Detect AC voltage - 24-240VAC

Discussion in 'The Projects Forum' started by 1999F250, Oct 19, 2010.

  1. 1999F250

    Thread Starter New Member

    May 14, 2010
    1
    0
    Hi,

    I would like to monitor my well pump and heating system with a microcontroller.
    My well pump is 240VAC (I am in the USA so 60 Hz)
    The pumps on my boiler are 120VAC.
    The zone valves are 24VAC.

    I saw a circuit somewhere that used a capacitor to pass a small current that was used to drive a LED (In my case the input of an optocoupler, with the photo transistor in the optocoupler driving a pin on a microcontroller). But I can't find that circuit now.

    Ideally I would like a circuit that would accept 24-240 VAC and when present drive the LED. I don't care about zero crossing.

    I have 6-8 things I would like to monitor so inexpensive and compact would be good.

    I assume this has been discussed before but just can't seem to find the proper search string - either here or Google.

    I plan to tap into the voltage parallel to the load.

    Thanks,
    Carl.
     
    Last edited: Oct 19, 2010
  2. marshallf3

    Well-Known Member

    Jul 26, 2010
    2,358
    201
    Ideally you'd want to build two different circuits, one for 24 and one for 240 however a hall effect device could be used.
     
  3. DonQ

    Active Member

    May 6, 2009
    320
    11
    There are certainly optocouplers you could use that could be made to cover the range from 24-240VAC, but it might just be easier to put a small signal transformer at each higher voltage location to convert to 24VAC before you do the sensing. You could even use some variety of 'wall-wort' type power-supply, for a few bucks each. Doesn't even have to be exactly 24V or does it need to be AC. Just some reasonable voltage at a tiny available current.

    You will probably be needing to run wires to the remote locations where the pumps are, and it would be better to run a bunch of low voltage wires (some telephone cord) rather than string a bunch of 240VAC wires (risking electrocuting someone, fires, etc).

    Then, everything coming into the microcontroller is 24VAC. Now it's easy.
     
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