Power Meter Modbus Modbus Register 107: Reactive power

Technical Definition

The register Reactive power at address 107 is used to monitor reactive power on the Power Meter Modbus.

• Protocol: Modbus RTU
• Data Type: S WORD
• Unit: VAR
• Access: Read Only

How to Read (Python pymodbus)

Use this code snippet to read this specific value via RS485:

from pymodbus.client.sync import ModbusSerialClient

client = ModbusSerialClient(method='rtu', port='/dev/ttyUSB0', baudrate=9600)
client.connect()

# Read Reactive power (Address: 107)
# Note: Check if your device uses 0-based or 1-based addressing
result = client.read_input_registers(address=107, count=2, unit=1)

if not result.isError():
    print(f"Raw Value: {result.registers}")
else:
    print("Error reading register")

client.close()

Integration (Home Assistant)

Paste this into your configuration.yaml:

- platform: modbus_controller
  name: "Reactive power"
  address: 107
  value_type: S_WORD
  unit_of_measurement: "VAR"

Connection Diagram

Here is the standard RS485 wiring for this configuration:

graph TD
    PLC[Host Controller / Home Assistant]
    Device[Power Meter Modbus]

    PLC -- "A+ (D+)" --> Device
    PLC -- "B- (D-)" --> Device
    PLC -- GND --> Device

💡 Engineer's Insight

Analysis: Reactive power (VAr). Measures the non-productive power component.

Troubleshooting: Zero means purely resistive load or no load. Verify inductive/capacitive elements and meter readings.