DIY Solar USB Charger - Altoids

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 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 places 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 inefficient. You can do it, and it works, but there are far better options.

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budhaztm1 year ago
Would one be able to use lets say a (or a couple) li-po battery for rc airplanes and have a dc-dc converter?
ctschoepe1 year ago
Will this work with the newer ipods/iphones? I heard some of them require special circuitry. Also, will the AA batteries recharge from the solar panel or no? And more batteries = more current = faster charging, correct?
JoshuaZimmerman (author)  ctschoepe1 year ago
It works with my iPhone 4. The AAs do in fact recharge from the solar cell (thats the point). More batteries would give you a higher capacity and make things charge faster.

Though to be honest the best solution is 3 AAs in a series to give you 3.6V, but then you'd need about 5V coming in to charge.
lespaul552 years ago
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 (author)  lespaul552 years ago
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.
spete6532 years ago
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 (author)  spete6532 years ago
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.
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!
JJman212 years ago
Like other comments, I was wondering if we could get any specs on your "DC to USB converter circuit,"? I have been looking on ebay and have found simple and cheap car chargers as well as wall chargers, but these deal with 12V Dc and ~110/240V AC. These both step to a 5V output, but I know these are not the circuits you are referring to. Could you help us out a bit and maybe give us a link or source to a possible circuit or charger we could pick up without bulk buying from Hong Kong? I think this idea is awesome and I want to build one but this part of the design has me hung up at the moment and would appreciate any input into this. Thanks!
JJman21 JJman212 years ago
I may have found something that will work for under $3. This seems just what I need, let me know what you think:

Just ebay "emergency USB charger" and I believe any of those work that are portable and take two AA batteries.
JoshuaZimmerman (author)  JJman212 years ago
Yup, those can work. Just be careful, I've gotten some bad units from various China eBay supplies before.

I also have the circuits on my website as well if you need them.
kanito1072 years ago
so an AC to USB circuit would not work?
gwbonline2 years ago
You mentioned that I can't use a 12V car charger for this project. On I can buy several usb chargers. But what is the right one? I mean, an usb car charger is dc to usb. Can you point me to the right device?
twalsh23 years ago
could u post some examples of "cheap chargers". that would be helpful. thanks
shneddie3 years ago
Hi, thanks for the tutorial, I think I'll be giving this a go. Only one problem, I can't seem to find a DC to USB converter, can you please tell me where I would be able to buy one, or what you get them in (Or is it a trade secret?) ;)

Thanks Edd.
Oh, I forgot to mention, I'm in the UK...
acampbell53 years ago
Is there a way to use a 12v to USB car charger circuit and adapt it for use in this project?
JoshuaZimmerman (author)  acampbell53 years ago
No. You'd have to use 12V worth of batteries, which would mean you'd have to use 10-12 batteries.

You need a circuit that boosts the voltage, not drop it.

Thank you for your instructable, but whcih part do I nedd of my ''cheap usb charger from ebay''?

Thank you, pic below ;)
Probably all of it. I'm not familiar with with the one you've shown, but you can probably just leave it as it is.
devilmaycry3 years ago
can you please show the circuit from underneath please. thanks