Any way for Shelly 2.5 to control DC V+ rather than DC V- ?

    I'm trying to let a Shelly 2.5 control power for my 3D printer mainboard on one port and for the printer's Octoprint Raspberry Pi on the other. My 3D printer's 24V DC supply is powering the Shelly 2.5, whose port 1 switches the 24V printer's mainboard, and port 2 switches a 24V->5V buck converter driving the OctoPi. I wired it as documented with the V+ (DC 24V) directly connected to the mainboard and buck converter, and the V- (DC 0V/Gnd) to the Shelly's L ports. Thus the Shelly wants to control power to each device by controlling presence of 0V/ground to each device.

    The problem is the OctoPi needs a serial connection to the printer's mainboard, and using either USB or GPIO for serial means connecting their grounds together. Thus with the above wiring, when the Shelly turns on say O1 but not O2, both of the loads come on anyway because the serial ground still completes the power circuit for the 2nd load bypassing the fact that the Shelly is not connecting O2 to L.

    It would be nice if I could invert the polarity of the DC+ and DC- connections, as that would solve the problem as 24V would be controlled to each rather than 0V. But I assume the Shelly doesn't support that. Appreciate any suggestions, thanks.

    Presume my options are one of...

    • Use 2 Shelly 1's in place of the Shelly 2.5 (Cons: expensive; overkill/complex from a management perspective)
    • Use the Shelly 2.5 to control AC line voltage to separate DC supplies: 24V for the printer, 5V for the OctoPi (could kill myself working with line voltage unless I keep this in the wall, which I don't want to do; 2nd AC/5vDC supply likely less efficient than the 24V->5V buck converter)
    • Use the Shelly 2.5 outputs to drive ports on an external relay module like https://www.amazon.com/dp/B00LW2G7V6 which then drives the two loads with common ground (extra component adds cost; might not be as reliable or efficient)
    Zitat

    Thus with the above wiring, when the Shelly turns on say O1 but not O2, both of the loads come on anyway because the serial ground still completes the power circuit for the 2nd load bypassing the fact that the Shelly is not connecting O2 to L.

    Just two short hints:

    (a) Using diodes in DC circuits could help to decouple switches and loads.

    (b) The “overwhelming” discussion in this thread could possibly be generated by an axiomatic lack of diagrams. :) Drawing a tiny sketch would help…

    „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)

    Thanks, attached pic is what I was trying to do. The bottom part in red shows that when the Raspberry Pi was connected by serial to the 3DPrinter, it coupled their grounds together, even if e.g. O2 providing DC supply ground to the 3D printer is off/open circuit (red dashed line). Therefore even then the 3D Printer still gets a DC supply ground connection through the raspberry Pi serial and buck converter, as long as O1 is on/closed circuit. 3dpRpiV1.png

    Due to the fixed ground connection between Raspberry Pi and Printer dropping some diodes in the circuit doesn’t help! In this case, switching of +24V DC level is necessary. Thus you’ll need two additional relays: The relay coils (24V DC coils) connected between +24V supply and outputs O1/2 of Shelly 2.5. The relay contacts (NO) arranged between +24VDC supply and buck converter input and/or Printer power input.

    „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)

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