, 2 min read

Electricity Measurement with Shelly 3EM

Original post is here eklausmeier.goip.de/blog/2022/09-11-electricity-measurement-with-shelly-3em.

This week Peter Kammermeier installed two measurement tools in the switchbox and DC to AC solar converter box. Measurement tool is a Shelly 3EM, "Professional Energy Meter". Shelly is a brand of Allterco, headquarted in Sofia (Bulgary). On their website they say that they have sold over five million devices worldwide.

The package contains:

  1. Shelly computer
  2. Three wire-measurement tools, i.e., Hall effect sensors, labeled "A", "B", and "C".

The Shelly computer is the following:

  1. It has ESP8266 microchip inside with 4 MB flash
  2. Running Mongoose-OS operating system
  3. Running Mongoose web-server
  4. Shelly Script Language: modified mJS
  5. Supports MQTT
  6. Stores data for 365 days power consumption
  7. Power consumption < 1W
  8. Emits its measurements via WiFi 802.11 b/g/n
  9. Max. current 10A
  10. Can power one relay

1. Installation. The cabling is now:


For the installation Peter used multiple Wago cage clamps.

Before installation, from the breaker there is one cable going to the consumer:

graph TD B(breaker) --> C(consumer)

After installation of the Shelly, the Wago clamp connects three lines:

graph TD B(breaker) --> W[Wago clamp] W --> C(consumer) W --> S(Shelly)

The Shelly 3EM is a 1st generation model, see Shelly Family Overview Generation #1.

2. DC to AC converter. The Shelly 3EM can also be used to measure how much electricity is fed to the power grid. Below images show installation in SMA DC to AC converter.



3. Website or Android app. You can either use the Android app, or view the measurements on the web. The results looks similar to below screenshot.


The website shows a field called PF: This is the Power factor,

$$ \hbox{pf} := \hbox{power factor} = {P\over U_{\hbox{rms}}\cdot I_{\hbox{rms}}} $$

The results of the power measurements can easily be shared by inviting others via e-mail. They in turn can then view the measurements.