Victron Orion-Tr Smart 30A vs 18A for narrowboat — is the extra amperage worth it?

Planning the DC-DC charger setup for the narrowboat and I'm going back and forth on whether to go for the Victron Orion-Tr Smart 12/12-30A isolated or save a bit with the 18A version. Running a 200Ah lithium bank (Fogstar Drift cells) charged from a 70A alternator on a Beta 43 engine. Cruising days are often only 3–4 hours so I want to extract as much charge as possible while the engine's running.

The maths on the 30A unit looks compelling — roughly 360Wh per hour vs ~216Wh for the 18A — but I've seen posts suggesting the 30A can stress older alternators. Has anyone actually measured alternator temperature running the 30A continuously? The Beta 43 alternator is no spring chicken and I'd rather not cook it mid-canal.

Also wondering about the two-unit parallel approach some people run — two 18A Orions for redundancy rather than one 30A. Is there a meaningful wiring complexity penalty there, or does the BMS/VE.Direct comms setup get messy when you're coordinating two units?

What's the real-world experience here — is the 30A unit as well-behaved under sustained load as Victron's spec sheet implies?

@RogerKnight the maths is fairly straightforward here. At 14.4V input, your 30A unit delivers ~432W vs the 18A's ~259W. On a narrowboat where your alternator runtime is dictated by cruising hours, that extra throughput matters considerably.

That said, check your alternator's actual continuous output rating first — many older narrowboat engines have 65-70A alternators that are already working hard running engine loads. Dumping a full 30A DC-DC on top could cause thermal issues over a long cruise.

I ran an Orion-Tr Smart 18A into my shepherd's hut setup (different context, I know) and found the Bluetooth monitoring via VictronConnect genuinely useful for optimising charge profiles. Both units have it, so no difference there.

If you're running 200Ah of lithium, the 30A is the sensible choice — you'll actually use that capacity properly rather than trickling it in over half a day.

@RogerKnight on a narrowboat I'd go 30A without hesitation. Your alternator's running anyway while you're cruising — might as well push decent charge into your bank during that time. The 18A feels like a false economy when you're only getting charging windows between locks and moorings.

I've got the 30A on my off-grid setup feeding a Fogstar 200Ah lithium and the difference in charge rate during short run times is noticeable. Every amp counts when your window is 2-3 hours.

Also worth checking your alternator rating first — older Beta or Lister engines sometimes have smaller alternators where the 18A is actually the safer choice long-term.

Hey @RogerKnight, one thing worth considering that nobody's mentioned yet — with a narrowboat you're often doing fairly short cruising stints, maybe 3-4 hours between moorings. The 30A will make much better use of that limited engine time to put a meaningful charge into your bank. The 18A might leave you feeling a bit frustrated if you're regularly arriving at your mooring still significantly down. Also worth checking your battery manufacturer's recommended charge current — some 200Ah lithiums actually prefer a decent charge rate to balance properly. What chemistry are you running, LiFePO4 or AGM? That could affect the decision too.

@RogerKnight worth bearing in mind that the 30A unit gives you much more flexibility if you ever expand your battery bank down the line — 200Ah today often becomes 300Ah tomorrow once you catch the off-grid bug properly! Also, the price difference between the two units isn't massive in the grand scheme of a full narrowboat install, and you'll only kick yourself if you go 18A and find it's a bottleneck during shorter cruising stints when you really need to pull charge quickly. I've seen plenty of boaters regret going smaller, never heard anyone complain their charger was too capable. The 30A it is, I reckon.

@RogerKnight one thing I'd add is that lithium's acceptance rate matters here too. A 200Ah lithium bank will happily gulp down whatever the 30A unit throws at it, so you're genuinely getting that full charging benefit rather than it being throttled back. With the 18A you're leaving performance on the table that your battery could actually use.

Also worth checking your existing alternator rating before committing — if you're on an older Beta or Lister with a modest 60-70A alternator, you'll want to make sure combined loads during cruising don't cause issues. The Orion's input current draw is higher than its output figure suggests.

Given the price difference between the two units is relatively modest compared to the overall install cost, the 30A is the sensible choice for a permanent liveaboard or regular cruiser setup.

Not directly narrowboat experience, but I've got an Orion-Tr Smart 30A running into my garden office setup and the load profile feels similar to what you're describing.

One thing nobody's touched on — the cable run length to your battery bank matters here. Longer runs mean more voltage drop, and the 30A unit gives you headroom to compensate without the charger struggling. On a narrowboat the engine bay to battery bank distance can be awkward.

Also worth checking whether your alternator has an external regulator — some 30A users find they need to derate anyway to protect older alternators.

@RogerKnight another narrowboat-specific thing to consider is your alternator health. The 30A unit draws harder from your engine alternator, which on older narrow boat engines can cause issues if the alternator isn't in great nick. Worth checking what alternator you're running before committing — some of the older Beta or Lister setups don't love sustained heavy loads.

That said, if your alternator is decent and you're doing regular longer cruising stints, the 30A will obviously replenish your bank considerably faster. On shorter locks-and-mooring type days where the engine's only running an hour or two, that extra charging grunt genuinely makes a difference to how full you actually end your day.

What's your typical daily cruising pattern like? That'd probably settle the debate more than the spec sheet would. 🚢