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.

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

[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.

[ericb1]

do you have any left of the batch that worked with the iphone4? If so, I would like to get a few of those, thanks! just let me know

[swimfan2489]

Since your saying keep the input current at about 10% of the rated battery capacity, is that 10% for just one battery? Or is that for the total capacity if batteries are wired up in parallel?

For example, if i wire 2 packs of batteries, each cell with 1.2V and 2000mA together in parallel to make a combined total of 2.4V and 4000mA, should i buy a solar panel with a current output of 200mA or 400mA for best results?

Thanks!

[JoshuaZimmerman]

2 AAs in a holder are in a series and will come out to be 2.4V at 2,000mAh

Parallel = 1.2V at 4,000mah
Series = 2.4 at 2,000mah

10% of total capacity.

I've gone over 10% before, it really depends on your batteries and how trusting you are of them.

So in your case you'd want to use two battery packs, with a total of 4 batteries. Giving you 2.4V at 4,000mAh.

Go with the bigger cell. You'll never ever reach your max power for solar anyways.

[Matieland88]

I figure i might as well ask too.. I'm going for a bigger setup and want to use a 12v that puts out 100ma to charge 8 AA rechargeables. (that's 9.6V, i haven't bought said batteries yet so I'm not certain what mah i'll have)

will the 12v be sufficient? ... too much? will the 100ma allow me to charge the batteries in a reasonable amount of time given that it's solar trickle charge we're working with?

[JoshuaZimmerman]

From what I've read you should always go half again as much voltage as needed.

Meaning a 12V system should have at least 18V of solar panel in it.

So if you're doing 9.6V you should have at least 14-15V of power.

[Matieland88]

a number of sources have mentioned needing 1.4-1.6V/cell which calculates to 11.2-12.8V for the 8 cells.

It sounds like I can't very well blow anything up with 12v so I'm going to proceed with wiring the mock up and testing on the next sunny day.

also I might add, the panel only puts out 100ma, and that for 2500mah batteries would take forever so i've got two panels. Should suffice. The idea is that i can strap the device atop my backpack while hiking, trickle charging as i do, and then flip open to reveal both panels when the opportunity presents itself.

[budabob07]

Don't you mean 2000-3000 mAh of capacity, not 2000-3000 ma of current?

[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!

[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.

[MorNiLachnan]

If I wanted to do this but use 1 or 2 of the cheap solar yard lights from Lowes as donor parts, what would I need to modify? Do those have the right diode in them between the solar panel and the battery pack? Or is that irrelevant due to the USB circuit?

The ones I bought for the yard claim to be 4x bright. What would be the proper way to determine if I need 1 or 2 solar cells of these? Just test output of the panel with a voltmeter?

[JoshuaZimmerman]

The only thing you'd be taking out of the garden light would be the solar cell. (You could use the batteries, but they usually are low capacity and not worth their weight.)

You'd still need to get all the other parts. AA holder, 2 AAs, diode, wires, charging circuit.

Plus you should really use a multimeter to figure out what the voltage of your solar cells is. You need a combination that is greater the 3V. The bigger the better.

[lespaul55]

I am completely new to this experience of making USB chargers. I have an ipod touch 2nd gen and an iphone 4th gen. I've read online that it takes 5 volts to charge these devices although I'm now reading that this 5 volt charger will not charge newer apple products. Why won't it charge newer apple products and what do I need to change to get it to charge newer apple products?

[JoshuaZimmerman]

Newer Apple stuff does charge off 5V, but the gadgets check the data tabs on the USB to see what it's plugged into. Now seeing as no other product on the planet does this nearly every USB charger isn't compatible as the data tabs are not used. (Why would you throw perfectly good power at the data tabs when you'r just charging something up?)

Long story short you just need to find a newer charger that has this problem fixed.

[T-Prime]

Will this diode work for an 80mA panel?

[JoshuaZimmerman]

Sure. I've used higher amp solar cells before.

[RelientOwl]

Amazing Project! Thanks for posting!
Question: Do you know what kind of capacitors are on that circuit...just curious.

