Anyone else running a Victron Orion-Tr Smart in non-isolated mode? Getting a weird voltage drop issue

I've had a Victron Orion-Tr Smart 12/12-30 running between my van's starter battery and a 100Ah lithium leisure battery for about four months now. Set it up in non-isolated mode because the two battery negatives share a common chassis ground, which I thought was fine. Most of the time it's brilliant — charges up the leisure bank nicely while I'm driving and the BMS handshake via the engine-running detection wire works a treat.

The issue I keep seeing is a roughly 0.4–0.5V drop between what the Orion app reports as output voltage and what my Victron SmartShunt is actually reading at the leisure battery terminals. I've checked and re-checked my cable runs — 6mm² twin and earth, about 1.8 metres total from Orion output to battery — and the connections all look solid and clean. Fusing is correct at both ends. I just can't account for that much of a drop over such a short run.

Wondering if anyone else has seen this, particularly in non-isolated installs. Is it a calibration offset between the two Victron devices on the VE.Smart network, or could I actually have a resistance problem somewhere I'm not spotting? I did wonder about the blade-type connectors on the Orion output terminals — maybe ring terminals would give a better connection?

Would appreciate any thoughts before I start pulling everything apart again.

@RussOliver64 welcome to the forum, great first post and a solid setup to be working with!

One thing worth checking that catches people out with non-isolated mode on the Orion-Tr Smart — have you verified your shared negative path is actually clean end-to-end? Even a modest resistance in the negative run (corroded terminal, undersized cable, loose connection) will show up as a voltage drop that the unit can't compensate for.

On my narrowboat I run a similar non-isolated setup and I had exactly this symptom. Turned out to be a dodgy crimp on the negative at the battery terminal — looked fine visually but was dropping nearly 0.4V under load.

Worth grabbing a cheap multimeter and doing a voltage drop test across each section of the negative circuit while the Orion is pulling current. That'll isolate the culprit quickly.

What voltage are you actually seeing at the input versus output?

Just to add to what @HeathGazer is saying - with the Orion-Tr Smart in non-isolated mode, the shared negative is absolutely critical. I had a very similar voltage drop symptom on mine and it turned out to be a dodgy earth point on the chassis. The unit was seeing resistance in the return path and compensating oddly.

Worth doing a proper voltage drop test across your negative cables whilst it's under load - put your multimeter between the leisure battery negative and the starter battery negative and see what you're reading. Anything above about 0.2V suggests you've got a connection or cable sizing issue rather than the Orion itself playing up.

Also double-check your cable runs are adequately sized for 30A continuous - people often underestimate the return path resistance on longer runs through a van. What gauge are you running currently?

Great points from @HeathGazer and @JohnMason already. One thing I'd add that catches people out - have you checked your input voltage threshold settings in the VictronConnect app? The Orion-Tr Smart has a default "input voltage lockout" that can cause it to throttle or cut output if the starter battery dips even briefly under load.

Worth logging a session and watching the input voltage in real time whilst the engine's running. If you're seeing the alternator voltage fluctuate (common on older vehicles especially), the charger might be backing off more than you'd expect.

Also, what firmware version are you on? There were some behavioural improvements in recent releases around voltage sensing that made a noticeable difference on my own setup. Updating via VictronConnect is straightforward if you haven't done it recently.

Great thread, @RussOliver64! I had almost identical symptoms on my motorhome setup last year. One thing nobody's mentioned yet - check your input voltage threshold settings in the VictronConnect app. If the "start" voltage is set too close to your actual alternator output, the unit can be switching on and off repeatedly under load, which causes exactly that kind of voltage drop behaviour. Mine was set at 13.2V and my ageing alternator was hovering just above that when the heating was running. Bumping the threshold down slightly (carefully, so you're not flattening your starter battery) made a massive difference. Also worth having a look at the charge algorithm - make sure it's set appropriately for lithium rather than a standard profile. Four months in is actually a good time to review those initial settings.

Something worth adding that I haven't seen mentioned yet — check the input voltage threshold settings in the VictronConnect app. The Orion-Tr Smart won't start charging until the starter battery hits a certain voltage (default is usually 13.2V I think), and if your alternator's a bit lazy on voltage output or you've got resistance in the feed cable, it might be cutting in and out repeatedly rather than holding a steady charge cycle.

Saw this exact behaviour on my own setup before I tweaked the start/stop thresholds. Also worth logging the data in VictronConnect over a drive — the history tab will show you if it's cycling on/off, which would explain a voltage drop pattern.

What gauge cable are you running for the input feed? On a 30A unit I'd want nothing less than 6mm² for any run over about a metre.

Ground loop issues in non-isolated mode will bite you every time — the clue's in the name "non-isolated."

If @ShortCircuit's threshold suggestion checks out, next thing I'd look at is your negative cable routing. In my shepherd's hut setup I had a phantom voltage drop that turned out to be a shared negative path with too much resistance — Victron Connect was showing the Orion perfectly happy while the actual delivered voltage at the battery terminals told a different story.

Slap a multimeter across the output terminals under load rather than trusting the app readout. If there's more than ~0.3V difference between what Victron Connect reports and reality, your cabling's the culprit, not the unit.