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Buzzer soundless despite right voltage

Discussion in 'General Electronics' started by Viggo Simonsen, Sep 7, 2003.

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  1. Hi there,

    I am baffled by the following problem:
    Im trying to make a DC buzzer work. I've got a DC power supply 12V,
    4,8 W.
    Connecting the terminals directly to the buzzer produces a clear sound
    - so the buzzer is all ok.
    From the DC source there is a cabling of about 20 m to another room
    where the voltage is still 12,5 V. But here, the buzzer fails to make
    a proper sound; there is only a faint attempt, and there is no DC
    current measurable through the buzzer either.
    The voltage at the far end of the DC source suggests no breach of the
    line, the impedance of the cable is negligable compared to the buzzer
    (otherwise there would also be voltage drop), the current can easily
    light up a bulb - but it can't drive the buzzer.
    Has anyone got a clue what the problem may be?

  2. Mark

    Mark Guest

    You _may_ have made some false assumptions.

    Is the voltage reading at the far end taken under load
    (buzzer connected)? If not, it tells you nothing about
    adequate current reaching the far end.

    The truth as I perceive it to be.
    Your perception may be different.

    Triple Z is spam control.
  3. No - the voltage is measured across the open circuit (end of wire)

  4. Owain

    Owain Guest

    Viggo Simonsen wrote
    Are you *sure* the polarity at the far end of the cable is correct? If
    you're measuring it with a digital meter you might be misreading
    -12.5V as 12.5V. If you didn't install the cable yourself perhaps
    there is a mis-wired joint somewhere.

  5. Just for laughs, put a cap (100-1000 uF) across the buzzer terminals.
    You might have some droops you don't catch with a meter. The buzzer is
    a coil driving a spring loaded switch, right? The surges may be
    preventing the coil from fully activating. Just a thought.

  6. Make sure that the polarity is correct, and that you are testing the
    voltage with the buzzer connected.

    The wire guage may not be enough to supply proper current to the
    buzzer while loading. Never measure the voltage without the load.
    This will give a reading, not including the effective resistance of
    the cable.

    A larger cable guage is most likely required.

    Jerry Greenberg
  7. JeffM

    JeffM Guest

    This is why an electrician with any experience uses a Wiggy.

    Consider the voltage divider with the 1 ohm resistors
    representing the resistance of the wire (skinny?).
    If the termination is a meter with a 10 Mohm resistance,
    a lot of sins can get glossed over.

    1 ohm
    / termination
    1 ohm

    Now imagine a 10 ohm termination. The voltage drops change.

    A Wiggy is a tester with a real-world resistance.
    It never allows these near-open-circuit conditions to exist and to
    fool you.

    Load things out to do your tests.
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