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.

(If you want a more powerful USB Charger, a Heavy Duty one, I have an instructable for that as well.)

Step 1: What You Need

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

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 pleases 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 ineficient.  You can do it, and it works, but there are far better options.

Step 3: 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

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 Atoids 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

First, we're going to wire up our solar panel. 

I like to connect my 1N914 diode directly to 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!

Then attach a long wires to both the diode and negative tab on your solar cell.

Then tape it up for protection.

Step 6: 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).

Solder.

Easy as pie.  Sweet sweet solar pie.

Step 7: Prepare the Charger

So the charging circuit I use also has a couple of LEDs on it.  These in no way effect 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

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

I use Altoids Tins because they're the prefect 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

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

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!

Comments

[Houghie72]

I have got the USB charging circuit from a USB car charger that turns 12v into 5v. Does this mean in order to charge, I have to have 12v going into the USB charging circuit?

[scientist44]

On the brown dog gadgets website I found a 6V solar cell, and a 1.5V cell which would be best? I don't completely understand the voltage situation.

[ccc2]

I made this, and I am able to charge my simple keypad phone, but I can't seem to charge my ipod touch. I keep getting the message, "charging not supported with this accessory." I am guessing that this is because my ipod needs more power to be charged, but 'm not sure. Any ideas on how I could fix this?

[ttawi]

Hi~ u said "just connect all the red wires with all the black wires", but u r actually connect the red wires to the red wires. i dont know what to do. i think i should connect the postive wire from the solar panel to the postive wire from battery, right?

[yoji]

hello, i have a question. how can we know if the battery is fully charged? and is it possible that battery may explode due to overcharging? how to prevent it?

thanks.

[lg90221]

i have a question im new to this but i was wondering can you use the usb circuit found in car chargers? because those are 1.99 compared to the 8.99 dc to usb circuits. i know it takes 12v and drops it to 5v volts but if it receives 6v wont it just drop it to 5v? not really into the whole elctronic thing. or where can i buy cheap dc usb

[rev512]

Hey so it started charging for a few seconds and then my phone said something about my phone is not comparable with this accessory and now it won't charge!?!?

[tripperman79]

Sorry if this has already been asked, but will this one work with an iPhone 4s?

[bulletbkr]

just a note, if you use hot glue to secure and insulate the connections and wires on the back of you solar cells, be sure to put something under them when you put them in the sun to charge. I now have a ruined dashmat in my truck because the hotglue melted into the fibers as I was charging my batteries. Boo for hot glue. I thought it had a much higher melting point than that.

[BillMetrey]

Hello, I tried to access y our website several times with no success. Are you still accepting requests? I would like to buy at least one of your solar chargers. Thank you!

Bill Metrey

[kldtia]

I attempted this project. I have one question I'm charging a samsung Gs2 phone and I pluged it in. It says it's charging but when I look at the phone it seems like my battery is losing charge. What did I do wrong.

Thanks

[budhaztm]

Would one be able to use lets say a (or a couple) li-po battery for rc airplanes and have a dc-dc converter?

[tboultwood1]

Hello there, me and a friend have a project idea. We are planning to use a 12v battery of arrays of AA rechargeable batteries, also using a 12v panel. Will we need protection against overcharge?

[Gigean]

How do I know if I should use a 4V Solar Panel or something else? Also, where would I find a solar panel, a battery holder, and the diode? This may be the first Instructable project I tackle, so sorry for so many questions

[jpman]

f i use one of those Ipod charger usb thingos would it work??? i really dont have money to buy the minty boost usb circuit i have one of this usb charger things for ipods and phones so yea Email me @ [e-mail]

[kenkenken44]

hi this project is cool so i made 1 with a car charger and it seems to not work any help?
b.t.w im using a 6v solar panel

[valiantX]

In regards to batteries, I think people should try buying some of these new japanese 'water charging', that's right, batteries instead. Excuse my language here, but these batteries can be charged by any form of non-acidic water including urine, sewage water, creek water, your sweat, etc.

Check out the site info right here: http://waterbattery.com/

A cheaper site to buy from: http://shop.conics.net/nopopo-3pk.html

[Fashiondez]

Hey, does anyone know what to do when you hook everything up, and it is working/shows that the Iphone is plugged in, but it doesn't charge it? Should I cut all the wires and re attach them?

