OpenEnergyMonitor

How to build a basic energy monitor - measuring current only.

For the full energy monitor - voltage and current measurement have a look at this page.

New revision April 10th to make it more consistent with rest of documentation.

Picture: Setup plus nokia 3310 screen, for info on adding the screen have a look here.

This little guide details how to build a simple electricity energy monitor on a breadboard that you could use to measure how much electrical energy you use in your home. It measures current directly and takes a set value for voltage (if your in the uk 240V) to calculate apparent power all the calculations are done on an arduino, although not as accurate as when a voltage measurement is taken, it is a method commonly used in whole house energy monitors for reasons of simplicity and lower cost. Here's how to do it:

Step One – Gather Components

You will need:

1x Arduino oomlout £23.67 , nuelectronics £16.99 

1x CT sensor efergy £7.50 , seeedstudio $11.50, Sparkfun $9.95

2x 10kOhm resistors

1x 56 Ohm resistor (depends on choice of CT and power to be measure: see detailed design page) for calculation

1x 10uF capacitor

1x A breadboard and some single core wire.

Oomlout do a good arduino + breadboard bundle here £29 

Step Two – Assemble the electronics

The electronics consist of the current sensor (which produce signals proportional to the current in the mains) and the sensor electronics that convert these signals into a form the Arduino is happy with.

For a circuit diagram and detailed discussion of sensors and electronics look on the detailed system design page, the page details voltage and current so if you just want current ignore the voltage bit.

Assemble the components following the Fritzing diagram below:

Step Three – Upload the Arduino Sketch

The Arduino sketch is the piece of software that runs on the Arduino. The Arduino converts the raw data from its analog input into a nice useful values and then outputs them to serial.

Download the sketch here: powerMonitorCurrentOnly.tar.gz

and then upload it onto the Arduino. Then go to the Arduino serial monitor and you should see values being printed to the screen, looking something like this:

From left to right: Apparent Power, Irms.

Step Four - Calibration

If you compare the output from the serial monitor with the output from a reference energy monitor (like a kill-a-watt plug in meter) they probably wont be the same. To get accurate measurements the energy monitor needs to be calibrated, as follows:

For best results choose a load that's within but close to the maximum range of your energy monitor and your reference meter minus a couple of hundred watts, most domestic plug in meters go up to about 3120W so around 2000-2800W would be fine (as long as this is also within the range of the energy monitor)

If your using non-halogen heaters beware that the power that they consume decreases for sometimes up to 10mins as they heat up. To take an accurate calibration point wait until the power consumption is stable.

Note down the Current value off your reference meter and from the Arduino serial monitor and then calculate the calibration coefficients:

Look in the Arduino sketch for the lines:

double ICAL = 1.0;

Multiply the old ICAL by the new ICAL and replace the old value with the result.

Upload the sketch and now hopefully your values should be a lot closer to what they should be.