Buzzing Transfer Switch

[Mike Groves]

All,

While hooked up to 50amps I notice an annoying buzzing sound in the bathroom area of my 99 Beaver Marquis (same plan as 1998/2000/2001 40ft.  Is that the transfer switch that is causing that?  My assumption was the Prosine Inverter but when I disconnect 50amp, the buzzing goes away and I can turn on the Inverter and no buzzing. 

How loud should that buzzing be?  Anyone?

Thanks,
Mike

[Jerry Emert]

I'm not an RV expert as you all know but in my Navy electronics career, many many years ago, relays often started making that buzzing sound usually due to age.  If you had to you could probably clean up the contacts with fine sand paper if you can get to them.  Or replace the relay/s or the whole box or just live with it if it isn't too bad.  The louder they get the closer they are to failure.

[John Hennessey]

We've had the same thing happen. Sometimes is occurs in one campground and not another. Also check you plug at the post. We've unplugged and re plug in making sure the connection are good and the buzzing has stopped.

[Mike Groves]

We've had the same thing happen. Sometimes is occurs in one campground and not another. Also check you plug at the post. We've unplugged and re plug in making sure the connection are good and the buzzing has stopped.

Thanks John,

Turns out that my test of the issue, has actually corrected it, at least for now.  After flipping the 50amp switch off, and listening to no more buzzing, then turning the prosine off, still no buzzing, I turned the prosine off, turned on the 50amp and no buzzing. 

Haven't noticed the buzzing before, so this sounds like the experience you had.

Thanks all,
Mike

[Edward Buker]

Mike,

The noise is likely caused by the AC coils in the transfer relays. They make versions that use DC coils that are much quieter. It is a choice of the designer which they use. I have the same problem and depending on how the contact surfaces align and how intimate the contact surfaces mate will dictate how much vibration and noise will be emitted. Sometimes when you remove the AC from the coach and repeat the contact closure you will get quieter contacting. I pulled my relays and circuit board and used a rubber filled furniture glide under the relay mounts and it helped some but not enough to recommend going through all the work...For the most part this is something you learn to live with. The more I use my coach the quieter the hum seems to get and I cannot detect any hum now.

Attached is a photo of the relays and the furniture glide I used under the relays.

Later Ed

[Mike Groves]

Thanks Ed and all,

Noise still not present, so mama is happier about that.

Mike

[Fred Brooks]

      Hi Mike.

   Ed is correct concerning what particular alignment the contacts happen to end up when engaged. If they align perfectly when activated there is no buzz. What we need to discuss is what causes the "misalignment". For you older guys out there just imagine looking at the "Points and condenser" from a car distributor. The surface of the ponts CONTACTS are burned and pitted and that is why after 12000 miles you changed them.

     The transfer switch allows shore power OR generator power into the coach. I am pretty sure all of us understand that. Most relay manufactures make the "shorepower" the defalt position so when you plug into shore power you get 120volt power into the coach.

     Just imagine the following scenerio: You are getting ready for departure from your campsite and you have your air conditioners turned on and electric water heater turned on, domestic refer with icemaker turned on, galley instahot turned on and audio video equiptment turned on and so on (you get the point). So you go outside and turn off the breaker at the pedistal and unplug the shore cord. You arrive at your next destination and set up your coach. You plug your 50amp shore cord into the pedistal and turn on the breaker. Sounds good so far....... but let me share with you what just happened. All the components inside the coach just got electricity at the same time. That means you transfered in excess of 50 amps of electricity thru those "contacts" inside the transfer relay. That can cause some serious arcing or sparking just as the contacts close. This will burn the contacts over time. Once the contacts are pitted they will buzz when closed but not aligned. So you can try this several times until they do align.

        If your departure list reminds you to turn off all your Big Loads like air conditioners and such before you unplug the coach you will mitigate this arcing at the transfer switch contacts.

       For you coach owners who bought the coach used and continue to have this issue, you can try to access the contacts and file them (difficult task) or replace the transfer switch (expensive).
   Hope this helps, Fred

[Joel Ashley]

Couldn't have said it better, Fred    .  For that reason I try to turn everything off before unplugging.  Sometimes Momma kicks something on in the last minutes while I'm outside prepping, so the routine doesn't always go perfect.  At least it doesn't happen often enough, nor constitute particularly high current, to do much harm.  But many here may not have been aware of the issue before reading here.

Joel

[Jerry Emert]

Fred, I guess it's the Navy Chief in me but you said that much better than I did!  My language is "Broke, Fix, Drink Beer!!  I've since given up beer but you get the idea!
Jerry

[Mike Groves]

Regarding Fred's post, it could well be that when I transitioned to shore power, that I still had things switched on from when we were using the generator.  I don't remember.  Typically I always turn things off and let the generator run for little while after removing loads, and I know we turned off the air conditioner, but that still left the instant hot and the fridge.  But, then again, when I turned off the shore power, after hearing the buzzing all night, I don't remember, turning off the fridge or instant hot then either, so if this is similar to the points in an old distributer then I guess I just caught it right.

But, something to think about next time.  Thanks Fred.

Mike

[Frank Towle]

Another huge power sucker is Prosine when shore power plugged in immediately after running off batteries for a while. You know, Walmart camping etc.  Now, with shore power, converter is recharging the battery bank sometimes upwards of 70 amps DC showing on CMP.    Maybe shut-off charger at Prosine panel until other demands are met like air conditioner shut down/off, Hydrohot Electric OFF...

CMP is a great help in watching AC AMP draw on each side of 120 circuit.  Repeat comments made many times about keeping male plug ends nice and shiny with brass cleaner.  Not easy to do when dragging heavy cable thru the muck of campgrounds. 

Often thought putting heavy bag over plug end would be a good idea - haven't - probably won't - too lazy...

Crud on blades (or even in socket) can drastically reduce the ability to pull current thru connection AND cause the socket / plug to overheat [read MELT] when attempting to run all that AC stuff.   

[Joel Ashley]

Frank, I always unplug at the post, carry the plug end over to the power bay on the coach, then hold a paper towel or terry towel, kept handy in the bay, around the cord as it's reeled in.  In poor conditions, I don't let the plug lay there on the ground through the process.  Though not perfectly pristine, my cord and plug are always relatively clean and dry and the prongs unimpeded by any smudge or stain resistance, and dirt doesn't accumulate over time on the reel mechanism or in the cord bin.

Joel