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-- Power Up an ATX PSU without a Motherboard
-- 7.18.2001
-- By: GideonX
-- Page: 1

   Today we have a quickie guide on powering up a power supply without the aid of a motherboard.  This guide is aimed at the user who needs just a little more power to get that peltier working or to get more fans in your box.  A 250W may not be enough for those chores, so here we have a solution.  Get another PSU just to power those specific components.

   As most of you know, motherboards usually come with just one ATX plug.  How that works is, the two pins on the row of your motherboard is usually connected by a momentary switch.  To put it in layman's terms, the switch you press in front of your case causes a 'jump' in those two pins which in turn tells the power supply to turn on.

   The above picture is the general design of an ATX plug.  The green box and black box are the exact locations on the plug we will be working on.  The green (Pin 14) is designated as the power on line, while the black (Pin 13) is just a ground line.

   To keep a PSU alive, a momentary switch is not needed since you will not be going through a motherboard.  A permanent switch is needed though, to keep it powered as long as needed.  To do this, we will need the follow:

  • SPDT (single pull, double throw) Switch
  • ATX Compliant Power Supply

   That's it, all we need is a switch that can stay on all the time and the PSU will be continuously powered.  Some people have mentioned that just taking a wire and connecting the two points on the plug will do it.  To turn off the unit, just hit the switch on the back of the PSU.  Well, what happens if you don't have a switch on your PSU?  That's where the SPDT switch comes in handy.

   Here are the two wires that come out from the SPDT switch, you don't really have to worry about which goes where since the switch will just act as a pass through.  Either wire can be placed within the green or black connector on the ATX plug.

   You can solder those points into those plugs for a more permanent solution.  We just placed it in position for the time being to make sure everything was working.

   To test if the little mod worked, we will attach a small heatsink with a molex connected fan to the power supply.  We turned the power supply switch to the on position after attaching our SPDT switch.  The SPDT switch will be used to power on/off the unit from now on.  It is fortunate we have both switches to utilize, but if you are stuck without a master on/off switch on your PSU, the SPDT can be used instead.

   And there you have it, we have our little heatsink spinning up just fine.  Make sure when you plug more devices onto your extra PSU, to power down first to prevent any sparks and failures.  Take it from us : ) Good luck!

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