How many USB portable hard drives per hub?

Discussion in 'Mac Accessories' started by winkosmosis, Mar 22, 2015.

  1. winkosmosis macrumors member

    Joined:
    Oct 20, 2012
    Location:
    Hawaii
    #1
    With USB 2.0 the max amperage was 0.5amp and generally you could run a single 2.5" hard drive per port. To use multiple per hub you needed an AC adapter.

    But USB 3.0 max amperage is 2amp. Does that mean you can plug 3-4 hard drives into an unpowered hub?
     
  2. matreya macrumors 65816

    matreya

    Joined:
    Nov 14, 2009
    #2
    No, because the amperage on Mac USB3 ports is 0.95A.
     
  3. winkosmosis thread starter macrumors member

    Joined:
    Oct 20, 2012
    Location:
    Hawaii
    #3
    Thanks, I didn't know the max was so low, I figured the spec required 2A
     
  4. marzer macrumors 65816

    marzer

    Joined:
    Nov 14, 2009
    Location:
    Colorado
    #4
    I haven't confirmed it through another source, but this is from the USB Wikipedia page:

    "As with previous USB versions, USB 3.0 ports come in low-power and high-power variants, providing 150 mA and 900 mA respectively, while simultaneously transmitting data at SuperSpeed rates.[25] Additionally, there is a Battery Charging Specification (Version 1.2 – December 2010), which increases the power handling capability to 1.5 A but does not allow concurrent data transmission.[22] The Battery Charging Specification requires that the physical ports themselves be capable of handling 5 A of current[citation needed] but limits the maximum current drawn to 1.5 A."
     
  5. ColdCase macrumors 68030

    Joined:
    Feb 10, 2008
    Location:
    NH
    #5
    Regardless of power, hanging more that two USB3 drives off a USB3 hub is not reliable with many hubs. It is a USB3 thing, the simpler USB2 drives did not have as many issues. But multiple drives on a USB hub connected to a Mac has always been problematic.
     
  6. Mr. Retrofire macrumors 601

    Mr. Retrofire

    Joined:
    Mar 2, 2010
    Location:
    www.emiliana.cl/en
    #6
    Especially if you use USB 3.0 hubs with more than one USB 3.0 hub controller chip (all USB 3.0 hubs with more than 4 ports).
     
  7. William Auld macrumors newbie

    Joined:
    Mar 11, 2015
    #7
    My USB 3.0 hub supports only two drives, the third one i have to plug to my mac.
     

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