Heavy Duty Solar USB Charger (In a Tin!)

Introduction: Heavy Duty Solar USB Charger (In a Tin!)

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.

Last year I made several popular instructables on creating cheap and easy to build USB Chargers. Many people have emailed me about these and offered up many constructive ideas and comments, which lead me to reflect on ways to improve my design. So after a full year of minty smelling solar USB chargers, I submit to you my Heavy Duty Solar USB Charger (which still fits in a tin).

In my original designs I used a small 4V solar cell to charge up 2 rechargeable AAs, which in turn powered a boosting circuit which charged up your gadget. The construction difficulty was low enough that even beginners could accomplish this, and the cost was low enough that even if you did screw up, you didn't break the bank. The only weak part of the project was the 4V solar cell. While it was powerful enough to charge up the internal AA batteries, and small enough to fit into the tin, it was in no way powerful enough to directly charge a USB gadget on a sunny day. I'd also gotten quite a few emails from bikers and hikers who wanted a solar cell that they could mount on a backpack while traveling, something the 4V just wouldn't do.

To combat this, I've switched up the design and gone with a much more powerful solar cell. To combat the fact that no one likes to carry around a massive solar cell (unless you're a hiker) I've gone with a jack and plug system. Still easy to use, easy to make, and it won't break your monthly tinkering budget.

The USB Boosting Circuit in this kit works with most USB gadgets. I've tried it out on old and new iPods, iPhones, Kindles, GPS Units, and Android Phones. While I can in no way test every USB gadget on the planet, from what I have tested the circuit seems to play nice with most gadgets out there.

More or less, this is the last Solar USB Charger you're ever going to need to make.

Difficulty: Easy
Cost: Low(ish)
Usability: High
Cool Factor: High
Ability to get you a date: Low, unless your date is an electrical engineer in which case "high"

Step 1: Parts and Equipment

Soldering Iron
Hot (melt) Glue Gun
Wire Strippers

Optional Tools (Very helpful but not necessary)
Helping Hand
Dremel with metal grinding bit

DC to DC Boosting Circuit with USB
2 AA Battery Holder
2 Rechargeable AA Batteries
1N914 Diode
2.5mm Female Plug
2.5mm Male Jack with wire
A large solar cell, greater than 5V and with more than 200mA of current
An enclosure of your choice (a mint tin works wonders)

Also having some extra wire isn't a bad idea either.

Where to buy parts. You can buy a Heavy Solar USB Charger Kit from my site, or even a finished charger for those who don't have the time to make one. You can also find the parts individually off eBay, AllElectronics, and ElectronicGoldmine.

*** Update. I'm no longer selling this kit or a finished version. I do have a basic Solar USB 2.0 Kit and a more hard core Lithium Heavy Duty 2.0 Kit. If you're looking for something premade you should probably just grab a Folding USB Solar Cell. They're more powerful than this project ever was and at the same price.

The total cost of all these parts will be under $40 depending on what configuration you're going, or the quality of the parts you use. The largest cost of this project being the solar cell.

Though if you buy from me, 28% of all sales go to buying doggie treats for one very special brown dog.

Step 2: Of Tins and Solar Cells

Most people seem to enjoy putting these types of projects into mint tins. Tins such as Altoids are a perfect size for this project. I also enjoy the stylish designs of Newman's Own Organic Mints. You can also find blank tins off eBay, or fun Maker tins over at the Maker's Shed. But the point here is that you pick an enclosure that works for you. If you want a more rugged enclosure you may wish to go with a hard plastic enclosure, or even one that you can make a bit water proof. It all depends on your needs.

For this project I'll be using a Newman's Own Organic Mint tin in the flavor of Cinnamon.

Now about solar cells. For this project we're going to be using a good sized solar cell. If you want to use a small solar cell that fit inside a tin, check out my Solar USB Charger instructions. Same idea, smaller cell, smaller cost.

You want to choose a solar cell that is more than 5V of power and more than 200mA of current. Keep in mind that solar cells are rated at their peak output, not their average output. This means that whatever solar cell you use you will probably never get the output it's rated for.

