DIY Solar USB Charger - Altoids




About: I used to teach middle school science, but now I run my own online educational science website. I spend my days designing new projects for students and Makers to put together.

I've been reading a bunch of blogs this fine Earth Day morning and have noticed that most of them are posting little write ups about green solar powered USB gadget chargers. They're all quite nice, but also quite expensive. I don't think I've seen any for less than $60, and I've not seen one that really suits my style.

Instructables has quite a few guides on how to make Solar USB Chargers, including the very well done guide on how to combine a Lady Ada Minty Boost circuit with a solar + lithium ion battery. Great, but a bit expensive to make and not a very simple project for the weekend DIY person.

Well luckily for us I know how to make one for under $20 that is better in nearly every way and also completely fits into an Altoids Tin. Covert style.

*** Update: I've since retired this kit. It's not held up over time very well. I've done an updated version called Solar USB Kit 2.0 and a more rugged version called Lithium Heavy Duty 2.0. If you're looking for something pre made, especially for camping or emergencies, you should try out one of our Folding USB Solar Cells. They're inexpensive and much much more powerful than what you'll find here.

Step 1: What You Need

USB Charging Circuit
Solar Panel 4V or greater
AA Battery Holder
AA Rechargeable Batteries
1N914 Diode
Altoid Tin (or whatever)

Soldering Iron
Tin Snips
Melt Glue Gun and Glue

Cost is less than $30. I can make one for under $10 when I buy parts in bulk. Ihave a kit available at my website which has everything you need to make this project. Also, if you're lazy, I do sell made versions in a variety of tin styles.

Step 2: DC to USB Converter

The central brain of our project is a DC to USB converter circuit. This takes our AA power and changes it into the 5Vs we need for charging USB. There are several ways of doing this.

1) You can make one yourself using Lady Ada's Minty Boost kit. It's $20 and requires soldering. It also charges almost every gadget under the sun, including new Apple Products.

2) You can buy a premade circuit off ebay, or even off my website They cost around $10 and work with most everything. Kindles, iPhones, iPods, GPS, Android Phones. They're great.

3) You can rip one out of a cheap USB charger. eBay and or Amazon are great places to look. Some of them don't work with Apple stuff, so be careful or buy several.

Whatever you do, don't try and make a 6V or 9V circuit and then use a voltage limiter to take it back down to 5V. That's sloppy and inefficient. You can do it, and it works, but there are far better options.

Step 3: Choose Some Batteries

What I really find annoying is that on all the commercial solar USB chargers I see their internal battery is only 1000 ma. That isn't a lot. A rechargeable AA battery has between 2000 - 3000 ma of current in it. Once again, we can do better.

We need to use rechargeable batteries for this project. I prefer NiMh AAs over everything else because they're easy to find, cheap, and reliable. You probably even have a few at home. Since we're using two AAs in this project our charger will have 2000 - 3000 ma of current. You could even have two sets of AAs in parallel and boost that capacity to 4000 - 6000 ma.

An added bonus from rechargeable AAs is that you can take them out of the Solar Charger, charge them up or replace them, and be on your way.

If you're making this project into a very small container you can use a smaller NiMh battery pack. You can find these at places like American Science and Surplus as well as many places on the web.

Step 4: Choose Your Solar

If we use two rechargeable AAs that put out a total of 2.4Vs we're going to need a solar panel that is at least 3 - 4Vs just to meet basic levels of charging. The higher the voltage of our solar cell (or cells) the less light we need to charge up our batteries.

Now we're also trying to fit this into an Altoids Tin, so we're limited in space. I have found some great 4V solar cells that perfectly fit into Altoids Tins. They're the same ones I use with my Solar AA Altoids Charger.

Sure, a bigger and better solar cell would give us added power, but it wouldn't fit into our tin. (Something that has annoyed me with nearly every Altoids Solar Guide out there.)

You could also use a combination of several smaller cells to get your four volts. For example, 2V cells are very cheap and small on ebay. You could easily connect two of those in a series to get your 4Vs.

Just remember that when charging NiMh batteries we don't want to throw more than 10% of their capacity at them at any one time. For instance if your battery has a capacity of 2000 ma we can only use a solar cell that puts out 200 ma or less of current. This isn't usually a problem unless you're using a massive solar cell or a big combination of cells. None the less, keep this in mind.

Step 5: Wire Up the Solar

First, we're going to wire up our solar panel.

I like to connect my 1N914 diode directly to the Positive solder tab on the solar panel. When soldering make sure the black bar on the 1N914 diode is point away from the solar cell. The black bar is the Negative side and prevents power backflow. If we put it in wrong we're going to prevent power from flowing into our circuit!

Solder the diode's Positive side (non black diode) to the Positive Solder Point on the solar cell. Solder a wire to the other end of the diode. (In the photo it's the red wire.)

Solder a wire to the Negative solder point on the solar cell. (In the picture it's the black wire.)

Then tape it up for protection.

Step 6: Connect the Battery Pack

Now we connect the solar wires to the battery pack wires.

Just connect all the positive wires (red) with all the negative wires (black).


Easy as pie. Sweet sweet solar pie.

Step 7: Prepare the Charger

So the charging circuit I use also has a couple of LEDs on it. These in no way affect the USB charging and in fact are annoying. I remove them because they're useless and a waste of power. This is why I'm cutting them off in the pictures below.

You should NOT start cutting things away unless you know what you're doing. Seriously Ben, I know you're reading this. Stop cutting now. This is how you lost a finger.

Anyways, if you've bought a cheap charger to use you have to take it out of it's plastic, and disconnect any random wires or battery packs.

What you should be mindful of is where power connects to your board. Mine has a nice little + and - sign to guide me. You need figure this out on your own depending on your situation.

