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Thread: Power supply question...

  1. #1
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    Question Power supply question...

    Could you use a computer power supply in a projector? The have at least one 5+ volt, a 12 volt, and a 3.3 volt rail. I think the 12 volts are up to 25 to 30+ amps and some have more than one 12 volt rail...
    Love, peace, and grease,

    allthat... aka: aaron@pangolin

  2. #2
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    Sure you can..
    The newer ones I like esp because they dont require a load to fire-up
    Its the +5 volt rail that has the most current ~15 to 20amps
    The +12 is usually only good for about 5 or so amps..
    Your mileage may vary...
    "My signature has been taken, so Insert another here"
    http://repairfaq.ece.drexel.edu/sam/laserfaq.htm
    *^_^* aka PhiloUHF

  3. #3
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    I think an ATX supply needs a link between pin 4 (a green wire), to ground (a black wire). There's one next to it on pin 5 on the mainboard connector. Get a second opinion though, it's possible that new supplies don't need that sense wire OR the load that older supplies needed.

  4. #4
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    I use a computer power supply in my projector, it's working perfect
    I supply all of my lasers (replaced the 5V - 5A power supply for my Lasever modules).
    You can even have +24V if you use both +12V and -12V bridged.
    Yes you'll have to connect the remote wire to the ground to switch on the power supply. You can connect it through a commutator to have the possibility to switch on and off...

    This is the one at the center of my projector (I removed the case of the power supply) : http://picasaweb.google.com/sebastie...66566471918578

  5. #5
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    Thumbs up

    Awesome guys! Just what I thought, but I am no expert with power. I was going to ask if I could get 24 off two 12s.

  6. #6
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    You can, but don't isolate the mains grounds, find the DC ground instead and isolate that from the case, then you can ground each case safely but also connect red to black of another supply like you would with a battery. It's not always easy to find and isolate the DC ground, in general, the better the supply, the easier it is to do without damage or danger.

  7. #7
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    Be carefull about bridging the same PSU for 24V

    as the +12v can handle a couple of amps but the -12v can only drive a few hundred miliamps

    all the best ... Karl

  8. #8
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    Yep, Thats true, Be sure to Isolate both supplies.

    If you use 300w supplies the 12v could be good for at least 8 amps. A 200 was 6amps and a 150 was only 4amps.
    Again, Your milage will vary.

    I did a test on three different supplies while at work today (It was slow today).

    I found not only do you need to short the green wire to ground but you also need to short the voltage good wire (violet) to a
    (red) +5v wire for the supply to come up. Then you can use the green wire thru a switch to ground (black) if you like to power the unit on/off and still have a Standby +5v line to power an LED or feedback to a PC or something..also this way you could use the PC to power up the supply as well.

    On the three supplies I did find the 12v a bit on the low side (11.50 to 11.75)
    but should work on most things ok. The +5 was (5.05 to 5.19) .
    so keep that in mind when using them for projects.
    If I was going to use them on Laser supplies I think I would add zener diodes to the outputs to be safe as I did notice on the DVM (didnt bother with a scope) when measuring the +12 it did spike to about 12.5 or so very briefly.
    Looks like they need some settling time..looked like about a 1/10 of a second.

    Anyhow, I gotta get back to work...
    Last edited by marconi; 05-28-2007 at 19:35.
    "My signature has been taken, so Insert another here"
    http://repairfaq.ece.drexel.edu/sam/laserfaq.htm
    *^_^* aka PhiloUHF

  9. #9
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    Yeps, that true, -12V can handle 300mA only. But that's more than sufficiant for what I use it (the shutter).
    My 5V can give 30A, so I don't overload it a bit.

    But I don't had to connect the violet wire to +5V...

    About computer switching power supplies, I was thinking that computer motherboard and its components requires good quality voltages (great stability and noise free), so there will be no problem to use it for my laser projector (and I hope I was thinking right).
    But the zener is a good idea though.

  10. #10
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    ***WATCH FOR NOISE***

    I have come across MANY ATX power supplies that are incredibly noisy on the output signal. I was under the impression that ATX Supplies are well-regulated...but I was wrong. Don't go buying a $17 ATX expecting it to have a clean output voltage.

    ...and when the source voltage is dirty, it will track all the way down the line to your scanners.

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