Anyone else running a Victron Orion-Tr Smart in non-isolated mode? Getting odd behaviour at low SOC

I've had a Victron Orion-Tr Smart 12/12-30 running between my starter battery and a 100Ah lithium leisure bank for about four months now. Set it up in non-isolated mode as the van has a shared negative, and for the most part it's been brilliant — proper bulk/absorption charging, plays nicely with the BMS, all that. But I've noticed something a bit strange lately.

When the leisure bank drops below roughly 20% SOC, the Orion seems to kick in and out every few minutes rather than holding a steady charge. The input voltage from the alternator looks fine on the Victron Connect app (sitting around 14.1–14.3V), and the output is cycling between about 13.8V and dropping off entirely before ramping back up. It's not throwing any faults or error codes, which is making it harder to diagnose.

I'm running it alongside a 200W solar setup through an MPPT, so there's occasionally a bit of competition for the bank, but this cycling seems to happen even when solar input is negligible — early morning starts, for instance. Firmware is up to date (v1.31 I think). Has anyone seen similar behaviour, particularly on a lithium install? Wondering if it might be the BMS momentarily disconnecting under load and confusing the Orion, or something in the adaptive algorithm I've not accounted for.

Yeah had similar with mine between the car and the garden office battery bank. Non-isolated mode can get twitchy when the leisure bank drops below ~20% — the Orion seems to second-guess itself on whether to keep the engine-side voltage high enough to trigger the input threshold.

Worth checking your input voltage lockout setting in the VictronConnect app. Mine was defaulting to something daft like 13.2V which caused it to cut in and out constantly at low SOC when the alternator was doing light work.

Also make sure your shared negative connection is as short and beefy as possible — any resistance there causes voltage drop readings that confuse it further.

What firmware version are you on? There were some behavioural fixes in recent releases that sorted a lot of the low-SOC weirdness for me.

Just to add to what @Dizzy70 is getting at - worth double-checking your input voltage threshold settings in the VictronConnect app. The Orion-Tr Smart has adjustable start/stop voltages and I found mine was cutting out prematurely because the factory defaults were a bit conservative for lithium on the output side causing weird feedback on the sense circuit in non-isolated mode.

Try bumping your input start voltage down slightly and see if the behaviour changes. Also, are you on the latest firmware? There were some stability improvements a few versions back specifically around non-isolated configurations. Mine was doing something similar until I updated and tweaked those thresholds.

What voltage is your starter battery actually sitting at when it starts misbehaving? That'd help narrow it down.

Hey @AndyPalmer, one thing worth checking that nobody's mentioned yet - have you got the engine running detection set up properly? In non-isolated mode the Orion can get confused about whether the alternator is actually charging or if it's just reading resting voltage from the starter battery. If your input voltage threshold is set too low it'll try to charge off a battery that's already under load itself. Also worth looking at the tail current settings on the lithium side - at low SOC the BMS might be pulling the voltage down just enough to trigger a restart loop. What firmware version are you running? There were some stability improvements in recent updates that helped a few of us out. 👍

Hey @AndyPalmer, one thing worth looking at that nobody's mentioned yet - have you got the engine detection threshold set correctly? In non-isolated mode the Orion can struggle to distinguish between "engine running and alternator charging" vs "battery sitting at a decent resting voltage" if that threshold isn't dialled in properly. Default is something like 13.2V but depending on your starter battery's resting state that might be too close for comfort, especially as your leisure bank pulls the input voltage around at low SOC. Try bumping the threshold up to 13.7V and see if the behaviour stabilises. Also worth checking your cable cross-section is adequate for 30A continuous - voltage drop on undersized cable can cause all sorts of weird cut-in/cut-out behaviour that looks like a software issue but isn't. What gauge are you running?

@AndyPalmer I had similar weirdness with mine on the cabin setup — turned out my input under-voltage lockout was set too conservatively, so it was cutting out earlier than expected and then taking ages to reconnect once voltage crept back up.

Worth checking in the VictronConnect app under Advanced Settings — what have you got your input voltage lockout and restart thresholds set to? The defaults don't always suit lithium-to-lithium setups particularly well.

Also, are you monitoring through a Cerbo or just the Bluetooth app? I found the history graphs in VictronConnect really useful for pinpointing exactly when the dropouts were happening relative to SOC.

Good shout from @GemmaWood on the input under-voltage lockout — that's caught a few people out. One thing I'd add though: in non-isolated mode with a shared negative, have you checked for any voltage drop across your negative cable between the two batteries? Even a small resistance there can confuse the Orion's voltage sensing and cause it to behave erratically at low SOC when currents are highest. Worth measuring with a multimeter under load. Also, are you using the VictronConnect app to monitor in real time? The history graphs can be brilliant for spotting exactly when and why it's cutting out. Sometimes it's worth temporarily enabling the Bluetooth notifications so you catch the fault as it happens rather than piecing it together afterwards.

Good points from @GemmaWood and @JasonEdwards already. One thing I'd add - in non-isolated mode with lithium on the output side, make sure your absorption and float voltages are properly dialled in for your specific battery chemistry. Some folk leave them on the AGM defaults and the charger behaves oddly near the top end, which can cause confusing cutoff behaviour that looks like a low SOC issue but actually isn't. Worth double-checking what your BMS charge parameters actually require and matching the Orion's profile accordingly. What lithium cells are you running - are they branded with a proper spec sheet?

@Ian1968 makes a fair point but nobody's mentioned the absorption-to-float transition kicking in early if your engine's alternator voltage is drooping under load — Orion sees that as "battery charged, job done" and throttles back, looks mental on the app but it's actually working as intended. Check your Engine Detect threshold too, because if it's set wrong the thing's shutting down the moment you dip below it. Classic "why is my DC-DC asleep" symptom on the cut on my narrowboat constantly.

Something nobody's mentioned yet — have you checked your alternator output voltage under load? Some older or smaller alternators on vans drop below 13.2V when they're working hard (fans, lights, heated screen etc.), which can cause the Orion to repeatedly hit its input under-voltage threshold and cycle on and off. You'd see exactly the behaviour you're describing, particularly noticeable at low SOC when the Orion's drawing harder. Worth logging the input voltage over a run with a battery monitor or even just a cheap voltmeter clipped to the starter battery whilst driving. If it's dipping, a higher output alternator or adjusting your lockout threshold slightly downward might sort it.

@AndyPalmer one thing worth checking is your input voltage threshold settings in the VictronConnect app. The Orion-Tr Smart has adjustable start/stop voltages for the input side, and if your starter battery dips even briefly under load (lights, wipers, etc.), it can trigger a shutdown that looks really odd at low SOC because everything's already marginal. Try logging via the app during a drive and watch for those input voltage dropout events — they're easy to miss otherwise. What have you got your input start voltage set to currently?