Also keep in mind that you probably don't want to go over 400mA of current. Throwing too much current at the internal AAs will cause them to die on you. (Unless you want to use 4 AAs, but I'll talk more about that later.)

For this guide I'll be using a 5.5V 320mA solar cell. The current on the solar cell is probably pushing the limit of what my batteries can handle, but from the dozen of these that I've made and given people I've not had a single battery failure.

(To play it safe most people recommend that you don't throw in more than 10% of the current rating for the batteries you use. Meaning, if you have a 2000mA battery setup, you don't want to throw more than 200mA at it. The 10% rule. As solar cells NEVER get their amp rating in a circuit, you can go a bit above without having too much worry.)

You'll also see in the above picture a second solar cell rated at 6V 240mA. This cell also works quite well. Keep this in mind though. The higher the voltage your solar cell has, the less sunlight you'll need to get the batteries charging.

Step 3: Strip the Wire

Finding a 2.5mm Male Jack with a good length of wire on it is very important to this project.

If you look at the wire you'll notice that there are in fact two wires hooked together. One is all black, and one has a white strip along it. The all black wire is Positive, and the white strip wire is Negative.

You'll first want to use some scissors or wire cutters to split apart the two wires. Just a little bit. Don't pull them apart too much, as this makes things more difficult later on.

Then use some wire strippers to strip the plastic coating off of them.

Step 4: Solder the Wires and Add Glue

Now just solder the wires to their respective spots on the solar cell. White strip wire to Negative, and all black wire to Positive.

Again, don't pull the wires apart any more than necessary. Trust me.

Using a Helping Hand type tool makes this a whole lot easier, and if you don't have one, you should really get one.

Once the solder is cool take your Hot (melt) Glue Gun and cover everything with a thick layer of glue. This covers your solder points, and also secures the wire. You could also use Silicon Calk or even electrical tape, but I find that Hot Glue works quite well.

Step 5: Drill the Tin

Whether or not you're using a tin for this project, you're going to need some holes drilled.

To drill my tin I used a regular drill with a regular wood drill bit. I choose a drill bit that was about the same size as my 2.5mm Female Plug. If you can, start with a smaller drill bit and work your way up.

I also used a vise grip to hold the tin down while drilling. This is not always necessary, but it can be very helpful.

When drilling into a tin you need to be careful. Push too hard and your tin gets all bent out of shape. The best advice I can give is to not push hard. Let the drill bit do the work for you.

Once your hole is drilled, check it against the 2.5mm Female Plug. You're most likely going to need to make the hole larger. This is where a Dremel comes in handy, though you can easily just use a larger drill bit and make the hole larger. A file also works.

Step 6: Cut a USB Opening

There are two ways to do make an opening for USB.

The Quick and Easy

Measure out the width of the USB port, use a tin snip to cut down to the base of the tin. Fold the tin inside.

The More Difficult and Better Looking Way

You can easily get an opening that is just the right size for your USB port, but it takes a bit of effort.

First, put the USB circuit next to your tin and make an outline of it on the tin.

Second, drill a couple of small holes on the inside of your USB outline.

Third, use a file or Dremel to shape the hole.

The Dremel makes short work of this job. Use a vise grip to hold the tin in place. Also be sure to frequently check against your USB port so you don't make the hole too big.

Step 7: Cut the Battery Pack Wires

Choose a spot between 1/2 to 2/3rd of the way up the wire on your AA Battery Holder. Cut the wires there.

Then strip the ends of all the wires. Oh yes, even the wires you just cut off. We're going to use them.

(Or you could use some other wire as well. We don't need very much.)

Step 8: Wire Up the 2.5mm Female Plug

A 2.5mm Female Plug has 3 tabs coming off of it (usually).

Lay it in front of you so that you have all three tabs away from the table, and the tabs facing you. Meaning, the "empty" spot on the plug should be facing the ground.

From left to right the tabs go like this.

Left: Negative
Top: Positive
Right: Don't use this tab.
Bottom: Empty, no tab.

Take the little black scrap of wire you saved from before and hook it around the far left tab.

