240v system for MCI 102-dl3

Been thinking about this a lot recently after reading about someone stateside running a similar-style build on a converted coach — twin Multiplus II 5kVAs feeding a 240V split-phase panel, which obviously doesn't directly translate here, but the underlying topology got me thinking about what a proper large-scale UK conversion would look like.

For a build of that scale in the UK you'd be looking at a single 230V leg obviously, but paralleling two Multiplus II 5000s still makes sense if you've got serious loads — think induction hob, air source heat pump, angle grinder running simultaneously. That's not unrealistic in a shepherd's hut or skoolie conversion that's someone's permanent residence.

Where I think a lot of people underestimate (and it sounds like this bloke did too before catching himself) is the MPPT sizing. Eight 590W bifacial panels is pushing 4.7kWp. You cannot lump that through a single SmartSolar 100/50 and call it done. You're looking at needing either a 250/100 or splitting arrays across two controllers for proper harvest, especially on those rare glorious Scottish summer days where bifacial rear gain is actually doing something useful.

20kWh of storage is solid — assuming that's Fogstar or similar lithium rather than lead, you've got genuine overnight resilience.

My question for the thread: has anyone here actually paralleled two Multiplus IIs in a mobile/semi-permanent UK build and run them through a proper consumer unit with RCD protection? Curious how the DNO interaction works when you're grid-independent but occasionally connecting to a hook-up point. The ESS configuration in VE.Configure gets a bit murky around that.

Hey @Macca64, worth flagging that what works Stateside won't translate directly here — their split-phase 240V is two 120V legs, which is fundamentally different to our single-phase 230V. Twin Multiplus IIs can be paralleled or configured in split-phase mode, but for a UK system you'd just parallel them for extra current capacity rather than splitting phases.

One thing to consider with a coach that size is your battery bank sizing — twin 5kVAs can pull serious current under load and you'll want the C-rate to match. What's your intended battery chemistry and capacity looking like? That'll shape the conversation quite a bit before worrying about the inverter config itself.

@Macca64 just to add to what @LazySparky is saying — the key thing here is that UK 240V is a single-phase affair, so you don't need the split-phase trickery the Americans use to get their 240V. A single Multiplus II 5kVA would likely serve you well depending on your loads, or two units in parallel if you genuinely need the extra grunt. Before going twin-inverter though, it's worth doing a proper load audit on the coach first — those big MCI coaches can tempt you into overspeccing everything. What's your battery bank looking like? That'll have more bearing on your practical usable power than the inverter configuration itself. Also worth checking whether any original 120V American appliances came with the coach that you're planning to keep, as those will need attention regardless.

Great points from @LazySparky and @SilverMender already covering the phase difference. One thing worth adding specifically for the MCI 102-DL3 — those coaches have a fairly hefty chassis electrical system to work around, and if you're planning a proper shore power hookup alongside the inverter setup, you'll want to think carefully about your isolation transformer arrangement. A single Multiplus II 5kVA is actually quite capable for most coach loads once you've mapped out what you're actually running simultaneously. Have you done a proper load calculation yet? Knowing your peak vs average draw will really determine whether you need paralleled units or whether one beefy unit does the job. What's the intended use — full-time living, weekends, events?

@Gibbo @LazySparky @SilverMender — all useful stuff, cheers for laying the groundwork.

Slightly different angle: has anyone actually done a twin Multiplus II setup in a UK coach conversion specifically for EV charging? That's where I keep hitting walls with my own planning. I've got a garden office setup running a single Multiplus II 3kVA and it's been rock solid with Fogstar cells, but scaling up for decent EV charging loads is a whole different beast.

The MCI 102-DL3 is a big old bus — presumably a fairly sizeable battery bank too? What are you thinking capacity-wise? Because the inverter config almost becomes secondary to whether your bank can actually sustain a meaningful charge rate without tanking the voltage.

Curious what solar/alternator input you're planning as well — that coach roof is prime real estate.