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Posted by jamesgangnc on December 20, 2006, 1:36 pm
Only takes three to include the capability to activate the single
system limit while the generator is on. One relay powered by the
generator to enable the system, then one relay for each system to lock
out the other system while running.
I agree it's starting to reach the point where a control circuit with
solid state switches would be the preferred solution. But it takes
less background knowledge to rig up a small logic system with three
relays than it does to lay out the circuit for it using solid state
stuff. For a one off requirement the relays are still the way to go.
You could argue it's a potentially common need and design a control
board in a box that can do it. I'd go ahead and make it smart enough
to handle three or four systems since most of the whole house generator
customers tend to have bigger houses with multiple hvac systems. Then
market it to the generator companies.
Power's Mechanical wrote:
> gofish@gonefishin.net wrote:
> > "Power's Mechanical" wrote:
> >
> > >
> > >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?
> > >
> > >On 17 Dec 2006 18:47:49 -0800, 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?
> > >
> > >I assume you dont care if they both run when on normal power and its
> > >that if you switch to emergency power when you dont want both units
> > >running.
> > >
> > >If that is the case I would have a relay powered off the transfer
> > >switch or generator which would de energize one or the other a/cs.
> > >
> > >The relay, when energized, would break the control wire through a set
> > >of N.C. contacts to the condensing unit (your choice) compressor 24v
> > >contactor coil.
> > >
> > >Consult the installer of the generator for a specific wiring location
> > >to power up the relay when the generator starts. Done.
> >
> >
> > not done.
> >
> > you're forcing the customer to choose 1 of 2 when he could have both.
> >
> > the two 24v relays are the best choice. the ho can purchase them off
> > the web & install them himself. once in place, operation is automatic.
> >
> > customer has the option of using either ac, but never both at the same
> > time.
> >
> > now put a sticky on each t-stat that says:
> >
> > for ac, turn off the other thermostat
> >
> > done.
> >
> >
>
> Sorry but thats an idiotic idea imo. Now your forcing him to always
> use only one a/c at a time during non emergency conditions. The two
> relay idea is ok, but only if they are in play when the generator is
> running.
>
> Probably could use a bank of relays and really get crazy with redundant
> switching. Every time the stat calls.... click clack click clack
> relays pulling in and dropping out. Make sure to mount them on the
> duct work. :)
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