Re: Reduce volume of AC buzzer

default wrote:
On Wed, 06 Feb 2008 18:28:15 -0500, John Popelish <jpopelish@xxxxxxxx>
wrote:

Steve Greenland wrote:
I've got an old Gralab darkroom timer with a buzzer that is, to my
taste, way too loud. Some Gralabs had a volume adjustment knob, this one
doesn't. I'd like to add one.

The buzzer is labeled:

U.S. Controls Corp
120V, 50-60Hz. 4W
Pat. Pend. Int. Duty
25%W/Max. Ontime
30 Sec.@65C. Max
10037-63
(snip)
Or you might use a series capacitor that is rated for plenty of AC voltage (say, 250 VAC) to drop the extra voltage without producing heat. Something between 0.1 uF and 1 uF might do it.

Is that safe, in an inductive load?

I've never done it , in spite of using caps for LV supplies. My
concern is that I might form a series resonant circuit and get some
reactive voltages much higher than I was planning on.

Just curious on what you think.

I doubt it is a very high Q inductor, but, it is possible that there is a resonant capacitor value that would peak the voltage measurably above line voltage. That would make it louder, so I doubt the O.P. would use that value for long. But that possibility is the reason I said the cap should be rated at twice line voltage. No point in having the cap pop during a momentary test.

But as long as the capacitor value is considerably less than the resonant value (somewhere around 2 uF, I think), the cap will drop the voltage applied to the buzzer, even though the sum of the cap drop and the buzzer drop may add up to more than the line voltage. I.e. he might like the sound where the voltage across the buzzer is 3/4 of line voltage, and the voltage across the cap is also 3/4 of line voltage.

--
Regards,

John Popelish
.

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