All register values show zero or are unavailable. What is wrong?

The FEMS Modbus TCP read interface must be active. In the FEMS online monitoring go to Settings, open the system profile, and confirm the ctrlApiModbusTcp component is listed. If it is absent, the app has not been activated on the FEMS unit and no data will be returned.

Register addresses appear shifted by one compared to the FEMS documentation.

The FEMS Modbus TCP API uses zero-based register addressing. Some Modbus client tools default to a base address of 1. Set the base address to 0 in your client configuration. The ModbusCloud Gateway handles this correctly by default, so no adjustment is needed in the portal.

The Gateway connects but per-phase power readings look incorrect or implausible.

The active_power and reactive_power registers on this meter use uint16 data types. Values represent unsigned integers; if the FEMS firmware reports signed power flow through these registers in a specific version, the readings may wrap. Cross-check against the live FEMS monitoring dashboard and verify your FEMS firmware is up to date.

No TCP connection can be established to the FEMS unit at all.

Confirm the ModbusCloud Gateway and the FEMS unit are on the same physical network and that no firewall or VLAN separation blocks TCP port 502. The FEMS Modbus TCP interface only accepts connections from devices with direct network access to the FEMS IP address.

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Registers (14)

14 read / 0 write

Name	Address	Function	Type	Unit	Access
original_active_consumption_energy Cumulative active energy drawn from the grid, watt-hours.	11109	FC03	uint32	Wh	R
original_active_production_energy Cumulative active energy fed into the grid, watt-hours.	11111	FC03	uint32	Wh	R
current_l1 Instantaneous AC current on phase L1, amperes.	11136	FC03	uint16	A	R
voltage_l1 AC line voltage on phase L1, volts.	11137	FC03	uint16	V	R
active_power_l1 Instantaneous active power on phase L1, watts.	11138	FC03	uint16	W	R
reactive_power_l1 Instantaneous reactive power on phase L1, volt-amperes reactive.	11139	FC03	uint16	W	R
current_l2 Instantaneous AC current on phase L2, amperes.	11166	FC03	uint16	A	R
voltage_l2 AC line voltage on phase L2, volts.	11167	FC03	uint16	V	R
active_power_l2 Instantaneous active power on phase L2, watts.	11168	FC03	uint16	W	R
reactive_power_l2 Instantaneous reactive power on phase L2, volt-amperes reactive.	11169	FC03	uint16	W	R
current_l3 Instantaneous AC current on phase L3, amperes.	11196	FC03	uint16	A	R
voltage_l3 AC line voltage on phase L3, volts.	11197	FC03	uint16	V	R
active_power_l3 Instantaneous active power on phase L3, watts.	11198	FC03	uint16	W	R
reactive_power_l3 Instantaneous reactive power on phase L3, volt-amperes reactive.	11199	FC03	uint16	W	R