Introduction: Solar Battery Charging

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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!

Picture of 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!

Picture of 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

Picture of 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


SaswatSamal (author)2017-04-04

Very simple and nice too.....

AntonT27 (author)2017-03-12

Good article!

Ethan1976 (author)2017-01-22

We can recondition batteries at home and charge from solar. It is free energy for home devices

JamesS691 (author)2017-01-03

Can I use this method to keep a battery fully charged, on a device that consumes very little power, indefinitely?

MariaM252 (author)2016-09-25

Hi, I-m still learning about this stuff but I was wondering if I can use a 5v or 6V solar panel to charge 4AA batteries and have the batteries connected to an arduino with servo? Would the batteries charge and allow the arduino to work afterwards without sunlight or would this be useless? Would this set up be actually possible and something that can work?

keyurid (author)2016-08-28

Can we use a 9 volt rechargeable instead of 1.2Volt.

TrischaS2 (author)keyurid2016-08-30

yes, but you need to manage more than 9V from the solar panels.

Felix A.V (author)2016-07-15

Hi, ygrwat tutorial but the link to ebay is dead

Heyup (author)2016-05-21

Great tutorial thank you :)

millerman4487 made it! (author)2016-05-13

Put it in an Altoids tin for travel!

gdenyes made it! (author)2016-02-27

found a use for some old cell phone batteries. iot next step.

CorneliusC1 (author)2015-09-22

Hi, I have a system producing continuous direct current voltage at 0.5 V. Can I charge a battery using your system setup?

Max Cordell7 (author)CorneliusC12016-01-07

yes but, you need to check the sources current (Ma) make sure its under the battery's Mah then do this equation (battery Mah/sources Ma) to get the hours needed to charge.

MaheshR2 (author)2015-08-19

i charged a li-ion battery but the problem is that it is charging for a while and then stop charging..then again starts charging...this happened all over the time and my battery discharged.

p mishra (author)2015-05-01

awsome thanks

wormoil (author)2015-04-22

The moment I read that you wrote that modern LEDs don't need a series resistor... That's a preposterous thing to say and it's blatantly wrong.

paul.mendes.9 (author)2015-02-22

Why is the positive lead of the solar panel connected through the diode to the positive lead of the battery? This type of design will lower the potential energy rather than increase.

lfehrmann (author)2015-02-03

Hi there. great instuctable I already learned alot! now Im a girl haha but love to mess with junk. i set up the i sides of an old car charger input(12/24v) output 5v. I soldered a usb female to use for cellphone charge. I then put 10x1.2vAA in series to get the charger alive (10×1.2=12v) and It works! now my question is...i want to use it with solar for long bikerides. that is connect solarpanel to get juice for gps, phone, music ALL DAY riding. So can I charge ALL 10 in one go? they are now soldered in series. I get that the VOLTAGE should be around the packs size (12v) BUT WHAT ABOUT THE AMP?? My batteries are 380mah/a piece so in total (in series) 3800 what should i do? a 10th of 380mah not to overcharge or 1/10th of 3800mah?! or should i put individual wires from each battery to the panel (like a funnel) to make power go directely to each battery. sorry if i sound stupid but i cant work out HOW to do it-or if it is even possible to charge 10 AA's in series. thanks ANY HELP IS APPRECIATED!! Regards Lisbeth

akashsood4 (author)2015-01-15

what will be total cost...can anyone tel me?

yusuf.ali.520900 (author)2014-09-05

sir i have 3 watt ,12 v solar panel , i want to make recharble light through this panel, please help me to decide the value of light and battery

yusuf.ali.520900 (author)2014-09-05

sir i have 3 watt ,12 v solar panel , i want to make recharble light through this panel, please help me to decide the value of light and battery

KosherAnt (author)2014-08-16

can you do or share a link to one with a battery charger indicator and two USB ports as well

jimmysymo (author)2014-06-25

I have been using Solar panel 3.5 volt 400mA to recharge 2 ,1.5volt batteries and run up to 3 leds in my instuctable (Bronze steampunk solar light) I used an old solar garden light (broken) and used the circuit inside instead of a diode.Now I bought 5 new diodes and didn't know where to put it .today I found your (instuct"

and was very impressed with your explaining and now understand much more.

(SEE even at the age of 70+one can learn more .thanks Zvi..(JIMMY)

Keohohina (author)2011-08-22

Thanks this has really helped, Im trying tho get a pair of solar panels which are the same size as yours to power a water pump and charge a battery at the same time. Any suggestions

DerDok (author)Keohohina2014-06-17


Keohohina, did you ever get a answer to your post?

I'm trying to build one
that powers a fan for a dehydrator and also charges the Ni-cad batteries
for it and I'm running into snags. I'd like it all to be real simple, something I can build cheap, maybe with the stuff in my junk pile, but also have overcharge protection and an indecator that its charged. Looked all over the internet, cant seem to find what I want. How did you fare?

sjs2 (author)2014-05-06


i want to make solar charger to charge two batteries simultaneously of the spec

: 14.8V

Capacity : 5400

how many solar cells would be required , the circuitry and the weight of the total set including the solar pannels


miguipda (author)2014-04-09


some basic questions :

1) how to calculate the resister and diode value in regard of the Watts (solar panel). It means when we buy a 10W or a 30W or 60W how could we know (calculate) the best resister and diode to also buy ?

2) how to calculate the good battery to buy following the panel we choosed ? By example if we buy 4 panels of 3 watts that we will put in serie (or in parallel) how could we be sure to buy the best battery ?

Sincerely thanks ;-)

Pizzaenfeu (author)2014-04-08

Could I have another link to buy a little kit as shown? Or better that's not too expensive? The shop linked up is deleted :/

chuckiechan (author)2012-12-27

I'm using three dollar store yard light panels and I was wondering if a Zener diode would work. I have one in my junk box. 20V, Pd 1W. Will this fly?

