Automatic transfer switch loud buzzing keeps us awake!

[mcaimh]

In our 2011 Vacationer the PD52 automatic transfer switch is buzzing loudly in the compartment outside so loud we can hear it inside. It doesn't seem to matter how much load is going through it.

Is it bad? I'm not an electrician, but can it be replaced with an upgraded transistorized switch that doesn't do that?

[VanDiemen23]

it's just loose stuff. remove ALL power, and go tighten up anything and everything. what can't be tightened, put some kind of padding - like stick on foam tape. Eventually all the stuff will stop shaking.

Windings that have a a lot of 60 cycle hum can sometimes be quieted by a thick coat of epoxy.

[bborc]

Just had the same problem with a new PD52 transfer switch I installed. Called the factory tech and he said probably dirt in contacts to try blowing the switch out with air. I sprayed contact cleaner in the switch and then blew it out and the buzzing went away. Just make sure the shore power is unplugged and gen set off before doing this.

[mcaimh]

I tightened everything up good, and blew out what I could. This RV was new one month ago when I bought it, although it was a demonstrator, it had never been charged up with power, etc. The transfer switch looked brand new--saw no dirt, etc. I'm thinking it is maybe bad? My current efforts did no good.

[bluepill]

Some brands of ATS use Direct Current (rectified AC) for the relay coils to suppress hum. If the rectifier circuit leaks AC, the relay can hum.



You might want to contact PD directly:

PROGRESSIVE DYNAMICS SERVICE DEPARTMENT
507 Industrial Road
Marshall, MI 49068
Telephone – 269-781-4241
Fax – 269-781-7802
Service Dept. Fax – 269-781-8729
E-mail – Click to Email

[Stretch]

dirt on the contacts, or even dust will do it. you need something that you can get into the "open" contacts. then rub it back ad forth a few times. My guess is the bad hum will be gone......

[Vanwill]

I don't want to start any kind of flame war or offend anyone, but these are just facts. Regardless where or for what application an AC contactor is used, any hum it produces has nothing to with its power-transferring electrical contacts. The hum is produced by one thing and one thing only--it is the armature (the moving part consisting of steel plates riveted or welded together) not staying firmly on its seat. The contacts themselves are almost always connected to the armature by some sort of flexible device, like a leaf spring. They are connected with a flexible device for one reason--so the armature can completely "bottom out". Not only will a contactor with an AC coil hum if it does not "bottom out" completely, but if it fails to bottom out by a significant amount it will draw excess current and overheat. All your coach devices work perfectly even when your transfer switch contactors hum like crazy because the electrical contacts “make” well before the armature “bottoms out”. If the contacts themselves did not make good contact, you would have arcing and a fire hazard. From years of experience, I can tell you that many times you can cure hum by cleaning the seating surfaces of the armature, sometimes as simply as by blowing out with dry compressed air…but many times you cannot. Many AC contactors have a “shading coil” to hopefully decrease hum, and it helps, but still does not preclude all hum.

AS A GENERAL RULE, DC coiled contactors DO NOT HUM UNDER ANY CONDITIONS. That alone is the reason that several transfer switch manufacturers have switched to DC coils and adding a bridge rectifier to supply DC to the coil from the available AC supply.

You can inspect, clean, sand, file or otherwise try to improve the seating of the AC contactor’s armature. If that does not work (it frequently will work) the only alternative is to replace the contactor. If you replace it with a DC coil contactor which has a well-designed bridge rectifier and filtering capacitor, THE COIL WILL NOT HUM. It is remotely possible that some OTHER problem will cause some MINOR hum, but that chance is remote. If you have ever listened to heavy-gage AC wiring drawing a large current, you can hear a hum, but it is a “singing” of the wires themselves (similar to a guitar string), not the hum you hear from an armature that is making a mechanical hum due to “wiggling/vibrating” of an armature on its seat.

BTW, you cannot simply add a bridge rectifier to your present AC-coiled contactor. The STATIC resistance of coils designed to operate on 120VAC is much lower than the resistance of a coil designed to operate on 120VDC.

