The wallbox stops responding after a few minutes with no vehicle plugged in.

The wallbox enters standby mode by default when no vehicle is connected, which drops the RS-485 bus and causes Modbus timeouts. Write the value 4 to the standby register (address 258) to disable standby. This setting survives power cycles, so you only need to do it once.

Why does the wallbox blink and refuse to charge after a gateway restart?

The watchdog register (address 257) defaults to 15000 ms. If no Modbus frame arrives within that window, the wallbox enters timeout mode and stops charging. Either write 0 to register 257 to disable the watchdog, or ensure your polling interval is shorter than the configured timeout value.

The max_current register reads back zero and no charging starts.

Register 261 does not retain its value after a power cycle or standby exit; the default is 0, which locks out charging. Your control system must write a value in the range 60 to 160 (representing 6.0 A to 16.0 A) to register 261 on every startup before charging can begin.

Is it safe to write large current values to the max_current or failsafe_current register?

Write only values within the range configured by the hardware DIP switches, typically 60 to 160 (6 A to 16 A). Writing 0 to max_current silently disables charging without notifying the user. Setting failsafe_current to 0 places the wallbox into an error state on communication loss; always configure a non-zero safe fallback value.

Free Modbus template: Heidelberg Energy

The Heidelberg Energy Control is an AC wallbox for charging electric and hybrid vehicles at up to 11 kW over a Type 2 cable. It exposes a Modbus RTU interface over RS-485, allowing external load management systems to read the IEC 61851-1 charging state and active power, and to write the maximum current setpoint, failsafe current, watchdog timeout, and standby mode. This ModbusCloud template gives installers live charge-session visibility and dynamic current control from a single portal, without additional proprietary software.

Name	Address	Function	Type	Unit	Access
heidelberg_state IEC 61851-1 charging state: A1=2, B1=4, C1=6, ERR=11.	5	FC04	uint16		R
active_power Total AC power drawn by the connected vehicle, in watts.	14	FC04	uint16	W	R
watchdog_time Modbus watchdog timeout in milliseconds; 0 disables the watchdog.	257	FC16	int16		W
standby Standby mode control; 0 enables standby, 4 disables it.	258	FC16	int16		W
max_current Maximum charging current setpoint; value 100 equals 10 A.	261	FC16	int16	A	W
failsafe_current Charging current applied when Modbus communication is lost.	262	FC16	int16	A	W