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Thread: Powered USB hubs

  1. #11
    Low Bitrate 2000Jeep's Avatar
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    Quote Originally Posted by W3bMa5t3r
    Just make sure your polarity is right.
    How is the best way of doing this?

  2. #12
    FLAC W3bMa5t3r's Avatar
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    Quote Originally Posted by 2000Jeep
    How is the best way of doing this?
    well your ac power adapter should say which part of your plug is positive and which is negative, so taking that, and a multimeter, check the wires (once you cut the plug off from the adapter, and see which wire matches up with the positive/negative respectively. use the continuity/beep/short setting on the multimeter.

  3. #13
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    intersting... but what if you need something like 8 volts, where do you draw this from... or would you use the 12v line with a resistor?

  4. #14
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    What would you possibly need 8V for ?

  5. #15
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    Quote Originally Posted by Un_discovered
    What would you possibly need 8V for ?
    I have two usb hubs, one uses an 8v input, the other 3v... hence my question!

  6. #16
    FLAC W3bMa5t3r's Avatar
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    Provided my memory serves me correct, yes, you can use resistors to drop voltage ;-). to figure out how much resistance for the correct voltage drop, you'll need to use Ohm's Law :-)

  7. #17
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    That's really bizzare, considering USB ports are 5V

  8. #18
    FLAC W3bMa5t3r's Avatar
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    Quote Originally Posted by Un_discovered
    That's really bizzare, considering USB ports are 5V
    Ditto... cuz even my 7 port hub (d-link) runs off 5vdc external... but hey... every manufacture to their own I suppose...

    Damn it's waayyy to early for me to be up... off to work I go...

  9. #19
    Variable Bitrate kamikaze2112's Avatar
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    if you use a 12v as + and the 5v as - you'll get 7v

    I dunno how safe it is to do this, but I've done it before on a homebrew fanbus i made. 5v wouldn't start some of the fans for a low speed, but 7v would.


  10. #20
    Constant Bitrate RawsonDR's Avatar
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    Quote Originally Posted by kamikaze2112
    if you use a 12v as + and the 5v as - you'll get 7v

    I dunno how safe it is to do this, but I've done it before on a homebrew fanbus i made. 5v wouldn't start some of the fans for a low speed, but 7v would.
    If you use a 5V line as the ground on the USB hub, it's possible that the 5V would be shorted to your car's ground through the USB cable. If not that, then say perhaps you have a USB touchscreen plugged into the hub, which would short the 5V to your car's ground through your touchscreen monitor which is properly grounded..... both examples are only theoreticals, but the point is that there are a lot of ways the 12-7V trick can fail. It works on fans and such because they are simple, isolated devices which don't share any other connections.

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