ATX bench PSU

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    • New

      Frank_fjs wrote:

      I'm referring to the Molex 4 pin connector, the 8981 or whatever it is. It has 1 x +5V, 1 x +12V and 2 x ground wires and the connector itself is rated at a much lower amperage as it's only designed to run a hard drive.
      If I remember correctly, a "4-pin molex" commonly seen on ATX power supplies are rated at a non-additive (you're limited to pulling max amps at either 5 OR 12v, but not both) 10A per pin up to 16awg, 8 at 18awg, and 6 at 22awg.
      Not sure if there are any boards that draw even 8A of 5V.
      Of course thicker wire or doubled up wire is better than just a single wire, but you would expect the power supply's included cables to be able to meet (or meet 80% of rated) spec assuming no extensions attached.

      I want to again suggest to inspect the sense lines on the 24 pin. Most modern power supplies that include sense wires simply double up the sense line to a supply pin, but sense lines are not covered by the ATX spec (they are only mentioned as optional but recommended), so different power supplies may do it differently with some designs possibly relying on the motherboard to tie the pins together.

      That said, I think invzim is on to something regarding the power delivery through that supergun, as the simplest explanation is usually the correct one. Anybody know what supergun that is?
    • New

      I think "sense lines" is what I'm looking for but how can I identify them because there is no mention in the PSU's specs.


      I found below information from this site >>

      The 24-pin of the Type 4 cable set also has a unique feature not implemented in the standard Type 3 cables.
      There are a total of 28-pins where the cable plugs into the PSU's modular interface, instead of the usual 24-pins.
      The extra four pins are "sense wires"
      . While a +3.3V sense is part of the ATX standard and is found on most PSUs, it is not often implemented.
      The RMi not only utilizes the +3.3V sense on the ATX connector, but also utilizes an additional +12V sense and +5V sense.
      These sense wires read the voltages at the load (the end of the cable) and can increase voltage automatically if voltages drop.

      The post was edited 1 time, last by phoenix07 ().

    • New

      phoenix07 wrote:

      I think "sense lines" is what I'm looking for but how can I identify them because there is no mention in the PSU's specs.
      Sense lines are located on the 24-pin ATX connector. They feed the voltage at the connector back to the power supply to detect over and under voltage conditions and make corrections. Usually you will see these lines bundled to the same pin as a supply line, but others, like 3.3v sense for example, can sometimes be found on pin 13 all by itself. Generally, these will be thinner gauge wires of the same color as the supply wire it is monitoring (reminder to never rely only on color, always use a meter and pinout diagrams to check things!).

      You should first check that the problem is the power supply and not your supergun though, as no amount of messing with sense wires will help you if the supergun is the one causing the problems by not being able to handle higher current loads.

      Measure the voltage at the JAMMA edge, and then check the voltage at the molex connector you use to supply power to the supergun/board. If the voltage at the supply connector looks ok, but you're seeing huge drop across to the JAMMA edge, invzim is right, and your supergun is not designed well for power delivery.
      If that is the case, your options then are, I suppose, to replace the supergun with something better, or, to inspect the supergun design and see if you can modify it safely to supply power to the edge by jumping a wire to the edge or something.