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if you try to connect the usb cable to different usb port on the computer then it will start the charging. Ipad need a 2.0amp power output on the cable to charge the ipad however all usb ports dont produce the same current usb
The USB 1.x and 2.0 specifications provide a 5 V supply on a single wire to power connected USB devices.
A unit load is defined as 100 mA in USB 2.0, and 150 mA in USB 3.0. A device may draw a maximum of 5 unit loads (500 mA) from a port in USB 2.0; 6 (900 mA) in USB 3.0.
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