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Ask Slashdot: Reliable Powering of ATX Systems?

Posted by Cliff on from the coping-with-soft-power-switches dept.

David Muir Sharnoff writes in with this question: "ATX power supplies don't supply power unless the motherboard says to turn on. Many motherboards do not have a setting of: 'supply power all the time.' This means that ATX systems cannot safely be used a servers. Anyone know of an ATX power supply that ignores signal? " More appropriately: does anyone know of an ATX motherboard/power supply/case combination where powering is similar to AT systems?

5 of 173 comments (clear)

  1. ATX specification URL by Anonymous Coward · · Score: 5

    The ATX specification can be found here:

    http://www.teleport.com/~atx/spec/index .htm

    (Boy I hope this message get moderated up.
    That would be keen.)

  2. Do it in hardware by Booker · · Score: 5
    Pin 14 on the ATX power supply connector is the "PS-ON" signal. From the ATX spec:
    PS-ON is an active low signal that turns on all of the main power rails including 3.3V, 5V, -5V, 12V, and -12V power rails. When this signal is held high by the PC board or left open circuited, outputs of the power rails should not deliver current and should be held at a zero potential with respect to ground. Power should be delivered to the rails only if the PS-ON signal is held at ground potential. This signal should be held at +5VDC by a pull-up resistor internal to the power supply.
    So, you should be able to hack it together to have that pin permanently grounded, so that the PS is always on. I haven't tried this; I think it should work fine, but don't blame me if your motherboard burns! :-)

    There's also more info on ATX at http://www.teleport.com/~atx/

    1. Re:Do it in hardware by komet · · Score: 5

      We do this with all our servers (medium-size ISP in Europe) and it works without any problems at all.

      Just take a bit of the isolation off the wire of Pin 14 (usually, bit NOT ALWAYS green). There's a GROUND signal on either side of this; take the isolation off that as well. Then solder together and wrap with insulating tape. Works like a charm. The only thing you shouldn't do is tell the mobo to power off; it gets a bit confused then.

      This is where pin 14 is:
      Looking down onto the contacts: (wires on rear)
      v--(plastic tab)
      ===
      + + 0 # 0 + + + + +
      + + + + + + + + + +

      # is pin 14. 0 is ground signal, should be a black wire.

      --
      Any technology which is distinguishable from magic is not sufficiently advanced.
  3. Do it with hardware by SEWilco · · Score: 5

    At hardware and auto parts stores you can get solderless connectors which tap a wire into an existing wire. You can use two of them to add a wire which connects the wires for pin 14 and a neighboring wire. They're usually blue plastic with a metal tab which you push into the two wires. Faster than soldering and can be removed for maintenance.

  4. A couple options by Zachary+DeAquila · · Score: 5

    There're a couple of options

    Some ABIT motherboards can be strapped with a
    jumper between the reset and power switch connectors to make them act in an 'always on'
    fashion like AT motherboards do.

    If you feel like experimenting a bit, you can
    look in electronics parts catalogs for POST
    transistors... these basically act like delayed
    momentary-on relays. One lead goes to +5V,
    the others go to the power-switch jumper.

    --Z