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.

Comments

[DoctorDv]

Hey thanks for the great post! I was wondering if a transistor would be necessay to the completion of this project so you don't overcharge your batteries? Thanks again!
-Doctordv

[JeenJogi]

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[swimfan2489]

Great instructable! This has inspired me :)

I am looking to build a slightly different version of this instructable, but with supercapacitors instead, to make this "super-green". Do you know if it would be possible to just use supercapacitors to completely replace the batteries? Even if it would only work while in the sun, that would be fine with me... Any help would be great!

[joewein]

If you're worried about how "green" the components are, the NiMH battery is not the #1 candidate for concern: Unlike lead acid and NiCd cells, NiMH cells do not contain toxic heavy metals that need to be kept out of incinerators.

The biggest environmental impact will be the energy used to make the refined silicon for the solar cell, most likely from coal burnt in China. Switching to super caps would not resolve that.

[JoshuaZimmerman]

I don't see why not. You'd have to have solar panels to provide power, but I don't see why not.

The only downside is that super caps cost a lot of money compared to just using some AAs. Plus because of how little power this thing uses a set of AA batteries would last a very very long time.

[JoshThebBoss]

Will this work for Ipod touch 2nd Generation and ipod touch 4?

[diy_bloke]

if you get the right MintyBoost it may:
http://www.ladyada.net/make/mintyboost/changelog.html

Apple has apparently changed and rechanged their load protocal to make it difficult to charge. Adafruit has tried to keep up with it.

[JoshuaZimmerman]

No idea.

[JoshThebBoss]

What wires am i supposed to solder the USB cirquit ?

[Thermiter]

There is also the issue that supercaps do not hold as many watt-hours of power as batteries do and they have no internal resistance. So, in addition to putting a 1+ watt dissipation resistor across the caps, a flagrant waste of power, but a necessary element, you would not get nearly as much charge out of them.

[OT4]

I have a couple questions an di would love it if the author would please clarify. First i assume that when the phone is not connected to the usb the solar pannels will charge the battery. Second how will i prevent overcharging the batteries. Thanks.

[OT4]

Also, i want to use this on my android and on my ipod. How will i wire this for apple products? Again, i would realy appreciate it if the author would clarify. Thanks

[JoshuaZimmerman]

Actually the newer circuits I use in my kits work for both regular USB items and Apple gear.

You also don't need to worry about overcharging. We're not throwing enough current at the NiMh AA batteries to overcharge them.

[OT4]

Thanks

[MyTopFan]

Could I use 4 1.2v rechargeables instead of just 2? Or would that be too much for the USB?
If it makes a difference, I'm using the same USB from the same emergency charger as you did.

Thanks in advanced.

[JoshuaZimmerman]

Most certainly. Just wire them up in 2 sets of 2. In parallel. You'd double the capacity.

[Snowbox117]

Will there be enough power to completely charge a smart phone?

[JoshuaZimmerman]

Depends on the battery inside of a smart phone. Plus if you're getting sun at the same time.

[OT4]

Awesome idea. I will sooo do this. One question though. Shouldnt we use a tip31 transister to make sure the voltage doesnt get too great. Or maby itwas a resistor. Well i mean wichever one will stop the voltage from getting too great.

[OT4]

Also. Does the battery holder have to be especialy for rechargable batteries or just a plain one

[Fashiondez]

Which is more powerful for usb charging: 5V 1A Solar Panel 5W DC Power Supply or a 5.5V 320mA Solar cell?

[zkus]

The wattage is what defines power, and (i believe) how fast it will charge. your dc power supply is 5 watts, while your 5.5v 320 mA solar cell will do about 1.76 watts (which you can find using http://en.wikipedia.org/wiki/Ohm's_law). So your solar cell will be much less powerful.

I dont know if this curcuit would handle the 5watt DC power source (beyond my EE knowledge)

[Fashiondez]

Also, I was looking around and i was directed to the 5w solar cell i mentioned, and it is directly attached already to a usb port. He says it is good. But the disadvantage in that is, since it bypasses using batteries, it will not save the charge, right...because it is just a solar cell? So that means that the device I am charging has to stay out with my solar cell while it charges, whereas if i have a solar cell running to batteries, I can charge them up and then charge my device inside, right? If you are not sure, that is okay too.

