ATX Power Supply

Hi All - Need a little electronic guru help :-)

Have an old but functional power supply that I would like to use to run some accessories off my RV generator. How in the world do you make an ATX power supply turn on. Pin 14 of the ATX Main Power Connector says PS-ON (green wire) and I have tried grounding it with no success.

What type of signal do you use on pin 14 to turn on the power supply?

Also is it possible to wire it to turn on and off with the on and off switch?

Thank you for the help
Tom G
17 answers Last reply
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  1. There's another pin, but I forgot what it was. I once had a power supply where the two wires needed were thinner than the power wires. Look at the pin chart and figure it out, you have 12v, 5v, 3v, -5v, -12v, and the other two, I believe.

    <font color=blue>There are no stupid questions, only stupid people doling out faulty information based upon rumors, myths, and poor logic!</font color=blue>
  2. You also have to connect the power good wire (grey IIRC) with the ground next to it.
    Then connect the green whire with a switch just like the reset switch (which only switches on while pressed... doorbell works the same way) and with the ground next to it.
    It should work that way.

    My dual-PSU PC is so powerfull that the neighbourhood dimms when I turn it on :eek:
  3. You do not connect the grey Power_Good wire to ground because that wire is just a power-on reset signal for the computer. There is only one control line for an ATX supply, and that's the green Power_On wire on pin 14. Any remote voltage sensing wires are not absolutely necessary.
    Some ATX supplies will not run without a load on the +5V (red wires), which you can provide with a 10-50 ohm resistor rated for a wattage of at least 100/ohms (i.e., 10 watts for 10 ohms, 2 watts for 50 ohms). A few supplies require a similar load on the +5V (orange wires) as well.
  4. And how do you explain that you have most site's that have guides for dual PSUs say that you must connect the power good wire?
    Here is an example pic: <A HREF="" target="_new"></A>

    My dual-PSU PC is so powerfull that the neighbourhood dimms when I turn it on :eek:
  5. Quite simple: they're wrong. The Power_Good signal is an output from the power supply, so what purpose does it serve to ground it? OTOH it doesn't hurt to ground it because Power_Good is an open-collector signal, which also means that multiple Power_Good signals can be tied together to provide a signal that shows when all the power supplies are putting out proper voltages.

    Normally, the only wires you connect together in a dual supply system are the grounds (connecting the cases together is not enough, as some power supplies don't connect the output grounds to case) and the Power_On signals.
  6. According to the website that pic was from the power good signal functions as a security option that the PC wont power on if the mobo plug is wrongly connected. So according to their theory that wire is gounded inside the motherboard so the PSU can detect that the plugs are connected properly. Atleast that is what they state.

    My dual-PSU PC is so powerfull that the neighbourhood dims when I turn it on :eek:
  7. Anyway I tested it with an old AT PSU from a 286 and it works without connecting the power good. So I guess it doesn't count for (atleast old) AT PSUs.

    My dual-PSU PC is so powerfull that the neighbourhood dims when I turn it on :eek:
  8. That is ridiculous. The Power_Good signal is like a power-on reset that goes true within 0.1-0.5 second after the power supply voltages have stabilized, and it turns off if any of the voltages drops below its lower limit. This is what the ATX/ATX 12V Power Supply Design Guide ver 1.1 says:

    "PWR_OK" is a "power good" signal. It should be asserted high by the power supply to indicate that the +12 VDC, +5VDC, and +3.3VDC outputs are above theundervoltage thresholds listed in Section 3.2.1 and that sufficient mains energy is stored by the converter to guarantee continuous power operation within specification for at least the duration specified in Section 3.2.11, "Voltage Hold-up Time." conversely, PWER_OK should be deasserted to a low state when any of the +12 VDC, +5 VDC, or +3.3 VDC output voltages falls below its undervoltage threshold, or when mains power has been removed for a time sufficiently long such that power supply operation cannot be guranteed beyond the power-down warning time. The electrical and timing characteristics of the PWR_OK signal are given in Table 14 and in Figure 2.

    All this signal does is indicate the state of the power supply; it is not a security option (it's not an optional signal) that prevents PC turn-on if the motherboard connector is inserted incorrectly (very difficult, but it is possible to leave off the Aux and 12VATX connectors, which can lead to unreliable operation that will likely not be detected by the motherboard, except by showing unreliable operation).

    The only purpose served by grounding the Power_Good outputs is to disable them. I believe that this can be done safely because they're open-collector outputs, but it makes no sense to ground them because if the motherboard sees Power_Good as low all the time, it won't ever turn on but stay in a reset state constantly. It may make sense to tie both Power_Good signals together so the motherboard doesn't start until both power supplies are ready and turn off if either one fails.

    Please provide a translation of the text explaining the reason for shorting the Power_Good signals.
  9. Now this is interesting... I use 2 ATX PSUs and they are connected the way that website recommended.

    But after what you said I think I'm going to connect the power good signal of the pSU not connected to the mobo with the one that is connected with the mobo.

    My dual-PSU PC is so powerfull that the neighbourhood dims when I turn it on :eek:
  10. The reason you can get by with shorting the Power_Good signal to ground is probably because it's an open collector output, meaning it isn't bothered by being shorted to ground because it works by shorting voltage to ground. And many motherboards contain their own power-on reset circuit (capacitor charges up through a resistor) to let them get by without an external signal for this. Tying Power_Good outputs together makes sense, but shorting them to ground does not.
  11. LOL no your not! :)

    <b>"If spam wasn't totally bogus, Hotmail users would be well-endowed, slim people with hair who make big money working at home and having great sex provoked by free porn and herbal Viagra.</b>
  12. Que? Posting useless posts PooBaa?

    My dual-PSU PC is so powerfull that the neighbourhood dims when I turn it on :eek:
  13. Well thanks for all this information. Now I can give more correct advise about PSUs.

    My dual-PSU PC is so powerfull that the neighbourhood dims when I turn it on :eek:
  14. Maybe the motherboard internally protects itself by staying in a reset state. Is it possible that CPU socket power is not applied BY the motherboard until the PSU gives the power good signal?
  15. There's got to be some kind of award for reviving a 7 year old post, right ?
  16. jamarno said:
    Tying Power_Good outputs together makes sense, but shorting them to ground does not.

    Will not tying together two 5v constantly-on signals from two different PSUs fry one of them, or both?
  17. Thread is from 2003.
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