Picture of Heavy Duty Solar USB Charger (In a tin!)

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"

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mchang132 years ago
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!
JoshuaZimmerman (author)  mchang136 months ago

I do what I can.

It charges other gadgets but not my iPhone. Why?
mza1979m2 years ago
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.
JoshuaZimmerman (author)  mza1979m6 months ago

It depends on how hungry the dog is.

James Maring7 months ago

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
JoshuaZimmerman (author)  micheal relion2 years ago
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.
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!
webgiant btiu1 year ago

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.

btiu webgiant1 year ago

Thanks webgiant!

btiu btiu2 years ago
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
Saintred2 years ago
Saintred2 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

Schmidty162 years ago
Does this work with the ipad mini
jcornall2 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.
rcampbell102 years ago
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?
lhenson2 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
mchang132 years ago
I checked my notes. Phone went from 13% to 81% before batteries drained. Took about 1 hour and 15 minutes.
Alfonts2 years ago
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).
Has anyone had any issues where this circuit is putting out only about 2.5 volts? I have the 5.5 volt 320 mA solar cell and I'm using a 2 AA (1.3Volt) batteries (in series). With both batteries and the solar panel I'm getting 2.5 volts going into the circuit and 2.5 volts coming out. With just the solar panel attached and the batteries taken out I'm getting 4.7 going into the circuit and 4.7 coming out... I thought this circuit was supposed to bump the voltage to 5 Volts with an in coming voltage of >2 Volts
joshuapisia2 years ago
I've got a problem. the DC to DC Boosting Circuit with USB circuit is putting out more than 5 volts; almost 6 volts! I'm kinda afraid of pluggin my iphone into it. any help?
lizzyyang2 years ago
So why does this project require batteries if it is solar powered? How come the solar energy doesn't directly charge the device?
Arya422 years ago
I soldered everything together and used two regular AA batteries to test it and it charged my iPod touch like it should. Then I put in two rechargeable batteries and plugged the solar panel in and let the batteries charge to about half. I plugged my iPod into it but it would only show the 'plugged in' icon, not the 'charging' icon. I am fairly confident in my soldering abilities and I also made sure to solder everything in the correct places. Why doesn't it charge anything using the solar panel?
Arya42 Arya422 years ago
Never mind, everything works. I used some rechargeable batteries that didn't hold a charge anymore. Now I have different batteries and it works very well. I might post a picture sometime.
Arya42 Arya422 years ago
Now I do have a problem. My batteries were almost fully charged so I put the solar panel in the sun to charge a little. Later I took the batteries out and tested them and they were about half-charged but I didn't charge anything. What happened?
I'm not sure if this version requires it, but some solar chargers require a 'blocking diode' between the solar panel and batteries....although I believe Mr. ZImmerman said that the earlier version(s) didn't require one....maybe you could test adding one to see if it works.
liteGuyZ2 years ago
Hi, how do I wire my female power plug if it only has one tab instead of three tabs?
Thanks in advance!
Arya422 years ago
I am using the Apple charging circuit from your website. What should I do with the two metal tabs on the places where I solder the battery wires?
Arya422 years ago
I just received the last parts for this and my diodes have a narrow yellow band close to one end. Is this the equivalent of the black end on other diodes?
JoshuaZimmerman (author)  Arya422 years ago
Hello, this is a very nice project, congrats! I have a few questions if you don't mind.

I have two solar panels have, both 4V and 80mA. Can I hook up these two in series to get a max of 8V and 160mA, and connect it directly to the batteries?
Should I use 3 or 4 AA batteries? Is 8V too high to charge them? I checked my Sony charger and the output is about 6.4V, this got me worried.
Don't I need a switch in there to choose between Solar power charging the batteries and batteries charging the phone? If I just connect everything together and the solar panel is sourcing, lets say, 7V, wouldn't that damage my phone? Thanks!

JoshuaZimmerman (author)  ClaudioDonate2 years ago
You could do that. You'd get either 8V at 80mA, OR 4V and 160mA.

In my kits I now include 3 AAs for the Heavy Duty. I find they work better than just using 2. Four is overkill. The boosting circuit is designed to run between 2 - 4V.

No switch needed. The USB circuit only comes on when you "complete the circuit" by plugging in a USB device. Otherwise the circuit is "incomplete" and "off".

A higher voltage hitting the circuit won't hurt your phone. The most that ever comes out of the USB is 5V.
Arya422 years ago
I ordered the parts on eBay and browndoggadgets.com and now I just have to wait for them to arrive. I will post any questions I have regarding the setup once I can start making it. :)
Arya422 years ago
Where did you get this USB circuit? It looks different than the one on your website.
JoshuaZimmerman (author)  Arya422 years ago
I have two versions on the site. A generic one which does not work with Apple gear, and a more expensive one which does work with Apple gear. Trust me, it's on the site.
Arya423 years ago
What would the difference be between using the 6v 240mA and the 5.5v 320mA?
JoshuaZimmerman (author)  Arya422 years ago
One has a higher voltage, the other has a higher amperage.
ssaxena73 years ago
Will this or the regular battery charger work with 3rd Gen iPad
ktkacik23 years ago
Just joined the website this is the first thing ive made great project thanks!
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