[JoshuaZimmerman]

Yup.

[Fashiondez]

Thank you. Appreciate it!

[Alexjoy]

Do you know if excessive heat damages the solar cell? And if so, how hot does it have to get for that to happen?

Also, I know heat will damage the batteries for sure, however, again I'm not sure how hot exactly they can get before it damages them.

My situation is that I live in Phoenix Arizona and I really want to make one of these, however, I don't know how long I will be able to leave the charger in the sun without it getting damaged due to excessive heat. It's really the solar cell that I am concerned about as I am sure I could find a way to keep the batteries fairly cool in the shade while the solar cell is in the sun.

Do you have any suggestions?

[JoshuaZimmerman]

The solar cells are rather solid bits of technology. Unless you're baking them you shouldn't have an issues.

But yes, the batteries may be a different issue all together. Keeping them cool might not be a bad idea.

Try this out. External solar cell, long wire, jack and plug setup.

http://www.browndoggadgets.com/store/solar-kits/heavy-duty-usb-charger-kit/

[gatorgirl16]

Would it be OK to use a wall usb charger to get the circuit? I was able to find the positive and negative points. I connect the battery back and the light turns on but nothing charges. Is it because I left the light on?

Help? :/

[twright8]

Can I still play my games on my iPod while it is being charged with the solar USB charger or will my iPod died before it can be charged?

Does it create enough power to do this?

I would like to use the 4v solar panel or do I need a larger panel?

[JoshuaZimmerman]

It'll charge while you're playing, as long as the batteries have juice inside the charger.

The solar cell isn't powerful enough to power an iPod all by itself.

A larger cell, one outputting over 200mA, will probably be enough.

[twright8]

Do you sell a solar cell of that size on your web site?

[JoshuaZimmerman]

I sell several. There is a nice big 5.5V 320mA solar cell which is a beast, and a 6V 240mA solar cell which has a good kick to it. Both work well.

I just posted a new Instructable on how to make a Solar Charger using a big solar cell along with a Jack and Plug setup. Might be up your alley.

[coloskibum]

Actually original poster has a good question. I have a 2w 6v solar panel and bought a handful of bulk .9v-6v to 5v USB circuits like you have. The way you have this wired I'm trying to think through if this will push 8.4 or just 6 v to the usb circuit if I'm in the sun and have fully charged batteries (I'm a noob but go with me here)...I guess I'll just wire the panel and fully charged batteries and see what the good old meter says before I wire it to the USB...

[JoshuaZimmerman]

It depends on how well your circuit handles the extra voltage. The voltage regulating chip on it may be just fine, or it may burn down your house. I'd most certainly do some testing before hooking up any gadgets.

(Though I'm guessing you're going to be ok.)

[granolabar]

How would I wire the diode if I were to solder two 4V panels together in parallel? I'm trying to get a setup with two sets of 2 rechargeable batteries, and two solar panels.

[JoshuaZimmerman]

Put the diode between the solar positive input and the battery pack.

Two solar positives together, then the diode off of them.

[chreaus]

hey, i tried to scan through all the other comments on here but i couldnt find anything about efficeincy loss... any idea how to calculate for this build?

[hpfev]

Will it work charging an ipad? Cause i think iphone and ipas have different amp setting for chargin. Or maybe it doesnt matter?

[JoshuaZimmerman]

As a general rule I have been saying that this circuit doesn't work with iPod, iPhones, and iPads. I tested the circuit out on my iPhone 4 and it didn't work.

Well I recently tried with a new batch of these circuits and my iPhone 4 charged perfectly. Big surprise to me.

If you're going to be using this with only an iPad or iPhone you might want to use a different circuit. I have one that has a retractable iPhone/ iPod/ iPad cable on it, as opposed to a USB port. Handy.

[tonytolstykh]

If you have any left can you let me know, I would like to get my hands on one of those.