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Thread: Powering USB 2.0 Hub off HDD +5v Rail - Any problems?

  1. #1
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    Powering USB 2.0 Hub off HDD +5v Rail - Any problems?

    Do you guys see any issues powering my USB 2.0 Hub (requires +5v) off of my HDD rail, which supplies +5v from the PSU. ???

    I'm guessing the USB hub does nothing but regenerate the signals, so I doubt it would draw too much power during use.

    What do you guys think?

  2. #2
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    if you gonna let it get power from psu .... why not buy a self powered one .... one that works off the usb 2.0 power from mobo .. (that inturn gets it from the psu ) .... so .. seems kinda useless to get it from the same source

  3. #3
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    I couldn't find one.. Can you post a link for one of these "self-powered" ones?

    Anyhow, it's too late.

    What I did so far was hack off the 120vAC adapter head, and wired up some terminal clips to hook into the +5v molex adapter to get power from the PSU's +5v rail. Do you think this will suffice? I don't see how it is different from using the 120vAC adapter which ouputted +5v....

    Kevin

  4. #4
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    You should be fine. Just remember that each USB port on your hub is rated to 500mA by USB spec. Then add 500mA for some space. So a 4-port USB 2.0 hub needs 5V up to 2.5A regulated. Check your power-supply to make sure there's plenty available on the +5V rail.

  5. #5
    Maximum Bitrate fantomas's Avatar
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    Quote Originally Posted by Q_gamelogic
    if you gonna let it get power from psu .... why not buy a self powered one .... one that works off the usb 2.0 power from mobo .. (that inturn gets it from the psu ) .... so .. seems kinda useless to get it from the same source
    i heard (dont know if its true or not) that the hub that is self powered from the mobo splits the power (500ma) between each port....
    rebuilding carpc... kinda..

  6. #6
    Variable Bitrate NoPistonPC's Avatar
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    The USB port on your mobo isn't required to provide more than 500mA. So if you plug in a 5-port bus-powered hub, it has to split up this 500mA among its ports. This won't be enough if you have several high-powered devices plugged in.

    You did the right thing by buying a self-powered hub and wiring it directly into your +5V rail.

    Here is a really article on self-powered vs. bus-powered hubs: http://www.microsoft.com/whdc/system/bus/USB/hubs.mspx
    1994 RX-7, EPIA P4-ITX w/ Celeron 2.4 Ghz, Arise PSU, Xenarc 700TSV (new model)

  7. #7
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    Acctually I think Powered USB hubs can get up to 6As per port...I think the 500mA spec was on USB 1.x only. When USB 2.0 came out I think it was raised.
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  8. #8
    Raw Wave rando's Avatar
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    Quote Originally Posted by Defiler
    Acctually I think Powered USB hubs can get up to 6As per port...I think the 500mA spec was on USB 1.x only. When USB 2.0 came out I think it was raised.
    According to section 7.2 of the USB 2.0 spec at http://www.usb.org/developers/docs/usb_20.zip a single USB device can consume upto 5 unit loads. A unit load is defined as 100mA.

  9. #9
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    Quote Originally Posted by rando
    According to section 7.2 of the USB 2.0 spec at http://www.usb.org/developers/docs/usb_20.zip a single USB device can consume upto 5 unit loads. A unit load is defined as 100mA.
    Sorry, was thinking USB Plus power...

    http://www.usbpluspower.org/
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  10. #10
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    +5V @ 6A's. 6 amps down 20 Gauge USB wires.

    Sounds like fun!

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