question

libor avatar image
libor asked

Wiring data cables - Multi RS + Cerbo GX + two BMS batteries

Hi Victron community,

After reading a lot of docs & posts, I'm still not sure if I understand the proper wiring of data cables and applying it correctly to my use case.

This is what I think it should be - in short: At the start is 1st terminator, then Multi RS, followed by Cerbo GX, 1st battery, 2nd battery and finally 2nd Terminator.

1717834023272.png

...where the "Custom wiring" is based on Victorn's and battery manufacturer specification of the RJ45.

Function
 Victron VE.Can side
 Battery side
GND
 Pin 3
 Pin 8
CAN-L
 Pin 8
 Pin 2
CAN-H
 Pin 7
 Pin 1


Could you please comment - did I get this right?

cerbo gxBMSrj45 cable
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3 Answers
Matthias Lange - DE avatar image
Matthias Lange - DE answered ·

The Cerbo has VE.Can at 250kbit/s for Victron products and BMS-Can at 500kbit/s for (most) batteries BMS communication.

https://www.victronenergy.com/media/pg/Cerbo_GX/en/installation.html#UUID-0e69c6c5-f21f-4fcd-55a5-3fdb7be6a41b

VE.Can uses straight patch cables, for BMS Can most batteries need a cable with special pin-out.

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libor avatar image libor commented ·

Ah, yes, actually that was what I meant to use, but somehow when rushing to make the diagram put VE.Can for batteries too.


However, both ports are basically on the same bus, correct? So, the only thing which would change, is the BMS cable goes into VE.Bus...?

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Matthias Lange - DE avatar image Matthias Lange - DE ♦ libor commented ·

VE.Bus is also only for Victron products! MultiPlus, Quattro and older Phoenix inverter.

You need take another look at the manual and the device you.

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(VE.Can 2 = BMS-Can on "older" devices)

If you don't have VE.Can 2 or BMS-Can than you have a Cerbo-S GX and that only has one VE.Can bus.

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libor avatar image libor Matthias Lange - DE ♦ commented ·

Of course, I mixed it up again, BMS Can is on the left hand side. This is actual state (not powered on yet).

1717941735869.png

The big question is about the battery side. I think the terminator doesn't make sense here, since the wiring is completely different.

So I assume to connect 1st battery and use standard cable between 1st and 2nd battery.

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libor avatar image
libor answered ·

You're right, I mixed that up again. On my Cerbo GX, there's a BMS-Can on the left hand side.

Here's this part wired (but not operating yet).

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However, it's the battery side, that I'm unsure about. The more I read about it, the more confused I am. I think I can't use the terminator there (since the wiring is completely different). I wonder - is the terminator on the BMS-can required? And if yes, I assume I'd have to wire my own?

Based on this:

1717947677201.png

I think the terminators should be only on the Multi RS line (one in the Cerbo and one in Multi RS).

1717948580523.png

Unfortunately, while there are many schematics for very niche and unique solutions, I couldn't find any schematics for the simple use case I have, which I'd expect should be very decisive majority of installations for the devices like Multi RS or EasySolar. I know historically it was different, but that's what I'd expect Today.



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Duivert NL avatar image
Duivert NL answered ·

No need for terminator on bms can, only when your battery needs one, sometimes you can set a dipswitch, you didnt mention wich battery you are using

More info on battery compatibility is here:

https://www.victronenergy.com/live/battery_compatibility:start

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libor avatar image libor commented ·

Thank you, good to get some assurance.

Yes, there is a dipswitch (address selector) - the first battery is set to "1" and 2nd battery to "2".

I know about the compatibility list, my Sunstone Power SLPO48-100 batteries are not liested. I know there's a risk they won't be compatible, but taking into account there are only like 4 different BMSes in all the batteries, I think chances are high.
There's a chapter in the battery Manual, what parameters to set on the invertor's internal BMS, if communication cables are not / can't be used.

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libor avatar image libor commented ·

Data connection to the batteries still doesn't work for me. I found a schematics somewhere in Victron manuals (and of course I can't find it now again), that shows that terminator should be used on BMS-can. At least I found a photo of someone having it on BMS-can:

1718646082417.png

So I'm ordering 2nd set of terminators and will try again with them.

Documentation for the batteries I have doesn't state what speed the CAN is on (250/500 kBit/s) and if that is the case, then the only option is to either replace the batteries or put a proxy in between (perhaps another Raspberry receiving 250 kBps and sending 500 kBps). Or let it live with Built-in BMS and calibrate it from time to time.

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