Orion-Tr Smart 30A keeping my shepherd's hut battery topped up from the van — worth it?

So here's the situation. The shepherd's hut sits at the far end of the field, solar is doing its thing but we've had a grim few weeks of cloud cover and the Fogstar 200Ah lithium is sitting at around 40% most mornings. Meanwhile the Vivaro is parked up most days doing nothing, alternator just ticking over. Felt like a waste not to connect the two.

I've been looking hard at the Victron Orion-Tr Smart 30A isolated DC-DC charger. At around £180 it's not cheap, but the isolation matters here because the van and the hut are on completely separate earths. The plan would be a decent run of cable — probably 10–12 metres — out to a weatherproof connector on the hut wall, and just plug in for an hour or two whenever the van's parked up and the sun's been lazy.

The bit I'm unsure about is the cable sizing over that distance. At 30A I'm thinking 6mm² minimum, but some folk are saying 10mm² for a run that long to keep voltage drop sensible. The Orion does have compensation built in to a degree, but I'd rather do it properly first time.

Has anyone actually done a van-to-outbuilding DC-DC run like this? What cable spec did you land on, and did the Orion's Bluetooth app give you any grief pairing it up on initial config?

FinnRobinson | 847 posts

@VivaroBuild Sounds like a solid setup in principle. The Orion-Tr Smart 30A is genuinely one of the better bits of kit for exactly this situation — isolated output means you're not creating odd charging loops between two separate battery banks, which matters when one's in a vehicle and one's in a structure with its own solar.

Worth checking your cable run from van to hut though. If you're trailing any decent length of cable across the field, voltage drop will eat into your effective charge current noticeably. I'd be looking at 16mm² minimum for runs over about 8 metres.

Also, are you starting the van specifically to charge, or just connecting when it's already running? The Orion will work either way but your alternator will thank you for the latter.

QIH_Electric | 1,203 posts

@VivaroBuild The isolation side is what catches people out here — make sure you're running the isolated version of the Orion-Tr Smart, not the non-isolated. Connecting two separate battery banks (van vs hut) without galvanic isolation is asking for ground loop grief, especially with any length of cable run across a field.

On the 30A rating: at 12V that's roughly 360W continuous, so realistically you're looking at 2–3 hours of alternator run time to meaningfully recover a depleted 200Ah Fogstar. Worth factoring that into your van usage patterns.

One thing I'd add — configure the engine-running detection threshold carefully in the Victron Connect app. Default settings can sometimes trigger charging off a high resting voltage rather than true alternator output, which will quietly drain your van starter battery.

AlexPalmer60 | 214 posts

Running something similar for my garden office — different application but same principle of using the van as a backup source when solar's struggling.

One thing worth mentioning that I don't see covered above: cable run length matters a lot here. If you're stretching any distance across that field, even temporary runs, voltage drop will eat into your efficiency before the Orion even gets a look in. Size up your cable accordingly or you'll wonder why charge rates are disappointing.

Also worth checking whether your Fogstar BMS plays nicely with the Orion's charge profile — most do, but it's worth connecting via Bluetooth and watching the first few cycles to confirm it's actually hitting absorption properly rather than just floating prematurely.

KellyRobinson | 63 posts

Curious about the cable run between the van and the hut — what length are you dealing with? I've been eyeing up the same unit for my narrowboat-to-tiny-house situation and the voltage drop over a longer run is what's making me hesitate.

Also, @QIH_Electric raises a good point on isolation — is your shepherd's hut on a completely separate earth to the van? That's what's been tying me in knots trying to figure out my own setup.

One thing worth checking: does the Orion-Tr Smart 30A actually play nicely with Fogstar's BMS over Bluetooth, or are you just relying on the battery voltage profile? I can't find a straight answer on this anywhere.