2 Replies Latest reply: Apr 4, 2010 7:52 AM by romad
romad Level 3 Level 3 (590 points)
For those who were wondering, here is a probable reason.

The USB ports provide 500 milliAmperes of current or .5 Amp while the voltage is 5 volts. Using the formula Watts = Volts x Amps, we see that the USB port is providing about 2.5 watts.

The iPad charger is rated at 10 watts, so DIVIDING that by 5 volts shows that the current coming out of the charger is 2 amps.

Thus the USB port is only providing 1/4 of the power needed, so it will take almost 4x as long to charge the iPad.

Active: iMac (G5, G4), PB G4, iPad, iPhone, iPod, MP2100 Retired: iMac G3, A2c, Mac OS X (10.5.8), Mac OS 10.4.11, Mac OS 9.2.2, iPhone OS 3.1.3, Newton OS 2.1