USB current requirements - powered hub necessary?

Discussion in 'Mac Accessories' started by Half Rick, May 30, 2017.

  1. Half Rick macrumors member

    Joined:
    May 28, 2017
    #1
    Hi,

    I have two USB 2.0 drives that require 200 and 300 mA respectively, and an external 2.5" external hard drive requiring 144 mA, all according to the System information. From what I gather, my SDHC-card class 4 use maximum 100 mA when reading/writing. I am experienced enough to know issues might arise with peripherals acting up, disconnecting, and not being recognised by the computer when connecting too many into the same port using an unpowered USB hub, but that's about all I know...

    My complete rookie logic is the the hub requires 100 mA, and adding the 744 mA for the peripherals mentioned above it is still short of the 900 mA that the USB 3.0 port can provide. But I have no idea whether the power requirements are as linear as in my thinking, or even how to interpret the current requirements being reported, and I just can't seem to find the answer to my questions via Google.

    So my question is this: would an unpowered USB 3.0 hub with three ports plus an integrated SD card reader be able to handle this with no issue even if I for some reason would move files to/from all four peripherals at once? Or is it necessary to purchase a powered hub in order to not run into problems?

    In case anyone wonders, or if it might be relevant, these are the two hubs I am choosing between:

    - unpowered: https://www.amazon.com/gp/product/B01LWYCA1U/ref=ox_sc_sfl_title_1?ie=UTF8&psc=1&smid=A2071U4930RVPV

    - powered: https://www.amazon.com/Xcellon-4-Po...8&qid=1496172252&sr=8-8&keywords=xcellon&th=1 (But branded Orico in my local Amazon-store.)

    Thank you for reading.
     
  2. Fishrrman macrumors G4

    Fishrrman

    Joined:
    Feb 20, 2009
    #2
    Get a POWERED hub of your own choosing.

    If you want to connect multiple external drives at once, it will probably save you a lot of trouble.

    Decent powered hubs also offer one or more USB charging ports as well.

    (check offerings from plugable.com, among others)
     
  3. kschendel macrumors 6502a

    Joined:
    Dec 9, 2014
    #3
    I agree. Unless you have some overwhelming reason to not want the powered hub, get it. If the current draws are high by a few percentage points and the unpowered hub is a few points on the conservative side, it won't work, and that's even assuming that all the numbers are right. You're just too close to the edge IMHO. (and with things this close, rather than nice clean failures, you're likely to get recoverable errors causing slowdowns, drop-outs, weird stuff going on. Just not worth it.)
     
  4. Half Rick thread starter macrumors member

    Joined:
    May 28, 2017
    #4
    So in short, better safe than sorry, and it will also allow me more freedom should I want to connect other USB peripherals in the future. The cost is a somewhat more cluttered desk, but I guess it's not the end of the world.

    Thank you very much for your input!
     

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