Multiplus-II 12/3000/120 2x120 install in RV with Intellitec Transfer Relay

Interesting timing on this thread — I went through something similar last year when I fitted a Victron Multiplus-II 12/3000/120 into my converted horsebox (long story, don't ask 😄).

My situation wasn't an RV exactly, but the transfer switching headache was identical. I had an existing changeover relay from the previous owner that introduced a noticeable delay before the Multiplus could "see" the incoming shore power properly. Caused all sorts of confusion with the unit hunting between inverter and charger modes.

What sorted it for me was adjusting the AC input current limit in VE.Config and tweaking the transfer switch delay settings so the Multiplus had time to properly detect a stable supply before attempting to accept it. If you're running two separate AC inputs — which is where your Intellitec setup sounds more complex than mine — I'd be really curious whether you've looked at:

• How the relay prioritises between your two connections
• Whether there's any voltage sensing delay baked into the Intellitec unit itself
• If the Multiplus assistant settings are configured to handle that handover gracefully

The Victron community forum is brilliant for the technical deep-dive, but I find the real-world install experience tends to live on threads like this one.

Anyone else here running dual AC inputs into a Multiplus on a mobile setup? I know a few folks here have done similar things with garden office setups where they switch between grid and generator — the principles aren't a million miles apart.

Would love to hear how you get on with the Intellitec specifically.

@ExFarmer90 a horsebox conversion — so literally off-grid on the hoof 🐴

Curious what you ended up doing with the transfer relay side of things. The Multiplus-II's internal transfer switch is pretty rapid (20ms ish) but older Intellitec relays can be a bit... leisurely about

@ExFarmer90 What transfer relay did you end up using? That's always the bit people gloss over in write-ups and then wonder why their shore power switching is sluggish or the Multiplus throws a fault.

On my motorhome I ditched the OEM relay entirely and let the Multiplus handle the transfer switching natively — it's rated for it and the ~20ms switchover is more than acceptable. Saves adding another potential failure point in the circuit.

Worth checking your AC input current limit is set correctly in VE.Configure if you're on a limited hookup supply. Caught me out early on — Multiplus was pulling more than the site pedestal could handle and tripping the bollard breaker repeatedly before I figured it out.

@BodgeItAndScarper the transfer relay question is a fair one — most write-ups do skip it entirely.

With the Multiplus-II the built-in transfer switch handles most use cases cleanly, but the timing matters if you've got sensitive equipment on the load side. Victron's own spec is <20ms switchover which is fine for most things, but I've seen people still run an Intellitec relay upstream to isolate shore power cleanly before it even reaches the Multiplus.

Whether that's actually necessary depends on your wiring setup. In my horsebox I ditched the idea of a separate relay altogether — let the Multiplus do its job. No issues so far.

That said, if your RV already has an Intellitec relay baked into the original wiring, removing it might create more headaches than keeping it in. What does the existing wiring diagram look like?

@BodgeItAndScarper fair point — it's always the unglamorous bits that catch you out.

In my horsebox build I used the Multiplus-II's built-in transfer switch rather than adding a separate relay, which simplifies things considerably. The 120A AC transfer capacity on that unit is genuinely generous for a 12V system.

That said, if you're working with an existing Intellitec relay already wired in, the key thing is making sure your transfer timing doesn't fight the Multiplus's own switching — there's a configurable input current limit in VictronConnect that's worth adjusting before you assume something's faulty.

What's your shore power source — a campsite hookup or a generator? That changes how aggressive you want the transfer settings to be.