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Old 08-16-2011, 08:57 AM   #1
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Electrical hum

I posted this question last year and the problem has popped up again....or maybe I never actually understood the answers.
Fleetwood diesel bounder. In the shore power electrical compartment there is a
Relay - trombetta 114-1211-010. 12v/cont - that continually humms.
Is this a problem and if so how do I correct it.
Has posts leading to the batteries on the top and a couple white wires leading to a control box on the bottom. Round 4 inches high one and a half inches in diameter.

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Old 08-16-2011, 10:07 AM   #2
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A 12 volt DC relay should not hum..

A 120 volt relay may hum.

What make and model of converter do you have in that house?

And what is the control box?

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Old 08-16-2011, 10:09 AM   #3
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I have the Same type of Hum for 120....... it is not really loud, but in the compartment you can hear it......
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Old 08-16-2011, 10:31 AM   #4
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Trombetta relays are continuous duty relays. They will be hot to the touch but I have not noticed mine humming. The Trombetta 114-1211-010. has copper contacts that are prone to corrosion. Trombetta, also produce a version having silver alloy contacts, 114-1211-020. This version has lower contact resistance and is far less susceptible to corrosion. It might be worth the cost to replace the relay with the better version and save the old one as a spare. My 114-1211-010 failed this spring and you can see the pictures on the last post of this thread Dead Starting Batteries.
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Old 08-16-2011, 10:42 AM   #5
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Electrical hum

Thanks for the replies. Battery control center is by Rv custom products...charger/inverter is by magnum energy.
Fleetwood tech got back to me and said the control operates when either bank of batteries goes above 13.3. Said he is not sure if the hum indicates a problem.
I,m not sure what a previous post meant when he said there was a hum in his at 120v..I guess he means when his plugged in and not running.
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Old 08-16-2011, 12:02 PM   #6
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My vote is that you have dirty 12VDC control power to the relay. A small AC voltage is riding on top of the 12VDC control power such that the relay coil is acting like a transformer. If so, there may not be a easy way to find the source of it. It could simply be a 120VAC wire is running next to a 12VDC wire coupliing an 60Hz AC signal to it. In the electronics industry it's called Electromagnetic Interference (EMI).

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Old 08-16-2011, 12:38 PM   #7
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Ignore it and call it normal.
If you. Can't ignore it, replace the relay.

If u have an oscilloscope, put it on the coil power lead and see if there is anuything weird. But I doubt it.
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Old 08-16-2011, 02:06 PM   #8
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A lot of various electrical coils hum. That's not really a big deal.
(Have you ever heard, for instance, a hum from the outdoor section of a heat pump at a home or business. Many of them do. It's just the 24v reversing valve coil humming in it.)
So, what you have is the same idea.
Sometimes you can shim the coil so it doesn't vibrate so much, or put a soft gasket material between the relay and the wall that it is mounted on, so you don't hear it. But, it may hum for years to come. No big deal.
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Old 08-16-2011, 03:08 PM   #9
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In the utility industry we used to say that a transformer hums because they don't know the words! . It maybe normal or could be dirty contacts as others have stated.
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Old 08-16-2011, 05:26 PM   #10
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Disconnect one of the small control wires and see if the hum goes away. If it does replace the solenoid. It should not hum. They draw a strong 1-1.5 amps dc and should hold in hard and fast. Not an expensive repair.

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