Grab your 1N914 diode and hook it to the middle, Positive, tab. Notice how on the diode there is a black stripe on one side. That stripe should be facing away from the 2.5mm Plug and SHOULD NOT be connected to the 2.5mm Plug. The black stripe side should then be connected to the red scrap strip of wire you have left over.

Then solder all those points.

Step 9: Connect the 2.5mm Plug to the Battery Pack

And now for a very easy step.

Twist the positive wires from the battery pack and the 2.5mm Plug together. (They should both be red if we followed the directions.)

Twist the negative wires from the battery pack and the 2.5mm Plug together. (They should both be black if we followed directions.)

Now is a good time to have a cup of tea. It's not a necessary step in this project, I just enjoy tea breaks.

Step 10: Soldering the USB Circuit

There are many USB boosting circuits out there, but they'll all connect the same way.

Find the spots on the board labeled Positive (+) and Negative (-). All we have to do now is solder the wires onto those spots.

For this I'll be using a Helping Hand type tool.

My advice is to not put too much solder on. Some people seem to go overboard with solder. It's not necessary.

Also, I find it's helpful to take the bare ends of the wire you twisted together, and fold them over once. Often they're way too long and unruly, and this also gives you a larger surface area to solder onto.

*** If your'e using one of my kits, or a USB Circuit that looks like mine, you should do two things before soldering.****

1) Cut off both LEDs from the circuit board. They're useless. Even the white LED is useless as a flashlight. Your cell phone gives off more light. (No, you won't cause a short this way.)

2) You'll see a small switch on the side. It has three positions. Move the switch all the way to the back. Towards the + and - terminal posts. Away from the USB port. This sets the circuit to "Charge" mode, where we want to leave it.

Step 11: Add Some Tape

If you're using an enclosure that has a metal surface, follow this step. If plastic, don't bother.

Add some electrical tape to the inside of your tin where your USB circuit will be. This insulates your tin to prevent any short circuits from happening.

Adding some below your 2.5mm Plug isn't a bad idea either.

Additionally, some commenters have proposed using other products to insulate the inside of a tin, such as a sealer. This works too. Tape is just the easiest way.

Step 12: Test It Out!

Before doing any glueing, test out your setup. Add in some regular batteries, or rechargeables, and see if it works. If the circuit does not work, you have a problem.

1) Are your batteries dead?
2) Is the circuit set correctly? (Is the switch in the right place? If using a different boosting circuit, is the voltage set correctly?)
3) Are solder points good?
4) Did you get the positive and negatives hooked up right?

If Your Circuit Is On Fire
You may laugh, but this happens to me every now and then. Even after making over 500 of these things. If you smell burning, or see smoke, take the batteries out ASAP! You have a short somewhere. This is especially true once everything is inside the tin. If not properly insulated you can have a short happen and things can start to smoke.

When your batteries are out, inspect your circuit and solder joints. Most of the time your project will be fine, the components are tough that way.

Step 13: Glue It Down

First, test to make sure everything fits where you want it to. Screw the 2.5mm Plug into place, pop the AA holder into place, get the USB circuit in place. If everything fits well, then glue.

And to be honest, just use Hot (melt) Glue. Double sided foam tape also would work.

When using glue, put a small amount down under the USB Circuit. Hold the circuit down, and wait for it to cool. Then add a bunch of glue on top of the circuit and the solder points. This will help protect them from shorts and moisture.

When finished, add batteries, and you're done.

Step 14: Variations

The nice thing about this project is it's adaptability. You can easily swap in parts from anywhere.

You can easily add a suction cup to the back of the solar cell, or velcro, or even a snap. This allows you to mount it on a backpack or a window for easy of use.

One customer of mine who does mission work in Africa needed a lot of standby power. He choose to use 2 AA Holders and 4 AAs hooked up in Parallel. This doubled the amount of available charging time. To fit everything in he put the 2.5mm Plug up front next to the USB port. You can see his handy work in the picture above.

You could also build a small solar cell array if you have a bunch of smaller cells around. Or even use more than one 2.5mm Male Jack and have several solar setups to pick from. The plug in action makes this easy.

If you're an IPhone user you could use a boosting circuit that has a built in iPhone/ iPod dongle. While this does limit you to only Apple gear, it also saves you from carrying around a cable.

