Electricity Monitoring

Presentation

This is a minimalist but functional project to graph my in-house electricity consumption, inspired by Citizen Watt, and Open Energy Monitor.

Needed material

You'll need:

• A current transformer (CT), I used a SCT-013-000.
• An Arduino (I used a UNO R3).
• An Ethernet shield (I used A SunFounder Ethernet Shield W5100).
• A female jack plug (I found one in an old drawer…).
• 1 × 18 Ohms resistor.
• 2 × 10k Ohm resistors (or any equal value resistor pair up to 470k Ohm).
• 1 × 10uF capacitor.
• 1 breadboard.

How it works

The AC transformer, installed on a cable you want to measure, transforms the intensity to another intensity (ratio of 100A:50mA).

Considering the AC as an intensity generator proportional to the measured current, by using a resistor we get a voltage proportional to the intensity. Measuring a volteage is easy with an Arduino, we just need it to be in the range [0; 5] volts. This resistor, in this usage, is commonly called a "burden resistor".

Setup

From OpenEnergyMonitor, here is the setup I used:

I used a female jack plug to nicely connect the CT to my breadboard, next upgrade is to solder this to a strip board.

Next step is to find a cable for the CT, but for you safety follow those instructions carefully:

• Powering off the installation you want to measure, if it's your whole house, just power off the whole house.
• Never trust a circuit breaker label, so do measure the voltage of the installation you want to touch before actually touching it.
• If you have any doubts, seek professional assistance.
• Search a single-core cable, not a twin-core one, in which case the currents flowing in both direction will cancel each-other and your measure will be zero.
• Ensure the burden resistor is connected to your CT: Don't clip a CT without its burden resistor, it will accumulate dangerous voltages (the SCT-013-000 has a zener diode but still, don't do it).
• Check for exposed bare conductors, if there are ones, you installation is probably illegal → seek for professional assitance about this subject.
• Never attempt to fit a C.T. to a bare conductor, in other words, don't trust the insulation of the CT, if it fails, you can get hurt.
• Clip the CT around the cable you want to measure.
• Power on this section again.

Once the setup complete, you should probably assign an IP for the arduino in your DHCP server so you can find it easily, and start querying it:

$ curl 10.0.0.20
{"amp": 1.35, "watt": 323.98}

From here, you may install InfluxDB and grafana, and use the python script in a cron like:

* * * * * /usr/bin/python3 /home/mdk/.local/bin/query_watt.py 10.0.0.20 global 127.0.0.1:8086 conso

To fetch from the arduino and push to InfluxDB, from here you should get:

About using a Raspberry PI

It should be possible to use a Raspberry PI instead of an Arduino, but you'll need an analog input, the Raspberry PI doesn't have one, so you'll need an ADC.

Using a stripboard

As the circuit is simple, it's possible to make it on a stripboard as an arduino shell, I did mine like this (yes the bottom left blob is a fix, I wrongly cut the line):

And it mounts nicely like this (blue and red are blue and white from the SCT-013-000):