Coil in Transfer Switch energized extended periods?

Question

Looking to do an inverter install and would like to double up on my transfer switches, but I'm concerned because the way I'd like to do it would make it so that the coils in the added transfer switch would be energized when using shore power or generator. I plug into shore power during storage, so this could be months on end. Is there any reason having the coils energized for extended periods of time would be a bad idea, do the consume much electricity? Do they build heat? Is there any other problem I'm not thinking of?

Flow chart:
Transfer switch #1
WFCO WF-T57 wired in typical manner, shore power default, generator override. Coils are energized only when generator is on. "load" goes to Transfer switch #2

Transfer switch #2
IOTA (original to toyhauler, time delay module went out, works well in bypass mode) "load" from TS #1 to "generator" in TS #2, 2500 W inverter to "shore" in TS #2 load out to panel.

The switching in this scenario would work well, either the gen or shore power would override the inverter, also the inverter would only light up one leg in the panel which is already divided up putting most of the things I'd like on the inverter on one circuit, and most of the stuff I would not like on the inverter on the other circuit.

What do you guys think? Coils energized in one of the transfer switches 99% of the time a bad idea, or nothing to worry about?

golden_hvac · Answer

Hi,Most transfer switches are wired to be 'off' most of the time, and only energized while the generator is running, say only about 5,500 hours for the life of the motorhome.So use the 'shore' wire input to the transfer switch from your inverter if possible, so that it will not consume valuable inverter power while on the inverter and battery power.  Then when on shore power, the shore or generator power will provide 'unlimited' shore power to keep the 10 watt transfer switch energized.  The relays can run hours at a time without damage.  We have indoor fans at my work that run 24/7 for weeks at a time, nearly the whole 8750 hours per year, and at 15 years old they are not worn out.  In fact a contactor that is energized for 6 weeks at a time, and only off for a few minutes while the belt is being checked sees less 'on-off' cycles than the compressors, that might cycle on and off 5 times a hour, and only run 30 - 75 minutes at a time in the summer, as little as 10 minutes at a time in the spring and fall.  After 14 years of that kind of service, the compressor contactors are showing signs of wear (sparking pits in the contacts from energizing and going off several times a day) while the indoor fans look shiny (less amperage and only typically turn on once in the morning and off at around 11 pm!).Good luck!Fred.

drewe · Answer

If a coil can survive for an hour (say) being energized and not get too hot, there's no reason it couldn't be powered indefinitely. There's not really much to break in a coil; it's basically asking if it's okay to leave a wire energized for a long period of time. (A coil, after all, is just a long wire wound around a core.)

The relay contacts and mechanism can wear, particularly from switching under load, but steady-state operation again is not much of a concern provided it's properly specified for the application.

That's basically what Fred said in different words. I entirely agree with his assessment.

consumeratlarge · Answer

I wired my 2nd transfer switch the way you are talking about doing. It's a continuous duty relay, as far as I know. I also agree that switching with the big loads that cause arcing, would be the problem making there. I also leave mine plugged in year round.

I used the transfer switch that just slides on the back of the WFCO converter, and it doesn't seem to be hot. The load on the coil only has to be strong enough to overcome the spring, regardless of load going through it. I agree, though that little parasitic loads like this don't belong on the batteries, so that was my thinking for wiring it that way.

wa8yxm · Answer

There are two types of solenoid type relays.

Starter Solenoids used for the engine are designed for no more than 30-60 seconds of continuous operation.

AUTO Transfer relays are designed to be engaged no more than 25 hours in any single day.. Since in 24 hours it will be a new day.. that means 100% of the time if so reqauired...

We often read about transfer switches that hum.... This is a type that has one set of coils live on shore power and another live on generator.

They are designed for continous duty.

maddog1927 · Answer

Thanks so much for the replies.

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Coil in Transfer Switch energized extended periods?

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