If you want to make this project very small, you could use AAA batteries and a small Altoids Gum sized tin. Or a Dilbert Tin if you can find one.

Step 15: Enjoy!

And thats the project. Charge up your iPhones, GPS Units, Kindles, Phones, or whatever.

The thing I enjoy about this is that you can charge up your batteries during the day, and then disconnect the solar cell and take the tin with you at night. Or out hiking. Or just leave it in your office for the times when you forget to charge up.

This is a great project for people who want to build something practical. Something you can use every day. It also makes a really nice gift for a gadgety person in your life.

If you do make this project, please post photos of your finished charger.

Again, if you need the parts or would like one of these chargers made for you, visit my little website. 49% of all profits go into doggie squeaky toys.

*** Update. I'm no longer selling this kit or a finished version. I do have a basic Solar USB 2.0 Kit and a more hard core Lithium Heavy Duty 2.0 Kit. If you're looking for something premade you should probably just grab a Folding USB Solar Cell. They're more powerful than this project ever was and at the same price.

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    9 years ago on Introduction

    I ordered two charger kits from Joshua and assembled them this week.

    First off, Joshua has been very responsive — especially with one issue that came up (that I'll go into below).

    Solar panels: Soldering the panels was very easy. I hot glued a piece of thick felt to the back — with a cut shoelace loop notched in at the top. I thought this was more attractive and protective. It also minimizes sliding if placed on a car dashboard. The loop allows for hanging or attaching a carabiner.

    I did run into an issue with a bum panel. I tested both with a portable fan, and one panel registered half as much output as the other. Joshua was quick to respond and I await a new panel in the mail.

    Circuitry: The USB board differs from the one pictured above. It has two large battery terminals on the side. I couldn't figure out how to snip them. I thought leaving them in would increase chance of short circuiting. So I decided to desolder them. With some flux and a solder sucker, both terminals came out pretty easily, leaving empty slots that I was able to thread the bare wires through for soldering later.

    Removing the two LEDs was harder because I chose to desolder them as well. The pins and holes are tiny, but with some desoldering braid and sucker, I was eventually able to clear all holes. It's probably easier to snip off the LEDs with some low-profile snippers/scissors.

    Casing: I asked Joshua if I could buy pre-cut tins, but he said it wasn't good business for him. I respect that, but I did have to borrow a friend's Dremel and buy the right cutting attachment (think it was this one http://www.dremel.com/en-us/Accessories/Pages/ProductDetail.aspx?pid=9910). As instructed, I drilled the tins and then cut out the shape with the Dremel. First Altoids tin turned out great. The second one (an Ouija mint tin from World Market) was problematic because the lid overlap was different, resulting in a USB port drilled too low.

    Assembly: Again, the first unit turned out great with minimal effort. I put down a layer of tape and then hot glued the USB circuit down on top. Inserted and screwed in the female power jack. And then the battery pack (which, by the way is 3 AA now). I chose to drill a hole and use a retain screw, washer and nut to hold the battery pack in place. I happened to have two sets from a previous soldering kit/toy. The problem with this is that the screw and nut extend below the bottom of the tin. I chose to solve this with some adhesive half-circle feet. Again, this is purely optional, but I knew that I would be using the charger by swapping in fresh batteries (rather than the solar pane) from time to time, and I wanted a more solid assembly.

    The second, seemingly cursed, assembly started to smoke when I plugged in an iPhone. I quickly unplugged and removed the batteries, but one of the AA terminals and springs heated up and melted. I removed everything (including tape and hot glue under USB circuit) and tried again. Same smoking. Ugh.

    Luckily, I had a spare 3 AA pack from the same soldering kit/toy. I spliced this in. Tripled the layer of tape under the USB circuit. Removed the last tiny bits of solder that were plugging up the holes from one of the LEDs (now I could see through the board). I don't know which of these three things fixed the problem, but finally everything worked without smoking.

