How to Control a Victron GX with a WatchMon

Victron have advised us that all their GX models are the same for the BMS communication layer.

Here are the steps to configure the Victron Color control GX to the WatchMon Supervisor.

The same methods can be used to any of the other  GX device variants to the WatchMon Supervisor.

CAUTION: The example below has values shown for a demo LiFePO 4 cell pack, please ensure that you adopt values suitable to your application and comply with the battery suppliers recommendation. 

Step 1 - Install communication cable to CAN port on the supervisor.

For newer WatchMon supervisors these are 3 pin (note 120 Ohm resistor) shares CANbus High and CANbus Low

For older WatchMon with 4 pin CAN see below

Step 2 - Install communication cable to Victron GX canbus socket (extract from manual)

Plug the GX side of that cable into one of the VE.Can sockets on the back of the GX. Plug the other end into the battery. Then, plug a VE.Can Terminator in the other VE.Can socket on the GX. 

Custom Cable pinout for GX

Function VE.Can RJ-45 WatchMon
GND Pin 3 CAN isolate ground
CAN-L Pin 8 CAN low
CAN-H Pin 7 CAN high

For reference, here’s an Ethernet plug diagram. Be aware that some Ethernet Cables may vary.

To make up the custom Ethernet Cable for the GX properly, you should use a proper crimper and fresh RJ45 male connectors.  Label both ends of the cable and install it.

Step 3 - Navigate to Hardware, then Integration tab.

Step 4 - Select Canbus protocol to "Victron GX" and Save (previously labelled Victron ColorControl GX).

Step 5 - Navigate to Control Logic, then Charging tab.

Step 6 - Adjust the Charging control logic to suit the application.


  • Low power must be enabled.
  • Cell Hi Cutout should be above the CellMon bypass voltage threshold as a safe guard target.
  • Low power current should suit the bypass capability of CellMon.
  • When the bypass current is above Initial will trigger the system to low power.
  • When the bypass current for all cellmons is above Final the system will complete charging cycle.

Step 7 - Navigate to Hardware, then CellMon tab.

Step 8 - Adjust the CellMon bypass voltage to suit the application.

Note: Make sure to "Device Sync" the changes to the CellMons.

Step 9 - Navigate to Control Logic, then Remote tab.

Step 10 - Adjust the remote charging target to suit the application.


  • Scaling must be 10 for both voltage and current.
  • Low power must be enabled on charging tab.
  • Low power current should suit the bypass capability of CellMon.
  • Charger voltage target needs to be sufficient for all cells to reach bypass threshold.

Step 11 - Adjust the remote discharging targets to suit the application.


  • Scaling must be 10 for both voltage and current.
  • Do not run low power mode on discharging tab.
  • Control logic discharge voltage cutout should match the remote target.

Step 12 - Navigate to Telemetry, then Live Stats to observe system operation.

Step 13 -Within Victron software - VEConfigure settings

13.1 General tab
  1. Check “Enable Battery Monitor”
  2. Enter the battery capacity in Amp Hours ( i.e. 120.0 Ah)
  3. The other parameters ( “State of charge when bulk finished” and “Charge efficiency”) can be left to their default setting. They are not used in this setup.

13.2 Charger tab

Parameter Setting
Battery type Lithium
Charge curve Fixed
Absorption voltage 60.75 V
Float voltage 60.00 V
Absorption time 1 Hr

Note: make sure to double check the float voltage after completing Assistants, and if necessary set it back to 60.00 V.

This needs to be adjusted to match the BMS operating targets.

13.3 ESS (Energy Storage System) Assistant

Select the fourth battery type:


  1. Do not change the dynamic cut-off values, they have already been set correctly after selecting the lithium battery type.
  2. Sustain voltage: 50 V
  3. Same for the restart offset: do not change that.

Step 14. Within Victron software - device configuration

  • Select the  CAN-bus BMS (500 kbits/s) CAN-profile in the Venus device. Menu path:  Settings → Services → CAN-profile. Note that this changes the function of a VE.Can port: it is not possible to connect both VE.Can products and a BMS battery together on a Color Control GX. 
  • Select CAN-bus BMS (500 kbit/s)
  • After properly wiring and setting up, the BMS the ESS will be visible as a battery in the device list:
  • The Parameters option within the battery page shows the actual battery charge and discharge limits:

Additional useful screens to monitor:

  • Node Chart
  • Charging logic control 
  • Remote logic control
  • Live Statistics telemetry
Did this answer your question? Thanks for the feedback There was a problem submitting your feedback. Please try again later.

Still need help? Contact Us Contact Us