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Using HVAC 24VAC to power an AC adapter to generate DC output

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  • Using HVAC 24VAC to power an AC adapter to generate DC output

    I have an Aprilaire 800 humidifier. The aprilaire tech said the best way to monitor when the hum is running is to connect to the fan pack 24VAC output. However the monitoring device i have connected to HS required at least a 3 VDC to trigger.

    I tried a 24VAC relay, but it was really noisy and i still needed to add a DC voltage source to convert the relay output.

    So i tried a standard 100-120V AC adapter that outputs enough DC voltage. when i connect the HVAC 24VAC to the AC adapter, i get a DC voltage output that will satisfy my monitoring device.

    My question, is it okay to run a standard AC adapter at 24VAC?
    Mark

    HS3 Pro 3.0.0.435
    Hardware: Insteon Serial PLM | AD2USB for Vista Alarm | HAI Omnistat2 | 1-Wire HA7E | RFXrec433 | Dahua Cameras | LiftMaster Internet Gateway
    Plugins: Insteon (mine) | Vista Alarm (mine) | Omnistat 3 (by Kirby) | Ultra1Wire3 | RFXCOM | NetCAM | MyQ | BLRadar | BLDenon | Jon00 Charting
    Platform: HP h8-1360t, Windows Server 2012 R2, i7-3.4GHz, 16GB memory

  • #2
    If your "A/C Adapter" is a simple transformer(old style--newer/smaller units are usually full of active components and would not like 24VAC input) with some diodes to rectify the output to DC, then your probably OK.
    You could also just take your 24VAC output and add a diode to get DC and a 2 resistor voltage divider(7:1) to lower the max DC voltage to about 5 VDC so you don't fry your monitoring devices input.

    Comment


    • #3
      Originally posted by mnsandler View Post
      I have an Aprilaire 800 humidifier. The aprilaire tech said the best way to monitor when the hum is running is to connect to the fan pack 24VAC output. However the monitoring device i have connected to HS required at least a 3 VDC to trigger.

      I tried a 24VAC relay, but it was really noisy and i still needed to add a DC voltage source to convert the relay output.

      So i tried a standard 100-120V AC adapter that outputs enough DC voltage. when i connect the HVAC 24VAC to the AC adapter, i get a DC voltage output that will satisfy my monitoring device.

      My question, is it okay to run a standard AC adapter at 24VAC?
      If it is a transformer in the adapter, yes. If it is a SMPS (switch mode) it could be a problem, because their current consumption will go up as the supply voltage goes down. A transformer will consume the same current, no matter what the input voltage is. It is very unlikely that it is a switch mode, because they usually will not work at all once below half their minimum supply voltage. Most modern SMPS are designed for a supply of 100-250V so they can be used internationally. They usually fail to function below 50V.

      I think your your solution is safe and will work just fine.

      Randy Prade
      Aurora, CO
      Prades.net

      PHLocation - Pushover - EasyTrigger - UltraECM3 - Ultra1Wire3 - Arduino

      Comment


      • #4
        Wow! Two answers at the same moment that are essentially the same. Mark that down
        Randy Prade
        Aurora, CO
        Prades.net

        PHLocation - Pushover - EasyTrigger - UltraECM3 - Ultra1Wire3 - Arduino

        Comment


        • #5
          Originally posted by rprade View Post
          Wow! Two answers at the same moment that are essentially the same. Mark that down
          You know what they say about great minds!

          Comment


          • #6
            Here's an alternate approach that may work and may be simpler to install though it depends on whether your air handler is controlled by the humidifier or by the thermostat directly. Some humidifiers (mine are Honeywell) have a dry contact relay which closes when there is a call for humidity. This can be wired to your air handler to cause the fan to start blowing. However, in some installations that relay isn't used and, instead, the thermostat directly controls the fan in the air handler. Thus, the relay on the humidifier is unused. You could wire a dry contact Z-Wave sensor directly to that fan relay and trigger based on that (unusued) air handler dry contact opening / closing. Aeotec used to make a dry contact sensor (ZW097A) that I think wold work for this and some door contact sensors also have internal terminals that allow use as a dry contact sensor (I think Monoprice sells some like that). It seems this wold be simpler to try than wiring additional relays / transformers. Admittedly, this is "off the top of my head" thinking based on my experience installing my own home humidifiers - I haven't tested it out, but it seems you only need a $20 dry contact sensor so it may be worth experimenting..

            Comment


            • #7
              Hey Guys,
              Thanks for all the suggestions. Based on the input, i'm getting something like the following. Easy to mount and wire up while keeping everything clean, and low-voltage.

              https://smile.amazon.com/gp/product/...?ie=UTF8&psc=1

              Mark

              HS3 Pro 3.0.0.435
              Hardware: Insteon Serial PLM | AD2USB for Vista Alarm | HAI Omnistat2 | 1-Wire HA7E | RFXrec433 | Dahua Cameras | LiftMaster Internet Gateway
              Plugins: Insteon (mine) | Vista Alarm (mine) | Omnistat 3 (by Kirby) | Ultra1Wire3 | RFXCOM | NetCAM | MyQ | BLRadar | BLDenon | Jon00 Charting
              Platform: HP h8-1360t, Windows Server 2012 R2, i7-3.4GHz, 16GB memory

              Comment


              • #8
                Originally posted by mnsandler View Post
                Hey Guys,
                Thanks for all the suggestions. Based on the input, i'm getting something like the following. Easy to mount and wire up while keeping everything clean, and low-voltage.

                https://smile.amazon.com/gp/product/...?ie=UTF8&psc=1
                It looks like a good solution and likely very efficient.
                Randy Prade
                Aurora, CO
                Prades.net

                PHLocation - Pushover - EasyTrigger - UltraECM3 - Ultra1Wire3 - Arduino

                Comment


                • #9
                  Originally posted by mnsandler View Post
                  Hey Guys,
                  Thanks for all the suggestions. Based on the input, i'm getting something like the following. Easy to mount and wire up while keeping everything clean, and low-voltage.

                  https://smile.amazon.com/gp/product/...?ie=UTF8&psc=1
                  Just make sure you won't fry your sensor with 12.5 volt input---may still need a divider

                  Comment

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