The soc register reads zero even though the battery is charged. Why?

Address 39424 uses function code 3 and returns an int16. If the gateway is sending function code 4 or reading as uint16 with the wrong byte order, the result will be wrong. Confirm the template is using FC3 and that your gateway applies big-endian byte order, which is standard for FoxESS Modbus TCP registers.

The gateway connects to port 502 but power and energy registers return errors.

The MQ2200 obtains its IP via DHCP, so the address can change between reboots. Assign a DHCP reservation for the device's MAC address in your router, then update the host entry in the ModbusCloud portal. Also confirm slave unit ID is set to 1.

Sending a write to batterymode_f has no effect on actual battery power.

The remote control active power command only takes effect when the mode bitfield in batterymode_a is set to enable remote control and the timeout in batterymode_e is non-zero. Write batterymode_a first to activate the control session, then write the power value to batterymode_f.

Is it safe to write large power values to the batterymode_f setpoint register?

Use caution with write registers. The MQ2200's internal BMS and inverter firmware will clip commands that exceed hardware limits, but sending values outside the device's rated power range repeatedly may trigger fault conditions or cause the device to exit remote control mode. Test with conservative values and monitor the power register response before automating large setpoints.

Free Modbus template: FoxESS MQ2200 (battery)

Name: FoxESS MQ2200 (battery)
Brand: FoxESS
SKU: 4a35f83f-8c0d-4fbc-aedf-6cc4ff0a18c1

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Free Modbus template: FoxESS MQ2200 (battery) | ModbusCloud

Registers (8)

3 read / 5 write

Name	Address	Function	Type	Unit	Access
power Instantaneous battery power; positive = charging, negative = discharging.	•••	•••	•••	W	R
energy Cumulative battery energy throughput counter.	•••	•••	•••	Wh	R
soc Battery state of charge, integer percentage 0 to 100.	•••	•••	•••	%	R
batterymode_a Remote control mode bitfield: sets power direction and target source.	•••	•••	•••		W
batterymode_b Remote control charge period start time register, slot 1.	•••	•••	•••		W
batterymode_c Remote control charge period end time register, slot 1.	•••	•••	•••		W
batterymode_e Remote control session timeout in seconds.	•••	•••	•••	s	W
batterymode_f Remote control active power command setpoint, in watts.	•••	•••	•••	W	W

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FoxESS MQ2200 (battery)

Overview

Use cases

Installation

Things to watch for

Registers (8)

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