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ATX pox supply controlled outside of box.

Discussion in 'Electronic Basics' started by Neil Jackson, Sep 16, 2003.

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  1. Neil Jackson

    Neil Jackson Guest

    Micro P4ATX 200W (3 Screw SFX)
    Switching Power Supply

    AC INPUT: 115/230 Vac~ 8/4A
    60/50Hz
    DC OUTPUT :

    COLOR : BROWN RED WHITE YELLOW BLUE PURPLE BLACK
    GREEN ORANGE
    DC : +3.3V +5V -5V +12V -12V
    +5V-SB COM PS-ON PW-OK
    OUTPUT : 11.5/18.7A 16/13A 0.3A 11A 0.3A
    2.0A RETURN REMOTE P.G.

    (3.3V and 5V Max Output 120W, Peak Surge Max Output 208W)

    Hello all,
    I'm having some trouble turning the above label power supply on. I.E. I'd
    like it to run outside of the computer.
    I'll be using this power supply to run a CNC engraver. The motors are
    three(3) 6vdc unipolar.
    I read elsewhere that I have to supply a small load across one of the red
    and com leads.
    Such as an old cdrom or 25ohm resistor. I really don't want to use the cdrom
    drive as it will increase the weight of
    my unit and I'm sure one of you guys are quite capable of creating a load
    that would be necessary to make this work.

    The site below and accompanying text is the controller unit that drives the
    motors
    http://www.stepper3.com/index.htm?31.htm&1
    (S3ROC) Stepper3 Rev OC - 3 Axis 3 Amp Unipolar Stepper Motor Driver



    I do have an older style AT box that will come on with the switch, but it
    seems to power down as soon as my three motors are running in unison. The
    fella at the site indicated below used 10ohm/10watt power resistors. How
    exactly he set them up is beyond me. He called them power limiters. I was
    assuming that the current draw from three motors running simultaneously
    (6vdc unipolar) would cause the power supply to shut down???????

    http://www.theworkshop.ca/metcastmach/FoamMill/foammill13/FoamMill13.htm

    Any help or a crude schematic would be extremely helpful.

    Peace
    Neil
     
  2. For ATX power supplies the PS-ON lead (green) must be connected to ground
    (black) to switch the PS on. You can safely keep it always connected there
    and mount a switch to the mains cable.
    How did you connect the motors to the PS? Did you use the +5V or the +12V
    connectors? If you used 12V and stepped it down somehow, it would be rather
    natural for the PS to shut down because it expects the load on the 5V lead
    to be much higher than on the 12V one. DO NOT USE -5V AND -12V! They are
    rated for very small power consumption only. Consider connecting the 3
    motors to the +5V connector and let them run with one volt less than rated.
    If this proves impossible for whatever reason and you have to use 12V, just
    get a 6V motor-cycle lightbulb and connect it to one of the +5V lines. This
    will make the PS run as rated and you can use the lightbulb as an auxiliary
    light mounted to the engraver. If this does not help consider reducing the
    maximal current at motor startup, maybe a simple 0.2-0.5 Ohm resistor to
    catch the peaks. Make sure you do not overload the motors by connecting
    them accidentally directly to the +12V line.

    I hope, this helps, if not, drop me a line.
    Dimitrij
     
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