Using a computer power supply as a bench supply

Discussion in 'General Electronics Chat' started by SteveGalvin, May 19, 2012.

  1. SteveGalvin

    Thread Starter New Member

    Oct 4, 2011
    I have an ATX power supply from and old PC and want to convert it to a 12V 5V and 3V bench supply to run a charger to power up lipos etc. I have connected all the 12V 5V and 3V and -Ve cables together and connected the green cable to ground.

    When I first just connected the green wire to ground with all the computer plugs still connected to the leads but unplugged from the computer the unit worked fine. The fan was running and all seemed OK. Now that I have removed the plugs ends and have all the cables grouped together with the white and purple are left not connected to anything, all that happens is the fan spins up for a fraction of second and stops. There is no 12V 5V and 3V at the terminals.

    What am I doing or have done wrong?

    Many thanks Steve
  2. MrChips


    Oct 2, 2009
    Some SMPS require a minimum load before they start/continue operating.
    Try installing a resistor load on the 5V supply line.
  3. K7GUH


    Jan 28, 2011
    While you're at it, look up one or two of the many articles on the web on how to perform such a conversion, then compare that with what you have in front of you.
  4. takao21203

    AAC Fanatic!

    Apr 28, 2012
    They are rather bad to use for such purposes, no good short circuit protection.

    Electronic transformer is better, and not expensive.
  5. Wendy


    Mar 24, 2008
    On the other hand, computer power supply power supplies are much cheaper, even free, in many cases, much cheaper than other alternatives. It is a common project, if you were to do a search on them you would find many writeups.

    I buy into the concept that current limiting is needed. But it is not absolutely necessary.
  6. dataman19


    Dec 26, 2009
    Have you tried applying the +5V to the power OK terminal (pin 8 on an ATX Power Supply - I believe this is normally a gray wire).
    The power on pin (pin 14 on an ATX power Supply) will turn on the power supply, but it will shut down if +5v isn't supplied to the Power OK pin (pin 8 on ATX units). And yes - you can use the +5v from the same power supply to keep it running, just in case you were wondering.
    Incidentally, here is a link to converting a PC Power supply to a bench power supply..
  7. absf

    AAC Fanatic!

    Dec 29, 2010
    Last edited: May 21, 2012