DIY Solar USB Charger!

Happy Wednesday, folks!


Before we get into the neato item I played with the past couple days, I wanted to announce that The Astounding Rooikat is the winner of the cap from that I reviewed last week. To keep it fair, I put all the names in said Justice Cap, and had my 13-year-old son choose a name. Congrats! If you could please contact me with your mailing address at I’ll get that right out to you!


On to the post!


I’ll admit, I love my cellphone.  Probably way more than someone who tries to stay self-sufficient should. I use it for the obvious phone functions of calling, texting, taking pictures, social media, etc., but I also use it as a tool when I’m outdoors. The Trimble GPS Hunt app, ActInNature app, and a couple GPS/geocaching apps populate the screen and get used with regularity, making it a nice, easy-to-use digital addition to the compass and map that generally stay in the backpack for emergencies. I know some may scoff, but it’s a great to show you exactly where you are at any given time within a few feet on a topo, road, aerial, or other map. Plus, of course, if it has reception, it can be used to summon help in an emergency or tell your wife that, no, you can’t get a gallon of milk – you’re on top of a damn mountain!


But, as anyone who runs a smartphone knows, with all the accessories, such as GPS, wireless access, Bluetooth, and big, bright, high-definition screens, they just RIP through batteries. Like Whoah. With normal use, I get about 10-12 hours of use before I have to worry about charging the phone. Turn that GPS on to track yourself moving through unknown territory on an app, and you can halve that battery time. So, swell, neato, it works great…until you’re in the middle of nowhere and the battery goes in the red. Hopefully you’ve been keeping track on your physical topo map where you are and recognizing landmarks, and not depending on this phone to get you back to the car. (See Jarhead’s fantastic Compass Orienteering series, linked on the main page on the right hand side, to help yourself out in that department!)


So, what are solutions, if you wanna use the phone, for whatever purpose? Well, you can keep the damn thing off, use it sparingly, but that still just delays the inevitable. You can carry extra batteries (if your phone allows it – my Motorola can be pulled apart to swap batteries, but iPhones can’t.), and that works okay, but you have to keep track of which ones are charged, and which aren’t. And they run out too, especially if you’re on an extended foray. I did some research online to try to find useful solutions… enter Brown Dog Gadgets. (


I’d heard of people making USB-port chargers from Altoids tins, and so I did a web search for that, and it brought me to BDG. This neat website has lots of info, parts, and kits to make all kinds of neat little doo-dads, from noisemakers to robotics to….solar chargers! Just what I was looking for. I looked about, and found the Solar USB Kit. This little baby was just what the doctor ordered, some assembly required. I forked over the $22.99 (shipping brought it to $29) for the 4 volt, 60mA kit. It arrived about a week later.


Here’s what I got in the kit: (minus the Altoids tin…I had that.)



Clockwise from upper left: 4v solar panel, two rechargeable AA batteries (damn nice of them to include batteries!), battery case, 1N914 diode, USB converter port, and two lengths of black wire. To attempt this hijinkery,  you will need the following tools:

-A soldering iron

-Solder (I used .022″ rosin core)

-Tin Snips

-Hot glue gun and glue

-Electrical tape

-Wire strippers



Since instructions didn’t come with the kit, I went to the kit-referenced instructions on the website. First up: Wire up the solar panel. The Solar panel is available in different power levels: 4 volts (the one I got since it fits in an Altoids container), 4.5 volts, and 7 volts. The bigger panels will charge the batteries or the device faster.


To start, we strip the ends of the two loose black wires that came with the kit. We attach one of them to the diode. The Diode is kind of a one-way check-valve for the power…it ensures the power from the solar cell goes TO the batteries, but not back out, draining the batteries. I know the photo above has a red wire shown…pretend it’s black. Wrap the stripped end of one of the wires around the side of the diode with the BLACK BAR (you can see how the diode has a black stripe on the body closest to the wire). Solder it on.


Then solder the other wire on the other side of the diode to the POSITIVE tab on the solar cell. Again, pretend the wire is black.




Next, solder the other loose black wire to the negative tab on the panel. Snip off the extra lengths of diode wire.


We’ll need to attach the black wires that run from the solar panel to the black and red wires that come from the battery box. This is as simple as twisting them together, then soldering them together. Combine the wire that comes from the POSITIVE tab on the solar cell to the red wire on the battery case, and the wire that comes from the NEGATIVE tab to the black wire.



As you can see in the picture of the USB converter above, it has two contact points, one positive, one negative. Solder the corresponding wires (where they were twisted and soldered together) to the correct tab (red to positive, black to negative)…and your wiring is complete! Very easy, and I am definitely in the “amateur” category when it comes to soldering and wiring.



Before I mounted the USB converter, I tried everything out…the little red LED glowed when I snapped the batteries in, indicating a charge, and lo and behold, it charged my cell from the batteries! Huzzah! I had a beer to celebrate and had my son pat me on the back.

