Threshold voltage for a switch to be considered 'on'

  • I have a pair of lights on a circuit controlled by two separate switches, at opposite ends of the room, one of which is a dimmer-switch. I'd like to add a Shelly 2.5 in 'cycle' mode at the ceiling rose, using as the wall-switch 'input', the 'output' of the dimmer & toggle-switch pair that previously fed the lamps. Of course this working as intended is dependent upon a number of factors:

    1) Will the Shelly operate on the reduced voltage from the dimmer?

    2) If #1 is 'no', I can power the Shelly from the mains, but then what gets passed to the lamps -- the mains? or the 'signal' from the switch input? (of course #1 is moot if the answer to this one is the latter.

    3) If #1 is 'maybe', what is the minimum voltage required for the Shelly to operate itself?

    4) What is the threshold voltage on a switch input on the Shelly to be considered 'on'?

    5) Do some models provide independent 'dry contacts' switches, while others are internally linked? I think I know the answer is 'yes', but where can I find a list of which models fall into each category. I can make NO SENSE out of the model numbers, and cannot find the secret decoder ring to tell me what the letters and numbers mean. Example: Plus vs not 'Plus' vs Pro vs 'Gen3' vs 'PM', etc. Underwriters Laboratories (UL) is the only piece I happen to know. 'PM' in my world means after noon, and 'plus' is the opposite of 'mini', but neither of those seem to be the case here, and 'Gen3' doesn't seem to be just improvements to 'Gen2'.

  • Welcome to the forum!

    To some of your questions:

    3) If #1 is 'maybe', what is the minimum voltage required for the Shelly to operate itself?

    Shellies suitable for supply with mains voltage are working from 90V AC upwards.

    4) What is the threshold voltage on a switch input on the Shelly to be considered 'on'?

    The SW inputs of Shelly actors are triggered by current, not by voltage: A very small current, flowing from pin SW to L, activates the input. Activation happens with approximately 17μΑ, SW and L shorted by contact or wire gives 34μA. Driving voltage is approximately 3V DC.

    5) Do some models provide independent 'dry contacts' switches, while others are internally linked?

    Shellies wit dry contacts are: Shelly 1 (EoL), Shelly plus 1 (SELV certified), Shelly mini 1 (NOT SELV certified), Shelly pro 1, Shelly pro 3, Shelly pro 3. Dry contacts are also to find with Shelly EM, Shelly 3EM and Shelly EM-50. For Shelly pro 3EM is a special Add-On available, which incorporates a dry contacts also. And, for small voltage applications, Shelly UNI and Shelly plus UNI have dry contacts too.

    “PM” is an abbreviation for power measurement, “EM” for energy measurement.

    „Habt Geduld. Alle Dinge sind schwierig, bevor sie einfach werden!“ (aus Frankreich)

    „Nothing in life is to be feared, it is only to be understood.“ (Marie Curie, 1867-1934)

    „Es reicht nicht“, rief Schiller, „Gedankenfreiheit zu fordern, man muß auch denken können, sonst fordert man Gedankenlosigkeitsfreiheit und die ist die Freiheit zur Dummheit, welche wiederum die schlimmste Unfreiheit überhaupt ist!“
    (Aus „Besuch aus Weimar“ von Gert Heidenreich, Schriftsteller, *1944 in Eberswalde)