Lastly, and most importantly, you should watch out for any switches. For instance mine has a little switch on the side to go from "Light" to "Off" to "USB." I just keep mine set to "USB" as we don't lose any power unless something is plugged in.

Step 8: Solder the Charger

Now all you have to do is solder that bundle of positive, in my project red, wires to the positive point on the board. Then all the negative, in this project black, wires to the negative point on the board.

You're done with the circuit. You can test it now.

Usually I can charge a gadget just from sun. If it's not sunny the circuit should charge via batteries.

Step 9: Cut Your Tin

I use Altoids Tins because they're the perfect size for this project. Plus very cute. I also enjoy mints.

Just use some tin snips to cut a hole big enough for the USB port.

If you want to be fancy you can also use a Dremel and make a nice rectangle hole in the side of the tin. I'm lazy, so I just cut it away.

Step 10: Glue Everything In

To be on the safe side I put down some electrical tape below my bare circuit board. Just to play it safe.

Now all you need to do is glue in your battery pack (though I use foam tape for that) and glue down your USB circuit.

Notice I use ample amounts of hot (melt) glue. Yummy.

Done and done.

Step 11: Enjoy

Now you're done. Enjoy the fact that you're being very green and clean.

Also, before someone chimes in... yes I do know batteries are not entirely green. If you want to be super green you should use some super capacitors for this project. They last forever, are super green, but are also quite expensive.

What I like about this project is that it's simple and handy. It makes for a nice gift.

If you need any parts you can always get them from my website, All the money I make goes to doggy treats and more projects.

Thanks for reading! *** Update: I've since retired this kit. It's not held up over time very well. I've done an updated version called Solar USB Kit 2.0 and a more rugged version called Lithium Heavy Duty 2.0. If you're looking for something pre made, especially for camping or emergencies, you should try out one of our Folding USB Solar Cells. They're inexpensive and much much more powerful than what you'll find here.

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390 Discussions


1 year ago

I am in middle school and thinking about doing this for my science fair. Any advice that i might need for this?

1 reply

Reply 1 year ago

Don't use this kit for a Science Fair Project. You're not collecting data or getting any meaningful information from it. You can't ask a good question. (As a former middle school science teacher, thats my advice.)


1 year ago

Okay, so I'm trying to make it more efficient from what I have gathered you need to have the charge port at 5V and at 1 amp which is similar to chargers. What I am not understanding is how do the batteries play into the circuit design I am thinking of using two AA at 2600 MAH which it says it is at 1.2 V does this mean we have 5.2 Amps x 1.2V so the power of 6.24 W. So then we have this power to play around to get it to 5V and 1 amp.


No, you'd need a charge controller in the mix. At the start of the write up I link to my Lithium Heavy Duty 2.0 project, which uses 18650 lithium battery cells. It's not too much different from this write up.


1 year ago

I have a max 5,5v solar cell connected to step up converter

converter says output 1,2max constant but what i get is 700ma so my
android cannot charge. and i have it under the Greek summer sun where
the temperature get to 40 Celcium

Any advise?


1 year ago

Very good project! I used the pdf guide from the above link "Solar USB Kit 2.0". I have a question....I used 2xAA NiMh batterries 2300 mAh each (connected in serie with battery holder) pre-charged and when i tried to charge my phone stopped after 20% of charging, and the tin was very very hot. Did i make anything wrong??


3 years ago

Hey so I've made my first solar usb charger, but I'm having strange issues. I'm starting to wonder whether these usb circuit boards are crap, because, when I check for continuity on the board, touches the leads of my multimeter to the positive and negative all I get is an OL and silence (yes I'm in the right mode on the MM). Whenever I try to charge my phone, my battery drains if I'm charging off the battery. Or, if I'm trying to only use the solar panel, I get this weird pulsing of a few volts. It's really weird. I'm only a novice, but I'm very interested in troubleshooting this problem. I think I'd learn a lot if anyone had ideas on what was going on. I'm about to stick some non-rechargeable batteries in and get some reading so I at least have a control here. Anyway, please some advice or help would be greatly appreciated. I want to solve this puzzle!!! Thanks.

2 replies

Reply 2 years ago

so the problem might be how many batteries you're using you need 4aa batteries to give you enough volts to fully charge your phone (1 aa battery gives 1.5 volts and you need 5 volts to charge your phone) if you have say 2 then your phone will try to charge the batteries or if the phone started out dead or close to it it would just not get much charge at all because they would equal out in volts. Or it might be that your panel does not put out five volts so one of the same problems will happen


Reply 2 years ago

Thanks CalebS68! I made some progress and realized that the solar panels are really sensitive and output 6v in direct direct, emphasis on the direct, sunlight, and the usb circuit converts down to 5v. But you're right, I only have 2aa batteries in my charger, which would explain why it doesn't output the right amount when the solar panel isn't used. Strange that the tutorial mentioned that the ma are the only thing that matters in charging via batteries. I bought 2700 mAh batteries... I will look into this further! Thank you for the heads up!! Much appreciated!


2 years ago

how are you creatong more energy through the controller

X Caliber

2 years ago

Do you have to use that specific diode? or could you use a different diode?


2 years ago

Im looking to create this project but i was wondering if i could wire in the solar panel to a portable charging bank?


2 years ago

Would you be able to adapt this concept for a bigger battery to get a longer charge? Also for the battery listed would you be able to over charge the batteries or can you just let this sit out all day?


2 years ago

If i don't want batteries I need my system, just a direct charge. Would it harm anything to leave out the battery pack and wire this directly to the USB charge controller?


2 years ago

i have IN4007 bmc will it work fine


3 years ago

Is there a way of adding a led power indicator into the the circuit to monitor how full the rechargeables are?