"available current" on USB port

Discussion in 'Mac Pro' started by Morpheo, Aug 13, 2016.

  1. Morpheo macrumors 65816

    Morpheo

    Joined:
    Feb 26, 2014
    Location:
    Paris/Montreal
    #1
    I just noticed this yesterday. My cMP (1,1 flashed to 2,1) reports an available current of 1000 mA. Isn't it supposed to be 500 mA for USB 2.0? According to this page, it's 500:


    ...so I don't know what to make of this, is there something wrong with my USB ports?


    Screen Shot 2016-08-13 at 12.18.39 PM.png
     
  2. ActionableMango macrumors G3

    ActionableMango

    Joined:
    Sep 21, 2010
    #2
    USB 2.0 spec is for 500mA, but you can have a port rated for far more than that, it's fine. The way DC works, only as much amperage as the device needs is used. So if you hook up a device that needs 200mA for example, it will pull 200mA. That fact that the port can supply up to 1000mA doesn't mean it will harm the device.

    Even though USB 2.0 is rated for 500mA, 1000mA is helpful on a port because it can charge an iPhone or iPad twice as fast as 500mA.
     
  3. benjaprud macrumors member

    Joined:
    Apr 9, 2015
    #3
    Recent macs (post iPhone) can output more than 500 mA to allow for faster charging. I think the most recent ones can output up to 2000 mA.
     
  4. Morpheo thread starter macrumors 65816

    Morpheo

    Joined:
    Feb 26, 2014
    Location:
    Paris/Montreal
    #4
    The thing is, it's a Mac Pro from 2006 we're talking about, a machine made and bought in the pre-iPhone days. I could swear the "available current" part was 500 mA when I looked at it recently in my system report on 10.9.5. I'm not saying this has anything to do with El Capitan, but I was using Mavericks at the time. A couple days ago my usb hub stopped responding for no apparent reason. I restarted, still nothing, I thought one of my ports was dead. Reset the SMC, and it was back again. That's during this little troubleshooting bit that I checked my system report and noticed the value.

    It's not a big deal, and maybe it was always 1000, although I still doubt it and I was surprised when I saw it.





    (Actionable Mango I love your avatar! :))
     

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