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

Picture of 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.

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I tried that at first too... It doesn't work. The USB converting from car chargers are designed to dump 12V DC down to 5V DC, what the op is using is designed to take 2-5V DC and bump it up to 5V DC. You need a different USB converter.

JoshuaZimmerman (author)  Animag7718 months ago

Bingo. It's easier to bump up than bump down.

Merahu1 year 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.

JoshuaZimmerman (author)  Merahu8 months ago

Two things.

1) Metal tins are bad for electrical projects, exactly what you felt. Shorts causing uncontrolled power usage. Plus you can't fit more than 2AAs and a small solar cell inside.

2) Bigger gadgets mean bigger batteries. In the past three years the size of phone and mp3 player batteries have more than doubled. Using 2 AAs isn't going to cut it. Using a Lithium Battery provides a larger power output in a small size. Plus you can charge up lithium batteries faster than AAs. Much much faster.

In my new USB charger kit I use 3 AAs (which helps out quite a bit) and a wooden box. Since I switched to the wooden box the number of emails from customers (having problems) has dropped dramatically. I love Altoids tins, but they do cause many issues.

mkovtchega10 months ago

Do you think I can replace the Dc to USB thingy with a female end of a USB extension cord?


mmcl2655410 months ago

Couldn't you use an LM317 as a current limiter and then higher voltage of 4 or 5 NiMh cells won't matter?

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?

jody341 year 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
TheArtVark1 year 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.
Schmidty161 year 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
xJValx1 year 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?
There should be diodes in the device and on the USB-DC converter to prevent that from happening.
Snakera1 year 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.
rsantos241 year 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.
rweiss1 year 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.
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.
cnephew1 year 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.
jayc1601 year 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/
Fashiondez2 years 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.
gowtham771 year 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
henryd1061 year ago
Just how many devices at once could this support?
Is the USB constantly putting out charge? Because a switch would be needed to turn on and off the output, right?
Schmidty161 year ago
can I find another dc to usb converter that is cheap on RadioShack that will work on my iPod or is there a cheaper 1 that I can find in an old device if there is 1 at RadioShack what would it be called?
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