Power Management the DIY Way

by Kenny Myburgh on December 15, 2020

It’s easy to save electricity, Just braai…

Yes, this would most definitely be what my family opts for as an excuse to have a braai. I don’t think there is such a thing as too much braai for them…

But to get a bit more to the point, “Electricity usage” is one of those general topics of conversation that rears it head around the braai quite often and usually steers in the direction of how expensive electricity has become followed by everyone’s attempts at implementing some or other strategy toward reducing usage to save money.

One of the most common solutions is usually associated with some or other timer which is installed on energy hungry appliances such as the geyser or a pool pump to control when it is allowed to turn on or turn off.

I have done this myself in the past, but the question around what the actual saving in this approach was always in the back of my mind. So how can we do it better you may ask…

What’s the better option ?

So instead of the “old school” timers approach,  a good way to understand your electricity consumption in our opinion is smart power monitoring devices.

Yes this can be quite a daunting task at first, as there are quite a few options out in the market but in my case I was looking for a solutions based on the following criteria which I felt narrowed down the options.

1.) It had to be cost effective. There are extremely expensive options out there.

2.) Available to my home network and not rely on the internet or cloud services.

3.) Integrate with my existing Home Assistant platform so that I can easily track usage and cost from a central location.

Our Options

As mentioned previously, there are many options as far as smart power monitoring devices go and having specific requirements helped but another contributing factor was that we already had experience in working with the Sonoff and Shelly product range as far as lights, switches and sensors, so these suppliers offering smart power monitoring was the cherry on top.

 Sonoff :

Sonoff POW R2


Shelly 1PM

Shelly EM

Both of these manufacturers have cloud connectivity options but... as always I want to avoid this like a plague and keep it local to my network and with these that is completely possible and why they were the easier choice for this application.

Preparation of Smart Power Monitor

The first appliance I wanted to monitor and understand power usage of was the 3D Printer as this device runs for hours with a heat bed that is at a constant temperature  of 60°

I opted to use the Sonoff POW R2 for this application as the amp draw of the 3D Printer is a maximum of 15 Amps . Sonoff POW R2 is rated at a maximum of 16 Amps so it was fine for this use.

With Sonoff there are a few more steps to take for ensuring local management  of the device in the sense of flashing it with Tasmota firmware which I have supplied some links for in the Additional Resources section of this blog. 
Once the Sonoff POW R2 has been flashed with Tasmota and integrated to Home Assistant I then had the ability to control the 3D printer power together with viewing statistics associated with :
  • Usage for the day, yesterday, year
  • Amps Drawn by the Printer
  • Watts Drawn by the Printer
  • Live Voltage
  • Overall Status
The second and third area/s I wanted to monitor was a bit more involved.
1.) The main feed to the electrical distribution board in the house to see overall consumption
2.) The geyser overall electrical consumption.
For this purpose the Shelly EM was the choice of application as the unit has the ability to monitor two inputs using CT (Current Transformer) clamps. There are different amp options for these CT clamps but for my application a 150amp clamp was used for the main feed and 50amp for the geyser.
Please Note: If you would like to perform a similar installation I would strongly advise getting hold of your local electrician to perform the installation as you are working with high voltage!
Configuring the Shelly EM was a breeze once the device was wired into the electrical distribution board as Home Assistant supports Shelly integration. It was essentially a matter of adding the new device as an entity voila! you are ready to display some default information within Home Assistant. Once the information is there the dashboard is probably where you will spend more time in getting the relevant information applicable to your application to be displayed.
Again the default information you receive is very much the same as with Sonoff:
  • Usage for the day, day before, year
  • Amps Drawn
  • Watts Drawn
  • Live Voltage
  • Status

Geyser Monitoring and Control

It is worth the mention that the Shelly EM also have the ability to control a DIN Connector (relay). During the installation of the Shelly EM you could ask your local electrician to install a separate DIN connector to control the desired appliance.

In our case we had a 25Amp DIN Connector installed to the electrical distribution board which would then control the  geyser power based on a peak and off peak electricity schedule and slightly more cost effective over setting a traditional timer schedule which is usually adapted to your lifestyle.

Apologies for the rustic wiring diagram!


Dashboard Information

The information displayed on the Home Assistant Dashboard requires a bit more effort and innovation in the sense of displaying information that is useful to you.

Information such as trends of the last week,  month,  year or placing a value to the amount of electricity consumption is possible. Please view the Additional Resources section of the blog for links that you can use as reference for  implementing such dashboards.

Additional Resources

Purchase Sonoff & Shelly EM 




Flash Sonoff POW R2 with Tasmota


Power Monitor Dashboard