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Humming sound near the foot of the bed?

January 19, 2012, 08:16:46 pm

With no shore power, no gen running (12volt on) and most everything turned off I hear a hum that seems to be coming from the power switch box or boxes on the passengers side under the cover at the foot of the bed. Any ideas?

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Re: Humming sound near the foot of the bed?

Reply #1 – January 19, 2012, 08:39:40 pm

That should be simple,  Should be the contactor that pulls up when you plug into the 50 amp post.  Reason for the humming is from dust between the two pole shoes preventing full mating of the magnet poles.  You can imporve it by blowing out the dust, replacing the contactor, or wiping the dust out.  Blowing seems the be a good choice.  Or turn up the TV and ignore it.

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Reply #2 – January 19, 2012, 08:59:36 pm

Like Dave says, thats where the transfer switches are. Mine hums when the inverter is on no gen or shore power. Should you deciede to open them up and clean them turn ALL the power off before you get in there lots of wires and tight spaces. If you don't want to hear it while sleeping just turn the inverter off when you go to bed, if you are dry camping you battery will last longer as well.

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Reply #3 – January 19, 2012, 10:25:32 pm

Is the rear radio off ?

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Reply #4 – January 19, 2012, 11:48:33 pm

transfer switch.

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Reply #5 – January 20, 2012, 09:12:54 am

It looks like there are two but how and or why would it hum with out AC power?

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Reply #6 – January 20, 2012, 09:17:32 am

Now that is a good question.  Where is the inverter on that rig?

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Reply #7 – January 20, 2012, 09:55:49 am

In the bay storage.

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Reply #8 – January 20, 2012, 11:45:13 am

When you need inverter power (turn the inverter on) the transfer SW closes and transfers the power the inverter makes to the AC panel(s) for distribution to the coach 120v wiring. You have 2 transfer switches one for Gen/shore power, and one for the inverter so the system will function automatically, as well as keep one system from backfeeding the other one, example if your generator or inverter was on you would not want the prongs on the shore power cord hot while it's unplugged. I believe I'm correct there are others here that maybe able to explain it better or type faster than I do.

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Reply #9 – January 21, 2012, 10:00:16 am

Do the switches get 12v power?

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Reply #10 – January 21, 2012, 04:25:23 pm

The transfer switches are powered by 120 volts. If the inverter is turned off and no shore power or generator should not be any humming coming from them.

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Reply #11 – January 21, 2012, 04:54:56 pm

I only get the hum with the inverter on and no shore power.  When the inverter is off, no hum from the transfer switches. 

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Reply #12 – January 21, 2012, 08:27:49 pm

You can try cleaning the contacts, may or may not work. Or replace it, mine has had a slight hum for the last 6 years. One for those things (a round to it project)

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