Orion XS 50Amp 12V DC/DC Charger

Got one of these fitted on the boat last spring and it's been mostly brilliant, but there's a quirk that took me a while to get my head around.

Running a 70A alternator on the engine, and once my Fogstar lithium bank climbs above roughly 80% SOC the Orion XS starts throttling back hard. We're talking dropping from a healthy charge down to what feels like a trickle. At first I thought something was faulty — spent a frustrating afternoon poking around connections before I realised it's actually doing exactly what it's supposed to.

The absorption phase behaviour on these units is more aggressive than I expected. Victron's logic is sound enough when you understand it, but the documentation doesn't exactly shout about it. If your bank is already reasonably topped up, don't expect the full 50A to keep flowing — it won't.

What I would say is that for the 20–80% range it's genuinely impressive. Motoring down a canal for a couple of hours off a decent alternator and the bank comes up lovely. It's only that final stretch where people seem to get confused and start worrying something's wrong.

Curious whether anyone's adjusted their absorption voltage settings to change this behaviour? I've been tempted to tweak things through VictronConnect but I'm cautious about messing with settings I don't fully understand on a boat that occasionally has me sleeping aboard in the middle of nowhere.

Also — anyone running these alongside solar? Wondering how the two play together when the MPPT is already pushing decent watts into the bank at the same time the engine's running.

@WezFisher I've had the exact same setup for about 18 months now — Orion XS 50A feeding a 200Ah Fogstar Drift lithium bank from a 70A alternator.

The quirk you're hinting at is almost certainly the input current limiting kicking in, yes? Once the Fogstar BMS opens fully and demands everything, the Orion throttles back to protect the alternator from thermal stress. It's actually doing its job correctly — a 70A alternator running flat-out on a narrowboat tick-over isn't sustainable for long.

Worth checking in VictronConnect whether you've got the input current limit set appropriately. I've got mine capped at 40A input which keeps the alternator comfortable at idle without cooking the brushes.

Also — what's your alternator temperature like? If you haven't got a sensor on it, that's worth adding before summer cruising season.

Has anyone noticed whether the Orion XS plays nicely with a split charge relay still in circuit, or does that cause issues? Asking because I'm planning something similar for my garden office — small engine-driven setup rather than a boat, but same principle.

Also wondering whether the 50A model is overkill if my alternator is only 55A? Feels like there'd be barely any headroom once the Orion's drawing its share, and I've read the alternator can get stressed if it's running near capacity constantly.

Is there a way to configure the Orion XS to cap its input draw, or does it throttle itself automatically based on what's available?

@WezFisher this rings very true from my cabin solar setup — I've got the smaller Orion XS 30A but the same current-limiting behaviour caught me out initially.

Worth knowing: the XS will actively negotiate what it pulls based on what it sees available, so if your alternator's already sweating on a hot day or the engine's at low revs, it'll throttle right back. I noticed mine dropping to barely 15A sometimes on a sluggish idle.

@SaltyRigger on the split charge relay question — from what I read in the Victron docs, the XS is designed to be the only thing managing charge from the alternator to your leisure bank. Running a relay alongside it can confuse the input sensing. Better to ditch the relay and let the Orion do its job properly.

Bit of a different angle here — I'm looking at fitting one of these in my shepherd's hut build where the vehicle alternator would be the backup charging source when solar's been poor for a few days.

@SaltyRigger the split charge relay question is something I'd also like answered — my instinct is the Orion XS is designed to replace that relay entirely rather than work alongside one, but I'm not certain.

What I'm not clear on: does the Orion XS need a dedicated ignition sense wire to wake it up, or can it detect input voltage rising on its own when the engine starts? My routing options in the hut are a bit awkward and running an extra cable to the cab would be a pain.

@TQ_Builds shepherd's hut with a vehicle alternator is giving me very specific "I've definitely done something questionable with a caravan and a Land Rover" energy — the Orion XS would be spot on for that, it's basically built for exactly that kind of "unconventional power source meets lithium bank" situation that us offgrid weirdos specialise in. 🏠⚡