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taede avatar image
taede asked

Cerbo CAN bus ve.can / bms.can not isolated

On my electric propulsion sailboat I use a Victron system (multiplus/cerbo/ touch panel) and a REC BMS with a 48V baterry.

The Cerbo is connected to the Multiplus, Touch 50, multi control panel, REC BMS and the NMEA2000 network for displaying data on the Raymarine MFD. The Cerbo power supply is connected to the 48V system

The REC-BMS uses the BMS-CAN and the VE-CAN to NMEA2000 cable uses the VE-CAN port.

All buses on the Cerbo are isolated except for the CAN buses, the GND for the VE-CAN and BMS-CAN are connected.

The problem is that the CAN buses connects the 48V power supply GND to the GND of the BMS CAN and the GND of the VE CAN port, which in turns grounds the whole 12V system via the VE-CAN to Nmea2000 cable/network to the 48V GND.

This creates an unwanted extra ground loop when the 12V and 48V batteries are already grounded to a star GND point onboard via the battery terminals

Secondly there is no option to have the 48V system floating/fully isolated as it is grounded to the 12V system to the Cerbo CAN buses.

Are there options to resolve the unwanted ground loop, or use the 48V fully isolated?

Would you normally want to ground each system? Currently I have the GND connection from the isolation transformer, the 12V minus and 48V minus all connected via separate cables to the GND point onboard (prop shaft post)




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1 Answer
Mike Dorsett avatar image
Mike Dorsett answered ·

As a matter of practice, I would keep all systems grounded to a common point. If you have a problem with the CAN data providing a ground loop, this can be overcome either with a special CAN bus isolator, or by inserting a small resistor in the can bus ground. The CAN physical layer signal is a differential voltage shift, and should be relatively immune to minor ground potential differences. Larger voltage differences (e.g. inductive spike noise) may block a CAN transmission temporarily.

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taede avatar image taede commented ·

Thanks for your answer! As suggested I will ground all the systems and I like the idea to add a small resistor in the CAN ground wire as this will also protect the CAN ports and internal connections in the Cerbo between the CAN ground and supply in case there is a fault condition Thanks for the explanation

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