DIY Solar USB Charger - Altoids

Picture of DIY Solar USB Charger - Altoids
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.
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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.  I have 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 pleases 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 ineficient.  You can do it, and it works, but there are far better options.

Step 3: Choose Some Batteries

Picture of 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

Picture of 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 Atoids 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 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!

Then attach a long wires to both the diode and negative tab on your solar cell.

Then tape it up for protection.

Step 6: Connect The Battery Pack

Picture of 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 effect 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

Picture of 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

Picture of Cut Your Tin

I use Altoids Tins because they're the prefect 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

Picture of 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.

Quick question. I was able to salvage a DC to USB board from a car charger. I actually left the LED on the board for ease of checking if power was flowing or not. I can not seem to get it to light up unless my power source is 9v or greater. In your tutorial your using 2.4 volts of output to charge a device via batteries. I am running a 1watt 6volt panel and it wouldn't light it up either although I was only getting about 3.5 volts due to cloudy weather. Any thoughts?

Merahu27 days ago

The update above says that Joshua Zimmerman has retired this charger as unreliable. I have one, plus one without a USB port, produced by BrownDogGadgets, that I have been using to charge four AA batteries for my camera. Yesterday I picked up the tin with the USB port and the metal was hot at one end of the batteries, very hot. It was in the shade and cool surroundings, not in direct sun. I pulled one battery out and set it aside to cool so I could toss it in the garbage. Then I noticed (smell, not visual) acrid fumes. I was using ordinary rechargables, not lithium batteries. (Rayovac.) Since lithium batteries can burst into flames when exposed to high heat, I would be very cautious about using such products with lithium batteries. Given that mine developed a serious problem without lithium batteries, I will be cautious with any use. I am glad I was present when the problem was developing.

One possible contributing factor may be that I have regularly used this on the dash of my car. They have certainly had a chance to get overheated, and perhaps the wiring or components themselves are capable of melting under those conditions, though they were not in the sun at the time I picked them up and found the one hot. I am very pro solar and very pro do-it-yourself. There is some safety risk here, and I hope it will be further clarified in the future, and fixes presented for safe function in sometimes hot conditions.

Thank you to everyone who advances clean energy such as solar, and to those who improve safety as well.

kenkenken448 months ago
hi i had done everything ou said and even bought the equipment but my phone still cannot charge the red led light is on i am outside with batteries but it still wont work??

You're essentially charging two devices, the external backup battery and your phone, at the same time. This instructable explains what kind of charge controller and power is required to perform this task and give constant phone charge even under non-ideal conditions:

Could you fit a triple AA battery holder in here?

brburrous made it!2 months ago

Cool looking and easy to make, but not to effective.

jody344 months ago
Where did you get the USB charging circuit?
You can use a voltage regulator. I made a similar one (currently making the instructable). When charging a device via USB then the voltage will always be 5.0 volts. Check my page.
Hey there! This is an excellent looking project that I plan on completing soon! I do have one question: what is the best way to go about harvesting the usb charging circuit from a usb charger?

Thanks so much!
Rip that puppy open.

Find that that turns 2 or 3 AAs into 5V USB.

(Not a wall one. Bad idea.)
Can I use an AC to USB converter? I ripped apart a kindle charger cord; would this work?
Did you ever find out? I'm wondering the same thing, I have an MP4 charger cord
electro181 year ago
I bought a 5v solar panel and connected a diode to it....... and connected it to my phone. It was charging well so is there any need of the DC-USB converter?
Please forgive me, I am NOT trying to be a smart aleck....but to use only a solar panel would be like only eating bologna sandwiches. Your solar panel may not give 5V 100% of the time (e.g. cloudy day, shady area, etc). The IC on the DC-USB converter ensures you will always be pushing 5V. The other items help ensure the quality of the voltage is that of a prime rib. lol
Well, thanks ! but i am not able to find any sort of DC-USB converter ,so is there any way to make it ?
Could you show us how you connected it to your phone?
TheArtVark7 months ago
If I understand correctly, if I leave the batteries in and place it in the sun it will use BOTH the solar panel out and the batteries ate the same time if I want to charge anything, right? No need to take out the batteries? When the it's less sunny the batteries drain faster, when it's scorching the batteries drain slower?