[HondoFlatty]

Originally Posted by Vanwill

I don't want to start any kind of flame war or offend anyone, but these are just facts. Regardless where or for what application an AC contactor is used, any hum it produces has nothing to with its power-transferring electrical contacts. The hum is produced by one thing and one thing only--it is the armature (the moving part consisting of steel plates riveted or welded together) not staying firmly on its seat. The contacts themselves are almost always connected to the armature by some sort of flexible device, like a leaf spring. They are connected with a flexible device for one reason--so the armature can completely "bottom out". Not only will a contactor with an AC coil hum if it does not "bottom out" completely, but if it fails to bottom out by a significant amount it will draw excess current and overheat. All your coach devices work perfectly even when your transfer switch contactors hum like crazy because the electrical contacts “make” well before the armature “bottoms out”. If the contacts themselves did not make good contact, you would have arcing and a fire hazard. From years of experience, I can tell you that many times you can cure hum by cleaning the seating surfaces of the armature, sometimes as simply as by blowing out with dry compressed air…but many times you cannot. Many AC contactors have a “shading coil” to hopefully decrease hum, and it helps, but still does not preclude all hum.

AS A GENERAL RULE, DC coiled contactors DO NOT HUM UNDER ANY CONDITIONS. That alone is the reason that several transfer switch manufacturers have switched to DC coils and adding a bridge rectifier to supply DC to the coil from the available AC supply.

You can inspect, clean, sand, file or otherwise try to improve the seating of the AC contactor’s armature. If that does not work (it frequently will work) the only alternative is to replace the contactor. If you replace it with a DC coil contactor which has a well-designed bridge rectifier and filtering capacitor, THE COIL WILL NOT HUM. It is remotely possible that some OTHER problem will cause some MINOR hum, but that chance is remote. If you have ever listened to heavy-gage AC wiring drawing a large current, you can hear a hum, but it is a “singing” of the wires themselves (similar to a guitar string), not the hum you hear from an armature that is making a mechanical hum due to “wiggling/vibrating” of an armature on its seat.

BTW, you cannot simply add a bridge rectifier to your present AC-coiled contactor. The STATIC resistance of coils designed to operate on 120VAC is much lower than the resistance of a coil designed to operate on 120VDC.

Hi, I know this post is old and I'm sorry for bringing it back alive but I have a problem.

I have 2 switches to control shore power, generator and an inverter.

My good switch is fine, it has DC control and surge/wiring protection built-in and there's also an EMS on the shore power so all 3 sources are protected.

My factory installed switch conked out today, it has a short from L1 to neutral, L2, in one of relays.

My question or curiosity is if I can just rebuild it with 110V DC relays rather than ponying up the big bucks for another good switch with all the protections built-in deeming my EMS virtually a waste of money.

Or, is there a complete DC switch on the market without the built-in protections, I can't seem to find one.

The system is 50 amp set up on a fifth wheel trailer.. Below is a picture of the type/configuration of my bad gear that needs to be replaced so I think if I were to go the rebuild route it would have to be the same configuration for ease of install, if nothing else..

Thanks for any help you can offer!!!

[twinboat]

I can't imagine an internal short in a contactor, unless it's been smashed.

Have you confirmed the short with all of the wires off ?

[HondoFlatty]

Originally Posted by twinboat

I can't imagine an internal short in a contactor, unless it's been smashed.

Have you confirmed the short with all of the wires off ?

Thanks for that, I didn't think about the control/sense wires underneath, I only had the black disconnected to check ohms. The short is in the board, not the relay. Guess I'm calling for warranty..

[broadrun]

I had the same problem last year. I removed the switch, and found several stink bugs smashed in between the contacts. They were matted so tight in there that I don't think just blowing compressed air would have worked unless I had a visual on it. I actually used a long flathead screw driver to scrape the contacts clean, then used compressed air to finish the job.

The buzzing went away.

[Vanwill]

It is certainly possible for someone with considerable electrical savvy to change his contactors from AC coil type to DC coil type, but in most cases I would not recommend it. Better to buy a transfer switch with the DC contactors already installed. If you object to any kind of surge protection or other unwanted features, perhaps you can disable/remove them.

I seldom cite any type of insurance liability, but a "homemade" transfer switch would certainly pose a legal problem for you if you had any sort of calamity for which your device could be blamed.