2 Watt Meter method

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The default setup proposed for 3phase is the three watt meter method which requires measuring voltage between each phase and neutral.

There is an alternative method called the Two Watt Meter method. As the name suggest is uses two watt meters hence two voltage sensors and two current sensors. The voltage sensors have to be connected between two phases this time.

Background

Typically this is how all sensors would be connected.

Two watt meter.png

The two associated sensor pair will produce what is commonly callled W1 and W2.

CT1/V1 -> W1
CT2/V2 -> W2

The total power being the sum of both.

Total Power = W1 + W2

The pros and cons

TwoWattMeter method allow for less sensors and less computation. Therefore we can achieve greater sampling rate in two watt meter.

  • The three watt meter sampling rate is 1.7kHz.
  • The Two watt meter sampling rate is 2.4kHz.

There is no requirement for a neutral line with the two watt meter method.

However the two watt meter method theory implies a balanced load. Which does not make it suitable for installation where a number of single phase devices are connected to a three phase supply.

Library and firmware

To support TwoWattMeter the library must be RPICTlib_v1.5.3 or later.

A special firmware has been build for this purpose. You can install it with the commands below.

wget lechacal.com/RPICT/sketch/RPICT_MCP3208_2wattmeter_v4.1.3.ino.hex
lcl-upload-sketch.sh RPICT_MCP3208_2wattmeter_v4.1.3.ino.hex

Source code is available at http://lechacal.com/RPICT/sketch/RPICT_MCP3208_2wattmeter_v4.1.3.ino

Configuration

Once the above firmware loaded the configuration is the same as with the ThreeWattMeter. Just add as many 3phase node as required.

This is the online version of the general configurator.
http://lechacal.com/RPICT/config/generator/v1.0.4/index.html

You will find more information on the configurator in the guide below.
Upgrading to sketch version 4

Special condition
When the pairing are entered the user must add a third entry. The content of this entry does not matter as it will be ignored by the firmware. However it must be here as a placeholder so the configurator can work.

Screenshot 2022-06-15 22-09-56.png


Note that it is not possible to mix ThreeWattMeter and TwoWattMeter node at present time. The choice of the firmware dictates only one of the two methods.