Relay madness ....

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DBCOOPER

DBCOOPER

Minister of Fire
Hearth Supporter
Jan 23, 2010
509
Stowe, Pa
My heat pump is pretty efficient when it's above 30 degree or so and I have been manually switching back and forth based on outside air temperatures. Decided it was time to make it automatic.
First I put two relays in my heat pump control circuit using the normally closed contacts for the compressor, fan, reversing valve ,aux and emergency heat. Heat pump runs normal in this configuration.
To control these relays I made up a control circuit that uses an inexpensive temperature controller marketed to control aquarium heaters, another ice cube relay a room thermostat a latching relay and a 24 volt transformer.
The controller is in Celsius so I have it set for . 3 C to go into heat mode and off at 1.5C. When the temperature drops below .3 the circuit closes sending voltage to the heat pump relay thru a relay which also has the stove thermostat circuit running thru it. So the heat pump relay contacts open and the stove contacts close and the thermostat for the stove to take over normal operation. If the stove fails for any reason the separate thermostat tells the latching relay to open the control circuit an the heat pump takes over.
It was a lot of fun figuring it out and so far seems to be working .
 
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Sounds like you used one of these > (broken link removed to http://www.ebay.com/itm/Temperature-Controller-Thermostat-Aquarium-STC1000-Incubator-Cold-Chain-Temp-i-/251240580707?pt=LH_DefaultDomain_0&hash=item3a7f1b0663)
I found one that was in F, to make like easier and I use it to control a chest freezer as a refrigerator. I use an external relay for the higher current. You are in the same boat as I am with manually switching between the two systems. I like your idea a lot. My only concern is if the system switches off the heat pump and then back on right away. There's protection in the heat pump system to put some time in there before it restarts and I wonder whether your system defeats that protection. Maybe that latching relay could be a delay-off relay?
Other than that, you have me thinking now! :)

REPOST: Thinking about it, the separate thermostat set at a lower room temp would probably give you the needed safety time.
 
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tjnamtiw said:
There's protection in the heat pump system to put some time in there before it restarts and I wonder whether your system defeats that protection. Maybe that latching relay could be a delay-off relay?
Click to expand...

I agree with tjnamtiw. You wouldn't want the relays switching back an forth between the two systems in short intervals. If you have unusual weather patterns moving through, I could see temperature swings causing the heat pump not to restart because of the time limits.
 
Fantastic ingenuity, folks. Nice work!

I have a Quad MVAE with its proprietary tstat (hate that part of it) but if I could figure out a way around that this is exactly what I want to do. The house itself is automated and can figure things out easily based on outside temps, even communicating with the Nest tstat on the heat pump. But that blasted MVAE tstat is my Achilles heel!
 
altmartion said:
can you change the stat?
Click to expand...
If referencing the MVAE, no. It contains the "brains" of the stove. Horrible design, IMO. Good stove, but I hate that part of it. If I could figure out their communication protocol I might be able to replace it, but seems proprietary.
 
tjnamtiw said:
Sounds like you used one of these > (broken link removed to http://www.ebay.com/itm/Temperature-Controller-Thermostat-Aquarium-STC1000-Incubator-Cold-Chain-Temp-i-/251240580707?pt=LH_DefaultDomain_0&hash=item3a7f1b0663)
I found one that was in F, to make like easier and I use it to control a chest freezer as a refrigerator. I use an external relay for the higher current. You are in the same boat as I am with manually switching between the two systems. I like your idea a lot. My only concern is if the system switches off the heat pump and then back on right away. There's protection in the heat pump system to put some time in there before it restarts and I wonder whether your system defeats that protection. Maybe that latching relay could be a delay-off relay?
Other than that, you have me thinking now! :)

REPOST: Thinking about it, the separate thermostat set at a lower room temp would probably give you the needed safety time.
Click to expand...

I can't think of an event that would make it short cycle. There is a temperature differential (swing) that's programmable in the controller like in yours. I may still put a time delay relay in the circuit just in case.I could have made it simpler by just interrupting the 24 volts going to the red on the thermostat but I want the hp thermostat to remain powered not just running on battery.
The latching relay driven by a thermostat locks the system back to the heat pump normal control thru its own thermostat in case the house gets to cold due to the stove not putting out heat for any reason. It's set to 62.
 
altmartion said:
are you an electrical engineer?
Click to expand...
Nope, just a facilities guy that takes parts out of junked equipment thinking " I could use that someday"
 
DBCOOPER said:
Nope, just a facilities guy that takes parts out of junked equipment thinking " I could use that someday"
Click to expand...
I do the same thing. I always save controls I remove from a job. they are great when a friend needs something. then I don't have to charge them for new parts.
 
DBCOOPER said:
The latching relay driven by a thermostat locks the system back to the heat pump normal control thru its own thermostat in case the house gets to cold due to the stove not putting out heat for any reason. It's set to 62.
Click to expand...

I DO like the idea of the extra protection latching relay in the event that the pellet stove takes a dump.. I have to admit that I didn't think of that when I was contemplating what you're doing.
 
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