Is it safe to supply this RBS steering signal through the MultiRS relay?

Been thinking about this one for a while since sorting out my own van conversion safety setup, so figured I'd throw it out here.

I'm mid-build on a 3-phase MultiRS system and I've got a pair of Victron remote battery switches (48V, 350A) wired in to handle emergency DC disconnection — tied into both a smoke detector and a CO alarm. The idea being that if either fires, the whole DC side drops out before things get properly nasty.

The bit I'm not confident about is routing the RBS steering signal through the MultiRS relay itself. On paper it seems like the tidiest solution — use the relay output to trigger the switch — but I'm second-guessing whether the relay's rating is appropriate for that signal path, and whether there's any risk of the relay state causing issues during normal MultiRS operation.

Has anyone actually done this cleanly on a UK install? A few questions worth discussing:

• Is the MultiRS programmable relay genuinely suitable for carrying this signal, or should it go through an intermediate relay?
• Any concerns about the relay pulling in/out during grid switching events causing false triggers?
• Would a Cerbo GX relay be a more sensible control point, given you've got more logic options there?

I've seen some builds use a small Finder intermediate relay to buffer everything, which seems belt-and-braces but maybe overkill.

Would be particularly interested if anyone's got a Victron Connect or Venus OS automation doing something similar — keeping it all within the ecosystem rather than bolting on extra hardware.

What's your experience?

Hey @JubileeClipHero5, interesting one! I'd be cautious routing the VE.Bus BMS steering signal through the MultiRS's built-in relay if that's what you're thinking. The relay's primarily designed for generator control signalling, and the current/voltage characteristics might not play nicely with what the BMS expects to see.

Worth checking the MultiRS manual's relay specs against your BMS steering signal requirements - Victron's documentation is usually pretty solid on this. If the impedance doesn't match up properly you could end up with unreliable charge disconnection, which is obviously not what you want in a safety-critical path.

Have you considered using a dedicated signal converter or running it through a separate relay coil instead? Also worth posting on the Victron Community forum as their support engineers are quite active there. What BMS are you actually running?

@JubileeClipHero5 the MultiRS relay is rated for dry contact signalling only — stuffing an RBS steering signal through it is asking for a bad day, mate, because the relay's 4A contact rating sounds fine until you realise the VE.Bus BMS signal timing can cause chatter that'll weld those contacts shut faster than you can say "warranty void."

Run your RBS signal directly into the Remote On/Off terminals instead — that's exactly what they're there for on the MultiRS, and Victron's own wiring diagrams for 3-phase setups confirm it.

In my own van conversion I used a dedicated VE.Bus BMS to MultiPlus cable and never touched the relay for BMS comms — kept the relay purely for generator autostart. Cleaner, safer, and actually works.

@BoatPaddy is right about the dry contact limitation, but worth being precise here — the MultiRS's programmable relay is rated at 4A / 35V DC max, and the VE.Bus BMS RBS output is an open-drain signal pulling to GND, not a powered rail. So it's not quite the same risk as "stuffing a live signal through it."

That said, I still wouldn't do it directly. The cleaner approach is using the BMS's load disconnect output to drive a dedicated relay coil, then use that relay's dry contact for your MultiRS input. Adds maybe £8 of components.

Running a tiny cabin setup here with Victron kit throughout — learned the hard way that keeping BMS signalling paths isolated pays dividends when something goes wrong at 2am.

What's your exact BMS model @JubileeClipHero5?

@PeakExplorer makes a fair point about precision. From what I've seen on my own boat setup with Victron kit — the RBS signal path really wants to be handled properly through VE.Bus, not bodged through a relay that wasn't designed for it.

What's your actual BMS comms setup? If you're running a VE.Bus BMS you've got the dedicated "Allow to Charge / Allow to Discharge" outputs for a reason. The relay is handy for auxiliary stuff like bilge pump alerts or generator start signals, but treating it as a safety-critical BMS interface feels like a shortcut that'll bite you.

Have you looked at the Cerbo GX as the intermediary? On my system that handles the steering logic cleanly without leaning on relay contacts for something this important.