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Tibor Johancsik avatar image
Tibor Johancsik asked

To terminate or not to terminate? VE.can 2 N2K interface on Cerbo

Hi,

All Cerbo (and canbus) description tells to terminate the VE.Can bus on Cerbo (should the Cerbo be at one end). However some descriptions regarding N2K tells the opposite.

I have an NMEA2000 interface connected on one side to my boat’s NMEA network, the other side is plugged into the Cerbo GX VE.can port, but the other VE.can port on Cerbo is empty, no termination. I have some inaccurate readings (i.e. tank level not seen for days), and wonders if it can be the reason?

So: Do I need to plug in a termination to the empty Cerbo VE.can port, or not?

Thx,

Tibor

NMEA 2000 - N2K
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6 Answers
christern avatar image
christern answered ·

As I have understood the NMEA 2k network is that everything shall be connected via a drop-cable and the main net cable shall be terminated in both ends.

Not sure if it is the same thing to terminate one port in a device though but why not just follow the standard?

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Trevor Bird avatar image
Trevor Bird answered ·

@Tibor Johancsik ….VE.Can and NMEA2000 have the same physical characteristics. It is essential that the bus has two terminations, one at either end. In the case of a CerboGX connected by VE.Can to a single other VE.Can device the spare RJ45 connector on the CerboGX needs a termination to be installed and so does the other device.

It is not a “nice to have” but rather absolutely essential to have the correct voltage levels on the bus.

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Tibor Johancsik avatar image
Tibor Johancsik answered ·

Dear Trevor,

Thx for the answer. Your answere was reassuring me, that in the shipyard they simply have forgotten to install the termination on the the Cerbo side, I will do it.

If I am correct, the other side of the interface cable is the N2K network itself, so I will not look for the other termination in the interface cable, but at the other endpoint of the chain already among the marine devices.

Thanks again for the clarification,

Tibor

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bathnm avatar image bathnm commented ·

@tibor Be very careful. It depends how they have structured the network. A CAN network N2k, K1939, VE.Can, etc must have a termination on each end of the buss. Therefore 2 x 120ohm resistors. Devices connected to the backbone via a drop cable do not need terminations.

If the Cerbo is connected to the N2K network using a Victron VE.Can to N2K adapter cable and the N2k end is plugged into a the drop side of a T piece, it is acting as a drop cable and the second port on the Cerbo should be left empty.

If the Cerbo is connected to the N2K network using a Victron VE.Can to N2K adapter cable and the N2k end is plugged into the backbone portion of a t piece, then the backbone is being extended and a terminator is required.

See diagram, sorry for the hand scribbled nature.


img-9354.jpg



Note if the Cerbo is forming part of the network, as per right hand side, I would remove the fuse from the N2K adapter cable. If the fuse is left in then 2 power sources are likely powering the bus and that is not good. The Cerbo and any other VE.Can devices connected to the extended backbone do not take power from the N2K network.

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Trevor Bird avatar image
Trevor Bird answered ·

@Tibor Johancsik ….Hello, my impression was that your system was simply VE.Can connecting to another VE.Can device. If your system is connected to a NMEA2000 backbone ( by switching the VE.Can output of the CerboGX to NMEA2000 mode) I imagine the NMEA2000 backbone in the boat will have two terminations. In that case the CerboGX spare RJ45 does not need a termination so it is probably ok.

Sorry for the confusion.

Trevor

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Tibor Johancsik avatar image
Tibor Johancsik answered ·

Ok, so the n2k bus two ends need to be terminated, (and is probably so -will chk), while the ‘leafs’ are not terminated. In this case, the Cerbo Gx is a leaf.

Thx,

Tibor

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Trevor Bird avatar image Trevor Bird commented ·
@Tibor Johancsik yes, I think the terminology is backbone and drop cables for the ones that go to the individual devices. The drop cables don't need to be terminated. If the CerboGX and another VE.Can device formed what is essentially a backbone the devices do need to be terminated.


I hope this makes sense.

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Tibor Johancsik avatar image
Tibor Johancsik answered ·

Thx Trevor,

Clear and understood.

Tibor

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