Multiplus II GX über VE.Can mit 2 CAN-bus BMS verbinden

Been scratching my head over a CAN-bus setup question and wondered if anyone here has tried something similar.

I'm planning a 48V system for my van build using two separate battery banks, each with its own BMS. The idea is to keep them independent for redundancy — if one bank has an issue, the other carries on. Both banks would communicate with the Multiplus-II GX via VE.Can.

The question is: can the Multiplus-II GX actually handle two separate CAN-bus BMS connections simultaneously through its two VE.Can ports?

From what I can tell, VE.Can is essentially a single shared bus regardless of which physical port you plug into — meaning both BMS units would need to have unique CAN IDs to avoid conflicts. Has anyone managed to get two BMS units (thinking Pylontech or similar) talking to the same Multiplus-II GX without them clashing?

A few specific things I'm unsure about:

• Does Venus OS aggregate the two BMS state-of-charge readings sensibly, or does it just get confused?
• Would DVCC still work properly with two separate BMS units asserting charge/discharge limits?
• Are there BMS options available in the UK (Fogstar Drift springs to mind) that handle this cleanly?

I've had a poke around the Victron community forums but most threads go deep into ESS territory which isn't really relevant for a straightforward van setup.

Anyone running a dual-bank CAN-bus setup on a Victron system in the UK? Would love to know what BMS hardware you ended up with and whether Venus OS plays nicely.

Hey @DownsDweller, interesting project! I've not personally run dual CAN-bus BMS setups on a Multiplus II GX myself, but from what I recall from my working days with industrial control systems, you'll want to be careful about address conflicts on the CAN network if both BMS units are broadcasting simultaneously.

Worth checking whether your BMS units support unique CAN IDs - some cheaper units are hardcoded and will clash horribly.

Also, the Multiplus II GX only has one VE.Can port natively, so you'd likely need a CAN-bus hub or daisy-chain arrangement depending on what your BMS supports.

Have a good read through Victron's ESS documentation too - there are some specific requirements around how battery monitors report to the GX device that might affect your setup considerably.

What BMS units are you actually using? That'd help narrow things down.

Has anyone actually got this working with two separate BMS units on a single VE.Can port? That's the bit I'm struggling to get my head around — the Multiplus II GX only has one VE.Can port, so how does it arbitrate between two BMS devices sending charge parameters?

I'm currently running a single Fogstar Drift 200Ah with a Daly BMS on CAN, and even getting that talking properly to the MPII GX took some fiddling with the termination resistors.

My concern with two BMS units would be conflicting DVCC signals — what happens if one bank is full and the other isn't? Does the Victron firmware handle that gracefully or does it just get confused?

@RetiredElectrician10 — do you know if there's a specific firmware version that improved dual-BMS support on the VE.Can bus?

@George1972 this is actually the crux of it — the Multiplus II GX has a single VE.Can port and the DVCC system only recognises one BMS as the "controlling" BMS at a time. Victron's own documentation is pretty clear that running two CAN-bus BMS units simultaneously on that port is unsupported.

What I've seen work in practice is using a CAN-bus to VE.Can adapter with one BMS taking priority, but honestly you're fighting the architecture at that point.

The cleaner solution @DownsDweller might want to consider is running one BMS over VE.Can and managing the second bank separately — perhaps through a Cerbo GX if budget allows, which gives you considerably more flexibility with parallel inputs. Might be worth posting over in the Victron Community forum too, their engineers do actually reply.

@OffGridJess is absolutely right, and this is where most people hit a wall.

The DVCC architecture on the Multiplus II GX is fundamentally designed to take charge parameters from one BMS "master" — it won't aggregate two BMS units on the same VE.Can segment. Victron's own documentation is annoyingly quiet on this.

Practical workaround I've seen work reliably:

• Designate one BMS as the VE.Can master (whichever has the more conservative limits)
• Wire both banks in parallel before that BMS, or use a Lynx Smart BMS which can handle this elegantly
• Alternatively, a Venus GX running a custom Node-RED flow can bridge the second BMS via a separate CAN interface, but that's proper rabbit-hole territory

For a van build specifically, honestly reconsider whether parallel banks with single BMS oversight is cleaner than fighting the protocol limitations. What BMS units are you actually running?