noisy relay

I just installed a high amp relay like used on air conditioners for my well pump, part 6564K55 McMaster Carr, rated at 40 amp. The enclosure box is
mounted to the floor joists just below the dining room (big mistake).
About once in 50 starts the relay buzzes. The floor joists make a nice sounding board. SWMBO is NOT happy. It would be a difficult job at best to move the control box at this point. I could replace the box, but I have rigid conduit going to this location both from outside the house and over to the main panel.
Such a thing as a 0 noise relay??? Probably not. Sound deadening ideas(that meet electrical code)? other suggestions?
Karl
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Karl Townsend wrote:

If the relay box is just screwed to tthe floor joists you might try placing rubber washers between the joist and the box and between the screw head, with a washer and the box. that SHOULD isolate the box from the joists and end the problem. I hope I explained my idea sufficiently. It would also help if one of the washers extended into the mounting hole on the box to keep the box isolated from the screw completely.
Jim
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"Jim Chandler" wrote: If the relay box is just screwed to tthe floor joists you might try

^^^^^^^^^^^^^^^^^^ That would fix it. You may run into some difficulty raising the box enough to fit the necessary rubber washers, because of the conduit that is already in place. You might be able to just squeeze in a layer of rubber between the joist and the bottom of the box. It that doesn't fix it, then consider removing some wood from the side of the joist, so the box doesn't touch it. Let the conduit support the box, or add some other support (like springs.)
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Can you use an appropriately rated solid state relay?
i
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Karl Townsend wrote:

Yeah, an SSR. But it would have to be rated for the max (start) current.
Bob
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Rectify the voltage to the coil, use a decent size of smoothing capactor, and it should be nice and quiet - you'll need to put a voltage dropping resistor in series to limit the current to the original value.
AWEM
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Andrew Mawson wrote:

You beat me to it! I was gonna suggest a bridge rectifier, cap and dropping resistor too.
However, upon rereading the OP, he states that the relay only buzzes "about once in 50 starts".
That says to me there's something not right with that relay, likely mechanical sloppyness, and if he recently purchased it, perhaps he might be able to swap it in for a warranty replacement that never buzzes?
Jeff
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...
I originally dismissed this suggestion. Remember, I want 20+ year reliability. Sounded a bit cobbled together to me. Will this really work well?

Its McMasterCarr. They are great on warranty. Is replacing more than a long shot? More likely, I should go to a different brand; another will do same thing.
Karl
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work
It'll only be cobbled together if that's the way you execute it! It's a good technical solution - use quality components and well engineered mounting and it'll be reliable
AWEM
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On Wed, 13 Aug 2008 11:59:55 -0500, "Karl Townsend"

Bosch makes nice 40 amp relays for automotive use, that are totally enclosed cubes. They would be prefect except it's dc.
This isnt what I have used in the past but will work.
Here are some ac solid state units.
http://www.crouzet-usa.com/catalog/_ssr.shtml Daveb
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On Wed, 13 Aug 2008 18:54:18 GMT, the renowned snipped-for-privacy@nt.org (DaveB) wrote:

12V-rated automotive relays should not be used on the mains. They don't generally have high enough breakdown voltages guaranteed to get UL/CSA approvals, for one thing.
If it doesn't start too often you could look at the Potter and Brumfield (or Siemens or Schrack or Tyco or whoever owns them these days) T92.
http://www.pandbrelays.com/schrack/pdf/T92.pdf
Check the ratings, obviously, before buying. They're not expensive- maybe $12-$15. each in singles.

Best regards, Spehro Pefhany
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If you try to reduce the sound (instead of switching to a SSR), I would suggest trying to increase the mass of the box which is holding the relay in addition to trying to isolate it from joists. The heavier it is, the less it will vibrate which translates to less sound radiated. If you can for example mount it to a nice heavy piece of steel, and then isolate that with some rubber mounts from the joists, it should help reduce the level of noise produced.
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The "once in 50 starts" says you have a bad relay or some sort of low voltage in the driver circuit. I'd be looking at that. Hook up the meter, wait for it to buzz, see what voltage is across the coil.
Karl Townsend wrote:

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Karl Townsend wrote:

Pull the relay box loose and suspend it with a rubber strap. Pull it loose and use some silicone caulk around each screw to stop the transfer.
Convince SWMBO that this is a safety feature so you can monitor the pump! Buy SWMBO a pair of ear plugs! Replace SWMBO!
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Ease rubber sheet or washers under the box. Make a fiberglass enclosure and those will help deaden the sound.
Martin
Martin H. Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net TSRA, Endowed; NRA LOH & Patron Member, Golden Eagle, Patriot's Medal. NRA Second Amendment Task Force Charter Founder IHMSA and NRA Metallic Silhouette maker & member. http://lufkinced.com /
Karl Townsend wrote:

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    I suspect that the buzz comes from a small bit of dirt or grain keeping the solenoid from closing fully. If you can keep it fully clean, it should not buzz -- but that may be difficult.

    Look into a SSR (Solid State Relay). Opto isolater input, something like 3V to 32V DC to turn it on, anything less and it turns off.
    The ones which I use are 20A 240VAC ones, but I'll bet that you can find 40A or 50A ones. You'll want to mount it to the metal box with a heat-sink goop to keep it cool -- especially if you are using it near its rating.
    Good Luck,         DoN.
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others have suggested the SSR approach - there is another approach - energize the relay with DC instead of AC - presuming it's a 24 VDC relay (or is it a 220V coil?) just rectify, and add a filter cap

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Ned convinced me that SSR is not that good for my application. The coil on this one is 120 VAC. McMaster sells the same relay with 24 volt DC coil. Will a DC coil not buzz? I'll switch it right out if this is true.
Karl
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On Thu, 14 Aug 2008 05:20:48 -0500, "Karl Townsend"

It shouldn't buzz, but you'll still get the clank when in operates, of course. But I don't see 24VDC, only 24VAC, which will be no better.
DC coil contactors are also more efficient so the coil will run cooler.
Best regards, Spehro Pefhany
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you don't need to change coil voltages. Others have provided good info. here is some more background
the buzz is because your AC current goes through zero 120 times per second, and so if the actuator is not fully retracted, the spring will lift it a bit - it is exactly the design of a buzzer. An AC relay coil has an extra small copper winding to help this but the buzz is not fully eliminated, and as you have discovered, it can be pronounced. Going to DC eliminates the passage through zero, but only if you add a filter capacitor also - if you use a 120V coil, pretty much any motor start or run capacitor will do the trick (I'm picking parts you may have lying around). If you are worried about current limiting, add a series light bulb whose current is near the coil current (light bulbs, conveniently, are kinda sorta constant current devices over their useful operating range) - 100 watts per amp aproximately

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