Webasto HVH50

Webasto HVH50 water heater

The Webasto HVH series are electrical water heaters typically used in popular PHEV.

Connectors

Webasto HVH50 connectors

The HV connector is a Tyco HVA280 connector with A-key (might be different on other devices).

The small center pins are for interlock (detect that the connector is seated). The right pin (with tab facing upwards) is HV+, the left one HV-

The LV connector is best found by the VW part number 1J0973714

• Pin 1 is permanent 12V
• Pin 2 is an analog output
• Pin 3 is an analog or PWM input
• Pin 5 and 7 are interlock - not sure what to do with it, can be left floating.
• Pin 6 is LIN
• Pin 4 and 8 are unused

Ground must be connected to the case via a stud.

Communication & Control

While there is a document describing the LIN interface , Webasto seems to have altered the interface for different OEMs. According to the document, LIN bus speed is 19200 but on a unit obtained from ebay it was 9600. So always try both.

The data format found on one device is as follows. The scaling is identical to the document. The document is not clear on bit positions, so they may or may not be compatible

HVH LIN Protocol

Command	Possible IDs	Byte 1	2	3	4	5	6	7	8
Write power	35 or 21	Power limit 1 digit=40W	Temp setpoint 1 digit=1 degree Offset -40	0	8=on	-	-	-	-
Read Status	40 or 23	various	status	info
Read Meas	24 or 22	Status 4=running	Outlet temp Scaling as above	Inlet temp	-	Voltage LSB	Voltage MSB - 2 bits Power LSB - 6 bits	Power MSB 1 digit=20W	Unknown

Some units allow control via a simple on off signal on Pin 3 (12V=heat up liquid to 85°C) and some units allow a strange PWM control between 50-100Hz where 25%-81% duty cycles allow setting various power levels. On my ebay unit this did not work. Only 12V and LIN needed to be connected, all else unconnected.