-Relient Owl

[JoshuaZimmerman]

Umm... just a couple of little 10uF (I believe, don't quote me on this one) electro caps. Nothing too fancy.

The caps just help the power flow more smoothly in the circuit. They're not for storing large amounts of power. That is why we have batteries in the circuit. Though some people have instead used some massive capacitors instead. They're nice, but cost an arm and a leg.

[JoshThebBoss]

What wires am i supposed to solder the USB cirquit ?

[pigione]

Hello Joshua. I have some questions for you.
I don't understand two things:
1) i have a lithium batthery 3.7V 2800mAh with a internal circuit for the protection: can i use it in your circuit? I need an battery charching circuit for it? Can I disassemble something to use?
2) if i put in parallel a simple AA ni-mh battery, the 10% of their maximum limit for charging it from a panel will double it? So i have a solar panel that give me 700mA, so if i put in parallel a 2200mah battery to arrive at 6600mAh, is it sufficient?
Thanks a lot.

[JoshuaZimmerman]

Either stick with NiMh batteries or your lithium ion battery pack. Don't mix and match batteries.

You would need a small changing circuit to handle your Li-ion pack. You can pick them up most anywhere. For instance I know adafruit.com has some that work well in similar circuits. Otherwise ebay is your friend.

I wouldn't try and take a li-ion charger out of something else. Just buy a small circuit from somewhere. Adafruit.com has directions on how to hook up a li-ion pack to a very similar circuit to the one I use in my project. Seriously check out her site.

[pigione]

Thanks a lot Joshua. I've understood. I have found something in adafruit.com.

Bye!!!!

[JoshuaZimmerman]

No problem. I do what I can. Adafruit is a solid site with really good stuff. I've been known to buy things off there from time to time.

[spete653]

Ok, so I'm trying to figure out what I'm going to need for this. In your opinion, what is going to be better to get, an emergency charger, or a wall charger?

Also, I saw a video on youtube and this guy used 4 AAA's. Which is better, AA's or AAA's?

[JoshuaZimmerman]

AAs hold a higher capacity, use them.

Wall chargers step down voltage, we need to step it up. This means you need a little emergency USB charger that uses 2 AA batteries. It'll boost the voltage up to the right levels.

[spete653]

Ok, thanks for the reply, I'll be working on it soon. I got my diode and switch yesterday at radio shack and my solar panel is on order!

[spete653]

One more question, as far as the diode goes, I bought a 5.1 volt diode, is that too big? I saw that you said you only want a trickle charge going to the batteries, hence the smaller diode? I'm afraid of over charging, I don't know anything about diodes so before I start, I want to know that the parts I put in are correct.

[T-Prime]

Hi, having some small problems. I purchased and built the MintyBoost Circuit, which works wonderfully. And I purchased a 4V 60mA Solar Cell from you, but my 2000mA rechargeable AA batteries don't seem to be charging very well. Any idea why that could be?

[JoshuaZimmerman]

2000mA divided by 60mA gives you the total hours needed to charge your batteries to 100%.

(Assuming they're completely dead, though you'll always need about 10% more time than needed to charge up NiMh in my experiences.)

You'll also need full sunlight. If it's a bit cloudy then charging will take longer.

If you want fast charging (like very fast) you're going to need a bigger solar cell or several small solar cell. Solar is great, but you have to know it's limitations.

[T-Prime]

Okay. so to fully charge a pair of AA Batteries, each rated at 2000mA with my 60mA solar cell takes ~33 hrs of direct sunlight (you don't add the Amperage of the batteries do you?). And if I wire in a second cell parrallel to the first I got 120mA for a total of ~17 hrs correct?

[JoshuaZimmerman]

Correct. Or you could also buy a bigger panel and use that instead. You have many options.

Plus your batteries will never be 100% dead (well, usually) so you'll never need to charge them up all the way.

[T-Prime]

Thanks. I have ordered bigger cells for my next project, but I have the other 60mA on hand.

[JoshuaZimmerman]

You can never have too many solar cells around. They're always handy.

Shoot, I have a few hundred in my basement and I want more...