holder ... errrr holds your batteries.... and comes with two pins, one for the positive and one for the negative ends, they will be soldered into the stripboard.

100 Ohm resister - at one point this was needful in the kit as the LED couldn't cope with some of the voltages in the experiments - however the new LEDs do and the resistor is simply in there because it is advertised as such! Maybe you will have need of it when you expand the system.

LED - this is a high intensity light emitting diode. 3.2-3.6V forward voltage, with 10000mcd at 20ma. A LED must be placed in the circuit the correct way around. The longer leg should receive current from the positive terminal/direction.

1N5817 DIODE - this diode allows current to flow in only one direction - this prevents battery power discharging through the solar panel at night. It drops about 0.2V from the system. This blocking diode also needs placing in the circuit in the correct orientation. The diode has a circular band across its barrel at one end of the diode. This should be closest to the negative/ground.

Wires - Usually I include at least 4 wires - a black and red wire for the solar panel, a brown wire as a jumper and another wire for use in unsoldered testing.

Solar Panel - This image shows the back of the solar panel. On your solar panel in the centre of the left side and the right side you will see a small panel of smooth metal - this is the negative/positive terminals. I have marked the positive side by adding black dots on that side. This solar panel will output a max of 3V at 150ma.

Warning - I suggest you read the whole document before making any experiments - information is contained throughout the document which will improve your understanding of charging batteries using solar power.

HINT - you should probably purchase a multimeter and learn how to use it - this will tell you important information on typical voltages and currents you solar panel will produce in varying weather situations.


It is quite possible to use this kit without having to do any soldering at all - however at some point you will need to so I include both soldered and non soldered options. is a good site explaining soldering.

Step 2: The Solar Panel - Attaching Wires

Attaching the black and red wires to the solar panel

To attach the wire one can use the soldered or the non-soldered method. Soldered is the best way to go and I show you pictures of both - if you plan on using more panels or using the single panel a lot you will find it best to mount the panel onto a piece of sheet wood or plastic. This will keep the wire in place and prevent strain on the contacts + wires.

You can see an example of the solderless method.... Yes that is cellotape! The red squares indicate where the contacts are. The wire ends were stripped and then flattened onto the contacts and firmly taped in place. I don't suggest using glue! - you wont get the wire staying in touch with the contacts as the glue gets in the way. Allow some tape to move round to the solar side to ensure a firm placement.

Also shown is the soldered method. Not the most fantastic job in the world but it is held securely. Always make sure the contact points are clean and free from grease.

Step 3: Main Experiment

Place a full charged 1.2V rechargeable Nimh battery into the battery holder - I assume you know the right way round to insert it. The 1.2V battery on its own will not be enough to light the LED. The 2-3V solar panel will also have a lot of trouble lighting the LED by itself. We can attempt to use the voltage of the battery PLUS the voltage of the solar panel to operate the LED. Below is the solderless version.

Connect the RED POSITIVE terminal of the solar panel to the NEGATIVE leg of the battery holder. Use the extra wire supplied to connect the POSITIVE end of the battery holder to the longer of the two legs of the LED. The longer leg of an LED is always connected to the positive side of the circuit. Then connect the NEGATIVE wire of the solar panel to the other LED leg. If the battery is fully charged and you have a sunny day the LED should light up. You can even power the solar panel from a powerful torch or lamp by shining it onto the panel. Try experimenting by attempting to light the LED with the battery alone, or with the solar panel alone.

Step 4: Charging Your Battery - Part 1A

And now we come to making your own battery charger. Below is the circuit diagram for it.

The solar cells positive terminal is connected through the diode to the positive terminal of the 1.2V battery. If the voltage of the solar cell drops below 1.4 volts then with the 0.2V the blocking diode takes there wont be enough potential to charge the 1.2V battery. The purpose of the diode is to disallow current dissipating out from the battery to the solar cell when this low voltage situation occurs in the solar cell.

Step 5: Charging Your Battery - Part 1B

The next photo shows the front of the completed and soldered circuit.

The red lines at the bottom show how the copper tracks are aligned on the other side of the board. The blue lines show how the circuit completes through its electrical common points ( i.e. the tracks ). See how the small silver band at the top of the diode is toward the positive terminal of the battery. It allows flow towards the battery but not from it.

It is of course possible to do away with the brown wire and connect the black/negative wire the same track as the negative end of the battery. We simply wanted to show a more 'closed' circuit form.

Step 6: Charging Your Battery - Part 1C

From below you can see the soldered connections and how they run along the copper tracks. I have added in the brown wire as a brown line and the diode as a blue line, I have also added in the positive and negative makers for the battery. Remember the position is flipped from the previous photo.


The maximum output of the solar cell is 150ma. This is with the best conditions. A high capacity rechargeable Nimh can hold 2000mAH. This means that it would take ( 2000/150 ) hrs to fully charge it. This is about 13hrs!

When choosing solar cell arrangements one needs to work out

a) How many batteries do you want to charge at once
b) How fast do you want them to charge.

By adding extra solar panels one can charge more batteries, charge batteries faster or even both at the same time.

So how does this work?

Step 8: I Want More Voltage!

In order to double the voltage you need to join two solar panels in series. i.e. you need to connect the negative terminal of one solar panel to a positive terminal of the other solar panel. This will then leave you with a positive terminal from one panel and a negative terminal from the other to connect your wires to. In this case you would then have a solar panel rated at a maximum of 6V at 150ma ( the maximum voltage of a single panel is 3V ). More voltage would allow you to charge more batteries at one time - just remember that although 3V is the maximum rating of the solar panel you need to get an idea of the typical output for your climate. The batteries would also need to be connected in series ( negative to positive like in most multi-battery devices ). The circuit diagram shows below the solar cells in series and their accumulative voltage

Step 9: I Want More Current!

More current would allow you to charge your batteries faster. To double the current output you need to connect the solar panels in parallel. Connect the positive terminal of one panel to the positive terminal of the other panel and also connect the negative of one to the negative of the other. This will give you a max rating of 3V at 300ma. The circuit diagram below shows the solar cells connected in parallel. You can see that the voltage is the same at 3V but now the current will be doubled.

Step 10: Gotchas

Just a few gotchas to help you avoid any errors or misconceptions.

1) Get a multimeter and get a good feel for how your solar panel operates in various weather conditions and at various times of the day. Maximum ratings are all well and good but we don't all live in sunny Florida.

2) Be careful about how much current you pass through your battery. Most modern batteries can be charged at quite a high current. For example you could charge a 2000mAH battery with a 500mA current for just over 4hrs and it would be fully charged - keep on charging it beyond that 4hrs and you could seriously damage the battery ( or even cause an explosion). Nimh batteries have a protective mechanism when they get overcharged and attempt to dissipate the excess current as heat. However they can usually only managed to discharge one tenth of their total current as heat. What this means in practical terms is that if you charge a 2000mAH battery with 200mA then it will survive without a problem if you overcharge it for a while. However if you are charging it with a 500mA current and then overcharge it things get more serious.

I will attempt to expand this tutorial further - if you have any suggestions, additions, corrections then please contact me at

To purchase this kit or any extra solar panels please go to