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Voltage from a plugpack measured with no load

Discussion in 'Hobby Electronics' started by T.T., Mar 2, 2011.

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  1. T.T.

    T.T. Guest

    I have a no-brand plugpack that is labeled "output 9V DC".
    If I try to measure the voltage using a DMM, I get a value of 14odd volts.
    I believe trying to read the output voltage of such a device without load
    gives unreliable results.
    Is this so?
    If so, how can I check the output voltage on this plugpack?
     
  2. T.T.

    T.T. Guest

    That was quick! Thank you.
    The plugpack is labeled 9Volt DC 1 Amp. It is from an old Casio music
    keyboard.
    I will hunt around for a suitable globe.
     
  3. T.T.

    T.T. Guest

    I don't know. The keyboard must be twenty years old, and I was asked to look
    at it by the organist at the church. The keyboard had died and at first
    sight it looked as if the plugpack was dead. A closer look revealed that the
    coaxial plug that plugs into the keyboard had pulled out of the two-pin
    connector on the end of the cable from the plugpack. It wasn't easy to see
    because the join was covered in heat-shrink. It was hard to see which way
    the co-ax plug had been connected to the cable, and I assumed that the
    centre connector was the positive and the outer was the negative. That is
    when I used the DMM, to check the polarity. And that is when I became a bit
    worried about the high voltage reading. I'm still looking for a globe.
    I guess the correct answer to your question(s) is I will be running whatever
    load was being required of it before.
     
  4. atec77

    atec77 Guest

    I would check the input for possible voltage and resistance , it might
    have electros in there or a diode which should offer a clue as to polarity
     
  5. T.T.

    T.T. Guest

    All is well. With a taillight globe the voltage read about 9V.
    I was wrong about the polarity. Centre pin is negative and the outer
    connector is positive.
    Thanks again for your help.
     
  6. Tom

    Tom Guest

    Lot of problems I've noticed with DC plugpacks are dried out electrolitic capacitors. Affected plugpacks show reasonable valuevoltage under no load but at normal operation produce excessive ripple that affect powered circuit. I observed a lot of that with modems, routers and other stuff with microprocessors.

    I guess the best test to find out if the plugpack or the keyboard is faulty is to get another 9-12 V known good power supply and power the keyboard from that.

    Tom
     
  7. Baron

    Baron Guest

    T.T. Inscribed thus:
    Oddly enough I have one of these in my Daughters old toy box. It is
    marked as you say 9V 1A. The manufacturer is "Niko" who ever they
    are ! Off load it measures 14.52 volts, into a 15 ohm resistor load it
    drops nicely to 9.15 volts.

    HTH.
     
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