Why do all register reads return zero or timeout?

The GoodWe StsBox requires Modbus TCP to be explicitly enabled via the device interface or the paired inverter's LAN module. Confirm the LAN module is installed, Modbus TCP is active, and that the ARM firmware meets the minimum version requirement. Also verify that port 502 is reachable from the ModbusCloud Gateway.

The serial_number register returns garbled characters. What is wrong?

The serial_number is stored as a multi-register string using big-endian byte order. Ensure your Modbus client is set to big-endian word and byte order. Reading fewer consecutive registers than the full string length will produce truncated or misaligned output.

Write registers are not accepted and the device returns an exception code.

GoodWe devices may reject FC16 writes if the unit ID is incorrect or if the LAN module firmware does not support write operations. Confirm the unit ID matches (default 247), check firmware version, and ensure no other Modbus master is holding a concurrent session, as GoodWe TCP allows only one active connection at a time.

Is it safe to write genset voltage limits or start mode remotely?

Use caution with all write registers on the GoodWe StsBox. Writing incorrect genset_upper_voltage_limit, genset_lower_voltage_limit, genset_upper_frequency_limit, or genset_start_mode_selection values can cause the StsBox to reject valid generator output, prevent automatic backup switching, or trigger protective shutdowns. Always verify values against the site's generator specifications before writing, and test changes during a scheduled maintenance window.

Free Modbus template: GoodWe StsBox

Name: GoodWe StsBox
Brand: GoodWe
SKU: 2636c3e1-1460-4d32-bf28-e751bb3ec9b7

The GoodWe StsBox is a Static Transfer Switch designed for commercial and industrial energy storage systems, managing automatic switching between grid, battery inverter, and generator sources. This Modbus TCP template reads device identity (serial number, firmware version and sub-version), generator voltage and frequency acceptance limits, contactor voltage thresholds, delay-before-load, start mode, charge limit, and rated power. Matching write registers allow remote reconfiguration of all genset parameters from your ModbusCloud portal. The template gives installers a single monitoring and configuration point for GoodWe StsBox generator integration without on-site access.

Registers (29)

16 read / 13 write

Name	Address	Function	Type	Unit	Access
serial_number Device serial number, string identifier for this StsBox unit.	33288	FC03	string		R
version Main firmware version number of the StsBox.	35039	FC03	uint16		R
sub_version Sub-version or minor firmware revision of the StsBox.	35040	FC03	uint16		R
port_mutliplexing_mode_a Port multiplexing mode selection, read: current active mode.	45300	FC03	uint16		R
genset_upper_voltage_limit_a Generator upper AC voltage acceptance threshold, read value.	45593	FC03	uint16	V	R
genset_lower_voltage_limit_a Generator lower AC voltage acceptance threshold, read value.	45594	FC03	uint16	V	R
genset_upper_frequency_limit_a Generator upper frequency acceptance threshold, read value.	45595	FC03	uint16	Hz	R
genset_lower_frequency_limit_a Generator lower frequency acceptance threshold, read value.	45596	FC03	uint16	Hz	R
delay_before_load_a Delay time before transferring load to generator, read value.	45597	FC03	uint16	s	R
genset_start_mode_selection_a Generator start mode: manual, automatic, or scheduled, read.	47745	FC03	uint16		R
one_click_enable_a One-click generator enable flag, current state read.	47746	FC03	uint16		R
genset_charge_limit_a Maximum charge power allowed from generator, read value.	47747	FC03	uint16	W	R
open_voltage_a Generator contactor open-circuit voltage threshold, volts, read.	47756	FC03	uint16	V	R
closed_voltage_a Generator contactor closed-circuit voltage threshold, volts, read.	47757	FC03	uint16	V	R
genset_run_time_a Configured or accumulated generator run time, read value.	47758	FC03	uint16	s	R
genset_rated_power_a Rated power of the connected generator, watts, read value.	47759	FC03	uint16	W	R
port_mutliplexing_mode_b Port multiplexing mode setpoint: write to change active mode.	45300	FC16	uint16		W
genset_upper_voltage_limit_b Generator upper AC voltage acceptance threshold setpoint, write.	45593	FC16	uint16	V	W
genset_lower_voltage_limit_b Generator lower AC voltage acceptance threshold setpoint, write.	45594	FC16	uint16	V	W
genset_upper_frequency_limit_b Generator upper frequency acceptance threshold setpoint, write.	45595	FC16	uint16	Hz	W
genset_lower_frequency_limit_b Generator lower frequency acceptance threshold setpoint, write.	45596	FC16	uint16	Hz	W
delay_before_load_b Delay before load transfer to generator setpoint, write.	45597	FC16	uint16	s	W
genset_start_mode_selection_b Generator start mode setpoint: write to select manual or auto.	47745	FC16	uint16		W
one_click_enable_b One-click generator enable setpoint: write 1 to activate.	47746	FC16	uint16		W
genset_charge_limit_b Maximum generator charge power setpoint, write value.	47747	FC16	uint16	W	W
open_voltage_b Generator contactor open-circuit voltage threshold setpoint, volts.	47756	FC16	uint16	V	W
closed_voltage_b Generator contactor closed-circuit voltage threshold setpoint, volts.	47757	FC16	uint16	V	W
genset_run_time_b Generator run time setpoint or reset register, write value.	47758	FC16	uint16	s	W
genset_rated_power_b Rated power of the connected generator setpoint, watts, write.	47759	FC16	uint16	W	W