Buzzer soundless despite right voltage

[Viggo Simonsen]

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?

/Viggo

 

[Mark]

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?

/Viggo

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.
--
Mark

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

Triple Z is spam control.

 

[Viggo Simonsen]

No - the voltage is measured across the open circuit (end of wire)

/Viggo

 

[Owain]

Viggo Simonsen wrote

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?

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.

Owain

 

[Glenn Gundlach]

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.

Owain

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.

GG

 

[Jerry Greenberg]

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
http://www.zoom-one.com

 

[JeffM]

This is why an electrician with any experience uses a Wiggy.
http://www.google.com/search?num=10...&q=wiggy+electrical+tester&btnG=Google+Search

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.