6k5: Dynamic current limiter - physical Relay/Contactor?

Been mulling this one over after a similar rabbit hole on the boat last summer.

I'm running a Victron Multiplus 48/3000 with a Honda EU22i as backup, and the dynamic current limiter via VE.Bus is genuinely clever — but I keep wondering whether there's a case for a physical relay or contactor in the mix rather than relying purely on the software-side limiting.

The scenario that worries me: generator kicks in under heavy PA-style transient loads, the DCL is playing catch-up, and you get a brief overcurrent spike before the Victron has a chance to throttle back assist. On a boat with a clean, predictable load profile it's mostly fine, but throw in a sub-bass kick drum at 3am and all bets are off.

A physical contactor — something like a decent DIN-rail unit from Finder or even a Victron Battery Protect upstream — could act as a hard backstop rather than a soft limit. The question is whether that actually adds resilience or just introduces another failure point.

Has anyone here done a hybrid approach? Particularly interested in:

• Whether a contactor adds meaningful protection or whether the DCL is genuinely fast enough
• Any UK suppliers who stock suitable contactors rated for 48V DC switching (it's a minefield)
• Whether this even makes sense on a 6k5 where the inverter response time is presumably quicker than a 3000

Feels like the kind of thing that looks overengineered on paper but saves you at 2am in a field somewhere in the Cotswolds. Would love to hear from anyone who's actually stress-tested their generator/inverter combo under live event conditions.

@Del the dynamic current limiter via VE.Bus is generally solid, but I've seen situations where a physical contactor makes sense as a failsafe — particularly if your control wiring is vulnerable or you're running unattended.

Worth looking at a normally-open contactor wired through a voltage sensing relay. If the Cerbo/CCGX loses comms, the contactor drops out and limits draw automatically rather than relying solely on software.

On my static caravan setup I run a similar belt-and-braces arrangement — the Honda EU22i is quite sensitive to overload and a hard trip is far more disruptive than a controlled current limit.

One practical note: make sure your contactor coil draw doesn't upset your standby power budget overnight. Some of the cheaper DIN-rail units can be surprisingly hungry.

@Del nothing like a Honda EU22i and a prayer to keep the shepherd's hut warm at 2am when the Fogstar bank decides it's had enough 😅

On the physical contactor question — I added a Carlo Gavazzi contactor upstream of my Multiplus purely as a belt-and-braces job, and honestly it's the best £40 I ever spent on peace of mind.

The VE.Bus dynamic limiting is clever but it's still software, and software has opinions at the worst possible moments. A physical relay triggered by a simple current transformer gives you a hard ceiling that doesn't care about firmware updates or comms dropouts.

@RetiredPlumber is right to flag those edge cases — I've seen the Multiplus get briefly confused during gen startup transients before the limiter kicks in properly.

@Del one thing worth considering alongside the VE.Bus dynamic limiting is what happens during the handshake delay when the Multiplus is still "deciding" on input current — that brief window can still pull enough to stall a sensitive inverter-generator like the EU22i before the limiter kicks in.

I've seen people use a simple time-delay relay on the AC input contactor to hold back non-essential loads for 3–5 seconds post-transfer. Not elegant, but it's a genuine belt-and-braces layer.

With the EU22i specifically, I'd also look at whether you've got the correct UPS function timing configured — the eco-throttle interaction with sudden load steps is a known weak point. A physical contactor rated for your full surge current (rather than just running current) is worth the few quid extra on something like a Schneider LC1D-series unit.

Good thread this. @Del one angle I'd add — if you're going down the physical contactor route, have a look at what inrush current your loads are actually throwing at the EU22i during startup, not just steady-state draw. A contactor switching at the wrong moment can actually make things worse if you've got compressor loads or inverters downstream that surge on reconnection.

I've used a Finder 22.32 series contactor with a simple current transformer feeding a relay logic circuit as a belt-and-braces approach alongside the VE.Bus limiting on a similar Multiplus setup. Adds maybe £40-60 in parts and gives you that hard backstop @RetiredPlumber is hinting at.

The Honda EU22i is a cracking little genny but it really doesn't like being bullied — keeping that handshake window clean as @MistyTinker mentions is worth the extra layer of protection.

Good shout @RayTaylor on the inrush side of things. One thing I'd add for @Del — if you do go physical contactor, worth thinking about coil suppression. Contactor coils on DC control circuits can throw a nasty voltage spike when they de-energise, and I've seen that cause grief with sensitive control boards before. A simple flyback diode or RC snubber across the coil sorts it. Also, depending on how your wiring is laid out, a normally-closed auxiliary contact feeding back to the Multiplus control logic can give you a decent confirmation signal that the contactor has actually pulled in rather than just assuming it has. Belt and braces, especially on a remote setup where you're not there to notice if something's misbehaving overnight.