Re: [iPad] Re: Charging from computer?

 

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.amazon.com/Utstarcom-Universal-Adapter-Female-Connector/dp/B0041CFFBM/ref=sr_1_1?ie=UTF8&qid=1338827152&sr=8-1 

On Mon, Jun 4, 2012 at 12:15 PM, Julia Mavity-Hudson <julie.mavity@gmail.com> wrote:
 

When I plug my iPad into my Lenovo (regardless of if it is on or asleep) no lighting bolt appears, just a note which appears near the battery symbol "not charging".
Julie



On Mon, Jun 4, 2012 at 11:11 AM, Charles Carroll <911@learnasp.com> wrote:
 

The MacBook Pro and Air the USB are directly wired to the power even if computer is off, sleeping, hibernating, etc.


This was a pleasant surprise when I discovered it. What I don't know is if it is unplugged from wall does battery power the USB port for charging.

If it is a Wintel Machine let me know model and I can do some research. Easiest test is empirical. Plug in your phone or iPad and see if the lightning bolt is indicated when plugged into wall, but computer not on. Then unplug from wall, and see if battery powers the USB port as well. The lightning bolt charging indicator is your friend.


On Mon, Jun 4, 2012 at 9:15 AM, Carol Corley <floridabouvs@gmail.com> wrote:
 

Dumb question, but if I want to charge from the computer, and the computer has auto sleep mode after several minutes of no activity, is the iPad still charging? Or do I need to find a way to keep the computer on while charging?
Thanks,
Carol



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