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Need House Thermostat To Trigger 120V Outlet


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radarcontact 
Copper - Posts: 54
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Joined: June 16, 2009
Location: Florida, United States
Posted: February 20, 2023 at 8:27 AM / IP Logged Link to Post Post Reply Quote radarcontact
Hi.
(Long post, sorry)
Here’s the situation:
I (wife) have a whole-house air freshener (“scent machine”) that can pump aroma directly into HVAC, to make the entire house “smell pretty”.
If you hook directly into a/c ductwork, you can’t have it run when the a/c is off, only while a/c fan is running. Fragrance oil will pool up inside the plenum (?) and start to grow bacteria, etc.
So I have two choices and I want choice number #2.
1) run the a/c fan constantly, and let the machine cycle on/off throughout the day as it does by default. Easy, but costly on the electric bill plus wear/tear on air handler.
2) rig a 120v receptacle to be “tripped” or energized only when the a/c fan turns on and off. The unit will still cycle on off, but only when only the a/c fan is running. Hard, but so much better.
I figure the thermostat is 24v (?) so a 24v to 120v relay connected where thermostat connects to air handler.   Then run a simple pigtail female plug or receptacle mounted inside HVAC closet; 120v power would come from another receptacle in the adjoining bedroom.
Relay? “Contactor”?
Here’s what a local electrician told me along with his estimate of $400-$450!
“there are multiple types of relays to accomplish this, depending upon the load the relay has to handle. Being I do not know the load created by this machine you wish to operation, I would do it with a contactor, verse a relay, so it does not stand a chance to be overloaded.“
The scent machine only pulls 14w, so I don’t think there’s an overload concern.
Any words of advice??
Thanks.
// Radar //
RadarContact
geepherder 
Platinum - Posts: 3,668
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Posted: February 20, 2023 at 9:32 AM / IP Logged Link to Post Post Reply Quote geepherder
I don't have specifics on your unit, but if it were me, I would tap into the feed for the fan itself, not the thermostat. When the fan gets power, a separate contactor can energize and allow your scent machine to operate.
My ex once told me I have a perfect face for radio.
radarcontact 
Copper - Posts: 54
Copper spaceThis member has made a donation to the12volt.com. Click here for more info.spacespace
Joined: June 16, 2009
Location: Florida, United States
Posted: February 20, 2023 at 10:30 AM / IP Logged Link to Post Post Reply Quote radarcontact
I’ll have to research contactors, I’m not familiar. But that’s an interesting approach… need to pull the HVAC schematics and take a look!
RadarContact
geepherder 
Platinum - Posts: 3,668
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Posted: February 20, 2023 at 10:47 AM / IP Logged Link to Post Post Reply Quote geepherder
The thermostat connects to a board inside the unit but it doesn't determine when the fan is running. That's why you're best bet is to use the motor hot lead to control a contactor.
My ex once told me I have a perfect face for radio.
radarcontact 
Copper - Posts: 54
Copper spaceThis member has made a donation to the12volt.com. Click here for more info.spacespace
Joined: June 16, 2009
Location: Florida, United States
Posted: February 20, 2023 at 11:15 AM / IP Logged Link to Post Post Reply Quote radarcontact
Understood. Great point.
I researched contactors and that seems like overkill as the unit only draws 14w total. So, I will try to figure out which relay to use based on that info.
(From www.engineerfix.com: “ The load capacity of relays is mostly used for applications that carry 10A or less. Any applications that use 10A or more normally use contactors.”
RadarContact
geepherder 
Platinum - Posts: 3,668
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Posted: February 20, 2023 at 11:55 AM / IP Logged Link to Post Post Reply Quote geepherder
Yeah, it's definitely overkill. You could use a solid state relay to do the same thing.
My ex once told me I have a perfect face for radio.
radarcontact 
Copper - Posts: 54
Copper spaceThis member has made a donation to the12volt.com. Click here for more info.spacespace
Joined: June 16, 2009
Location: Florida, United States
Posted: February 20, 2023 at 12:27 PM / IP Logged Link to Post Post Reply Quote radarcontact
Sweet. I’ll try to find one and then I’ll come back for a thumbs-up! Lol!
RadarContact

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