Is That Hum From Your RV Automatic Transfer Switch Driving You Crazy?

RV Automatic Transfer Switch

I remember it all too well, sitting in our brand new motorhome and looking over the interior, grateful to be so fortunate to have such a nice RV.  Then I noticed it, a hum, was it my tinnitus acting up?  No, this was different, it was a lower pitch and even more annoying.  After some hunting I located the offending component, it was the RV Automatic Transfer Switch!  Since it was in the bottom of the pantry and we did not have carpet to dampen the sound, it was extra loud.  I tried the usual potential remedies, tightening the screws on the terminal block, blow air in and around the contactors to remove any dust or debris, but nothing worked.  I even tried to insulate the area but to no avail.  By the end of camping season I had had it and needed to replace this RV automatic transfer switch, but with which one?  I definitely did not want to repeat the problem.

So after some investigating and a few phone calls to technical departments, I was filled in with the issue.  An RV automatic transfer switch is basically a 3 way switch, redirecting power from a generator to shore power and vice versa into the RV’s power center, never allowing either power source to come in at the same time.  To do this the transfer switch uses relays, and in the case of my unit, AC powered relays.  So to keep things somewhat simple, in an AC relay, the alternating current supply looks like waves on the ocean when seen through a scope. As that wave goes above and below flat calm, the current flowing through the coil in that relay becomes zero. The resulting loss of magnetism in the coil for just a few milliseconds creates the hum we hear in the transfer switch.   There are a few more factors that can contribute to the hum, but suffice it to say if it is bothering you, you will need to replace the unit.

What’s the solution you ask? Thankfully, RV automatic transfer switch manufacturers are now selling a version that uses DC relays which have virtually no hum. With this new technology, versions like the Progressive Dynamics PD52DCSV Automatic Power Transfer Relay Switch even feature surge protection as well as open neutral and reverse polarity protection.  While transfer switches with DC relays are slightly more expensive due to the added circuitry required, the benefit far outweighs the hum AC relay versions can cause.  Since I already had a surge protector, I opted to go with the ESCO Lyght series of RV transfer switches and could not be happier.  The hum is gone and I am now able to enjoy peace and quiet.

SHOP RV Automatic Transfer Switches

Is That Hum From Your RV Automatic Transfer Switch Driving You Crazy? was last modified: January 21st, 2016 by Bill Rowell

About the Author

Bill Rowell
I have been camping and RV'ing with my Wife and 2 children for the past 20 years. We began our RV'ing careers in a 1995 Jayco pop-up camper which we got caught in the rain in every time we used it. In 1998 I found a 1989 Winnebago Chieftain 23' Class A motorhome which we loved. During that time I was always looking online for good RV information but unable to find it. So I decided to start a website called which is a forum for RV'ers to share information. We wanted a family friendly site in which members were willing to help each other and leave the drama out. In 2000 I purchased our first new RV which was a 30' Coachmen Mirada Class A. For a new RV I had to make a lot of modifications to this motorhome just to make it a road worthy RV. My displeasure with traditional RV's lead me to Truck Conversions and in 2002 we built our first Showhauler motorhome. In 2004 we built our second Truck Conversions which was an improvement over the first, but a trip to the Winnebago factory in 2006 sealed my fate with the rest of the family who saw a Winnebago Vectra diesel pusher in our future. So in 2006 we made the move and enjoyed traveling the country in that until 2010 when we thought we would downside since the kids were off doing their own thing. Somewhere in that time we found ourselves with way to many irons in the fire and decided to focus all our energy on as well as another business we own and thus said goodbye to This was a very tough decision since we had made so many RV'ing friends and great memories, but times had changed and it was time to leave it in new hands to continue it's growth. In 2010 we downsized to a Winnebago Cambria Class C which I really liked, but we quickly found was not the most roadworthy choice for long range travel. So in 2012 we went back to Showhauler and with all of the updates they made to their product found the last motorhome we will ever buy. (Sound familiar) There is never a last RV you'll ever buy when your a die-hard RV'er :-)

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