One of the most fun and useful projects on instructables is to create your very own solar USB/ iPhone charger. They're not overly difficult to make, nor are the parts overly expensive or hard to find. For the most part they do a rather good job of charging up small gadgets. Mostly.
The big flaw in the DIY solar charger world are the batteries. Nearly all the designs on instructables (including all of my designs) use standard NiMh rechargeable batteries. They're cheap, easy to find, and very safe to use. The problem is that their capacity and voltage are both low, and the gadgets we keep wanting to charge are getting bigger and better batteries.
For instance an iPhone 4 has a 2,000mAh battery inside of it. Now that isn't too tough to charge up decently with a well made solar charger using 2 or 4 AA batteries. On the other hand an iPad 2 has a 6,000mAh battery pack on it. Not so easy to charge up.
The solution for these problems is to ditch NiMh batteries and turn to Lithium batteries.
In this guide I will show you how to make your very own Lithium battery charger. One that is cheap to make, easy to build, and most importantly safe to use.
(Oh and help me win the Instructables Green Tech Contest by voting for this project! An iPad would be great for my classroom! Even better, I'll build a massive Lithium powered charger to run the iPad. It'll be 100% green in my classroom.)
5V (or greater) Solar Cell
3.7V Lithium Ion Battery: 2,600MAH, 4,400MAH, 6,600MAH
Lithium Battery Charge Controller
DC-DC USB Boosting Circuit
2.5mm Female Panel Mount Plug
2.5mm Male Jack with Wire
Double Sided Foam Tape
Altoids Tin (Or other enclosure)
Hot Glue Gun
Dremel (Not necessary but good to have)
This guide will show you how to make a Solar powered version of this charger. You can also easily ditch the Solar section completely and rely on USB to charge up the Lithium battery.
While many of the parts for this project can easily be found at most online electronics store, a few items like the "DC to DC Boosting Circuit" and the "Lithium Charge Controller Board" are more difficult to find. As this guide continues I'll provide you with several options on where to get most of the parts as well as a detailed rundown of what each one does. Then you can make an informed decision as to which one best meets your individual project needs.
As a disclaimer I will say that I do sell both finished versions of this charger, parts to make this charger, and complete kits on my website BrownDogGadgets.com. We currently have two kits available, a basic Solar USB Kit and an updated Lithium Heavy Duty Kit.