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






  • 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
    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

    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.