Output power on USB 3

Kappy wrote:

The spec I found stated 4.5 watts. Is Apple using their own "upgrade" to their USB 3.0 ports?

Just curious, but which spec? I know that USB 3 ports should supply 5V at 900 mA (I've got an external USB drive enclosure that requests 896 mA), but Apple usually allows supplemental current for iOS devices and other Apple-specific devices. I was thinking of the 500 mA limit that used to be for USB 1/2.

I found this, which seems to be all over the map:

Powering peripherals through USB - Apple Support

Apple devices can request extra power

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

• Apple MacBook Air SuperDrive (when connected to supported computers)
• Aluminum Wired Keyboard*
• iPod
• iPhone
• iPad

Some Apple computers and displays** can provide up to 1100 mA at 5 V through the port the Apple device is connected to. This power is available under certain conditions:

1. An Apple device must be plugged directly into an Apple computer or display. Apple devices connected to hubs won't have access to extra power above the standard USB specification of the port the device is connected to.
2. Your Apple computer or display must be powered on and be awake. If it's asleep, all ports provide their normal maximum output.
3. The port providing extra power is determined by the first Apple device to connect to the Apple computer or display that requires extra power. The remaining ports continue to offer their normal maximum output. Some Apple computer and displays offer the ability to operate more than one USB port at 1100 mA at 5 V. On those computers, the second or third port is enabled when an appropriate device is connected.
4. An Apple computer started up to Windows via BootCamp doesn't provide extra power.

However, in my experience the USB 3.0 port on my mid-2012 MBP provides 2100 mA (10.5W) to an iPhone or iPad, although I'm not sure about a MacBook Air. Apple doesn't say really say anything about how fast it should be on a Mac, but 2100 mA is what I've heard.

Charge your iPhone with an iPad or Mac notebook power adapter - Apple Support

For the OP, the way to find out is to plug it in and check System Report in >About This Mac>System Report, and checking the tree under Hardware>USB. For my computer it typically breaks it down (when directly connected to my iPhone or iPad) as 500 mA "Current Available" plus 1600 mA "Extra Operating Current", or 2100 mA "Sleep Current".

Kappy wrote:

Have you been able to measure that amperage? At least you answered my question, i.e., does Apple provide different specs that USB 3.0? I've seen the same information about the nominal wattage for USB 3.0. Apple's design allows the USB 3.0 port to deliver more current than is specified.

Not really. I've been thinking of getting one of those inline USB current/voltage readers though. Although that Apple article (from Feb 2017) says 1100 mA, I know it's more than that although it may just be a typo. Heck - that picture and later text in the article contradicts it. I believe this should be fair use especially since I'm just reposting this part of the support article back to an Apple forum:

In the example above, the USB port offers the default 500 mA, as shown in the Current Available (mA) entry. The Current Required (mA) entry indicates the current the device needs to operate. Extra Operating Current (mA) indicates that this USB port is providing an additional 1600 mA for use with the device.

What device are you connecting?

Standard devices with USB-A are usually limited to 500 mA. Apple has specific devices that can draw more than 500 mA. On USB 3.X an iPhone/iPad should be capable of drawing 2100 mA, which is 10.5W at 5V. A USB SuperDrive is supposed to draw more than 500 mA.

Have you been able to measure that amperage? At least you answered my question, i.e., does Apple provide different specs that USB 3.0? I've seen the same information about the nominal wattage for USB 3.0. Apple's design allows the USB 3.0 port to deliver more current than is specified.

As stated in Wikipedia

The USB 1.x and 2.0 specifications provide a 5 V supply on a single wire to power connected USB devices.

A unit load is defined as 100 mA in USB 2.0, and 150 mA in USB 3.0. A device may draw a maximum of 5 unit loads (500 mA) from a port in USB 2.0; 6 (900 mA) in USB 3.0.

Joseph023 wrote:

As stated in Wikipedia

The USB 1.x and 2.0 specifications provide a 5 V supply on a single wire to power connected USB devices.

A unit load is defined as 100 mA in USB 2.0, and 150 mA in USB 3.0. A device may draw a maximum of 5 unit loads (500 mA) from a port in USB 2.0; 6 (900 mA) in USB 3.0.

Certainly those are the USB Implementers Forum requirements, but of course Apple has had produced nonstandard devices since at least the first MacBook Air. I mentioned iPhones and iPads, but I recall that the MacBook Air introduced the USB SuperDrive, which could request more current than what a USB 2.0 port was required to produce.

I believe they max out at 4.5 watts per port.

The spec I found stated 4.5 watts. Is Apple using their own "upgrade" to their USB 3.0 ports?

Yes. I should have looked there. Clearly, Apple has spec'd extra current of 1.6A over and above the nominal 500 mA. That's pretty clear, I'd say. 😀