The battery pack snaps right into the Altoids container perfectly, and stays right in place. There’s actually room for a four-cell AA holder, which I plan on upgrading to ASAP for extra voltage and power capacity. I snipped the battery retaining tabs off of my case like it recommends in the instructions; it makes battery swapping MUCH easier.



To mount the USB converter, line it up on the side of the tin, where you will want the USB port to have access. I made a couple little red lines to guide me, then I grabbed my ancient tin snips and cut it away, leaving about 3/16 of an inch of material remaining.




I set the USB converter in place, and plugged the phone in. I noticed a very slight arc, and the Altoids tin started getting hot, which told me the circuit was grounding out to the tin. So I took some black electrical tape and laid a layer where the metal parts of the converter would touch. Success! Everything worked great.


The  instructions say to liberally hot-glue the converter to the tin, but alas, I was woefully devoid of a hot glue gun. So, being the balls-to-the-wall electronics rebel car guy I am, I just J-B Welded the shit out of it. Worked great and I got a “resourceful dude point” according to my son.




The whole works can then be fit into the Altoids tin, with just the USB port visible on the side to tell anyone otherwise. I like the tin idea, because it gives the whole system a convenient armor plating of sorts, and depending on type of Altoids you got, a wonderful minty aroma.






Cable not included in the kit.


The really cool thing about this kit is that the USB port is pretty much standard and universal these days, and charging cords for pretty much everything are made to fit this USB. I tried my wife’s iPod, her iPhone, and my cheapo mp3 player…all of them seem to charge with this setup, making it quite versatile.


Testing the charger


After a couple days of screwing around with my new toy, I did discover a few things: AA batteries are 1.5 volts apiece, making this setup put out 3 volts on batteries alone. The two cellphones I looked at in my household had 3.7 volt batteries, so this will not charge from batteries alone. Thankfully, the solar cell is 4v, and it does just fine charging a 3.7v battery with good sun. Since I have the room in the tin, and since it’s as easy as de-soldering a couple wires and soldering new ones, I’m going to upgrade to a 4-AA system. That will give me 6v of output, more than enough to charge my cellphone (though I suspect the 4v solar cell will only charge up to 4 volts.). Also, this kit will charge devices on just the solar cell alone, no batteries required – providing you have adequate, direct sunlight. I tried charging the batteries with the solar cell on the dashboard of my truck; this doesn’t work, as auto glass has coatings that limit UV ray penetration. If I rolled the window down and put the charger on the seat in the sun, it worked great. Roll the window up, it stops charging. Just a heads-up. It will also ONLY charge rechargeable batteries. It will charge FROM non-rechargeable alkaline batteries if the sun isn’t available, but those batteries won’t play nice when trying to charge them.


This is a killer little setup to charge your rechargeable AA batteries (well worth the extra money, by the way) too. After a couple hours in the sun, the batteries had a full charge (from what I could tell) and when inserted in my Mini-Maglite, it shone as bright as it ever has. So, on a good sunny day, you can charge up several rechargeable AA batteries and have them good to go for whatever purpose you may deem them worthy.


It also is very light, compact, and rugged enough so that I don’t feel bad about dropping it in a zip-lock bag and it finding its way into my BOB and camping gear. The initial cost, having to buy the solder, electrical tape, kit, and shipping, was about $36 all told. But now, it will be cheaper, and I can make a few more of these kits as money and time allow (entire elapsed time to construct this charger, even with mistakes and reading instructions, was about 20 minutes) and have them in my vehicles, give them as gifts, whatever. It’s a neat idea, practical, and pretty snazzy. I think I’m going to try putting velcro on the back of the solar cell and and on the back of the Altoids tin, so I can just mount it to the velcro pad on my backpack and have it charge as I walk around.


What do you guys think? Comment below and stay safe!




P.S. If you’re not too Radio Shack-savvy and want one of these, I bet you could sweet-talk me into building one for ya…maybe my dog will like the mints. Lord knows he needs them. Contact me at

23 comments… add one
  • Northeastern prepper June 5, 2013, 7:53 am

    Road warrior been thinking a lot about solar USB recharger I use an I pad to store a lot of useful shtf info and kids use I pad touch would invaluable to be able to still use these items in the grid went down great article lot of useful tips like the altoids can genius it will definitely be adding a few of these to my preps plus can be very useful now camping trip thank for the info.

  • Mike the Gardener June 5, 2013, 9:13 am

    this is awesome … is there not anything you can’t do with an altoids tin? They are great.

  • irishdutchuncle June 5, 2013, 9:48 am

    I’d want a large assortment of diodes, and other “solid state” goodies on hand for post TEOTWAWKI. they are the “crystal” in crystal radio…
    USB seems to be the way to go with charging stuff today. my wife just got us a charger with an internal battery. it charges USB devices, then gets itself recharged from a USB. (only slightly larger than the Altoids tin) of course now, I’ll have to make a solar charger to re-charge it…
    (as if I needed to start another new project)

  • The astonished Rooikat June 5, 2013, 10:08 am


    I know I am off-topic, BUT… Thank you so much for the cap!
    All the citizens of Rooville are rejoicing!

