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Old 11th April 2010, 11:57 AM   #1
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Default Buzzing AC relay coil

Hi all,

I have a largish AC relay I want to use for B+ switching. The coil is rated 230V 50-60Hz. I get a rather loud buzzing sound from the coil when energized. This makes it not so suitable for audio use, of course.

Occasionally, though, it slides into a state where it is very quiet. It would be great if I could get it to do that every time. Anybody have experience or ideas on how to snub AC relay coils?

Thanks
Kenneth
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Old 11th April 2010, 12:46 PM   #2
Mooly is offline Mooly  United Kingdom
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It's all been covered here,
Swappin' Mech Power Relay for Solid State
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Old 11th April 2010, 01:05 PM   #3
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Hi Mooly, I forgot to mention the relay is to switch 1500VDC, 500mA. So replacing with a SSR is not an option.

Kenneth
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Old 11th April 2010, 01:28 PM   #4
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You might try reducing the relay's spring tension slightly. That will make it operate at a somewhat lower voltage and might stop the annoying buzzzzzz.
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Old 11th April 2010, 01:44 PM   #5
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Quote:
Originally Posted by Mooly View Post
It's all been covered here,
Swappin' Mech Power Relay for Solid State
OK, I read the entire thread now, thanks for the link. Will try to operate it from low DC with a 'kick start'.
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Old 11th April 2010, 02:53 PM   #6
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You need voltage to drive current through a coil to produce a magnetic force to close the contacts. When your 60 Hz AC cycle falls to zero there is no voltage, therefor no current and no magnetic flux to pull in the magnetic circuit.

The AC relay you have has a shading pole ring on the armature. What it does is keep current flowing in the ring when the instantaneous AC voltage drops during the low part of the cycle. (I will not go into how and why it works.)

Sometimes the ring gets loose and it will buzz. Other times it could be a loose lamination in the armature that causes the hum. The hum is intermittent in your case so it sounds like a mechanical issue with your relay. You could try a drop of cyanoacrylic glue to bond the loose part together.

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