All registers return zero or no data after connecting. Why?

The FEMS Modbus TCP App must be explicitly installed and activated in the FEMS App Center. If the app is not running, the TCP port is closed and all reads return nothing. Confirm the app status in the FEMS UI under App Center, then retry the connection.

Register values look correct but the base address seems shifted by one.

FEMS Modbus TCP uses zero-based register addressing. Some Modbus tools default to a base address of 1, which shifts every address by one. In your client or in the ModbusCloud portal configuration, set the base address offset to 0 to align with the register map.

PV power limit written to set_pv_power_limit stops being applied after about a minute.

The FEMS write-access app includes a built-in watchdog with a default timeout of 60 seconds. If no new write is received within that window, the setpoint is cleared and the system reverts to autonomous control. Send a refreshed value at least every 30 seconds to maintain the limit continuously.

Should I write to set_pv_power_limit during normal operation without a specific reason?

Exercise caution. Writing an incorrect or zero value to set_pv_power_limit will curtail PV generation immediately across the system. Only write this register when deliberate curtailment is required, and always validate the intended value before sending. Incorrect setpoints can reduce yield and may interact with FEMS protection thresholds.

Free Modbus template: Fenecon COMMERCIAL40 CHARGER

Name: Fenecon COMMERCIAL40 CHARGER
Brand: Fenecon
SKU: d68e4ba5-412e-4235-91c5-cb37cb8899b5

The Fenecon COMMERCIAL 40 CHARGER is the dual-string DC-DC charger subsystem inside the Fenecon COMMERCIAL 40 commercial battery storage system, managed by the FEMS energy management platform over Modbus TCP. This template reads per-string voltage, current, power, IGBT and reactor temperatures, and cumulative charge and discharge energy for both the BMS-side DC-DC converters and the PV-side DC-DC converters across strings A and B. The single write register allows you to cap PV input power. Together, these registers give installers and asset managers full visibility into DC power conversion health and energy throughput for each string independently.

Registers (57)

