The gateway connects but all register values are zero or absent.

The Heidelberg Connect enters standby when no vehicle is plugged in, and Modbus communication is suspended in that state. Plug in a vehicle or check whether the standby function is active. Once a vehicle connects, the wallbox wakes and register reads will return valid values.

Charging current setpoint writes to register 261 have no effect.

Register 261 resets to 0 after a power cycle or standby exit on some firmware versions, which the wallbox interprets as a Modbus fault. Write a valid current value (within the min/max current limits) immediately after reconnection. Also confirm the remote lock register 259 is set to 1 (unlocked) and the external lock input is not asserting a hardware lock.

The wallbox blinks an error LED during Modbus polling. What is wrong?

The built-in watchdog is enabled by default. If your controller does not refresh the watchdog within the configured timeout interval in register 257, the wallbox enters timeout mode and signals a fault. Either send regular Modbus traffic within the timeout window or write 0 to register 257 to disable the watchdog during initial setup.

Is it safe to write charging current or phase switch commands remotely?

Yes, but take care: writing a current value outside the hardware-configured min/max range (readable from registers 100 and 101) will be rejected or clamped by the wallbox. Setting the failsafe current register 262 to an inappropriate value means the vehicle may charge at an unintended rate if Modbus communication is interrupted. Always set a safe, non-zero failsafe current before enabling remote current control.

Free Modbus template: Heidelberg Connect

Name: Heidelberg Connect
Brand: Heidelberg
SKU: 183b2def-b171-44c3-ae49-1ccd8d258364

The Heidelberg Connect is an AC wallbox for electric vehicle charging, designed for residential and commercial installations with built-in dynamic load management. This ModbusCloud template connects over Modbus TCP and reads per-phase voltage and current on L1, L2, and L3, active power, PCB temperature, external lock state, and cumulative energy counters. Writable registers let your system command the charging current setpoint, toggle a remote lock, configure the watchdog timeout and failsafe current, and switch between single-phase and three-phase operation. The result is full remote visibility and control of every Heidelberg Connect charger in your portal.

Registers (25)

20 read / 5 write

Name	Address	Function	Type	Unit	Access
layout_version Modbus register layout version; verify before using version-dependent registers.	4	FC04	uint16		R
charging_state Current IEC 61851-1 charging state between vehicle and wallbox.	5	FC04	uint16		R
current_l1 RMS charging current on phase L1, in amperes.	6	FC04	uint16	A	R
current_l2 RMS charging current on phase L2, in amperes.	7	FC04	uint16	A	R
current_l3 RMS charging current on phase L3, in amperes.	8	FC04	uint16	A	R
temperature_pcb Internal PCB temperature of the wallbox electronics.	9	FC04	uint16	°C	R
voltage_l1 RMS line-to-neutral voltage on phase L1, in volts.	10	FC04	uint16	V	R
voltage_l2 RMS line-to-neutral voltage on phase L2, in volts.	11	FC04	uint16	V	R
voltage_l3 RMS line-to-neutral voltage on phase L3, in volts.	12	FC04	uint16	V	R
extern_lock_state Status of the external hardware lock input; overrides remote lock.	13	FC04	uint16		R
active_power Total active power currently drawn by the connected vehicle, in watts.	14	FC04	uint16	W	R
active_production_energy Cumulative energy delivered since wallbox commissioning, in watt-hours.	17	FC04	uint32	Wh	R
heidelberg_energy_session Energy drawn by the vehicle since the last wallbox power-on, in watt-hours.	19	FC04	uint32	Wh	R
raw_maximal_current Hardware-configured maximum allowable charging current, in amperes.	100	FC04	uint16	A	R
raw_minimal_current Hardware-configured minimum allowable charging current, in amperes.	101	FC04	uint16	A	R
watchdog_timeout_a Current watchdog timeout value; triggers failsafe if Modbus traffic stops.	257	FC03	uint16	s	R
watchdog_timeout_b Watchdog timeout setpoint; write to configure or disable the Modbus watchdog.	257	FC16	uint16	s	W
remote_lock_a Current remote lock state; 0 means wallbox is locked via Modbus.	259	FC03	uint16		R
remote_lock_b Remote lock setpoint; write 0 to lock, 1 to unlock charging via Modbus.	259	FC16	uint16		W
set_charging_current_a Currently active charging current limit setpoint, in amperes.	261	FC03	uint16	A	R
set_charging_current_b Charging current limit setpoint; write to command maximum charge current.	261	FC16	uint16	A	W
failsafe_current_a Current failsafe current value applied on watchdog timeout, in amperes.	262	FC03	uint16	A	R
failsafe_current_b Failsafe current setpoint; charging falls back to this if Modbus communication is lost.	262	FC16	uint16	A	W
phase_switch_control_a Current phase switching mode; single-phase or three-phase operation.	501	FC03	uint16		R
phase_switch_control_b Phase switch setpoint; write to command single-phase or three-phase charging.	501	FC16	uint16		W