Modbus connection is refused or times out. What should I check?

The Webasto Next accepts only one simultaneous Modbus TCP connection. If another client such as a home-automation system is already polling the wallbox, the Gateway will receive a connection-refused or i/o-timeout error. Disconnect all other Modbus clients and retry with only the ModbusCloud Gateway connected.

All registers return exception code 2 (illegal data address). Why?

HEMS mode must be explicitly activated in the Webasto Next web interface before any Modbus registers become readable. If HEMS is enabled but the error persists, confirm the unit ID is 255. Some firmware versions also require a reboot of the wallbox after enabling HEMS.

The wallbox falls back to a fixed current and ignores my EMS setpoint. What is happening?

The Webasto Next uses a life-bit heartbeat mechanism. The EMS must regularly write a toggled value to the life_bit_b register at address 6000. If writes stop, the wallbox applies the safe_current fallback value after the com_timeout period expires. Ensure the ModbusCloud Gateway polling interval stays within the configured timeout.

Is it safe to write charge_current and start_cancel_charging_session in production?

Use write registers with care. Writing a charge_current value above max_cable_current or max_ev_current will be clamped by the wallbox, but sending an out-of-range power limit via ev_set_charge_power_limit or issuing start_cancel_charging_session at the wrong moment can interrupt an active session unexpectedly. Test setpoint writes during a controlled session before deploying to live sites.

Free Modbus template: Webasto Next

Name: Webasto Next
Brand: Webasto
SKU: e15d81b1-fd60-4776-aec7-6b1c33c467fa

The Webasto Next is an AC EV wallbox available in 11 kW and 22 kW variants, designed for residential and light-commercial charging with built-in dynamic load management. This ModbusCloud template connects to the Webasto Next over Modbus TCP on port 502 and reads charge-point state, EVSE and cable status, per-phase current and power, cumulative energy, and per-session timestamps. Write registers let an energy management system control the charge current, set a power limit, and start or stop sessions. The life-bit heartbeat pair keeps EMS control active and prevents automatic fallback to the configured safe current.

Registers (29)

25 read / 4 write

Name	Address	Function	Type	Unit	Access
charge_point_state Overall charge point operational state as an enumerated code.	1000	FC03	uint16		R
evse_state EVSE internal state, indicates readiness and charging progress.	1002	FC03	uint16		R
cable_state Cable lock and connection state as an enumerated code.	1004	FC03	uint16		R
evse_error_code Active EVSE fault code, zero when no error is present.	1006	FC03	uint16		R
current_l1 AC charging current on phase L1, amperes.	1008	FC03	uint16	A	R
current_l2 AC charging current on phase L2, amperes.	1010	FC03	uint16	A	R
current_l3 AC charging current on phase L3, amperes.	1012	FC03	uint16	A	R
active_power Total active charging power across all phases, watts.	1020	FC03	uint32	W	R
active_power_l1 Active charging power on phase L1, watts.	1024	FC03	uint32	W	R
active_power_l2 Active charging power on phase L2, watts.	1028	FC03	uint32	W	R
active_power_l3 Active charging power on phase L3, watts.	1032	FC03	uint32	W	R
active_production_energy Cumulative energy delivered to the vehicle since installation, watt-hours.	1036	FC03	uint32	Wh	R
max_hw_current Maximum current allowed by the wallbox hardware, amperes.	1100	FC03	uint16	A	R
min_hw_current Minimum current allowed by the wallbox hardware, amperes.	1102	FC03	uint16	A	R
max_evse_current Maximum current the EVSE is configured to supply, amperes.	1104	FC03	uint16	A	R
max_cable_current Maximum current rating of the connected cable, amperes.	1106	FC03	uint16	A	R
max_ev_current Maximum current requested by the connected EV, amperes.	1108	FC03	uint16	A	R
last_energy_session Energy delivered in the most recently completed charging session.	1502	FC03	uint16	Wh	R
start_time Timestamp of the current or last session start, Unix epoch.	1504	FC03	uint32		R
charge_session_time Elapsed duration of the current charging session.	1508	FC03	uint32	s	R
end_time Timestamp of the last session end, Unix epoch.	1512	FC03	uint32		R
smart_vehicle_detected Flag indicating whether a smart-charging capable EV is connected.	1620	FC03	uint16		R
safe_current Fallback current applied when Modbus communication is lost, amperes.	2000	FC03	uint16	A	R
com_timeout Communication watchdog timeout period before safe current is applied.	2002	FC03	uint16	s	R
ev_set_charge_power_limit Charge power limit setpoint written by the energy management system.	5000	FC16	uint32	W	W
charge_current Charging current setpoint commanded by the energy management system, amperes.	5004	FC16	uint16	A	W
start_cancel_charging_session Command register to start or cancel a charging session.	5006	FC16	uint16		W
life_bit_a Heartbeat read register; wallbox increments this to signal it is alive.	6000	FC03	uint16		R
life_bit_b Heartbeat write register; client must echo the value to keep EMS control active.	6000	FC16	uint16		W