dynamically add second multi RS based on load

Been mulling this over for my narrowboat setup and it feels like a genuinely underexplored approach for larger off-grid systems.

The core idea: run a single Victron Multi-RS Solar as your base unit, handling typical domestic loads, then bring a second unit online dynamically when demand spikes — washing machine, induction hob, that sort of thing. Standby losses on these units aren't trivial at scale, so if your second inverter is sitting idle 20 hours a day, you're haemorrhaging energy for nothing.

The question is how you'd trigger the second unit reliably. A few options I've been considering:

• Current transformer on the AC output feeding into a Cerbo GX, triggering a relay via Venus OS scripting
• Node-RED automation watching the MQTT feed and energising a contactor when load exceeds, say, 2kW for more than 10 seconds
• Simply using the ESS assistant load-sharing logic, though I'm not convinced it handles dynamic unit switching cleanly without both units being permanently live

The synchronisation handshake between RS units when paralleling is what concerns me most. There's a non-trivial startup delay, and if someone fires up an angle grinder unexpectedly, the second unit won't be online fast enough to prevent a voltage sag or shutdown.

Has anyone actually implemented something like this rather than just theorising? Particularly interested in whether the VE.Can parallel configuration tolerates one unit being powered down whilst the other remains in active operation — the documentation is characteristically vague on this specific scenario.

Would be relevant for clubs, community off-grid setups, or anyone running a larger liveaboard system where standby efficiency actually matters.

Really interesting concept @DefenderAdventure — does the Multi-RS actually support parallel operation in a hot-swap or dynamic sense though? My understanding is that parallel Victron units need to be configured together from the off, not added reactively mid-load.

I've been thinking about something similar for my static caravan setup where EV charging creates sudden spikes. What I actually want is the load management side — telling the system to shed or defer the EV charger rather than physically adding inverter capacity on the fly.

Wondering if a smarter approach is:

• Oversizing slightly with two units configured in parallel from day one
• Using Victron's ESS or DVCC to dynamically allocate power rather than dynamically add hardware

Is the bottleneck you're hitting genuinely inverter capacity, or is it more about battery discharge limits? Those feel like different problems with different solutions.

@IvyWalker the parallel support on Multi-RS is there but it's not quite the plug-and-play dream — you need both units configured identically beforehand via VEConfigure, and the sync cable has to be in place. "Hot" addition mid-load is where it gets murky.

From what I've seen messing about with my shepherd's hut setup (single Multi-RS, much smaller scale I know), the VE.Bus comms need to negotiate properly at startup. So realistically you're looking at a pre-wired standby unit that you bring online cleanly rather than true dynamic hot-swap.

Could work brilliantly on a narrowboat if you design the switching around it — maybe a proper transfer switch arrangement so you can spin up unit two during peak loads like induction cooking, then gracefully drop it back out.

Would love to know if anyone's actually done this rather than theorised about it though!

Tried something vaguely similar on my boat last summer. Fired up a second inverter mid-voyage because I'd somehow convinced myself I needed a coffee machine and an angle grinder running simultaneously. Spoiler: I did not need that. The canal did not care.

The "dynamic" part is where it gets spicy though — you're essentially asking Vict

Great thread @DefenderAdventure. One practical consideration worth flagging — the Multi-RS requires a shared DC busbar and proper current sharing cables of matched length between units, otherwise you'll get imbalance issues that can confuse the parallel logic. On a narrowboat that physical layout constraint is often the tricky bit before you even get to the dynamic switching question.

The other thing I'd think carefully about is your trigger mechanism. Are you looking at a purely load-based threshold, or factoring in battery SOC and available PV at the moment of switching? Because spinning up a second unit when the batteries are already stressed could be counterproductive. A bit of hysteresis in your control logic would help avoid that second unit constantly cycling on and off around a threshold. What's your proposed switching mechanism — ESS automation or something external?