Very interesting Rivetboy! Thank you!!
I think you are talking about something like this: (which I obtained from here
I started looking at these contactors (from DigiKey)
and thinking about one NC and one NO (normally open/closed) which would then eliminate any power consumption (by the contactor itself).
Then, as I was messing with my diagram, it occurred to me that I already have a "switch" to control an automatic transfer switch (and do not need to fabricate a manual switch). So, I had better share what I am thinking...
With two roof air conditions (120VAC), I would like to run them from shore power (one on each leg of 50amp service), the bus alternator (270 amp @ 24 volts), or just #1 from solar. With that in mind, my 'idea' is this:
The point of interest is what I have labeled 'Automatic Transfer Switch' and is connected to "Air Cond #1" (almost in the middle of the diagram). The switch that I already have available is the remote switch for the 5000 watt inverter. Simply turning it on/off will control the transfer switch (using its built-in inner workings).
The only limitation that this seems to present is that I could not run A/C #1 from solar and A/C #2 from alternator. I don't see that as a real issue.
I have some questions about running the A/C from the alternator which I don't think can be answered until tried. Such as... Is the alternator really able to keep up with the demand (even though the book values says it can)? What happens when the engine is at low RPM (idle)? The 24VDC chassis battery bank is a pair of 12VDC 8D batteries so it has some capacity but certainly not enough to power the inverter (at least not for very long).