Another very basic question (universal Power supply)

Discussion in 'General Electronics Chat' started by Etbauer, Jan 17, 2010.

  1. Etbauer

    Thread Starter New Member

    Jan 17, 2010
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    I purchased a universal power supply (sk600ns) no matter where i set the power selector it outputs 33V (as read by a multimeter) I also tested the voltage accross a solenoid, and it still reads about 25V no matter where i set the selector. Any suggestions about what I am doing wrong?
     
  2. retched

    AAC Fanatic!

    Dec 5, 2009
    5,201
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    Ummm, I hope you have the receipt.

    You hooked it up to a load, and tried multiple settings and they didn't change?

    Are you SURE you weren't adjusting the CURRENT?
    Are you testing for DC ?
    If so, the voltage wouldn't change. Try again and test for amps.

    [ed]
    Sorry, I just looked up the supply. There is no current adjustment. It's broke.
    http://www.electronickits.com/kit/complete/powe/powersupply.htm
     
  3. SgtWookie

    Expert

    Jul 17, 2007
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    Sounds like something has gone awry inside the supply itself.

    The regulator is running "wide open". These are not kit-built supplies. At this point, it's an unknown whether it's a switching supply, or if it might have a linear regulator such as an LM317M inside it, and the switch simply connects various resistors as R2.

    If it's a switching-type supply, it would have a similar arrangement; but it would be more efficient.

    One very likely cause is that the switch itself has failed. This would open the feedback loop for an LM317-type of regulator, and cause it to "run wide open"; regulator putting out as much voltage as it possibly can, because it's "being told" that the output isn't high enough.

    In a switching type supply, it would be more likely that the resistor from the output to the switch has failed as burned open. This would tell the switching circuit that the output is at zero volts, so it needs to increase the output current to bring the voltage up.

    If you have just purchased the supply, see if you can exchange it for a working supply.

    If not, you might try to open it up; but I'll bet that it's filled with epoxy or some sort of resin. They do that to keep the parts from flopping around inside, and it also makes it a lot harder to reverse-engineer them. If it's still under warranty, don't open it; exchange it.
     
  4. Etbauer

    Thread Starter New Member

    Jan 17, 2010
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    ok, sounds like its shot, dont think i kept the reciept, but oh well, it seems like it was workign when i got it, what could i have done to blow it?
     
  5. SgtWookie

    Expert

    Jul 17, 2007
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    It's hard to say what you might've done to cause it. If you overloaded the output, that might have caused it - or perhaps used it on an inductive load that caused large voltage spikes.

    Those supplies are probably made in China, and even though the quality of products coming from there have improved over the last decade, such low-end supplies will not have many (if any) built-in protections.
     
  6. Etbauer

    Thread Starter New Member

    Jan 17, 2010
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    ahh, and now that i think about it, i remembered i tested a solenoid with it, so im guessing thats what did it
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    If you did not have a "flywheel" diode across the solenoid coil, that could very well have damaged it.
     
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