I one of the first things I tweeted after connecting my iPad to my Mac’s USB port (not a hub) was:
iPad plugged in to Mac. Interesting that it does NOT charge off of the USB
A response tweet a few minutes later confirming this with another iPad and a PC. Macworld’s Dan Frakes took a closer look at the situation and provides a few rules of the road for charging the iPad.
I guess my 2.5 year old Mac is an “older Mac” since I get the “No Charging” message on my iPad even with the USB cable plugged directly into one of the iMac’s ports. Frakes notes that lower power USB ports on older coputers and even powered USB hubs are not able to charge an iPad.
I assumed that something like this might be the case when I noted that iPads ship with a 10 watt power adapter. That is why I have a spare iPad power adapter on order. My personal rule is going to be to charge the iPad with its power adapter rather than take chances with the variety possibilities provided by various USB ports.
You can find me on twitter at: http://twitter.com/toddogasawara