The gateway connects to port 502 but all registers return errors.

Modbus TCP on the EMMA must be explicitly enabled by an installer account in the FusionSolar app under Communication Settings. The feature is disabled by default and the port remains closed until activated. Verify the EMMA firmware is a recent SmartHEMS release, as early firmware versions had Modbus TCP unavailable even after enabling.

The SOC register reads a value 100 times larger than expected.

The EMMA applies a gain of 100 to the SOC register. The raw uint16 value must be divided by 100 to obtain the percentage. Check your ModbusCloud template scaling configuration and confirm the gain factor is set to 100 for register 30368.

Power register 30360 shows unexpected large positive or negative spikes.

Register 30360 is a signed int32 representing battery charge/discharge power. The EMMA applies a gain of 1000 to this register, so the raw value is in watts multiplied by 1000. Confirm big-endian byte order is configured in your Modbus client, as the EMMA uses big-endian representation for all multi-byte values per the official SmartHEMS specification.

Modbus TCP was working, but readings stopped after an EMMA firmware update.

Huawei SmartHEMS firmware updates can reset communication parameters, including the Modbus TCP enable flag and unit ID assignment. After any firmware update, log in to the FusionSolar app with installer credentials, re-verify the Modbus TCP setting under Communication Settings, and re-confirm the unit ID matches what is configured in the ModbusCloud portal.

Free Modbus template: Huawei EMMA (battery)

The Huawei EMMA (Energy Management Assistant) is a DIN-rail energy management controller for residential and small-commercial PV installations. It integrates metering, communication, and load coordination for Huawei SUN2000 inverters and LUNA2000 battery storage. This Modbus TCP template reads the battery charge/discharge power, cumulative energy, and state of charge directly from the EMMA over its LAN interface. With these three registers available in ModbusCloud, installers can track battery behaviour, build SOC alerts, and verify ESS performance without accessing the FusionSolar cloud.

Name	Address	Function	Type	Unit	Access
power Battery charge/discharge power; positive = charging, negative = discharging.	30360	FC03	int32	W	R
energy Cumulative energy value reported by the EMMA for the battery.	30312	FC03	uint32	Wh	R
soc Battery state of charge as a percentage, 0 to 100.	30368	FC03	uint16	%	R