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As the new owner of an iPad, it was disappointing, but not surprising, to see a "not charging" in the upper right hand corner of my iPad when I connected it via USB to my Apple Keyboard from 2007. However, connecting it directly to my MacBook Pro from 2010 does charge the iPad, so it seems it's just a simple matter of my USB keyboard not drawing enough power.

Is this something that Apple has updated/changed about their USB keyboard since I bought mine in 2007? The products are otherwise identical. If not Apple, are there any third parties that have keyboards that will supply the necessary power to charge an iPad?

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4 Answers 4

up vote 16 down vote accepted

Yes, but only with the iPad in sleep mode.

The iPad requires at least 500mA from a USB port:

Apple peripheral devices may request more than 500 mA (Milliamps) at 5 V (Volts) from a port to function or to allow for faster charging. Such Apple peripheral devices include:

  • iPad
  • iPhone
  • Alluminum Wired Keyboard*

About wired keyboard we get the information:

*When connected to a computer that supports a connection of 1100 mA at 5 V, the first port on the keyboard to have a device or peripheral connected to it that requests standard 500mA power will receive that power. At that point, 100 mA at 5 V is available through the remaining port on this keyboard. This keyboard does not support extra power out of its two ports simultaneously; it requests extra power from the host computer to provide power out of either one of its two ports, then the second keyboard port receives the standard 500mA.

Note: Apple computers and displays that were introduced before 2007 support only 500 mA at 5 V from their ports and do not offer additional power.

[source 1 from support.apple.com]

As the wired keyboards can provide the minimum 500mA required by the iPad (just like older Macs can), it should be possible for it to power the iPad. However, it can not provide an additional current which would allow for faster charging.

But, the new iPad can only charge in sleep mode when connected to a low powered USB hub:

The fastest way to charge your iPad is with the included 10W USB Power Adapter. iPad will also charge, although more slowly, when attached to a computer with a high-power USB port (many recent Mac computers) or with an iPhone Power Adapter. When attached to a computer via a standard USB port (most PCs or older Mac computers) iPad will charge, but only when it's in sleep mode. Make sure your computer is on while charging iPad via USB. If iPad is connected to a computer that’s turned off or is in sleep or standby mode, the iPad battery will continue to drain.

[source 2 from support.apple.com]

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1  
Thanks for undeleting your answer - you and I both found the same article, but this is a better answer. –  Kyle Cronin Mar 29 '12 at 16:17
    
My fist answer was a bit messed up - so I deleted it while I was editing it in order to not confuse every one. –  gentmatt Mar 29 '12 at 16:20

This is standard. The keyboard USB port gives you enough power for a mouse, but not enough for most other devices.

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Apple has a habit of bending the rules when it comes to USB, otherwise how could I charge my iPad directy from my computer? –  Kyle Cronin Mar 29 '12 at 15:40
    
Actually Apple will send 1100 mA to it's keyboards to ensure that the first device connected can get the full 500 mA that USB allows "per the spec" –  bmike Mar 29 '12 at 17:00

Looking at this the other way, iPads want far more than the "standard" charge when in operation and show "not charging" to let you know that although power is present, the battery will not take any significant charging while not sleeping.

The article Apple Computers and Displays: Powering peripherals through USB is the canonical list of situations where Apple detects and sends more power downstream to operate things like the MacBook Air superdrive, the iPad and even iPhone and iPod now can take far more current to charge when connected directly to an Apple display or computer.

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The keyboard has a non-powered hub inside, and can only supply 100mA of power to any connected USB device.

Recent Macs will support 1,000mA (1A), and some very recent might support 2,000mA (2A), but since the keyboard hub doesn't, then attached devices will still only receive 100mA, too little to charge an iPad.

Newer hubs could support supplying more power when they are connected to 1A or 2A USB ports on the computer, but that's a very new standard (and it is now standard) so you're unlikely to find any, even apple products, that do so yet.

You can put a powered USB hub inbetween and get the standard 500mA, but if you want the fast charging you'll need to connect it directly to the USB port on the computer.

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The keyboard can provide 500mA, but apparently that's not enough. –  Kyle Cronin Mar 29 '12 at 16:09
    
@KyleCronin Which keyboard is this? 500mA is enough to charge the iPad very slowly when it's off, but of course if you turn it on to check the charge state it'll stop charging because it's on. Leave it off and plugged in for awhile, and you'll see the charge % go up if your keyboard does supply 500mA. –  Adam Davis Mar 29 '12 at 16:16
    
The Apple USB Keyboard - see gentmatt's answer –  Kyle Cronin Mar 29 '12 at 16:19
1  
Actually Apple will send 1100 mA to it's keyboards to ensure that the first device connected can get the full 500 mA that USB allows "per the spec". The first connection to an Apple USB keyboard actually is the same as a powered hub. The second connection is limited to 100 mA aka "mouse level" current. –  bmike Mar 29 '12 at 17:01

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