Aa, ok, that definitely does explain a lot.
Thank you kindly,
Christopher-Mark Gilland.
Founder of CLG Productions
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----- Original Message -----
From: "Esther" <mori...@mac-access.net>
To: "Mac OSX & iOS Accessibility" <mac-access@mac-access.net>
Sent: Friday, November 09, 2012 4:25 PM
Subject: USB ports on recent Macs can supply more than the USB standard
power[was Re: IPad isn't charging: what the heck!]
Hi Chris,
You wrote:
• So I wonder then why the macbook would charge it but not any windows
machine? Do macs tend to put out more vultage on their u s b ports? Wonder
what the amount of ampiers is it outputs.
The answer is that the standard USB port specification doesn't provide
enough power to charge iPads. That's one of the reasons that all the early
generations of iPods (way back before the iPhone or iPod Nanos) used
FireWire connectors. But they moved to USB connectors when iPods became
popular on PCs, and the lower power draw of these devices made that
possible.
Recent model Macs are designed to detect when iPods and iOS devices are
connected that require more power draw to charge than the default USB
standard adopted by most PCs. Depending on the load of what else you have
plugged in, they will attempt to provide it. Macs made before 2007 do not
have this capability. Here's a quote excerpted from an iLounge article:
• "Charging your iOS Devices on a Mac or PC" by Charles Starrett, September
1, 2011
http://www.ilounge.com/index.php/tips/comments/charging-your-ios-devices-on-a-mac-or-pc/
<begin quote>
On Macs newer than 2007, all your USB ports should supply at least 1100 mA
of charging power to any device—such as an iPhone or iPad—that needs it. The
extra power is doled out on a first come, first served basis, so the first
device you plug in is virtually guaranteed to receive the maximum amount of
power, while later devices are less likely. If you have a Mac that was built
this year, it might even support full 2.1 Amp fast charging of the iPad. Mac
users also have a very simple way to check how much juice each device is
receiving. Simply go the the Apple menu, select About This Mac, and hit the
More Info… button, which launches System Profiler. From there you can select
USB from the sidebar under Hardware, and select the device you want to check
on. It’ll show you the Current Available, the Current Required, and the
Extra Operating Current—by adding the Available and Extra Current together,
you’ll get the current power output for that port. For more info, see:
http://support.apple.com/kb/HT4049
<end quote>
The Apple Support document provides more specific details, but basically,
the standard USB port specification doesn't meet the requirement for
charging high-powered devices. You may get some low level of charging if
you connect to your PC's USB port with your iPad device turned off, and no
other USB peripherals connected. Recent Macs are built to supply more power
through the USB ports if iOS devices with higher power requirements are
connected, but that assumes that you don't have large numbers of other
peripherals also powered from these ports.
HTH. Cheers,
Esther
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