4 Replies Latest reply: Aug 31, 2013 8:37 AM by Allan Eckert
Fidelity Level 1 Level 1

Hi, does anyone know how the whole "extra current" thing works on the USB ports on a 2012 Macbook Pro? I'm trying to get the additional current draw to power a device that normally runs off a separate 12v line (but needs minimal current - likely ~ 8-12w). Is it available by default or is there some sort of signal sent by other apple devices? Am I going to short out my mac trying to run the device through a step-up converter?

  • jeremy_v Community Specialists Community Specialists

    Hi Fidelity,

     

    Thanks for visiting Apple Support Communities.

     

    See this article for some information about high power USB ports on a Mac:

     

    Apple Computers and Displays: Powering peripherals through USB

    http://support.apple.com/kb/HT4049

     

    Best,

     

    Jeremy

  • Eustace Mendis Level 7 Level 7

    "needs minimal current - likely ~ 8-12w"

     

    Watts = amps x volts.

     

    So to draw 8 to 12 watts of power from a 12 volt supply means a current of 2/3 to 1 amp. That's 667 to 1000 milliamps.

     

    You should confirm that your MBP can provide that current. I believe that built-in USB2 ports peak at 500 milliamps.

  • Lexiepex Level 6 Level 6
    expertise.macosx
    Mac OS X

    The output of the USB ports is 5Volts and 500-1000mAmps (max 5W at 5 volt), a device that needs 12 Volts and then 8-12 Watt should not be connected: it is much too heavy for the USB port and it will not work because the USB port is only 5V.

  • Allan Eckert Level 9 Level 9
    expertise.notebooks
    Notebooks

    My suggestion would be to see if you can find a powered USB hub that is capable of delivering that amount of power.

     

    I am skeptical of you finding it because I believe the 5V and 500 mA is in the USB spec.

     

    No matter what the Mac can't do it.

     

    The only other alternative I can think of is to talk to the vendor of the device to see if they can supply with something that provides that amount of power.

     

    Allan