56 read / 1 write

Name	Address	Function	Type	Unit	Access
set_pv_power_limit PV power curtailment setpoint; write to cap total PV input power.	•••	•••	•••	W	W
bms_dcdc_output_voltage_a BMS DC-DC converter string A output voltage, volts.	•••	•••	•••	V	R
bms_dcdc_output_current_a BMS DC-DC converter string A output current, amperes.	•••	•••	•••	A	R
bms_dcdc_output_power_a BMS DC-DC converter string A output power, watts.	•••	•••	•••	W	R
bms_dcdc_input_voltage_a BMS DC-DC converter string A input voltage, volts.	•••	•••	•••	V	R
bms_dcdc_input_current_a BMS DC-DC converter string A input current, amperes.	•••	•••	•••	A	R
bms_dcdc_input_power_a BMS DC-DC converter string A input power, watts.	•••	•••	•••	W	R
bms_dcdc_input_energy_a BMS DC-DC converter string A instantaneous input energy, watt-hours.	•••	•••	•••	Wh	R
bms_dcdc_output_energy_a BMS DC-DC converter string A instantaneous output energy, watt-hours.	•••	•••	•••	Wh	R
bms_dcdc_reactor_temperature_a BMS DC-DC converter string A reactor (inductor) temperature, degrees Celsius.	•••	•••	•••	°C	R
bms_dcdc_igbt_temperature_a BMS DC-DC converter string A IGBT module temperature, degrees Celsius.	•••	•••	•••	°C	R
bms_dcdc_input_charge_energy_a Cumulative charge energy into BMS DC-DC string A input, watt-hours.	•••	•••	•••	Wh	R
bms_dcdc_input_discharge_energy_a Cumulative discharge energy from BMS DC-DC string A input, watt-hours.	•••	•••	•••	Wh	R
bms_dcdc_output_charge_energy_a Cumulative charge energy at BMS DC-DC string A output, watt-hours.	•••	•••	•••	Wh	R
bms_dcdc_output_discharge_energy_a Cumulative discharge energy at BMS DC-DC string A output, watt-hours.	•••	•••	•••	Wh	R
pv_dcdc_output_voltage_a PV DC-DC converter string A output voltage, volts.	•••	•••	•••	V	R
pv_dcdc_output_current_a PV DC-DC converter string A output current, amperes.	•••	•••	•••	A	R
pv_dcdc_output_power_a PV DC-DC converter string A output power, watts.	•••	•••	•••	W	R
pv_dcdc_input_voltage_a PV DC-DC converter string A input voltage from the PV array, volts.	•••	•••	•••	V	R
pv_dcdc_input_current_a PV DC-DC converter string A input current from the PV array, amperes.	•••	•••	•••	A	R
actual_power_a Actual net power on PV DC-DC string A, watts.	•••	•••	•••	W	R
pv_dcdc_input_energy_a PV DC-DC converter string A instantaneous input energy, watt-hours.	•••	•••	•••	Wh	R
pv_dcdc_output_energy_a PV DC-DC converter string A instantaneous output energy, watt-hours.	•••	•••	•••	Wh	R
pv_dcdc_reactor_temperature_a PV DC-DC converter string A reactor (inductor) temperature, degrees Celsius.	•••	•••	•••	°C	R
pv_dcdc_igbt_temperature_a PV DC-DC converter string A IGBT module temperature, degrees Celsius.	•••	•••	•••	°C	R
pv_dcdc_input_charge_energy_a Cumulative charge energy into PV DC-DC string A input, watt-hours.	•••	•••	•••	Wh	R
pv_dcdc_input_discharge_energy_a Cumulative discharge energy from PV DC-DC string A input, watt-hours.	•••	•••	•••	Wh	R
pv_dcdc_output_charge_energy_a Cumulative charge energy at PV DC-DC string A output, watt-hours.	•••	•••	•••	Wh	R
pv_dcdc_output_discharge_energy_a Cumulative discharge energy at PV DC-DC string A output, watt-hours.	•••	•••	•••	Wh	R
pv_dcdc_output_voltage_b PV DC-DC converter string B output voltage, volts.	•••	•••	•••	V	R
pv_dcdc_output_current_b PV DC-DC converter string B output current, amperes.	•••	•••	•••	A	R
pv_dcdc_output_power_b PV DC-DC converter string B output power, watts.	•••	•••	•••	W	R
pv_dcdc_input_voltage_b PV DC-DC converter string B input voltage from the PV array, volts.	•••	•••	•••	V	R
pv_dcdc_input_current_b PV DC-DC converter string B input current from the PV array, amperes.	•••	•••	•••	A	R
actual_power_b Actual net power on PV DC-DC string B, watts.	•••	•••	•••	W	R
pv_dcdc_input_energy_b PV DC-DC converter string B instantaneous input energy, watt-hours.	•••	•••	•••	Wh	R
pv_dcdc_output_energy_b PV DC-DC converter string B instantaneous output energy, watt-hours.	•••	•••	•••	Wh	R
pv_dcdc_reactor_temperature_b PV DC-DC converter string B reactor (inductor) temperature, degrees Celsius.	•••	•••	•••	°C	R
pv_dcdc_igbt_temperature_b PV DC-DC converter string B IGBT module temperature, degrees Celsius.	•••	•••	•••	°C	R
pv_dcdc_input_charge_energy_b Cumulative charge energy into PV DC-DC string B input, watt-hours.	•••	•••	•••	Wh	R
pv_dcdc_input_discharge_energy_b Cumulative discharge energy from PV DC-DC string B input, watt-hours.	•••	•••	•••	Wh	R
pv_dcdc_output_charge_energy_b Cumulative charge energy at PV DC-DC string B output, watt-hours.	•••	•••	•••	Wh	R
pv_dcdc_output_discharge_energy_b Cumulative discharge energy at PV DC-DC string B output, watt-hours.	•••	•••	•••	Wh	R
bms_dcdc_output_voltage_b BMS DC-DC converter string B output voltage, volts.	•••	•••	•••	V	R
bms_dcdc_output_current_b BMS DC-DC converter string B output current, amperes.	•••	•••	•••	A	R
bms_dcdc_output_power_b BMS DC-DC converter string B output power, watts.	•••	•••	•••	W	R
bms_dcdc_input_voltage_b BMS DC-DC converter string B input voltage, volts.	•••	•••	•••	V	R
bms_dcdc_input_current_b BMS DC-DC converter string B input current, amperes.	•••	•••	•••	A	R
bms_dcdc_input_power_b BMS DC-DC converter string B input power, watts.	•••	•••	•••	W	R
bms_dcdc_input_energy_b BMS DC-DC converter string B instantaneous input energy, watt-hours.	•••	•••	•••	Wh	R
bms_dcdc_output_energy_b BMS DC-DC converter string B instantaneous output energy, watt-hours.	•••	•••	•••	Wh	R
bms_dcdc_reactor_temperature_b BMS DC-DC converter string B reactor (inductor) temperature, degrees Celsius.	•••	•••	•••	°C	R
bms_dcdc_igbt_temperature_b BMS DC-DC converter string B IGBT module temperature, degrees Celsius.	•••	•••	•••	°C	R
bms_dcdc_input_charge_energy_b Cumulative charge energy into BMS DC-DC string B input, watt-hours.	•••	•••	•••	Wh	R
bms_dcdc_input_discharge_energy_b Cumulative discharge energy from BMS DC-DC string B input, watt-hours.	•••	•••	•••	Wh	R
bms_dcdc_output_charge_energy_b Cumulative charge energy at BMS DC-DC string B output, watt-hours.	•••	•••	•••	Wh	R
bms_dcdc_output_discharge_energy_b Cumulative discharge energy at BMS DC-DC string B output, watt-hours.	•••	•••	•••	Wh	R

Loading registers…

Fenecon COMMERCIAL40 CHARGER

Overview

Use cases

Installation

Things to watch for

Registers (57)

Working with Modbus in your projects?

Question about your setup?

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