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Picture of DIY Solar USB Charger - Altoids
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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

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

Tools:
Soldering Iron
Solder
Tin Snips
Melt Glue Gun and Glue
Tape

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 BrownDogGadgets.com 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

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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 BrownDogGadgets.com. 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

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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

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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

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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

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

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

Solder.

Easy as pie. Sweet sweet solar pie.

Step 7: Prepare the Charger

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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

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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

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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

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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

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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, BrownDogGadgets.com. 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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koby7yesterday

i love it

dr_amazoyesterday
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?
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! :-)
JoshuaZimmerman (author)  Just4Fun Media1 month ago

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

ThomasW2017 days ago

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.

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

JoshuaZimmerman (author)  Di Immortales1 month ago

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.

Azzurro1 month ago

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.

JoshuaZimmerman (author)  Azzurro1 month ago

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.

ah well okay a diode is a lot better of course :)
Elmercab2 months ago
I got this circuit board off an LG travel charger . Trying to figure out where I would put the negative and positive wires. I also wanted to add a switch I'm not sure if that would makes things more complicated. Wondering if any of you could help
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those looks like a step-down? If they are they will work if you have a big solar panel to step the voltage down to 5vdc. You can get the battery powered usb charge at the Dollarama if you live in Ontario, they are like three bucks!

What the guy above me said. You have a STEP DOWN. You want a STEP UP. Two completely different things.

GaetanoM1 month ago

sorry, where have u find the usb charging circuit

JoshuaZimmerman (author)  GaetanoM1 month ago

My website, browndoggadgets.com

BilalK21 month ago

Does this work with 18650 battery cells?

JoshuaZimmerman (author)  BilalK21 month ago

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.

this instructable was posted in 2011, so this guy made it about 4 years ago.

Edbed1 month ago
These look awesome!
SeanC55 months ago

What was the problem with this kit? what batteries did you use?

JoshuaR8 SeanC55 months ago
aa batteries
SeanC5 JoshuaR85 months ago

Lithium aa?

Those would explode.

Lithium batteries are NOT rechargable. Lithium-Ion batteries are, but with special controlling hardware. He used Nickel Metal Hydride batteries (Ni-Mh), your standard rechargable ones.

use NiCads if you are not concerned about their self-discharge rate, they have a much higher mAh than their cousin NiMh.

JoshuaZimmerman (author)  waterlubber4 months ago

Rechargeable 1.2V AA batteries. Nothing special.

RodneyMori3 months ago

what happens when the battery is fully charged, nothing is connected but the panel is left out in the sun?

given the cell panel's low amperage, it should be safe to leave them in the sun once they are fully charged.

JoshuaZimmerman (author)  RodneyMori3 months ago

Nothing. It just kind of tops off. Thats why we keep the amperage low enough as to not harm the batteries.

SeanC55 months ago

What was the problem with this kit? what batteries did you use?

JoshuaZimmerman (author)  SeanC54 months ago

Not enough battery power, not enough solar power. Newer gadgets require more amperage and 2 AAs just doesn't do it any more.

will energizer rechargeable batteries work they are 1400 mAh

they would work, but it will give your device about a 10-15% charge before they drain.

So if i make this will it charge my galaxy s4? Because other comments arent specific

It would charge it but since the energy density of the two AA batteries aren't that high, it would charge your S4 to about 10-17% before the two AA batteries drain.

every time i plug my phone in it shuts off

whats wrong

Probably you've done something wrong with the connections and either there's a short circuit or the voltage is too high/low. Recehck all the connections and/or use another converter.

Will this work for the converter I took it out of a car charger
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Nope, thats a STEP DOWN converter which drops the voltage, you need a STEP UP converter to boost the voltage high.

You COULD use it, but you'd need a super super super large solar panel to do so.

Could I use energizer rechargeable batteries they are 1400 mAh
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