Anyone else using a DC-DC charger to top up a leisure battery from a tiny house vehicle hookup?

Running a small off-grid tiny house and trying to work out the best way to charge my 100Ah lithium (Fogstar Drift) from the van's alternator when I'm moving the structure. Currently looking at the Victron Orion-Tr Smart 12/12-30A — seems like the obvious choice but £150+ feels steep when I'm only doing this occasionally.

The main thing I'm unsure about is whether the 30A version is overkill for short journeys. If I'm only moving the tiny house 20-30 miles every few weeks, will it even make a meaningful difference to state of charge? The battery is usually sat at around 60-70% when I unhook from solar.

Has anyone sized this differently or gone for a cheaper alternative like the Renogy DC-DC units? Wondering if the Victron Bluetooth monitoring justifies the price premium in this kind of occasional-use scenario.

Hey @Gibbo53, great setup! I've been doing something similar with a Victron Orion-Tr Smart 12/12-30A and honestly it's been brilliant. The 30A output is plenty for a 100Ah LiFePO4 and the Bluetooth monitoring via the app is really handy.

One thing worth bearing in mind with the Fogstar Drift specifically - make sure you've got the absorption voltage set correctly as some of the Drift cells can be fussy. Victron's app makes tweaking that dead easy though.

Also worth considering whether you want the isolated or non-isolated version depending on your earth bonding setup in the tiny house. If your vehicle chassis and house negative are already connected, non-isolated saves a few quid. If not, go isolated to avoid any nasty ground loops.

What alternator size are you working with? That'll help narrow things down further.

Dave1986 | 847 posts

@Gibbo53 sounds like a solid setup! Just to flag - with a Fogstar Drift you'll definitely want a proper DC-DC charger rather than a direct connection, as the lithium's flat discharge curve can confuse older alternators and potentially damage them.

I'm running a Victron Orion-Tr Smart 12/12-30A isolated in my setup and it's been brilliant - the isolated version is worth the extra few quid if your van chassis and tiny house aren't sharing a common earth, which they likely won't be if it's towed separately.

One thing to check is your cable run length between the van battery and the charger - voltage drop can be a real issue if you're routing through a trailer connector. Uprate your cable accordingly and stick a decent inline fuse close to the source. What amperage were you looking at?

Worth adding — if the van's doing double duty as a tow vehicle and your primary charge source, pay attention to what alternator you're actually dealing with. Newer Euro 6 vans (Transit, Sprinter etc.) run smart alternators with variable voltage, which plays havoc with conventional DC-DC setups. The Orion-Tr Smart handles this fine, but worth confirming before you buy.

Also consider your cable run length between the van's battery and the tiny house connection point. Long runs mean voltage drop, and the Orion needs a decent input voltage to perform properly. I'd size the cable generously — 10mm² minimum for anything over 3-4 metres in my experience.

GeorgeHarris | 312 posts

@Gibbo53 one thing worth considering that hasn't been mentioned — check your van's alternator rating before settling on a charger amperage. Older or smaller vans (Transit Connects, older Sprinters etc.) can have fairly modest alternators, and if you're already running cab electrics, lighting, possibly a fridge, you don't want to hammer it with a 30A draw on top.

I ran a 20A Orion on my previous setup rather than the 30A purely because my alternator was only 90A rated. Worked a treat and the Fogstar Drift was comfortably topped up after a couple of hours on the road. Sometimes the sensible middle option beats going straight for maximum output.

Also worth double-checking the cable run length between van battery and charger input — voltage drop can really affect efficiency if it's a long route.