Simple Reason : PC USB is not giving enough USB power to charge IPAD. If you keep IPAD connected to the PC it may charge but it will take 4 times the actual charging time required.
Hereis the technical reasons.
Chargers:
|
Source |
Voltage |
Current |
Power |
|
PC USB |
5 volts |
0.5 amps |
2.5 Watts |
|
iPhone Charger |
5 volts |
1.0 amps |
5 Watts |
|
iPad Charger |
5.1 volts |
2.1 amps |
10 watts |
Will they all charge an iPad even when your PC shows “Not Charging”? YES your PC USB will charge your iPad, but very, very slowly because it is 1/4th of what an iPad charger is so it will take 4 times longer than an iPad charger (BUT YOUR SCREEN MUST BE OFF). To test that plug your iPad into your PC USB charger before you go to bed and write down what the battery percentage is and in the morning you will see it went up. Not much, but it will go up some. Reason it says “Not Charging” when you are looking at the screen when plugged into your PC is the USB is basically powering up your screen and doing nothing for the battery.
If you use an iPhone charger it will show the iPad is charging; now look above at the numbers and you see that it is about 1/2 of what the iPad charger is so it will take twice as long to charge up your iPad using an iPhone charger. Below these are totally hypothetical numbers and not realistical and I am using them to keep it simple and understandable.
If it takes your iPad charger 5 hours to charge up your iPad with the iPhone charger it will take 10 hours to charge it because it is about 1/2 the watts and amps. Make sense? Its basically just doing the math. I have not tried to do a full charge using a USB Port on my PC, but I believe like I said doing the math it will take 4 times longer because the USB port is 1/4 the output of the iPad charger and 1/2 the output power of the iPhone charger. But remember if you have your iPad screen on the USB on your PC is just powering up your screen and doing nothing for charging the battery. To test that I would have to take a guess and say let your iPad run down to say 20% or so, turn it OFF, plug it into your USB Port and power it up after I would say at least 12 to 16 hours to see where it is at. It will charge the battery I know that for sure, but it is going to take 4 times longer.
I hope this clarifies things up for everyone on this because it is all just math with the output because they all produce 5 volts only difference is Amps and Watts and the equations for that is Volts x Amps = Watts. Apple gives you the 2.1 Amp 10 Watt charger so it won’t take a day to charge your iPad due to the battery being much bigger.
Hope this info helps everyone…