M-TEC Energy Butler GEN3 (pv)

Installation

1. 1Enable Modbus on the Energy Butler GEN3 by confirming the built-in Wi-Fi/LAN module (labelled 'espressif' on your router) is active and reachable on your local network.
2. 2Connect the ModbusCloud Gateway to the same LAN as the Energy Butler GEN3, ensuring both devices share network reachability; no RS485 wiring is required for the TCP path.
3. 3In the ModbusCloud portal, add a new device, import the M-TEC Energy Butler GEN3 (pv) template, and set the unit ID to 247 (or 252 if using the built-in espressif module); use port 502 on firmware V27.52.4.0 or later, or port 5743 on older firmware.
4. 4Spot-check register 11028 in the live register view and confirm the returned value matches the watt reading shown on the inverter display or the M-TEC app during daylight.

Things to watch for

01

The gateway connects but register 11028 always reads zero or no value.

During night-time or heavy overcast, the PV power register legitimately returns zero. If the value is zero in full daylight, check that the correct slave ID is configured: older firmware typically uses ID 247 while the built-in espressif module uses ID 252. Verify with a Modbus scanner tool before adjusting the portal setting.

02

Connection times out even though the Energy Butler is on the network.

M-TEC changed the Modbus TCP port with firmware V27.52.4.0: units running that version or later listen on port 502, while older units use port 5743. Check your firmware version in the inverter menu or the M-TEC app, then update the port number in the ModbusCloud Gateway configuration to match.

03

Values look implausibly large or completely wrong despite connecting successfully.

Register 11028 is a uint32 spanning two consecutive 16-bit Modbus registers. If your framing is set to plain Modbus TCP instead of RTU-over-TCP, the byte and word order may be swapped. The GEN3 uses RTU framing over the TCP transport; ensure the ModbusCloud Gateway is configured for RTU-over-TCP (framer: rtu) rather than native Modbus TCP.

04

Readings drop to zero randomly for a few seconds during normal operation.

The Energy Butler GEN3 internal Modbus server is known to occasionally refuse or drop a request when the inverter is simultaneously writing to its internal cloud logging service. Increase the Modbus request timeout to at least 5 seconds and configure at least 3 retries in the Gateway settings to reduce missed readings.

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