Getting both positive and negative power readings for devices monitored via Pro EM-50

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  • Didn't find a subfourm for Shelly Pro EM-50 devices, so I'm adding a new discussion here.

    This week I've isntalled my latest Shelly device to my home newtork, It is a Shelly Pro EM-50 that I intend to use to monitor the power consumption of my induction cooktop and hooven appliances in the kitchen.
    I've installed it in the secondary switchboard in the kitchen, and everything seems to be working almost fine...

    I learned since I installed my first Shelly EM device, that after installation if getting negative readings, I need to invert the orientation of the current transformers or clamp sensors giving negative values.

    In the present case it happens that I also had to make such correction, although I sitll get a positive reading in the range of KWs when the respective kitchen appliances are working, but also negative readings when the appliances are not working (aprox. -17W for the cooktop and very small negative readings for the hooven), which jeopardizes the total consumption values over time.
    - What could be the problem?
    - Is there any way to calibrate the zero?
    - Could it be related with electrical wires or sensor cable routing inside the switchboard? The available space is quite thight and I'm affraid there is nothing I can do...
    Have another Shelly Pro EM-50 installed in the house main switch board and didn't observed such behaviour. Everything is working fine with that one!


    PS: BTW, much better if it would be possible to configure the reading signal (-/+) in the device settings via app, as inverting the sensor is not always that convinient because of routing issues in thighter spaces...

  • Induction cooktops have almost interference suppression components mounted directly at the power inlet of the device. These components are mostly condensers. Thus, the cooktop represents in off state a capacitive load to the mains supply, which is establishing a small negative reactive power source. This reactive power is counted by the Shelly EM50 as negative reactive power (power factor nearly zero). It is not possible (and even not necessary) to suppress this count. Simply ignore it!

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