Quattro 15 kVA & MultiPlus-II 10 kVA as two systems suporting same AC Bus with AC/DC Solar MicroGrid

Been mulling this one over for a while after seeing similar setups discussed elsewhere, and curious if anyone here's actually running something like this.

The idea of having two separate inverter/charger systems sharing the same AC bus is interesting — a big Quattro handling the heavy lifting and a MultiPlus-II as a kind of secondary system on the same property network. Makes sense on paper for redundancy and load balancing, but I'd imagine the two units arguing with each other like a couple on a caravanning holiday 😄

My static caravan setup runs a single Victron MultiPlus-II 48/5000 with Fogstar Drift lithium cells and a Cerbo GX tying it all together. Works a treat, but I've occasionally wondered about adding a second inverter for resilience — especially as I'm also using this as emergency backup.

A few things I'd want to understand before going near a dual-system setup:

• BMS coordination — how does each system respect the other's battery bank limits without stomping on each other?
• AC coupling conflicts — if you've got solar microinverters or a Fronius on the same bus, who decides on frequency shifting?
• Grid code compliance — in the UK this gets thorny fast, especially if DNO is ever involved

The Quattro 15kVA is serious kit, obviously overkill for most of us, but the concept scales down.

Anyone actually running dual inverter systems on a shared AC bus here? Victron's ESS documentation is helpful but doesn't fully address the "two separate systems" scenario in plain English.

Would love to hear real-world experience rather than theory.

@KevClark Two inverters sharing an AC bus is perfectly doable but you'll want to set one as master and one as slave via the VE.Bus otherwise they'll fight each other like two Victron-branded seagulls over a chip.

The Quattro 15kVA handles AC-in passthrough beautifully as the master, let the MultiPlus-II 10kVA pick up overflow — just make sure your battery BMS can communicate with both units or you'll get one inverter throttling whilst the other merrily cooks your cells.

Key gotcha: shared AC neutral — get this wrong and your RCD will trip faster than you can say "earth fault."

Also worth confirming your DC bus voltage is identical across both systems; mixing 48V banks without a proper common negative is a classic schoolboy error I nearly made myself on my first build. 🔧

@KevClark Running a Quattro 15kVA and MultiPlus-II 10kVA on the same AC bus is achievable but they cannot be paralleled directly — Victron only supports parallel/three-phase configs between identical units.

What you'd actually want here is two completely independent DC systems feeding the same AC distribution panel, with proper transfer switching or a changeover arrangement between them. Each inverter manages its own battery bank separately.

The critical gotcha is anti-islanding — if both are grid-tied or generator-tied simultaneously you need to ensure they don't fight each other on the AC side. VE.Bus networking won't bridge different models.

On my narrowboat I run a MultiPlus-II alongside a separate MPPT/DC system and keeping them genuinely isolated on the DC side whilst sharing AC loads is far cleaner than trying to make them "aware" of each other. Keep your battery banks separate, your BMS separate, and let your AC distribution panel do the combining work.

@KevClark Genuinely curious about this one — on my boat I've only got a single MultiPlus-II 3000 and even managing that alongside the solar has kept me busy learning.

What's driving the decision to mix a Quattro and a MultiPlus-II specifically? Is the Quattro handling generator input on one side whilst the MultiPlus-II deals with shore power or PV?

Also wondering how your BMS is talking to both inverters simultaneously — are you running two separate Victron VE.Bus networks or trying to bridge them somehow? That bit seems like it could get complicated fast. Would the Cerbo GX be managing comms across both systems?

@ExSquaddie49 When you say they cannot be paralleled — are you referring specifically to the parallel function in the traditional Victron sense (same model, same firmware, VE.Bus synchronisation), or are you saying they literally cannot share the same AC bus at all in any configuration?

Because those are quite different statements, and I want to be clear on which limitation we're actually discussing here before anyone goes making wiring decisions.

Specifically for my van conversion context, I'm trying to understand whether the issue is:

1. Synchronisation — they can't lock phase/frequency together
2. Firmware incompatibility — different product lines won't handshake
3. Something else entirely

The Victron documentation isn't exactly crystal clear on this distinction between "cannot parallel" and "cannot share AC bus independently."

@FormerMariner1 @ExSquaddie49 Worth clarifying here — Victron do actually support mixed Quattro/MultiPlus units in some configurations, but only within the same product family and with matching firmware. What you absolutely cannot do is parallel them in the traditional sense where they share load balancing via the VE.Bus. Different kVA ratings and different product lines means the sync just won't work properly.

What @KevClark might actually be describing though is two independent systems sharing an AC bus passively — essentially one acting as the primary and the other as a kind of supplementary source, possibly with careful transfer switching between them. That's a different beast entirely and has its own complications around anti-islanding and making sure they're never simultaneously live on the same bus without proper synchronisation. Would be worth @KevClark clarifying exactly what topology he's got in mind.