At one time or another, most of you will have plugged your smartphone or cell phone into computer to charge it. And on occasion, many of you may have charged a camera, GPS or other device on your computer. Using a computer or laptop for charging these devices is especially helpful in a pinch – most often when you forgot your charger at home and have a dead device.
I’m also sure that those of you that own an iPad or other larger tablet will have tried to charge it on your computer only to be frustrated by the “Not charging” message.
So why won’t an iPad or similar tablet charge when it is plugged into a computer? The answer is really quite simple. The USB ports on a computer just don’t have enough power to charge an iPad. The USB ports on computers or laptops (for both PCs and Macs) put out 5 volts at 0.5 amps; or about 2.5 watts. The iPad charger is much more powerful as it puts out 5 volts at 2.1 amps; or about 10 watts. You need the extra power to charge the larger battery in an iPad. Most USB hubs also don’t have sufficient power to charge and iPad.
Two tiny footnotes in case you find yourself in a real pinch with just a computer to charge your iPad. First, despite what I said above, computer USB ports can actually charge an iPad, but they do it very slowly, and only if iPad it turned off. The moment the screen goes on, the iPad sucks more power than the USB port can give it and the battery will start to drain. No peeking!
Second, you should also check the specs on your computer or laptop as some have USB charging ports that will have a higher output – these still won’t charge a device while it is on, but they will charge it a bit faster than a regular USB port will. On some computers these charging ports will even charge a device with the computer it turned off.