  • The tech-challenged Rooikat June 5, 2013, 10:10 am

    As far as the recharger goes, brilliant!
    I think it is very handy to have it sized for the altoids tin.

  • Jarhead Survivor June 5, 2013, 10:27 am

    Cool stuff! Hey – next week can you do a DIY about turning your Altoids tin into a TV set? You can just about anything else with them!

    • irishdutchuncle June 5, 2013, 10:52 am

      yeh, but then you’d be stuck with another device that needs to be recharged, and still nothing worth watching..

    • Lumberjok June 6, 2013, 10:40 am

      I have been messing around with ham radio for 40 years plus…..and believe it or not…altoids tins are a recurrent theme. The challenge is to build a morse code receiver/transmitter into a tin. This has been done successfully multiple dozens of times. Of necessity…..these devices are low power…..the challenge then becomes how far can you talk…..generally referred to as miles per watt.

      My personal best happened a few years ago when the gods who control the reflective layers of the ionosphere allowed me to have a half hour contact between northern Maine and Tasmania…(north island).

      There is no moral to this story…then again maybe there is….
      have you considered how to communicate once everything goes to crap ?????????

      Answer=ham radio.

      • irishdutchuncle June 7, 2013, 12:24 pm

        I’ve thought about it, but if I become a “ham”, then I’d be required to disclose my true identity, and the location of my shack…

  • j.r. guerra in s. tx. June 5, 2013, 1:39 pm

    Sweet! Thank you for the post. Does that generate enough power to keep a Kindle / Nook type of instrument going ? Phone I can do without (my present phone has two apps – on and off :^) but a document reader would be a fantastic resource for storing information.

  • loren June 6, 2013, 12:49 pm

    i hate to tell you but rechable batteries are 1.2 volts not 1.5. so you have 4.8 volts not 6 volts. need to learn what you are doing before you try to tell other people what an how to build something loren

    • irishdutchuncle June 6, 2013, 1:52 pm

      does that mean the solar cell array wasn’t charging his phone?

      • The Road Warrior June 6, 2013, 2:35 pm

        Thanks, Loren….I didn’t know that. Good thing I wasn’t trying.g to tell someone how to hook up three-phase…

        Irish, no it means that charging from the two AA rechargeable batteries only put out 2.4v, far from the required 3.7v. However, the solar panel puts out 4v, and therefore should work OK.

        I’m.actually working on that charger, researching modifications for more power….that will be another article!

        • T.R. June 6, 2013, 6:46 pm

          Get another one , then connect them in series . ( red open on first one , black on first to red on 2nd one , black open on 2nd one )

          • T.R. June 6, 2013, 6:48 pm

            Pannels in series *

  • David June 6, 2013, 2:03 pm

    I am fascinated with the solar charging concept, and this looks like an ideal solution. You CAN use L-ion 14500 batteries instead of the AA batteries – they are the same size, but are 3.7 volts each. If you can’t locate some easily, check with me. I have a few laying around, and they are GREAT!

  • The Road Warrior June 6, 2013, 2:37 pm

    David, that’s pretty intriguing… any idea where I could get some? Haven’t looked yet…

  • T.R. June 6, 2013, 5:19 pm

    Just read up on connecting solar panels in series and parallel to each other , this will give you higher voltages for bugger things , then velcro the set up to a piece of fabric for roll up storage .

  • S.Q. Whrill June 6, 2013, 7:59 pm


  • Joshua June 9, 2013, 4:44 am

    Hi, Josh here from Brown Dog Gadgets. Your a tad mistaken in your explanation of how the charger works.

    Cell phone batteries are 3.7V lithium, but they charge off 5V from USB. The little USB circuit inside the kit is a DC to DC boosting circuit. It takes the 2.4V from the rechargeables and boost it up to 5V for USB.

    The little solar cell is not powerful enough to charge up a gadget by itself, which is why we use the batteries to store up a charge. (Most small chargers go this route due to the fact that a decent solar cell is quite big.)

    You should also check out the Folding USB Solar Cells on our website! They’re a nice, easy, and powerful solution for people who might not want to make their own charger. (Plus they’re about 25 times as powerful as the little 4V solar cell in this kit.)

  • Road Warrior June 9, 2013, 8:54 am


    Awesome! I’m glad you found this, and even more glad you laid things straight. I can solder and follow instructions, but the “how and why” I’m a bit fuzzy on. Thanks for taking the time to help our understanding.


  • Fast micro usb charger August 29, 2014, 10:51 am

    Hey there! Do you know if they make any plugins to assist with SEO?
    I’m trying to get my blog to rank for some targeted keywords but I’m
    not seeing very good gains. If you know of any please share.


Leave a Comment

Cancel reply