I'm building an AA and AAA battery charger.

KBS Visual Media (author)2012-06-04

How can i use 4V 100ma Solar panel in the above manner?

jemor143 (author)2011-08-16

Can the 1N5817 diode be use with a 6v solar panel (130mah) to charge 4 AA?

Goodhart (author)jemor1432012-02-18

According to this Data Sheet, it appears to be a viable, if not over-kill type use. Is there any specific reason for using a Schottky Barrier Rectifier diode?

krishnan111 (author)2012-02-17

we can charge all types of battery?? ni-cd ,ni-pb or li-on batterirs??

Goodhart (author)krishnan1112012-02-18

No, if the battery doesn't have "rechargeable" on the outside (excluding the OLD style carbon rod batteries), then they are not rechargeable and will leak or explode of put in a charger for any length of time.

Callum Snowden (author)2011-10-15

An improvement: add a LED with no resistor in series with the positive line on the solar panel to the battery holder. It will serve as a current limiter and a basic display as to how the battery is charging
eg. Brightly lit = charging battery a lot
Not so bright = charging more gently
dim = trickle charge

Just my ten cents :)

TechKid67 (author)2011-08-04

Hi, I am new to solar energy and am trying to create an emergency power light kit. In my prototype I want a solar panel to charge somewhere around 10 LEDs. First off: Is this possible if they are aligned in parallel? Second: Is it possible to over charge the batteries and if so (which would probably have a horrific outcome) how can I prevent that? Third: How might I go about getting the solar panel to charge a large re-chargeable battery which then charges the smaller batteries. I want to do this so the suitcase doesn't need to be left in the sun in order to charge the batteries. If you can't help me with any of this its alright but thank you for any information you can provide. If some of this didn't make sense please send me an e-mail and I'll try and make it more understandable

kylengineer (author)2011-03-01

i found this very helpful.thanks but i ddnt gt to see the complete circuit with all the components listed from the start,i only saw piece by piece.i would like to see the whole complete circuit.

lionheartone (author)2010-11-19

I am making solar panel jacket. In order to charge phones and i-phones etc
I need some help with circuit. do not know what cicuit to use.

Please help

rcisneros (author)2010-09-01

Question. What happens if the solar cells aren't the same? Or one solar cell goes into shade before the other? So you could end up with a cell pumping out let's say 2v @ 20mA and the other 5v @ 100mA. Would they just add up to a 120mA output ? Wouldn't the flow change direction and head into the 2v 20mA cell?

rcisneros (author)2010-09-01

Question. What happens if the solar cells aren't the same? Or one solar cell goes into shade before the other? So you could end up with a cell pumping out let's say 1v @ 20mA and the other 3v @ 100mA. Would they still just add up to a 4v output ? or You could have a cell pumping out let's say 1v @ 100mA and the other 3v @ 20mA. Would they still just add up to a 4v output?

mdelzo (author)2010-06-24

what happens if i get a solar panel of 4V and I have 4 AA batteries in series. would it charge?or go the opposite way? tks :)

ebendersun (author)mdelzo2010-08-31

No, you need a higher voltage panel to charge 4 AA's in series. Here at we recommend at least 6V to charge 4 batteries.

rtyu (author)2010-06-03

thank you
pure energy

popa27272 (author)2010-05-08

i was playing around with my solar powered radio once and noticed that i got less static and the battery charged better when i focused a magnifying lens over it to the point where the solar panel appears at its largest,

just a simple way to increase efficiency of the panel

kroq-gar78 (author)2010-05-03

what is the voltage & current required for the solar cell?

mrziggy5000 (author)2008-07-03

Does any one know how many battries i could charge with a solar panel 1.5V at 500mA

If you are trying to charge a 1.25 volt battery (which is the typical voltage of a rechargeable battery in size AAA, AA, C, or D), then you can charge ONE battery with a solar panel that has 1.5V at 500mA. Be very careful when you charge your battery because 500mA is 5 amps, and that is a lot of amperage for a 1.25 volt battery. You are in serious danger of overcharging and making your battery leak or explode. Some of the fast chargers in the stores charge at a very fast rate (800mA), but if you decide to charge your battery using the 500mA straight from your solar panel you will have to monitor your battery very carefully and check it at least each hour to make sure it isn't over charging.If you want to make it slower and easier, you will need to add a resistor to take the amperage down to a decent level of about 100-200mA. There are websites you can use to calculate what resistor you need. Try googling "ohms law calculator" or "resistance calculator." Good luck!

Easymac79 (author)ShmemilyWoodey2009-02-12

500 milliamps is point 5 (.5) amps. one amp is 1000 milliamps. just like 1000 mililiters is one liter. 500 mA is still a lot, and may overheat the battery, but it is not as dangerous as you put in your comment. just dont stick it to your tounge, 60 miliamps is enough to kill you (stop your heart) but i have been electricuted with 15 amp ac line like 3 times, and i cant even count how many more than 60 miliamp dc lines! and obvously im alive, so i think the point of death is more like 20 amps.

ggarnier (author)Easymac792010-04-25

Can you reconcile "60 miliamps is enough to kill you" with "i think the point of death is more like 20 amps"?

Your statement is partially incorrect. 500mA is not 5 amps, it is 1/2 amp. mA stands for milliamps. Milli stands for thousand (even though you would expect it to stand for million). 5,000mA is 5 amps. I know nothing else about charging batteries, but I hope this helps! :) I need to find a way to reliably and safely charge a 7.2volt 40mAh (yes, forty, not four hundred, it's a small pack) Ni-MH battery pack without supervision. Any suggestions? DC

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