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Feed 24 VAC relay coil from 2 different 24 V sources

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Dan Villa

New Member
Want to feed a 24vac relay coil from 2 separate ac condensor 24 v thermostat wires, Contact side of the relay will control 12 V DC , 3 AMP load to a small water pump. I want to cover the case where one ac unit is on and powering the relay , then the 2nd unit comes on while first is on. I think I need to keep the voltage from one feeding back to the other if they are both on at the same time. Can I do this with diodes ? Would it be safer to current sense the the power going through the hot wires, this way the 24v lines never see each other. If I sense the current and convert this to a small voltage that I can measure using a microcontroller it could then make the decision to close the 12 v contact to turn on the pump.
 

MikeMl

Well-Known Member
Most Helpful Member
Two small AC relays; you can do anything you want with their contacts...
 

crutschow

Well-Known Member
Most Helpful Member
I go with Mike.
If the coils are AC, the easiest is to use two relays.
Connect a NO contact from one relay in parallel with the other relay NO contact to control the pump.
That way, energizing either relay or both will power the pump.
 

Dan Villa

New Member
ok NO contact to NO contact makes sense, Its like math when your stuck on a problem and someone shows you how the bulb goes off. I was gonna solve it the complicated way with current sensors and a micro controller, cost is the same but then I have many points of failure. Thanks all who responded.
 
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