Rctpower Inverter Modbus Register 40045: AC Reactive Power

Technical Definition

The register AC Reactive Power at address 40045 is used to monitor ac reactive power on the Rctpower Inverter.

• 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 AC Reactive Power (Address: 40045)
# Note: Check if your device uses 0-based or 1-based addressing
result = client.read_input_registers(address=40045, 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: "AC Reactive Power"
  address: 40045
  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[Rctpower Inverter]

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

💡 Engineer's Insight

Analysis: Reactive power (power for magnetic fields). Units: Volt-Amperes Reactive (VAR) or KiloVolt-Amperes Reactive (kVAR).

Troubleshooting: 0 means no reactive power exchange. Check load type and power factor.