A "Hello Kettle!" in Open Energy Monitor

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Open Energy Monitor is an Open Source and Open Hardware project for monitoring:

  • Energy consumption.
  • Energy generation.
  • EV charging.
  • Heat Pumps.

I heard about Open Energy Monitor for the first time at the Fully Charged Live (an event that has been renamed a few times run by Fully Charged Show) in September 2021. I saw someone (probably Trystan or Glyn?) in one of the stands with the "Open Energy Monitor" sign and I had to ask what that was about. I don't remember much of our conversation but since then I've been looking forward to put my hands on this project and learn more about it.

I received my EmonPi2 yesterday and I did a "Hello Kettle" 😂 with it.


(Power in Watts)

Let me show you what the EmonPi2 set up looks like for the most simple use case on a single-phase meter; Measuring the Power Consumption in your home: 


Key components:
  • Current Transformer (CT) sensor: Measures consumption current.
  • EmonVS: Powers the EmonPi2 and sends voltage data to the EmonPi2.
  • EmonPi2: Takes Current from CT and Voltage from EmonVS to measure Power consumption. The Raspberry Pi inside runs a server with EmonCMS, a User Interface where you can see your power consumption.

For this use case of monitoring my home consumption, there's a summary of the steps I followed:
  1. Make sure no cables are exposed and do not open the fuse box. If there are cables exposed or the installation looks scary, ask for assistance from an electrician.
  2. Figure out what's the max current sensor you need for your main. If in doubt, use 100A.
    1. My smart meter has a couple buttons and if you give them a go you'll find what's the current in Amps in your house.
    2. Turn all your appliances on and then read the current value on your meter; if it's much lower than 100A, then go for a 50A. Mine was about ~30A with EVERYTHING on, so I went for the 50A.
  3. Get the EmonPi2 (it comes already with the EmonVS) and the CT sensor you need.
  4. Connect the EmonVS to the EmonPI via the RJ45 cable (into the EmonVS port and not the Ethernet port). 
  5. Plug-in the EmonVS to a power socket.
  6. Carefully install the CT sensor with the sensor's arrow pointing towards the Fuse Box.
  7. Configure the Wifi on the EmonPi (or Ethernet if you went for the Ethernet-only version). This is done by enabling the Wifi Access Point and connecting to it with credentials emonPi, emonpi2016. 
    Extended documentation is available at the project's website.
  8. Log into the EmonCMS and create a graph out of your CT sensor as explained in the docs.
  9. Visualize the metric in a Graph and Voila! There's your real-time power consumption metering!
My overall initial experience has been good. I expected it to be more fiddly but I also expected the documentation to be more linear. I found myself jumping around links as the docs are structured per device or system component instead of by use case, so you need to understand a bit what each component does and which one isn't out of date vs. available for sale in order to get it done. The community forum and a kind knowledgeable trustable member responding questions have been essential for me to get started.

My next steps will be to dive deeper into what's inside the EmonPi2, skipping the EmonVS which is a 100% hardware component so I'll explain how the EmonPi2 works in the next post.

While you wait, take a look at this video introducing Megni, the company behind Open Energy Monitor: