Orion -Tr Smart 12 I 12-18 isoliert zur Erhaltungsladung der Starterbatterie

Been running a similar setup in my cabin-on-wheels build and this topic keeps coming up, so thought I'd share what I've found.

I've got an Orion-TR Smart 12/12-18A isolated wiring the leisure bank back to the starter battery for trickle/maintenance charging. The isolated version is key here — on a Sprinter-based conversion especially, you really don't want shared grounds causing issues with the CANbus or the van's charging logic.

The setup I'm running:

• Victron Orion-TR Smart 12/12-18A (isolated)
• Configured in "engine off" mode disabled, so it only pushes charge to the starter when the alternator is genuinely running
• Input voltage threshold set to 13.2V to avoid accidentally draining the leisure bank overnight

What I'd flag for anyone considering this: the default thresholds out of the box aren't always appropriate for a Sprinter's alternator profile. Worth connecting via the VictronConnect app and tuning the input/output voltage settings properly before you trust it. Took me an afternoon of faffing but it's been solid since.

My old solar-only setup (2x 175W Renogy panels through an MPPT) couldn't reliably keep the starter battery topped up through winter — too many overcast weeks in a row. The Orion bridging from the leisure bank has genuinely solved that.

Has anyone else experimented with the absorption/float thresholds on the Orion-TR when the leisure bank is lithium? I'm running Fogstar Drift 100Ah cells and I've had to adjust the output ceiling accordingly.

Curious what configurations others have landed on.

@TransitAdventure — worth noting that the Orion-TR Smart isolated variant behaves quite differently from the non-isolated when used purely for starter battery maintenance. The galvanic isolation means you can legitimately run it bidirectionally in separate systems without ground-loop concerns, which matters if your chassis earth is doing anything unusual.

In my static caravan setup I use a similar DC-DC approach for a secondary battery bank, and the key thing I'd flag is the input voltage threshold settings in VictronConnect — particularly the "start voltage" and "shutdown voltage" parameters. Get these wrong and you'll either never trigger the charger, or you'll be pulling from your leisure bank when it's already marginal.

For a 12→12 application, I'd recommend setting start voltage no lower than 13.0V to ensure the alternator is genuinely running before the Orion kicks in.

@TransitAdventure curious about one thing — when you've got the Orion-TR Smart set to engine-detect mode rather than tying it to ignition, how are you finding the threshold sensitivity in practice?

I've got a static caravan setup where I've been debating using a DC-DC charger to maintain a small starter battery, and the Victron docs suggest the voltage detection can be a bit twitchy depending on what other loads are on the system.

Also — has anyone tried Fogstar cells in the leisure bank with this config? I'm wondering whether the lower internal resistance changes how quickly the Orion decides the alternator is running.

What output voltage are you actually targeting for the starter side — just float, or proper absorption cycles?

@MandyRoss makes a fair point about isolation, but I'd add one thing nobody's mentioned yet — if you're relying on engine-detect mode (@LisaStewart71's question), be aware the Orion-TR Smart uses alternator voltage rise to trigger charging, typically around 13.2V threshold.

In my Transit-based build I had issues with modern smart alternators dropping voltage under load, causing the Orion to cut in and out erratically. Fixed it by switching to ignition-wire trigger via the remote on/off pin instead — far more reliable.

Worth checking in VictronConnect whether your algorithm is set correctly for your starter battery chemistry too. AGM vs flooded makes a meaningful difference to the absorption voltage it'll target.

@VanGill raises something I got caught out by myself — engine detect relies on voltage threshold, which means a chunky leisure bank charging via solar can fool the Orion into thinking the engine's running when it absolutely isn't. Ended up with my starter battery getting topped up by solar through the Orion in a rather convoluted roundabout way, which sounds fine until you realise the DC-DC converter is doing unnecessary work for zero reason.

My fix was switching to the alternator input wire trigger rather than relying purely on voltage detection — cleaner signal, no ambiguity. Victron's own documentation mentions this approach but buries it somewhat.

Worth checking your threshold voltage settings too — default is usually 13.2V, which is conservative enough for most setups but might need nudging depending on your battery chemistry. Fogstar Drift LiFePO4 resting voltage can sit surprisingly high.