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1998 U270 humming???

When I am lying in the bed I hear a humming noise when plugged into 50amp service. What am I hearing and is there a way to tune it down? After Vietnam I have a constant ringing in my ears that is a pain, so I would like to get rid of another noise. Thank you for all your inputs.
John
1998 U270 34'

Re: 1998 U270 humming???

Reply #1 –
Suspect it is the ATS (Automatic Transfer Switch).  Some have 120 VAC contactors that hum.  Others use 12 VDC contactors that don't.
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: 1998 U270 humming???

Reply #2 –
Seems you have the infamous 60 cycle hum.  It's almost certainly the ATS as Brett suggests.  Also if there is a ferroresonant battery charger somewhere they also hum.  On my coach the ATS is located under the bed, under a lift off cover, at the front of the bed.

Looks something like this:


Keith
Keith, Joyce & Smokey the Australian Cattle Dog
1995 U320 SE Extreme 40' WTBI Build # 4780, with a Honda CR-V hopefully still following behind.
Motorcade # 17030
FMCA # F422159

Re: 1998 U270 humming???

Reply #3 –
Hi John,

Most likely you are hearing the hum of the AC coils of the relays in the automatic transfer switch. Later models have "DC" coils or a diode full wave bridge to reduce the coil vibration by converting to DC voltage.

If you are an experimenter you could remove the lid from the ATS and try to reduce the noise by adjusting the mounting tension the relays and wiring...though this is a Rube Goldberg attempt. Be very, very careful doing this because the power must be on to hear the difference. If you are not used to working around live voltages, don't try it.

Jim

2002 U3220
Jim Frerichs
2002 U320 42'

Re: 1998 U270 humming???

Reply #4 –
This noise is usually due to dust / dirt / rust between the movable poles, the poles are kept apart from this material.  Sometimes you can blow the dust / dirt away, solving the humming noise, some timesz you need to take apart, remove tha rust / dirt then reassemble..
A common issue on magnetically held coils.
 

Re: 1998 U270 humming???

Reply #5 –
Thanks Dave,

Great additional information. 
Jim

2002 U320
Jim Frerichs
2002 U320 42'