USB Hubs - powered/ unpowered - whats the diff

Discussion in 'MacBook' started by jonjamesm, Dec 17, 2008.

  1. jonjamesm macrumors regular


    Nov 4, 2008
    Looking to buy a usb hub to run my keyboard, 2 external HDrives (one is USB powered) and my printer through.

    Looking for it to be about as slick looking as other mac products.

    What's the big difference between powered and unpowered - other than the obvious one runs through mains and one doesn't...

    Anyone have any suggestions?
  2. techound1 macrumors 68000


    Mar 3, 2006
    Depends on whether your computer's USB hubs are powered. If they are, then it doesn't matter. If they're not, go for a powered hub and save yourself a plugging-and-unplugging headache.
  3. PlaceofDis macrumors Core

    Jan 6, 2004
    powered ones will not draw power from you computer. which means its more than likely going to be more reliable with the more devices that you connect to it. seeing that you have an bus powered external drive, its probably best to get a powered hub.
  4. sickmacdoc macrumors 68020


    Jun 14, 2008
    New Hampshire
    The main difference is what level of power the hub can provide in total to the ports it has. A non-powered hub can only divide up the power that the single port it is plugged into is specified to provide- normally .5A@5VDC.

    So in that scenario if you have several devices that have USB powering requirements, they will all be fighting for that one .5A@5VDC source meaning most or all will not work (particularly since you mentioned an external USB powered drive which sometime require a Y cable to obtain power from two ports on the computer all by itself).

    A powered hub is able to provide the specified .5A@5VDC (or more) to each of the ports on the hub rather than dividing the single .5A@5VDC provided by the computer's port. A 4 port powered hub will have a power brick that is usually capable of supplying about 2.3A@5VDC (4x.5A+.3A reserve), and a 7 port hub brick is usually rated at 3.8A@5VDC (7x.5A+.3A reserve).

    That way, each port is able to work with all USB devices no matter what their individual USB power requirements are. Non-powered ones are generally only good for low power requirement devices like keyboards and corded mice.

    EDIT: BTW a powered hub also eliminates the draw on your battery so your working time is longer than if you hang the devices off a non-powered hub.
  5. Siriosys macrumors regular


    Dec 24, 2007
    New Zealand

    Firstly, thankyou for providing such a concise explanation! I've always wondered and your answer was just the medicine I needed!

    Would be able to explain this:

    I've heard from a number of people who believe that their onboard USB port that has a USB powered hub plugged into it has become faulty due to voltage problems (over or under) with the powered hub. Have you ever heard of this happening?

    In essence, the comment I've heard is that "not all powered usb hubs are made the same"

    Do you think this is true? I'm not going to go as far as getting you to recommend a hub (unless you have some special nugget of info about a particular model!) as I've seen countless threads on this and don't want to waste your time.



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