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Posted by jamesgangnc on December 18, 2006, 11:03 am
Over engineered the crap out of that one didn't you?
thrugoodmarshall@hotmail.com wrote:
> Since you weren't specific, let's say that it's just the AC function
> you're trying to interlock and not a heat pump and it's a 24V AC
> system.
> Again, you didn't specify what controls you already have (2 thermostats
> and some sort of txfer switch, I hope) so what follows is really
> academic.
>
> This will get you started.
> Please see the "notes" section for some followup you're going to have
> to do yourself!
> If you want to hack together all these features, you really don't want
> to do it with relays--see again the "notes" section.
>
> In this example, the "Y" wire of the first thermostat turns on the
> compressor or the 5T unit. Connect the coil of a 24VAC relay from the
> "Y" output of that thermostat and the opposite leg of the 24VAC
> transformer.
>
> Similarly, for this example, the "Y" wire of the second thermostat is
> used to turn on the compressor of the 3T unit. Lift the wire from the
> "Y" terminal of that thermostat and land it on the N.C. contact of the
> relay. Connect the common terminal (not the coil common--the common
> for the N.C. contact you just landed!) to the "Y" terminal of the
> second thermostat.
>
> Now, the signal to turn on the 3T compressor has to go through those
> N.C. contacts.
> This will give the 5T unit priority and both units will never be on
> together.
>
> If you want to be able to run both units together when you're not on
> emergency power, just put the N.O. aux contacts of the generator
> transfer switch in series with the coil of the new relay.
>
> Notes:
>
> Fan:
> Typically, the fan output is turned on whenever the thermostat calls
> for AC.
> Depending on your system, you'll have to deal with this.
> One way would be to use a double pole relay and wire the fan signal
> through the other set of N.C. contacts just like the compressor signal.
>
> Restart Lockout:
> You'll probably want to use a restart-lockout relay to prevent the 3T
> unit from starting up again too soon after it's been shut down.
>
> Short-cycle lockout:
> Once the 3T starts, you'd probably want it to finish its cycle before
> dropping for the 5T. You can install this circuit twice, once with the
> 5T as primary and once with the 3T as primary. To prevent relay races,
> wire N.C. contacts between the thermostat output and the relay coils in
> both instances. You get the added benefit of sharing priority equally
> if you do it this way.
>
> However, at this point, relay logic becomes silly. You should be doing
> all this on paper instead of just going out and buying relays, and at
> this point, your design is probably pretty complicated.
>
> Instead, buy a smart relay (a little tiny PLC is what it is) and
> program it however you like. Some sources--www.factorymation.com,
> www.automationdirect.com.
>
> Have fun, and let us know how it turns out.
>
>
>
> randall.reed@gmail.com wrote:
> > Alright, so I just had a 20KW generator installed to power the whole
> > house. I have two units, 5 Ton and 3 Ton and I don't want them ever to
> > run at the same time, because the two would be too much for the 20Kw.
> > The units are a year old, and I'm using the Honeywell digital
> > thermostats How can I keep the two from ever running at the same
> > time? Should I replace the thermostats with two that talk to each
> > other, or can the Honeywells do that?
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