Current reading with Shelly Uni

    Hello everybody,
    I woul like to monitor the AC current coming inside a box where I have a router under DC UPS.

    So I have a constant 12V outside the UPS and I would like to monitor the AC input with a current trasformer ( hall effect ).
    Is it possible to connect the 50A current transformer at the AC input of a Shelly Uni device and read the current? I don't need to know a precise value but just to detect a power failure.

    Thank you in advance, Lorenzo

    I know two types of Hall effect current sensors: One type (a) gives a current as output (e.g. 100:1 ratio), the other type (b) has a voltage as output (e.g. 10mV per 1A).

    To couple type (a) with the ADC input of Shelly UNI you need a shunt resistor which returns a voltage from the current flowing through the shunt. Typical shunt resistors have100Ω, giving a +/- 5V output with full scale output of 50mA (hall sensor HA4009 for example). And be aware: with this type, current output is plus or minus 50mA!

    Type (b) sensors can be coupled directly with the ADC input of Shelly UNI, but have a zero offset of 2,5V (for example). This is arranged for reading current in both directions with a single rail supply.

    Due to the fact, both types are giving AC output signal with AC current flowing through the primary wire, you’ll have to rectify the AC signal, because the ADC input does not deal with AC input.

    A real challenge, but to handle for an ambitious hobbyist…

    Addendum: The data sheet for the integrated circuit ACS712 (Click!) gives some applications, also for rectification of AC signals. And by the way, modules with this IC ready for implementation are offered by distributors…

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    Einmal editiert, zuletzt von thgoebel (13. Dezember 2021 um 15:51)