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Old 06-05-2018, 04:56 PM   #1
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120VAC Remotely Controlled Manual Transfer Switch?

Does such a thing exist? If so, can you point me towards it - maybe a link??

A 120VAC transfer switch that includes the ability to manually choose which input is "active" from a remote switch? The remote switch would be a simple two position electrical switch.

Ideally, it would be capable of at least 20 amps.

Thank you!!
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Old 06-05-2018, 10:28 PM   #2
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My guess is if you have remote control for manual transfer then your cost is going to be the same as an automatic transfer switch, which would seem more covienant.
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Old 06-05-2018, 11:24 PM   #3
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Originally Posted by JDOnTheGo View Post
Does such a thing exist? If so, can you point me towards it - maybe a link??

A 120VAC transfer switch that includes the ability to manually choose which input is "active" from a remote switch? The remote switch would be a simple two position electrical switch.

Ideally, it would be capable of at least 20 amps.

Thank you!!
How about a pair of two pole contactors with continuos duty rating and coil voltage you like controlled by a s.p.d.t.c.o. toggle switch. The output side of both contactors would be paralled to downstream loads and the input side on one would be generator power and the other one shore power. There would be no possibility of backfeed since they are operated in a either/or/off mode.
Get real fancy and use a d.p.d.t.c.o. switch and use the extra contacts as out puts for indicator lights or whatever.
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Old 06-06-2018, 07:39 AM   #4
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Very interesting Rivetboy! Thank you!!

I think you are talking about something like this: (which I obtained from here)


Yes??

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).
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Old 06-06-2018, 07:42 AM   #5
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My guess is if you have remote control for manual transfer then your cost is going to be the same as an automatic transfer switch, which would seem more covienant.
Thanks Tigerman67. Not about cost or convenience, it is about accomplishing a specific task - as you can see from my previous post. In the end, I think I can adequately control an automatic transfer switch. However; if I decide I want/need to run the two A/C units from different power sources, I will be back to needing a manually controlled transfer switch.
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Old 06-06-2018, 10:41 AM   #6
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That diagram looks like it'll implement automatic switching, with priority given to input A when both inputs are live.

One thing to keep in mind: ground bonding. I'm bringing it up since you mentioned shore power. Obviously the little diagram with the contactors is but a small piece of the overall system, but somewhere in the system there should be a relay that bonds ground and neutral while the system is self-powered and removes the bond when the system is shore-powered.

Since your shore power is planned to be split phase/2-pole/240 volt, use a 4-pole contactor for switching that input. This ensures that when the system looks like it's not on shore power, it truly isn't.
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Old 06-06-2018, 10:45 AM   #7
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One thing to keep in mind: ground bonding.
NOOOOooooooo!!!! This topic usually results in a massive number of confused posts. All of that is working just fine on my coach (and has been for over a year). Build thread is here. Let's focus on ONLY the A/C power question that I mentioned above please.
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Old 06-06-2018, 08:26 PM   #8
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"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)."

Hi JD from another JD (Joe Dene),

Anyhow the way I am interpreting it, TS 1 on AC 1 is fed from the engine generator and the load center which is fed off leg 1 or solar. So AC 1 can source engine generator, solar or leg one. Engine generator also feeds TS 2 along with leg 2 so AC 2 can source leg 2 or engine generarator. And since solar is the equivalent of leg one AC 2 will not run off of solar since it feeds off of leg 2..

As for the contactors, my thoughts were to use battery voltage for the coil and the switch was just to flip /flop them or de energise them.. Nice block diagram by the way.

Finally, my thoughts on output of your generator will depend on the size of the shiv in relation to alternator rpm vs. low idle rpm.
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Old 06-07-2018, 01:10 PM   #9
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Thanks Joe! Yes - all that you said is correct. Glad to hear the diagram made some sense.

You are using the term "engine generator" which confused me initially. It is actually an alternator. Are you making a distinction or point that I am missing??

I actually do NOT have a typical generator (and may never have one) but I am keeping it as an option.

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Originally Posted by Rivetboy View Post
Finally, my thoughts on output of your generator will depend on the size of the shiv in relation to alternator rpm vs. low idle rpm.
You got me here, I'm not sure what a "shiv" is (and not finding anything that seems likely). Can you explain/link please? I think we are talking about the same thing which is: Can the engine alternator provide sufficient power during idle/low RPM operation?


Without any real facts, I suspect/hope that short idle periods will be ok (stop light) but long ones will not be. That is acceptable. This "hope" is largely based on the fact that the existing chassis A/C system appears (not measured) to use a lot of electrical power and also the 225ah @ 24VDC battery bank. I don't know of an easy way to test this so it will be a 'wait and see' sorta deal.
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Old 06-07-2018, 01:20 PM   #10
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Hey JD,
I am old so generator and alternator are interchangeable to me. Was referring to your engine driven alternator. A shiv is another name for a pulley.
Output of the alternator depends on rpm which depends on the diameter of the pulley on it at slow rpm. Smaller pulley equals higher rpm.
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Old 06-07-2018, 01:27 PM   #11
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Ahhh!!! Makes sense now. I should have thought of that.
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Old 06-07-2018, 02:42 PM   #12
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A shiv is another name for a pulley.
Also spelled sheave. But I have no idea when to use sheave vs pulley, or whether they're entirely interchangeable.
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Old 06-07-2018, 02:59 PM   #13
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You are absolutely right on the spelling but if you ask any (older) reefer mech, they will tell you that shivs are adjustable and they go on the motor and the pulley is what is being driven.
Slang for sure my apology for any confusion caused.
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Old 06-14-2018, 09:05 AM   #14
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Does such a thing exist? If so, can you point me towards it - maybe a link??

A 120VAC transfer switch that includes the ability to manually choose which input is "active" from a remote switch? The remote switch would be a simple two position electrical switch.

Ideally, it would be capable of at least 20 amps.

Thank you!!
Would a device like this fit the bill?

Wireless Remote Control Outlet, Fosmon Outdoor Electrical Outlet Switch Weatherproof Heavy Duty, 3-Prong Plug-in ETL Listed (Battery Included) $10
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Old 06-14-2018, 03:41 PM   #15
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Would a device like this fit the bill?
Problem resolved but thank you!

That device is basically a remote on/off switch. A transfer switch allow one "thing" to be powered by more than one source (but not simultaneously).
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