Unable to set up new Paralell/Split Phase MultiPlus II system (Comp ID Issue)

Been down a similar rabbit hole recently with my garden office setup, so this caught my eye.

I'm running a pair of Victron MultiPlus-II units in parallel rather than split phase (we don't really do that 120/240V split phase business here in the UK obviously), but the companion ID / unit numbering issue is very much a real headache on this side of the Atlantic too.

When I first commissioned mine, VE.Configure kept throwing a wobbler because both units had shipped with identical device addresses. The fix — for anyone else stumbling across this thread — is to:

1. Configure each unit individually via VE.Bus before you physically connect them together
2. Set unit 1 as master, unit 2 (and beyond) as slave with the correct address increments
3. Only then daisy-chain the RJ45 cable between them

What I didn't realise until an embarrassing amount of time had passed, is that the firmware on both units needs to match exactly. I had one unit on a slightly older build and VE.Configure just refused to acknowledge the pair properly. Updating via VE.Flash sorted it.

If you're dealing with six units though — blimey, that's a serious install. Are you using a Venus GX or Cerbo to manage the whole lot? I'd imagine keeping firmware consistent across six devices is where things start getting properly painful.

Worth posting your VE.Bus system report if you can — someone here will almost certainly spot the issue faster than Victron's official support queue will respond.

What inverter size are you running across all six?

@Nige1977 ah yes, the Companion ID rabbit hole — where sane people go in and slightly unhinged people come out 😄

Worth double-checking that both units are running identical firmware versions before anything else. Victron's VEConfigure can be a right diva about mismatched versions — like trying to get two cats to

@Nige1977 parallel config on UK 230V single-phase is straightforward once you understand that the Companion ID assignment is physically position-dependent — VE.Bus addresses the units based on which cable they see first during the network scan.

What tripped me up on my narrowboat install was assuming I could just swap the RJ45 daisy-chain order without consequence. You absolutely cannot. Master is always the unit with the unconnected left-hand port.

Practical fix: with both units powered down, disconnect the VE.Bus cable entirely, reconnect starting from your designated master, then power up master first, wait for the LED sequence to complete, then power the second unit. VEConfigure3 should then see them cleanly assigned as #1 and #2.

Worth checking your firmware versions are identical between both units too — mismatched firmware is a silent killer for parallel detection that Victron's documentation barely mentions.

Just to add something I haven't seen mentioned yet — when I was setting mine up, I found that the order in which you power the units on during initial configuration actually matters more than you'd expect. The first unit to come online tends to assert itself as master regardless of what you've set in VEConfigure, which caused me no end of confusion until a Victron dealer pointed it out.

Also worth double-checking your VE.Bus cable is a straight-through RJ45, not a crossover — sounds obvious but I used one from my networking spares drawer without thinking and lost about two hours to that particular headache. 😅

@MoorLee — "slightly unhinged" is generous, I came out the other end questioning most of my life decisions!

@TransitProject that power-on order point is genuinely underappreciated — I got caught out by exactly that with my cabin setup. Worth adding that once you've got the Companion IDs sorted and the system's running stably, it's worth saving the VE.Config file immediately before you touch anything else. Had a unit need a firmware update a few months later and having that saved config made recovery about 10 minutes rather than starting from scratch.

Also — make sure you're running identical firmware versions on both units before attempting the parallel configuration. Mismatched firmware is a classic source of weird Companion ID behaviour that looks like a hardware or wiring fault but isn't.

@TransitProject @DODQueen — yes, this caught me out too. Worth adding: once you've got the Companion ID sorted and power-on sequence right, double-check your VE.Bus cable quality. I was getting intermittent comms faults between my two units and spent ages in VictronConnect scratching my head before realising one of the RJ45 connectors on my interconnect cable was slightly dodgy. Swapped it for a properly crimped Cat5e patch cable and it cleared immediately.

Also make sure you're on identical firmware versions across both units before you do anything else — mismatched firmware will cause weird behaviour that looks like a config problem but isn't.