Thanks for the explanation. I knew there was a difference between the different USB ports but didn't know what it was.
Pete
--- In iPad@yahoogroups.com, Charles Carroll <911@...> wrote:
>
> USB1 only supplied 100mA *per port*. USB2 supplies current in 100mA
> increments, up to a maximum of 500mA *per port*. the battery charging spec
> increases this to 1.8A if the device is only charging and not communicating
> (tho i don't know if that spec is part of USB2 or USB3). see
> en.wikipedia.org/wiki/Universal_Serial_Bus#Power
>
> Since an iPad requires 2amps (2000 ma) basically the Lenovo or any WinTel
> USB port can only provide 1/4th of its power requirement at best if it is
> designed according to USB 2.x standards. The MacBook Pro/Air or USB
> chargers don't follow the USB specs they can produce much more than 500ma.
> (500 ma is 1/4 of 2000ma/2a the iPad requires). And this is a max not all
> ports even put out 500mas if other devices are plugged in or just not fully
> maxed out to the spec.
>
> The per port limit is why you might see USB cables that plug into 2 ports
> top double the power output many external disk drives or devices that need
> 1 amp (1,000 ma) come with these of cables that plug into 2 USB ports.
>
> http://www.bixnet.com/5vps2powercord.html
> http://www.amazon.com/Utstarcom-Universal-Adapter-Female-Connector/dp/B0041CFFBM/ref=sr_1_1?ie=UTF8&qid=1338827152&sr=8-1
