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using a PC PSU outside a PC?

Discussion in 'Home Cinema Building DIY' started by MarkHudds, Jun 1, 2004.

  1. MarkHudds

    MarkHudds
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    How would I use a PC PSU to power 12v DC fans without a PC power switch?

    (It's a hushbox application).
     
  2. Chris Muriel

    Chris Muriel
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    A modern PC "silver box" PSU may not work right out of the box externally because these produce a 5Vsb signal as long as mains is applied via the IEC connector even of the PC power on/off switch is set to off ; this supplies the voltage-signal needed for the mobo's "Powergood" function.
    An older PSU (therefore not "P4 compatible") would work as long as it doesn't need some draw on the +5V supply to operate (some need this). An old (broken) hard-drive could supply this load if needed (or even something like a 50-ohm resistor).

    Chris Muriel, Manchester.
     
  3. tonyb

    tonyb
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    Hi Mark,

    Chris is quite correct when he says that the 'new' (ATX) power supplies require a load for them to power up, and that the older AT style units work fine without a load.

    The other problem with ATX units is that the power switch is often done electronically (don't ask me how!) rather than the mechanical switches found on AT units.

    But there is a solution! A few months back I wanted to run a few neon cathodes away from a pc, and using a pc power source seemed an easy option. I did a bit of looking around on the web to see what could be done to get round the problems of using an atx supply. The solution is that you simply place a wire loop between two of the pins on the motherboard connector and this allows the unit to be run without a load, it also solves the switch issue as the unit will fire up as soon as the mains is switched on. Provided that you link the two pins in a sensible manner there should be no problems.

    The only downside is that I cannot remember which two pins you need to link, but give me a couple of days and I'll post back with the details.

    Hope this helps,
    Tony
     
  4. tonyb

    tonyb
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    Mark,

    Finding the article wasn't as difficult as I had thought. I followed the steps in this article over at modtown.

    I can confirm that the mod works, though I would suggest you make it a little safer by cutting the two wires before they enter the motherboard connector and soldering them together and covering with heatshrink tubing.

    When testing after the mod, I plugged into the mains socket via an RCD, just in case anything went pear-shaped. Provided you are careful, and take your time you should have no problems, though if you are in any way uncertain about doing this DO NOT DO IT!

    Cheers,
    Tony
     
  5. MarkHudds

    MarkHudds
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    Many thanks for the info guys!

    tonyb - excellent link, thanks ... couldn't find any guides like that when I googled!

    Just got to decide between a PSU and a standard mains adaptor now ...
     
  6. Chris Muriel

    Chris Muriel
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    That little modification bypasses the electronic Powergood sensing lock that I mentioned.
    Should be ok though.

    Chris Muriel, Manchester.
     

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