Everything You Need to Know About Charging Your iPad

When you plug your iPad into your computer, do you get a message on the screen that says "Not Charging"? Here's everything you need to know about charging an iPad.

Your iPad (and iPhone, iPod, Kindle, Kobo, Blackberry, GPS, and more) charge from a USB source. Plug your device's charging cable into the USB port on your computer, or the supplied wall or car charger, and your device magically charges. Except that it isn't magic, it's simple physics.

If you closely examine a USB port or cable, you will see four conductors. The two inner conductors carry data, and the outer two carry power. In most cases, with the ports on a computer, both the data pins and the power pins are functional. The power pins can power a host of USB accessories like keyboards, mice, flash drives, hard drives, or webcams. You can even plug in USB powered lights, laptop cooling fans, and more.

There are two specifications that characterize the power from a USB port, voltage, and current. The voltage is not negotiable, all USB ports and chargers should provide 5 Volts. But the current is variable. Most USB 2.0 devices provide 500 mA (that's 0.5 Amps). On many laptops, other devices draw power from the same USB hub. For example, a the built-in webcam, even the keyboard and mouse, may draw some current. If this is the case, usually one port is full powered, offering the full 500 mA, but the second port could offer less.

With some older computers with two or more USB ports, sometimes only one port supplies power, the second port is just for data.

So how much current does the iPad need to charge? Turns out that it needs 2 Amps. That's four times as much as is supplied by a full powered USB port on most computers. That's why Apple supplies that beefy little power adaptor with the iPad. Unlike most USB chargers, the iPad charger offers a full 2 Amps. But wait! You say that you charge your iPad on your computer all the time. That could well be. If the computer or charger only supplies 500 mA, it will still charge your iPad, just much more slowly. If you plug your iPad into your computer before going to bed, it will probably get a full charge overnight. But if you plugged into the 2 Amp wall charger, the iPad would charge in about 2 hours.

So what does it mean when you plug your iPad in to your computer and get the "Not Charging" message. It could be that you have plugged in to a port that doesn't supply power. Or it could be that you have plugged into a lower powered port, one that is also powering other peripherals. Try switching to another port.

There is one other possibility. When you turn on the iPad screen, it draws a lot more power than when it is on standby. The extra draw could be enough to stop the iPad from charging. Ironically, with the screen off, the iPad could be charging. But how can you tell? If you turn on the screen to check, it stops charging! Try this. Note the percentage left on the battery (next to the battery indicator on the top right of the iPad screen). Plug in your iPad in and let it charge for an hour or so, then check the battery capacity again. If the capacity has gone up, the iPad is charging.

What about the little cube charger that comes with the iPhone. It turns out that the iPhone charger offers 1 Amp, twice the current of most computer ports. So, while the iPhone charger is less effective than the iPad charger, it is still better than using the computer.

Can you charge an iPhone or iPod with an iPad charger? Will the extra current available from the iPad charger damage the iPhone? No worries, the iPhone or iPod will not draw more current than they need. I charge my iPhone with my iPod charger all the time with no problems. I have read some reports that the iPad charger charges the iPhone faster, but I have not noticed it, and if it does, it's probably only a little bit faster.

One last point. Many new computers come with one or more USB 3.0 ports. The new USB 3.0 standard calls for 900 mA current at 5V. So if you have both a USB 3.0 port and an USB 2.0 port, use the 3.0 to charge your iPad.

In conclusion, your best bet for charging your iPad is the supplied high current charger, but in a pinch, you can probably charge your iPad from almost any computer or adaptor, it just might take a while.