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I'm looking for a way to monitor the power being drawn from the USB ports on my Mac.

System Profiler doesn't appear to display this and I haven't been able to find any applications or tools to do the job either.

Can anyone suggest anything (preferably software based)?

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2 Answers 2

USB power consumption information should be available in System Profiler. See the screenshot below:

System Profiler USB power consumption

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I had seen these figures however I'm a little confused by 'Current Required'. My initial thinking was that this is some amount that the device has requested be available for it to function and not that it is the actual amount being consumed. –  slackwear May 10 '11 at 19:44
    
@slackwear According to Apple (support.apple.com/kb/HT4049): The Current Required (mA) entry indicates the current the device needs to operate. So I would presume that most devices, when turned on and in use, would consume that much current. Do you need the exact amount being drawn by a specific device at any given moment? Or are you just trying to get an overall estimate of how much power your USB devices are drawing together? –  Austin May 10 '11 at 20:30
    
Exact figures was what I was after however it's more of a curiosity than a necessity. I have recollections of seeing figures down to single milliamps reported by Device Manager on Windows. –  slackwear May 11 '11 at 10:30
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The "Required Current" field is just one of the pieces of information passed from the device when it enumerates over USB. It does not reflect anything but a number in the devices ROM. In an ideal world, the person who designed the device would have measured it's current draw, and put that in the required current field, but this is often not the case. –  Fake Name Sep 8 '11 at 0:09
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Your best (and, frankly only) solution here is to buy a USB extension cable, and stick an ammeter in series with the power connection. That will give you real realtime power measurements. –  Fake Name Sep 8 '11 at 0:14
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There is an application that is part of the Developer Tools on your Mac called USB Prober. It should provide you with the details that you need.

It can be found by signing up (free) for a Mac Developer Account and downloading the latest Xcode tools at http://developer.apple.com/technologies/tools/.

After installation the application you are looking for is found in /Developer/Applications/Utilities.

Hope that helps.

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-1 Looking into USB Prober was a very time-consuming diversion that ultimately yielded lots of esoteric data about a USB device, but no special insights about its power consumption outside of what System Profiler offers relatively easily by comparison. Also, Xcode is no longer free as of version 4 -- it's included with paid Developer accounts (starting at $99/year) or can be purchased separately on the Mac App Store for $5. –  Austin May 11 '11 at 15:23
    
Did you try getting it from your install discs? Sorry about that, I was sure it was still free. What on earth? –  Link May 11 '11 at 19:40
    
It caught me by surprise too, when I found out. When Xcode 4 was released this past March they decided that it wasn't going to be free anymore. You can still use the old developer tools on OS X install DVDs -- but again, USB Prober won't be helpful in this particular case. –  Austin May 11 '11 at 20:06
    
xCode is free on the mac application store... –  XAleXOwnZX Sep 7 '11 at 23:59
    
@XAleXOwnZX - Only on Lion. On SL, it's $5 –  Fake Name Sep 8 '11 at 0:11
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