Shelly i3 and heating system - no events

  • I have the following heating circuit. This is single-phase 240V. The relays are thermostats that switch on or off via other means. The motors are 2-way motorized valves that control two water heating zones.Each motorized valve has another cable that goes to the boiler to turn it on or off like a switch. The boiler has also its own Permanent Live cable (this is an S-plan heating system with two zones).


    What I wanted to do is put an i3 device to monitor when the termostats request heat, and do plots etc. I dont want to control the circuit, just to monitor the switched live cables. This is the wiring I came up with.


    image.png


    The problem is that it doesnt work.


    When I connect the shelly as shown above, the shelly i3 device thinks that the relays are always in ON mode, even when they are off. When the relays get turned ON, the I1 and I2 inputs stay in ON mode - the shelly does not detect any changes in the input. Everything else works fine with the heating system. The event_cnt counter stays the same no matter how many times the motors get turned on or off.


    I have measured the voltage between the two sides of the relays (i3 L vs I1 for example) and there is 245V when the relay is OFF and 0V when the relay is ON. So I am not sure what is the problem here.


    I saw some mentions in this forum that this setup may require coupling relays, but not sure I understood why. Another solution would be to use a Shelly EM I suppose, with two clamps, one for each switched live. It seems like an overkill though, I do not want to measure the power (this is a gas boiler, it does not draw much electricity, the whole circuit has a 3A fuse).


    Any thoughts on that? cc @Olsche  @Guzzi Charlie

    Edited 2 times, last by trv4gr ().

  • If you are skilled in electronics (or you may a have a friend with this profession), you should add two resistors:


    i3.jpg

    Resistance is not critical: 470kΩ to 1MΩ will work. Each resistor should bear 1W - this is more than triple oversized. For a secure implementation look at this thread: click (unfortunately in German language). If you should have any question in the implementation or in sourcing the parts, you may send me a PM!

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


    „Wer die Vergangenheit nicht kennt, versteht die Gegenwart nicht und kann die Zukunft nicht gestalten.“ (August Bebel, 1840-1913)

    Edited 2 times, last by thgoebel ().

  • Must unbegrudgingly admit utschu ’s solution is much more convenient than mine! :thumbup: :thumbup:

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


    „Wer die Vergangenheit nicht kennt, versteht die Gegenwart nicht und kann die Zukunft nicht gestalten.“ (August Bebel, 1840-1913)

  • If you are skilled in electronics (or you may a have a friend with this profession), you should add two resistors:


    i3.jpg

    Resistance is not critical: 470kΩ to 1MΩ will work. Each resistor should bear 1W - this is more than tripple oversized. For a secure implementation look at this thread: click (unfortunately in German language). If you should have any question in the implementation or in sourcing the parts, you may send me a PM!

    Oh thats very interesting! I'll read the linked thread via google translate.

    So the i3 needs some small load in-line to understand the status of the switch?

    I thought the voltage differential between L and I1/I2 would be enough. I'll definitely try that.



    I tried reversing the inputs, there is no change. The shelly inputs gets stuck to OFF (instead of ON), no matter what the real relay status is.

    No events are counted when switching, still.

  • Not exactly. Allterco designed the SW (or IN) inputs to detect both live and neutral potential. Thus, any circuit with switch and consumer (e.g. lamp, heater, motor) and a connected SW or IN input leads to signalising of “active” in both positions of the switch, because both live and neutral polarity is giving a signal.

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


    „Wer die Vergangenheit nicht kennt, versteht die Gegenwart nicht und kann die Zukunft nicht gestalten.“ (August Bebel, 1840-1913)

  • Did you also swapped the wires, going to I3 inputs, of Thermostat output, from NO to NC?

    Actually the diagram is not very accurate, apologies for that. The relays only have one output that is "call for heat". There's no separate NC/NO output. The realays are normally open by default. When voltage is 0 the thermostat is off and the motorised valves are shut. When voltage is 240V the thermostat calls for heat and the motorized valves open.

  • Not exactly. Allterco designed the SW (or IN) inputs to detect both live and neutral potential. Thus, any circuit with switch and consumer (e.g. lamp, heater, motor) and a connected SW or IN input leads to signalising of “active” in both positions of the switch, because both live and neutral polarity is giving a signal.

    I do not have a 470kΩ to 1MΩ / 1W resistor to try right now but will get some.


    However, I have a few "Shelly Bypass" components ( Frage zum Bypass )


    I wonder if these would work. They are meant to be used in shelly1 installations without neutral (connected parallel to the consumer) in order to allow a small amount of current through but maybe this is an alternative use.


    These components have a small board on them and on the label of the board it says 220V - 2.2W. There's a resistor (unsure how big), a CS7N65 A4R mosfet and a few other small passive components on the board.

    Edited once, last by trv4gr ().

  • I would not recommend to try a bypass device! IMHO, these are designed to deliver a certain current despite of the voltage across the bypass. Hence, they are not behaving as resistors!

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


    „Wer die Vergangenheit nicht kennt, versteht die Gegenwart nicht und kann die Zukunft nicht gestalten.“ (August Bebel, 1840-1913)

  • I would not recommend to try a bypass device! IMHO, these are designed to deliver a certain current despite of the voltage across the bypass. Hence, they are not behaving as resistors!

    Thanks, so I will not try that :)

    I am having a bit of difficulty finding MMB MELF resistors in the UK (without importing).


    What about using 3x SMM02070C2403FBP00 or 1 x CSRV0207FTDT6803 ? I can find those locally.

  • Instead of using Shelly i3 you can use Shelly EM connected to two Current Transformer.

    If it will not be simple, it simply will not be!

  • Instead of using Shelly i3 you can use Shelly EM connected to two Current Transformer.


    Yes that is true. However I already have an i3 but not a shelly EM, and using the EM for this seems like an overkill; I do not need to measure power, just need the events to create plots and alerts! But certainly, if the i3 does not work with the resistors trick, I will buy an EM or some alternative.

  • I am having a bit of difficulty finding MMB MELF resistors in the UK (without importing).


    What about using 3x SMM02070C2403FBP00 or 1 x CSRV0207FTDT6803 ? I can find those locally.

    To whom it may concern: Issue solved by direct contact with trv4gr !

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


    „Wer die Vergangenheit nicht kennt, versteht die Gegenwart nicht und kann die Zukunft nicht gestalten.“ (August Bebel, 1840-1913)

  • And to whom it may concern, adding these resistor cables really makes the above setup to work perfectly well!

    A big thank you to all who helped and especially thgoebel