[pertamax11]

how much current can be drawn from this dc-usb converter?

[agqy2801]

Can rechargeable batteries above 2000mAh - 3000 mAh be used? I managed to find one claiming to be 3500mAh. Plus, the battery claims to be AA Lithium Ion and not NiMh, will that affect anything?

[electro18]

I bought a 5v solar panel and connected a diode to it....... and connected it to my phone. It was charging well so is there any need of the DC-USB converter?

[Fashiondez]

Okay, I finally began putting together the usb solar charger. I got all the supplies from your web, except for the usb circuit board.... I got that out of a cheap usb car charger. Anyways, when I got the solar cells, i wasn't sure what the soldering tabs were and found out the hard way that, without them, it is not really that possible to connect the wires to the glass of the solar cell lol. Anyways, I needed to attach a diode to the positive wire, so i had detached it from the solder tab, and ended up detaching the soldering tab itself (not knowing it was useful...as it wasn't in the picture in the instructions and this was my first time). I am wondering if there is any way to recover my supplies now that two of the tabs are gone.
I hooked up two cells in a series and connected it to two AAs and then those to the circuit board, even tho I am not 100% sure that i am hooking them to the correct place, because it does not have a + or -, so I am just trying to use common sense and I picked a place :). Currently the charger is not working, so i am trying to evaluate. Hope this was understandable.

[JoshuaZimmerman]

Car charger won't work. A car charger takes 12V from your car battery and lowers it to 5.

The circuit I uses takes 2-3V (such as 2 AAs) and boosts it up to 5.

Two completely different circuits.

I emailed you about all this as well, so check your inbox.

[electro18]

Can you email me the circuit diagram of the DC usb charger? Having a bit trouble with it :) .

[Fashiondez]

yes, thank you. I am pretty sure I got all of yours! I had written you via this and e-mail at first. I don't know if i received a reply to my last one though.

[paintphone]

What was your USB charging circuit originally from?

[JoshuaZimmerman]

Surplus from a commercial charger.

[4lifenerdfighter]

I would also like a schematic. It looks simple enough to cobble together.

[JoshuaZimmerman]

Quite simple.

[4lifenerdfighter]

So give it to us!

[johnestan]

Could you please tell me what the advantage of having a separate battery charging circuit is. Many of the other instructables use lithium batteries and require a LiPo charger circuit. Is this not needed when using NiMh batteries, or are you just saving money. Is it worse for the batteries in the long run?

[JoshuaZimmerman]

Lithium batteries need a charge controller because if their very specific power requirements. NiMh batteries do not.

It's a connivence and price thing when you choose batteries. Lithium are better, but are more expensive and are more work to wire up. NiMh are cheap and easy to use, but are not as effective.

[skeys2]

I salvaged a USB thingie from a DC-USB and am using that. It looks just like the one you have pictured; however, I can't seem to fing the negative or positive connections. It would be amazing if I got a response... Thanks!!!

[JoshuaZimmerman]

They should be labeled. Or marked on the board.

Or you could just take a 2AA battery pack and just touch the wires to the board. If it works, you have things right. If not, switch the positive and negative spots and try again. (Guess and check)

[Diggyx17]

Will the solar panel charge the batteries when its not in use???

[JoshuaZimmerman]

Thats the idea.

[dereksmalls1985]

Hey there! This is an excellent looking project that I plan on completing soon! I do have one question: what is the best way to go about harvesting the usb charging circuit from a usb charger?

Thanks so much!

[JoshuaZimmerman]

Rip that puppy open.

Find that that turns 2 or 3 AAs into 5V USB.

(Not a wall one. Bad idea.)

[Diggyx17]

I'm not understanding. how do you know if its just charging from the panel and not the batteries? and when you say "test it" do you mean its going to run off the solar panel and not the batteries?

[JoshuaZimmerman]

Well you can take the batteries out of the setup, then plug in a gadget, then stick it in the sun. If your gadget starts to charge, awesome.

Or you can just stick some batteries in and then plug a gadget in.

Though with this small of a solar cell a lot of USB stuff won't charge directly from the solar cell, they need the batteries in there as well to augment things. (Which is why I have more heavy duty versions of this charger setup with more powerful solar cells.)