Transfer switch buzzing

garry1p wrote:
Many transfer switches have a 110VDC relay coil if the DC has a ripple from a bad capacitor or rectifier diode you can get an ac hum.

Hey Gary, is there a way to check for this?

If you know what to look for and have a good DVM then yeah its repairable as a DIY project. I was posting to highlight what can cause the hum.

I'm sure I could repair mine for the hum however I would probably replace before repair since I would still have an older switch with old contacts. Even if you could replace the contacts you would never find replacements.

It could also be the contacts are pitted and need touching up as posted previously that could be an easy fix. If you don't have a burnishing tool use 800 grit sand paper. This fix could last a year or two.
Another easy check make sure the unit is fastened down tight and the whole unit is not vibrating.

If you take it to a shop for repair it will cost about the same as a new one $75 to $90 new. I would say if the two easy fixes don't work replace and be done with it.

Ahh, the transfer RELAY, aka Transfer switch is a 120 Vac coil. There would be no caps or diodes involved.

At least in older RV like a '96. It's just a relay that's wired with the coil powered ONLY when the genset runs. When the genset reaches full power after start, it applies 120 Vac and that closes it so it's contacts supply the RV. These are the Dumb ATS boxes. The smart boxes are basically the same only they sense when the AC is passing through zero before they switch. It looks the same for a 50 amp system only there are 3 poles. Note that since there is a 'coil' in the ATS, along with contacts, that buzzing can be caused by the coil itself, and/or dirty contacts if someone was not very careful and started the genset with the AC on too often.

I never said "all" have 110VDC relays but many do.

From the WFCO 57 series transfer switch manual.
Designed To Provide Trouble-Free Changeover Of Power Between Shore Power And Generator
Used For A 30 Amp Or 50 Amp AC Service
DC Coiled Relays Prevent AC “chatter” Noise And Drop-Out In Low-Voltage Conditions.

Iota also uses 110VDC relays as well many others manufactures.

Thanks guys! Any ideas on which switch I need for this control unit? I’m having a hard time figuring that out!

garry1p wrote:
I never said "all" have 110VDC relays but many do.

From the WFCO 57 series transfer switch manual.
Designed To Provide Trouble-Free Changeover Of Power Between Shore Power And Generator
Used For A 30 Amp Or 50 Amp AC Service
DC Coiled Relays Prevent AC “chatter” Noise And Drop-Out In Low-Voltage Conditions.

Iota also uses 110VDC relays as well many others manufactures.

Well, I did not know about those. None of the RVs I'm familiar with every had that type. Huh. Learn something new every day. Thanks for the info!

Feeling rather dumb right at the moment...just looked at mine and after some investigating find that it is a DC type. Uses a diode bridge to convert to DC.