Orion XS 50 connecting to battery while in Power supply mode

Been mulling over a similar setup on my boat and wondered if anyone's gone down this route with the Orion XS 50.

The idea is fairly straightforward — I've got a 100Ah Fogstar Drift lithium sat in the engine bay connected to the Orion XS running in power supply mode off the alternator. Works a treat for topping up the leisure bank while underway. But I'm now thinking about adding a small inverter into the mix, mainly to run a 12V compressor fridge and occasionally heat up food via a little inverter-fed microwave.

Here's where I'm getting a bit fuzzy:

• When the engine's running, the Orion XS is in power supply mode, effectively acting as a DC-DC stabiliser
• The battery sits alongside it, connected to the same bus
• If I hang an inverter off that bus, is the Orion XS going to play nicely, or will it start behaving oddly when the inverter pulls a big surge load?

My concern is that sudden inverter spikes might confuse the Orion into thinking there's a fault and it backs off — I've seen threads where people had weird behaviour with similar Victron kit when large loads dropped in suddenly.

Has anyone actually run this kind of hybrid arrangement — battery and Orion XS both feeding an inverter simultaneously? Curious whether the Orion just sees a slightly drooping bus and compensates, or whether it needs some tuning on the absorption/float thresholds.

Using VictronConnect so I can adjust settings if needed, just not sure what I'd be tweaking.

Anyone done something similar, especially on a narrowboat or small cruiser?

@TracyMitchell yeah ran something similar in my van build. The XS 50 in power supply mode basically acts as a DC-DC stabiliser rather than a charger — so it'll power your loads directly from the alternator/shore power without hammering the battery.

Main thing to watch with the Fogstar Drift is the BMS cut-off. If your supply voltage drops below the Drift's threshold it'll disconnect and the Orion can get a bit unhappy about the sudden load shift.

Victron's own docs are a bit vague on this tbh. Worth checking the .conf settings via VictronConnect — there's a input voltage lockout you can tweak.

What's your input source on the boat, shore power or alternator?

The XS 50 in power supply mode will still "see" your Fogstar Drift on the output terminals — Victron's own docs confirm it won't isolate the battery, so yes, current can theoretically flow back through the unit if your load drops below what the battery wants to push.

Key thing to watch: set your power supply voltage below the battery's resting voltage or you're essentially fighting the BMS in a passive-aggressive DC arm-wrestle.

If you're on a boat, also worth noting the XS 50 isn't ignition-protected — probably fine for a sealed engine bay situation, but worth double-checking your installation against the regs before BSS examination time comes round and ruins your weekend.

@ThingamyBob62's van context is slightly different; marine installs have a few extra hoops.

Done this exact dance with a Fogstar Drift on my motorhome — the key thing nobody's mentioned yet is output voltage matters enormously here.

In power supply mode, drop the XS 50's output to around 13.5V rather than letting it sit at 14.4V, otherwise you're essentially trickle-charging your Drift whether you want to or not — lithium doesn't love being held at absorption voltage indefinitely.

Also worth checking: the Drift's internal BMS won't interfere with the Orion seeing the battery, but if the BMS trips for any reason your supply rail collapses instantly, so factor that into whatever you're powering downstream.

@OldSailor is right that Victron's docs cover the output-terminal behaviour — their Orion XS manual is unusually readable for once.

@MarineGeoff is about to drop the voltage matching bombshell — but I'll add: watch your absorption voltage setting like a hawk, because if the XS 50's power supply output nudges above your Fogstar Drift's upper limit (typically 14.6V for LiFePO4), your BMS will throw a strop and disconnect faster than you can say "flat battery in Clacton."

Ran a similar lash-up in my motorhome — the Orion XS in power supply mode will charge incidentally, it's just unregulated and ignorant of your battery's actual state of charge, which makes me deeply uncomfortable from a longevity standpoint.

Short answer: it works, it's not ideal, and your Fogstar warranty probably won't survive the conversation.

@FormerCop @MarineGeoff both touching on the right stuff there — one thing I'd add from running a similar-ish arrangement on my shepherd's hut setup: the Orion XS will still try to charge if voltage dips below threshold, even in power supply mode. Caught me out badly.

Worth checking your Fogstar Drift's BMS cut-off behaviour too — if it disconnects suddenly under load the voltage spike can be... unpleasant for anything downstream.

Victron's VictronConnect app lets you tweak the output voltage quite precisely, which helps. Just don't assume "power supply mode" means fully passive — it really doesn't behave that way with a lithium sat on the output.