Introduction: 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.

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. 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

Picture of 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

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 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

Picture of 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

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

Picture of 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

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 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

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

Picture of 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.


sample0-0 (author)2018-01-08

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.

BilalK2 (author)2015-06-02

Does this work with 18650 battery cells?

BrownDogGadgets (author)BilalK22015-06-02

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.

wen i click on lithium heavy duty i get a 404 page not found

aioakeim (author)2017-08-05

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?

thansof (author)2017-07-12

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??

creektilghmank45 (author)2017-07-03

I bought instruction from inplix and I build it very very cheap.

excellent solutions

bdeventer (author)2016-05-26

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.

CalebS68 (author)bdeventer2017-03-07

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

bdeventer (author)CalebS682017-03-07

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!

CalebS68 (author)2017-03-07

how are you creatong more energy through the controller

X Caliber (author)2017-01-15

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

Banshee98 (author)2016-12-18

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

jswartz007 (author)2016-12-09

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?

Ploensec (author)2016-10-11

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?

NaveenY9 (author)2016-07-16

i have IN4007 bmc will it work fine

bgelzer161 (author)2015-10-08

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

Thats a common question. Unfortunately due to the simplicity of this project adding in a meter would be rather difficult. You're better off doing that if you make a lithium battery version of this kit. Most lithium charge controllers have a built in battery monitor that gives you some indication of charging.

ThomasW20 (author)2015-06-17

Could this be done using an 18650 battery? I am thinking this way I could set it in a window to charge all day and get a full charge or 2 to my cell phone off it.

Kolby12309 (author)ThomasW202015-11-19

use 3 18650s and a 3.7 to 5v boost circut and charger in one in an altoids tin, if you get really good 18650s then you can have 10400 mah in an altoids tin, enough to charge your phone many times

Yup, lithium is better provided you're safe about it.

georgeyhere (author)2015-07-13

By 'USB charger' do you mean the cable or a wall adapter?

AlexB163 (author)georgeyhere2015-12-11

It would be more like a wall adapter

BrownDogGadgets (author)AlexB1632016-07-13

Wall adaptors convert AC to DC. You want a DC to DC boosting circuit.

RyanM187 (author)2016-04-01

Does this work for apple lightning charger such as those used with the newer iPhones?

BrownDogGadgets (author)RyanM1872016-07-13

That is will.

Jon surratt (author)2016-04-23

Could i cannibalise part of a wall charger minus the transformer

No, thats an AC to DC converter. It'll take 120V AC and turn it into 5V DC.

What we're doing is taking 2.4V or 3.6 V (2 or 3 AAs) DC and turning it into 5V DC.

Jon surratt (author)2016-04-23

Also could i use solar cells out of landscape lights and the batteries

You could. But you'd need the USB aspect to charge a phone.

tanef (author)2016-07-07

There is, of course, an easier and cheaper way to acquire the materials needed to make this project, including the case itself, depending on whether or not you can locate the item in the attached picture.

The attached image is an aluminum post light. I purchased a few of them, and payed 10$ for each. However, I found more appealing and higher-quality lights, so I decided to do something with them. You will need two of these for this.

The top of the post is an aluminum screw-top containing a number of small electronics: a small circuit board controlling the LED light based on whether or not energy is coming from the solar panel, a 3V white bright LED, a 1.5V solar panel, and a 1.2V Ni-CD rechargeable battery. Though it is optional, you may use the LED as an attached flashlight.

Dissassemble the light, then use a flat-head screwdriver to remove the various parts inside, making sure to leave the plastic, solar panels and battery contacts in both parts remain intact and in place; it will make your work easier, though it is purely optional.

Remove enough plastic to allow an opening for the USB output, then bend the aluminum shell inward to make an opening. Insert the USB output, solder the proper wires and connections, then hot-glue the two halves together.

Congratulations! You saved 10$, plus postage and the time spent waiting for the parts to arrive.

BrownDogGadgets (author)tanef2016-07-13

Except it's missing the entire USB voltage boosting aspect of the circuit, a USB port, and a decent battery capacity. What you have right there is a circuit that'll put out around 3V of power and has a battery capacity of around 800mA. More or less useless when trying to charge up a phone seeing how a phone, or any USB gadget, needs 5V. So theres that whole aspect.

juggadmaster (author)2016-02-06

Oh ur made version is a way too costly.......

catiec1 (author)2015-11-03

Whenever we get the charger to work the batteries start smoking, the battery pack melts, and the charger breaks. My teacher was wondering if we could get your phone number or email to ask further questions. Please get back to me as soon as possible. Thank you!

Rishik Perugu (author)2015-09-23

Nice project...!! Useful one......... But what is the alternative of regular batteries ?

GaetanoM (author)2015-05-28

sorry, where have u find the usb charging circuit

Gomi no Sensei (author)GaetanoM2015-09-20

The DC-DC charge circuit for this project costs 57c on AliExpress with free shipping.

BrownDogGadgets (author)GaetanoM2015-06-02

My website,

turbofiat124 (author)2015-08-12

I purchased a cell phone battery pack extender and was not impressed so I'm looking into making my own. I first tried connecting one of those cigarette lighter USB converters into a 12V power point adapter connected to a 9V battery but the phone would not constantly charge. If that makes sense.

But charges perfectly fine off the 6V car battery on my Trabant. The only thing I can think of is the milliamp per hour rating of the 9V battery I was using was too low to support charging.

koby7 (author)2015-07-04

i love it

dr_amazo (author)2015-07-03

the OP mentioned that you can take the circuit out of a phone charger and use it for this project. what I'm wondering, though, is that the project calls for a DC to USB circuit, whereas the wall chargers would be AC to USB circuits, right? if this is correct, do I need to do anything to alter the chip I take out of the charger in any way to fit with the project, or can I use it as is and just insert it into the new circuit?

Just4Fun Media (author)2015-06-02

Nice build. Do you think if you placed a mirror in the lid you could use it to refract more light onto the solar panel?

Have a great day! :-)

Nah, it would be a super duper tight fit then, and you're better off just angling the panel at 45 degrees.

justForFun's idea [ i think ] was to have direct sun on the panel PLUS reflected light from a mirror to increase output LOL i think you misunderstood the idea trying to be conveyed. JustForFun did not mean for the mirror's light to be the only light applied to the solar panel. personally i thought it was a fantastic idea!!!!!! be well my friends

Di Immortales (author)2015-06-04

have you thought about using super capacitors? they charge in seconds

Super caps are nice, but they hold very very very very very very very little amperage compared to even the cheapest AA. Sure, you could get giant soda bottle sized super caps (and spend hundreds of dollars per cap), but thats a bit above and beyond the scope of this. With current technology it's not financially or practically a good solution.

Azzurro (author)2015-06-02

nice and simple, i like it. a question: why don't you add a switch for solar charging? just because when there is no sunlight, the panel will slowly drain the batteries. better to open the circuit when you don't use the panel.

BrownDogGadgets (author)Azzurro2015-06-02

Thats why there is a diode, to prevent drain. A lot of people add switches to this project, no reason why you couldn't. Just not necessary.

Azzurro (author)BrownDogGadgets2015-06-03

ah well okay a diode is a lot better of course :)

About This Instructable




Bio: 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 ... More »
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