Hum and Vibration

[expressbus]

Hello,

I have been a subscriber to Bus Conversions Magazine since October 2005 and a bus owner since January 2007. I need some direction on a problem that cropped up this past weekend while in Bryson City, NC. We had been hooked to shore power for about three hours when suddenly, about midship, a distinct hum with an accompanying vibration started. Of course the sun had gone down and it was dark outside. I tore into the underbay from which the sound was the loudest. Turned out to be the bay with the two hot water heaters and the propane tank. Now I did not think either of these two items could possibly be the source of the problem. The underbay on the opposite side of the bus has the battery chargers/converters and a Heart 2000 inverter. No luck there either. On Saturday I tore into the plumbing bay. Again no luck. We do not have a disposal but when inside the bus the hum and vibration is most notable at the galley sink.

This problem is consistent regardless of the power source. I disconnected the shore cable and went on generator. Still humming and vibrating. Shut off the generator and went onto the inverter. Still humming and vibrating. The only way I could get the hum and vibe to stop was to turn off the "Domestic Battery Disconnect" switch on the overhead panel in front of the passenger seat. Of course everything goes dead when this switch is off.

Now if that was not frustrating enough. I get a Monday appointment at Carolina Coach and Camper in Cleremont, NC. Well I pull in on Sunday evening and no hum or vibration. I plug into their 50 amp pedestal and turn the "Domestic Battery Disconnect" switch back on, no hum or vibration. However, now the system monitor tells me, "Danger - Faulty Ground Shore Cable." OK, now I turn everything off, uncouple the towed so my wife can drive the rest of the way home while I overnight in the parking lot.

On Monday morning I move into the service line, give "Sheila" my information and describe the problem. Now Carolina Coach is a dealer and provides service on Country Coaches. After meeting half a dozen people and spending 2 hours, I am told they do not consider themselves to be competent to work on the bus. I tried to tell them they were not working on the bus, only the systems that had been installed by Country Coach. They called Tom Johnson in Concord and the earliest available appointment was in November.

So you can see it is pretty much up to me to diagnose and repair the problem. That job has gotten to be a bigger challenge now that the hum and vibe have become intermittent. The hum is loud enough that my wife thought the generator was left on while parked curbside in front of the house - the generator was not on but the "Domestic Battery Disconnect" switch had been left on and she was humming away.

Is there anyone on the forum that has any insight as to what may be the problem source. Thanks for any and all comments provided in response to this posting.

Will Garner

[luvrbus]

You did not tell us if it is a Eagle or Prevost conversion but I have friend that has the Country Coach Eagle conversion and we chased that problem for 2 days and found out it was loose connections in the main panel  good luck

[Tenor]

A long shot here, and since I'm really tired, I'm probably really wrong.  Do you have rooftop air?  One of mine needs adjustment and it hum's and has a low frequency vibration.  Good luck!

Glenn

[Marcus]

Does yor inverter have a built-in charger? This could cause vibration if its faulty. Marc

[Ednj]

Do you have a Macerator pump left running?

[RickB]

flojet water pump? just throwing it out there...

[Ncbob]

Hi Will,

It's the nature of weak contactors to 'Hum' and drive us nuts. Generally speaking the problem is a weak or diminishing holding coil. If you can live with the problem, even if it means inserting your plug into 'shore power' and checking to see if you have the 'Hum' and repeating the process until you get home then you can have one of your friends or a local electrician check that contactor. It might be a problem in your inverter which would mean having it pulled and repaired.

Sure hope you find the problem.

NCbob

[Lin]

Just to be clear here, does this only occur when there is 120 volt power?

By the way, I thought from the title of the posting that it was about a geriatric rock concert.

[expressbus]

Thanks to all. I think the culprit has been found. I'll know for sure this weekend when I get more intimate with the inner workings of the bus. It looks like the Aux Air Compressor is the source of the problem. The AAC should be behind an access door on the back wall of the first underbay.

I really appreciate every one of the responses to this post. Maybe we will get to meet some of you somewhere on down the road.

Be safe out there, be happy and be careful where you put your money!

Will

[pvcces]

One other thing to check is the hot water heater elements, if there are any. A bad element could cause a humming sound when connect to any 120 volt AC power. If that happened, you would also get current from the element going to ground, which could cause the ground error message that you saw. You also would get some contamination of your hot water.

Otherwise, a bad connection in a high current AC circuit would be my next choice.

Good luck with your troubleshooting!

Tom Caffrey