Thanks for the instructions!
The temperature of the air doesn't matter as much as you might think. The panel will output more mA when it is 60 degrees and sunny...compared to 110 degrees and mostly cloudy. But yes, leave the batteries in.
Ah, thanks for your answer. No hassle charging then, just stick it out in the sun. With 'warm' I actually meant 'sunny', but good to know that temperature is not an issue either :-)
No problem...but as another user mentioned I would add a small circuit to prevent overcharging the batteries.
Schmidty1610 months ago
I was wondering if I could use another usb connector if so can I fond 1 at RadioShack if so what is it called and if I can where can I find one in stuff ling around my house
This has a "USB Type A" for charging electronic devices, you shouldn't need anything else because it's the industry standard. To use anything else would be over-complicating things or risking damage to your equipment. Your best bet is to buy the kit: and add a solar panel to it.
I don't have access to your store
xJValx9 months ago
is it somehow possible for the charger itself after it is complete, to pull juice out of the phone that its supposed to be charging?
nitewing76 xJValx7 months ago
There should be diodes in the device and on the USB-DC converter to prevent that from happening.
Snakera9 months ago
Do you know if this will charge the iphone 5?
The iPhone5 and iPad4 both require more wattage than their predecessors (that's why Apple changed the plug). I'm not exactly sure of the iPhone5 power requirements, but my iPad4 requires 12W of power (12W/5V=2.4A). Thus I cannot charge it in my vehicles, laptop/desktop computers (500mA max), etc. If the components of the USB-DC converter can handle it, then yes. But, you'd have to check the appropriate datasheets. I would send an e-mail to AdaFruit and ask her.
rsantos249 months ago
I have a 6 VSolar panel wired to 2 rechargeable batteries, and the battery wires and solar panel wires are soldered to the USB connector. The USB connector is lit up so there is some power going to it but the device is not charging.
One of the IC's could be bad or there could be a bad solder joint.
rweiss8 months ago
I am wondering, if we're using some internal batteries (ie. AA in your case), that are wired directly to the solar cell, are they at risk of overcharging if the device is left in the sun?
Thanks for the great tutorial.
nitewing76 rweiss7 months ago
Electronics should never be "left out" in the sun long enough to overcharge the batteries and you should be able to find a solar panel that will fit in the tin. However..."stuff" happens! So I do plan to incorporate a protection circuit in mine.
cnephew8 months ago
When you say "You can rip one out of a cheap USB charger" what exactly do you mean by that?
Some wall warts and car chargers have a USB connection on them. I assume that is what he's referring to. I'm going to build my own USB-DC converter using AdaFruits Instructable. It calls for a 22uH inductor and I did find a 20uH inductor in a Motorola RAZR charger.
jayc1607 months ago
I tried making with with two recharchable 9v batteries and im not making any headway does it only work with the AA's ? Or do I need to add something in the line to make it work ? im also going to use a plastic pelican case instead of an altoids can just seems a little more rugged.
Pelican cases are awesome! If you are using 9V batteries you need to add a LM7805 circuit or you risk frying your electronics. But you will be wasting a lot of power and therefore, money. To know more, read AdaFruit's Instructable:!---Small-battery-powered-USB-charger/step2/The-Process-Come-up-with-an-idea/
Fashiondez1 year ago
Hey, does anyone know what to do when you hook everything up, and it is working/shows that the Iphone is plugged in, but it doesn't charge it? Should I cut all the wires and re attach them?
Ever solve this? Same problem.
gowtham778 months ago
If I rip out a USB Charging Circuit from a cheap charger would it work. I mean the transformer in the circuit is designed to reduce 230volts into 5 volts required for output. But when the input is just 6 volts would it work
henryd1068 months ago
Just how many devices at once could this support?
RallyDriver10 months ago
Is the USB constantly putting out charge? Because a switch would be needed to turn on and off the output, right?

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