Is their no-hum tranfer switches out there?

[Jim Blackwood]

Mechanical AC contactors hum. There is just no getting around it. Sometimes it is more, sometimes it is less, but it is always there. Usually other running equipment covers up the sound. There is no easy way to know if a contactor is going to hum more, or less except to try it.

The way I see it you have 3 choices.
-Rewire the contactor to NC
-Replace the contactor with solid state or DC
-Replace the entire unit.

Or, I suppose more drastic measures could have to do with ignoring certain things... not a happy solution.

Jim

[Geoff]

I can give you the part number for a magnetic relay that doesn't hum, but you would have to figure out how to wire it in. Especially with a circuit board that delays the generator feed.

My SW Trace delays the generator feed, so I don't have to worry about it.  I don't have the relay part number handy, so if you want it I'll find it for you.

--Geoff

[dtcerrato]

I appreciate it Geoff but don't bother. I'm not comfortable modifying a piece of equipment like that. I could maybe use it for an ATS on the house for Genny power during hurricanes - so at least it's not a total waste. Thanks

[solardude]

Dan - I only skimmed the comments, so someone may have said the same thing already. As you have found most ATS' are built with "normally open" relays, if you don't want the huuuuummmmmm, you need to find one with normally closed relays on the shore side. With the normally closed on the shore side, the relay is energized by the generator, so you always hear the generator over the relay buzzing. Each type of setup has it's advantages and disadvantages as usual. Good Luck.

Solardude

[dtcerrato]

solardude - 10-4 on NC relays. The lack of information given when shopping for ATSs is ominous! Does anyone on the board know a manufacturer & model no. of an ATS with a NC relay on the shore power side?! That was my first choice but can't nail one down. Was considering a purchase of an ATS with DC coil relays that advertise "silence". IE: the WFCO WF-T57 or the ESCO LPT 50 BRD. Comments please!

[Jim Blackwood]

Is there any reason why you can't wire the shore power to the Gen input and vice-versa? Would it make any difference to the ATS where the power comes from and are there any functions available from it on shore power that are not available on generator power?

Jim

[dtcerrato]

Don't think so Jim, its more involved than that. There's a delay circuit board on the Generator contactor - but what do I know? I got a call into ESCO to talk to one of their techs. If I learn more I'll post it. Thanks

[Geoff]

Here is an ATS that is NC for shore power:.  Power Max PMTS-50. Available on eBay.

[dtcerrato]

Thanks Goeff. Was curious how you know this unit has a normally closed shorline contactor. I'm not questioning your response but heck I can't find nothing stating that and this unit is so much lower in $$ than what I've been serching for. Uninformed bus nut wondering how you guys find your info. Thanks.

[Geoff]

I know this unit because I installed one in a customer's bus recently.  I have the installation instructions which details that it is NC to shore power and has a generator delay switch.  No problems with the unit, it is well made.

[dtcerrato]

Thanks Geoff. Sorry for all the questions but you seem to be the go to guy for my transfer switch issues. One other issue that I'm having (besides the annoying hum) with my current transfer switch that I'd like to steer away from (maybe with your help). The AC contactor for the Genny "drops out" with low voltage. Specifically when we're on genny power and I start up the auxiliary electric air compressor, if the compressor starts at high PSI (90 or higher) the transfer switch "drops out" & goes through another delay cycle. The only way I can get around that is to exhaust the compressor air down to below 50 psi before trying to energize it. Okay, with that in mind - while ATS shopping there is language stating with only the DC coiled "relay" ATSs (that I mentioned this morning on this post) that the DC coils have reduced (if any) hum and "don't drop out" during low voltage. With all this being said I'm thinking I may need to stay away from the AC magnetic contactor & go with the DC coil relays. Please give me your take on that. Thanks

[eagle19952]

Thanks Geoff. Sorry for all the questions but you seem to be the go to guy for my transfer switch issues. One other issue that I'm having (besides the annoying hum) with my current transfer switch that I'd like to steer away from (maybe with your help). The AC contactor for the Genny "drops out" with low voltage. Specifically when we're on genny power and I start up the auxiliary electric air compressor, if the compressor starts at high PSI (90 or higher) the transfer switch "drops out" & goes through another delay cycle. The only way I can get around that is to exhaust the compressor air down to below 50 psi before trying to energize it. Okay, with that in mind - while ATS shopping there is language stating with only the DC coiled "relay" ATSs (that I mentioned this morning on this post) that the DC coils have reduced (if any) hum and "don't drop out" during low voltage. With all this being said I'm thinking I may need to stay away from the AC magnetic contactor & go with the DC coil relays. Please give me your take on that. Thanks

Your compressor is out of spec/worn/under size cord...lots of possibles for start amps. The contactor "falls out" at 105v.

[chessie4905]

Check the unloader first. It should drain pressure from compressor pump so it starts unloaded. You can usually hear a slight hiss as comp. shuts off. It is usually part of the pressure switch assembly.Also check one way check valve between pump and tank. It could be leaking back keeping pressure on pump head.Finally, compressor should be fed with 12 gauge wire.

[dtcerrato]

Thanks for the quick response eagle & chessie. I must admit you gents caught me by surprise when you mention the compressor. I have to admit it is a forever running old Craftsman compressor but a real gem. It doesn't give me any problem when on shore power, only when transferring to genny power through the ATS. It is wired with 12 gauge copper. I do hear the hiss as comp. shuts off. I will check for the check valve. I was asking the question about drop out because the only mention of "eliminates drop out" is on ATSs advertised with DC coil relays. More important than drop out for us is eliminating the hum which can be done with a NC shoreline contactor &/or DC coil relays. Thanks

[buswarrior]

If all else fails, is it possible to use a soft start capacitor for the air compressor, same as done for air conditioners?

wrestle this beast to the ground!!!

happy coaching!
buswarrior