    Performance: Of course by the time I finished everything, the skies above started to cloud over and remain such as I type this. So I swapped in three freshly charged Sanyo Eneloop AAs and plugged in my iPhone 5. The Eneloops have a bit less capacity than the provided Tenergy AAs, so I expect a bit more charging when I use them. The 3 Eneloops brought my 18% phone to 75% in just over an hour before they were drained. Probably not optimum conditions (I'm not 100% sure if the Eneloops were fully fully charged), but probably indicative of real-life scenarios.


    Overall: I am happy with my builds (especially the first, trouble-free one). I look forward to charging and use via solar. And I'm happy with the performance and flexibility of this kit. Thanks for putting it together, Joshua!


    7 years ago

    It charges other gadgets but not my iPhone. Why?


    9 years ago on Introduction

    There is a major contradiction in your instructable, and I would strongly urge you to rectify this.
    On the first page, you clearly stated that 28% of all sales goes towards doggie treats, but in the last page, it says 49%. I'm confused.

    James Maring
    James Maring

    7 years ago on Step 2

    Can I just get a cord from the solar panel, make an adapter to a cord leading to female usb, then plugging in usb cables into it?

    i really like the project, just have a few questions.
    is there a way to add more batteries to your system, so they could collect more charge? also, if i were to make 2 of these chargers and have them alternate charges, take 1 out per day, what solar pannel would be big enough to charge it in one day? thanks, get back to me when possible


    Reply 9 years ago on Introduction

    You can easily add a second set of 2 AAs in. Just wire them up in Parallel. No extra special parts or planning needed.

    It would take longer to charge them up (they'd hold more charge), but they'd also be able to charge a phone longer.


    Reply 9 years ago on Introduction

    I have some follow-up questions regarding the 2 sets of 2 AA's in parallel scheme..

    1)Would that produce 3 positive wires (one from the solar panel, and one from each pair of AA's) twisted together and another 3 negative wires twisted together?
    2)Would that scheme need another diode to prevent a pair of batteries from draining each other?
    3)Don't we need another diode after the 3-wires lead I mentioned in no. 1, (before connecting them to the boosting circuit) so that the battery of the phone would not get drained by the internal batteries?
    4)Do the data lines in the female USB port in the boosting circuit have resistors attached to them already? (just thinking that maybe this was the cause of being not compatible with the iPhone 3GS..)

    Thanks for this great instructable you made! I can't wait to make one!


    Reply 8 years ago on Introduction

    1) Two sets in parallel would lead to 3 positive wires and 3 negative wires.

    2) The circuit should not need a second diode for the battery pack.

    3) A second diode here would be helpful but not really necessary.


    Reply 9 years ago on Introduction

    Mr. Zimmerman, please answer my questions in your nearest possible time please :) I really need some answers. Or maybe someone else could help me? Thanks again :D


    9 years ago



    9 years ago

    First of all I would like to thank you for posting so much valuable information. I've built two solar chargers already and I've even places an LED Indicator. I actually figured that out on my own. Once again thank you!! JoshuaZimmerman


    9 years ago

    Would this work with a 5w 12v solar panel. I have one already that is designed as a trickle charger for a car battery?
    I would use 4 AA's (or more if it wouldn't hurt?) because space is not an issue. I love the idea of making one of these but would rather use items I already have to save money.


    9 years ago on Introduction

    I have been trying to find the DC to DC boosting Circuit with usb in stores for a few days now, does anybody has any suggestions on a store wich I can purchase it at?


    9 years ago

    Would it work if i replaced the battery pack and charging circuit with one of those emergency mobile chargers that you can connect to wall mounted usb chargers? The ones that already have a fixed battery inside. Thanks for the feedback


    9 years ago on Introduction

    I checked my notes. Phone went from 13% to 81% before batteries drained. Took about 1 hour and 15 minutes.


    9 years ago on Step 2

    You say that the higher the voltage, the less sunlight you need to get the batteries charging. I assume there's a theoretical maximum, but what would that be? I'm planning on making a charger with either three or four AA batteries, so that's 3.6-4.8V depending on what I settle on.

    I'm looking at a panel that's 8V and 260 mA. I know that with a lower mA it will take longer to charge, but my bigger concern is getting the most out of the available sunlight (where I live I don't always get the best sun).