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I'm considering charging a bunch of my iPod Touches with a USB 3.0 PCI add-in card.

In my research, I've found that USB provides 5 volts per device.

The differences come in charging speed. The more amperage, the faster a device charges.

USB provides "Unit Loads" of amperage for each device based on need.

USB 2.0 provides 100 milliamps per Unit Load, with a maximum of 5 unit loads per device. USB 3.0 provides 150 milliamps per Unit Load, with a maximum of 6 unit loads per device.

When a device is connected, it draws 1 Unit load until it asks for a higher amount based on need. That means a device can draw maximum 500 milliamps (or 0.5 amps) from USB 2.0 and 900 milliamps (0.9 amps) from usb 3.0.

The Apple wall charger for iPhones provides 1 amp (1000 milliamps).

Does that mean that an iPhone or iPod Touch plugged in to a USB 3.0 port will charge nearly as fast as one plugged in to Apple's AC plug?

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4 Answers

up vote 4 down vote accepted

I have tested an iPhone 5, and on my system it charges from a USB 3.0 port at the same rate as a 500 mA USB 2.0 port. As you would expect, the included 1 A wall charger is about twice as fast.

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Bam! coneslayer joins Ask Different with a vengeance! –  Kalamane Sep 26 '12 at 0:00
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Thanks, @Kalamane. I now have a followup that might be of interest to Windows PC users who are looking for a faster way to charge over USB: ASUS Ai Charger –  coneslayer Sep 27 '12 at 0:14
    
If USB 3 and USB 2 charges at the same rate on your setup, that implies to me that the drivers for fast USB charging aren't installed or aren't working. I can charge twice as fast on USB 3 as I can on USB 2 so there's something wrong with your test set up if your USB 3 is acting like USB 2. –  Nick G Sep 24 '13 at 12:52
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Actually the power delivered by USB does not really depends of the generation. Some USB 2.0 will deliver more power than others. It depends of the hardware and how the USB is powered by the motherboard.

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Any references to back this up? My research reflects the actual USB spec. –  Kalamane Aug 23 '12 at 0:37
    
support.apple.com/kb/HT4049?viewlocale=en_US. Here Apple says some Apple computers delivers up to 1100 mA over the USB they are called "High power USB" on somme support pages. –  Matthieu Riegler Aug 23 '12 at 8:58
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Apple has created something of a superset of the USB charging spec for devices with a dock connector, like the iPhone. It's compatible with USB 2, so you can plug it into any USB port or charger and draw the standard 0.5A. However with a bit of voodoo (I believe it has to do with resistors on certain pins and so forth), it can draw a 1A charge.

However this doesn't mean an iPhone can draw the full power from a USB 3 port. Currently iPods and iOS devices aren't compatible with the USB 3 spec, only USB 2. So, like any other USB 2 device, they're limited to drawing 0.5A, unless the charging device speaks Apple's custom protocol. This could of course change in the future, but at the moment, that's how it is. You might be interested in these pinout details of the dock connector, which offers some insight into how the charging works.

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I use the gigabyte ultra durable LGA 1150 Z87-D3HP motherboard and it came with a software program that actually speeds up the charging times of devices hooked up to its USB2.0 and 3.0 slots significantly. I love it for my iPhone!

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