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Relay triggered by 24v AC?

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    Relay triggered by 24v AC?

    I am considering connecting a relay to my heater and AC lines such that I can have HS or the ELK track how often my heater and AC kick in. While some of this could be done via tracking of the t-stat values, I am thinking that if not too difficult of wiring in a relay and then feed the NO and common of the relay outputs to inputs of the ELK.

    So, I figure that 24 volt AC on the trigger side of the relay will continuously cycle the relay 60 times per second, right? This would be bad.

    While not a electronics engineer, I am only aware of DC triggered relays. Are there AC triggered relays?

    Thoughts?
    HomeSeer 2, HomeSeer 3, Allonis myServer, Amazon Alexa Dots, ELK M1G, ISY 994i, HomeKit, BlueIris, and 6 "4k" Cameras using NVR, and integration between all of these systems. Home Automation since 1980.

    #2
    Yep your hunch is right, AC on a DC relay will give it a bit of a beating and make a nasty noise and wear out the contacts. Couple of options:

    1) Bridge rectifier - either build one with four diodes or just get a packaged one, will convert AC to DC and then you can use a DC relay. AC in one end, DC comes out the other.

    2) AC Relay - they do exist and Mouser has a selection here, http://www.mouser.co.uk/Electromecha...5g31?P=1z0x3ba

    3) Whilst you may wish for mechanical isolation you could do it also most likely with an opto isolator on the 24V line (would need a bridge rectifier, resistor and opto) in a small circuit, nothing mechanical then.

    Comment


      #3
      Originally posted by mrhappy View Post
      3) Whilst you may wish for mechanical isolation you could do it also most likely with an opto isolator on the 24V line (would need a bridge rectifier, resistor and opto) in a small circuit, nothing mechanical then.
      I use AC opto couplers for this exact purpose (furnace zone valves), you could do it with external components as well. Youi'll also need a capacitor on the DC side if you want a steady signal (opto will pulse at 60Hz)
      Attached Files

      Comment


        #4
        24 AC type relays are very very common, and in HVAC industry are used all the time.
        What you want to do is very easy and the relay dry contacts will work well and give you a clean and constant close signal if the relay has triggered.

        I am a bit confused as to why you think the relay continuously cycles 60 times per sec?
        Once the coil is energized, the NO&common are closed and stay that way until coil is de-energized.

        24vac relay should cost you <$10
        some relays come enclosed with spade connectors, and some the relay and base plug into each other.

        good luck.

        Comment


          #5
          Originally posted by Amigo View Post
          ...I am a bit confused as to why you think the relay continuously cycles 60 times per sec?
          Once the coil is energized, the NO&common are closed and stay that way until coil is de-energized...
          I think it was the thought of using a DC relay on AC that the relay would cycle at the AC frequency (or at whichever speed the contacts could actually keep up with!) which it would do and make a bit of a chatter.

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            #6
            Ok yeah, I missed the part that op may have been thinking of using DC on AC circuit.

            Comment


              #7
              Here's an example of one: http://www.ebay.com/itm/152166719784. A lot of relays come with pins, so having a socket for it makes it easier to use and replace.

              Cheers
              Al
              HS 4.2.8.0: 2134 Devices 1252 Events
              Z-Wave 3.0.10.0: 133 Nodes on one Z-Net

              Comment


                #8
                Thank you!
                HomeSeer 2, HomeSeer 3, Allonis myServer, Amazon Alexa Dots, ELK M1G, ISY 994i, HomeKit, BlueIris, and 6 "4k" Cameras using NVR, and integration between all of these systems. Home Automation since 1980.

                Comment


                  #9
                  Easy fix. RIBMN24C-4T. Comes in a 4 pack configuration with a bracket. I have one mounted in my Elk panel and it monitors the thermostat 24vac control line. I monitor the 24VAC supply voltage, Fan, Compressor and Change Over Valve lines for my Heat Pump HVAC system.

                  Already have TR-16 thermostat hooked to he Elk panel so its lines are already there and easy to tap with the RIB setup. Outputs from the four relays go into input on the Elk.

                  HS alerts me if I lose power and also logs what the HVAC system is doing. Have some events to alert if Cooling/Heating is selected and running and temp is way out from set point. Have had AC compressor failure in the past and came home from a vacation to a very hot house.

                  http://www.functionaldevices.com/bui...el=RIBMN24C-4T
                  Attached Files

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