iPhone USB Charging Adapter: How does it work?

Being the owner of many things that charge via USB (iPhone, work Blackberry, girlfriends Pre, PS3 controllers, cameras, etc.) I had the brilliant idea of buying a powered USB hub, plugging that in, and hooking up all my short USB cables to it. Everything would charge without having to leave a computer on, it would be much more convenient, etc.

Problem is the iPhone wouldn’t charge. Just about everything else didn’t care that their was never a chance of data being exchanged and happily sipped away on the 5.5v that was made available to it. I googled a bit to try and find some way of tricking the phone into charging. Even thought if I hooked up the hub to a computer, let it start charging, and then disconnected it, that might work. It didn’t.

So I gave up on the hub months ago. Today whilst perusing Think Geek I found this little guy:


Seems like it’s the answer to my problem. The solution must be tiny enough to fit into the USB male/female adapter, but I have no idea what it is. So, what does this thing do that I could probably do myself with a spare USB extender? Is their a transistor/resistor/capacitor/some other random tiny piece of electronics that tricks the iPhone? Does anyone know the possible reasoning behind not being able to charge via any powered USB port?

I anxiously await your response as I debate whether or not it’s worth it to just purchase this thing for $7.99. Thanks in advance!

You can do it yourself with a few resistors on the data lines: DIY iPhone 3G Charger.

Apparently the phone is looking for certain voltages on the data lines before charge is allowed.

There’s a big misconception about USB charging that its just like outlet charging. You plug something into the usb slot and you get power.

Well, thats not really true. USB has two modes of charging. The basic mode is something around 100mw and should be available to all devices. Most likely your hub has the brains to give out 100mw. Devices can request 500mw but they need to do a digital handshake with a USB2.0 controller that supports this. Your hub may not support this mode. So your iphone is trying to get that juicy 500mw and your hub wont let it. I believe the iphone will still use power but it cannot charge its battery at 100mw.

One of the problems with hubs and cheapo usb adapters is that they dont have the logic or the means to deliver 500mw. They’re just dumb 100mw devices. You can buy apple’s official charger, buy a 3rd party device designed to give 500mw, or plug it straight into a computer. Im not sure what brand/model of hubs can do 500mw without a computer on (if that even makes a difference).