Connecting and configuring a WattNode power meter

Wiring the communications

The WattNode power meter connects to the ezeio via Modbus. Since the WattNode is self-powered, it only needs three wires from the Modbus connection: A, B, and Common.

The A and B wires are the data wires. Note that a Common wire is also required.

Several (up to 20) WattNode meters can be connected together to the same ezeio simply by connecting them in all in parallel.

Addressing the WattNode

The WattNode has a DIP switch bank on the front with eight switches.

Switch 1-7 defines the address of the WattNode, while switch 8 sets the speed. The ezeio defaults to 19200 bps on the Modbus, so switch 8 should be in the ON (up) position.

Switch 1-7 is a binary representation of the Modbus address. Here are some examples:

Address  1 :  ON-OFF-OFF-OFF-OFF-OFF-OFF
Address  2 : OFF- ON-OFF-OFF-OFF-OFF-OFF
Address  3 :  ON- ON-OFF-OFF-OFF-OFF-OFF
Address  4 : OFF-OFF- ON-OFF-OFF-OFF-OFF
Address  5 :  ON-OFF- ON-OFF-OFF-OFF-OFF
Address 10 : OFF- ON-OFF- ON-OFF-OFF-OFF
Address 21 :  ON-OFF- ON-OFF- ON-OFF-OFF

Any address from 1 to 127 can be set with these seven switches. If you have multiple WattNodes connected together, you must make sure they are set for different addresses.

Adding the WattNode to the ezeio configuration

Navigate to Configure->Devices and click Add Device.

Select the WattNode device type, and enter the address you set on the DIP switches. Click Save Changes.

Configuring the WattNode

Now navigate to the Devices screen again and select your new WattNode. At the bottom of the screen is a Modbus Direct Control box. This allows you to directly read/write commands to the WattNode.

Usually the only configuration required is to set the CT size. This is done by writing the CT size in Amperes to register 1603.

Make sure the WattNode is correctly connected and powered. Then enter 1603 in the Read field and press GO. You should see a number other than zero come up. It may take a few attempts, so if you get zero (0), try pressing GO again.

If the number returned match your CT rating, all is well and you can skip the next step.

If you need to change the setting, write 1603 in the Write field, and the new value in the Value field and press GO. Then press GO on the Read-line again to verify that the WattNode is reconfigured.

There are several other configuration fields in the WattNode, but the CT size is typically all you need to change in a normal installation.

Power Int Scale

While on the Device screen, enter register number 1609 in the Read box and click GO. This should return one of 1, 10, 100 or 1000. Please write this value down as we will need it later.

Configuring the inputs

With the WattNode connected and added per above, we are ready to start receiving data from it.

Navigate to Configure->Inputs and click Add Input (or select an existing input to repurpose).

Under Hardware/Device setting, select the relevant data point from the WattNode. There is a lot to choose from here, but the most common are the Total Energy and Total Power registers.

Select the Total Energy register. Then select input type as Energy Modbus. This will populate the scale and unit fields as well as apply the correct scaling to the input.

Add a second input, and select Total Power under Hardware/Device setting. For the most common CT sizes, the Input type Modbus Power will work, but this is where we need the Power Int Scale from earlier. If that value was not 10, we need to change the scaling of the power input.

Select input type Custom. This will display the math used to scale the input value, and should show x/100 and x*100 if the previous setting was Modbus Power.

If the Power Int Scale was 1, enter x/1000 and x*1000 respectively in the math boxes.
If the Power Int Scale was 100, enter x/10 and x*10.
If the Power Int Scale was 1000, enter x and x.

The math for other registers on the WattNode are:

Voltages: x/10, x*10
Currents: x*CTsize/20000, x*20000/CTsize
Power factor: x/100

Refer to the WattNode manual for more details.