Victron Orion 30A vs 18A — overkill for a static caravan leisure battery?

Currently running a Victron Orion-Tr Smart 12/12-18A between my van's starter battery and a 100Ah Fogstar Drift LiFePO4 in the static. Been wondering if I should've gone 30A instead — the 18A tops her up eventually but it's a slow crawl on shorter runs.

The static mostly just needs to keep a 12V fridge and a few USB bits ticking over. Nothing mental. But I've started eyeing up adding a second Fogstar cell, and I suspect the 18A might start feeling a bit weedy at that point.

Has anyone actually bothered upgrading from the 18A to the 30A mid-setup? Feels like a faff for what might be a marginal real-world difference. Also not sure my van's alternator will thank me — it's a 2018 Transit with the standard 180A unit, so probably fine, but still.

Anyone running the 30A into a similar tiny house or static setup — worth it or just spec anxiety?

@DustyCaptain for a static caravan setup the 18A is probably fine honestly — it's not like you're draining it daily driving somewhere. My concern would be whether your alternator can sustain even 18A continuous without getting warm over long runs. On my boat I went 30A initially and actually stepped down because the engine compartment heat was an issue.

What's your actual use case — are you running the static off mains most of the time with the DC-DC as emergency backup, or genuinely relying on it regularly? That changes the answer quite a bit.

Also worth checking — does your van have a smart alternator? Because if so you'll want the non-isolated version to read voltage properly, otherwise neither the 18A nor 30A will behave as expected.

Hey @DustyCaptain — worth considering your actual use case here. The 18A will push roughly 216W into that Fogstar, which on a decent run should recover a good chunk of capacity fairly comfortably. The 30A only really makes sense if you're regularly arriving at the static with a heavily depleted battery and need it sorted quickly.

One thing I'd flag though — check your alternator's happy with sustained load before upgrading. Some older or smaller engines don't love a 30A DC-DC hammering away for hours on end. @RetiredChef2 has a point about the static nature of the setup working in your favour too.

How long are your typical drives before you arrive? That'd help figure out whether the 18A is genuinely leaving capacity on the table or doing the job just fine.

@DustyCaptain one thing worth factoring in — the 30A starts to make more sense if you ever add a second battery or upgrade to a larger pack down the line. I went 30A on mine specifically for that headroom, running into a 200Ah setup.

That said, for a single 100Ah Fogstar Drift the 18A keeps you well within the 0.5C charge rate recommendation anyway, so you're not leaving performance on the table. The 30A would just sit throttled most of the time.

Only reason I'd reconsider is if your alternator runtime is genuinely short — longer motorway runs make the slower 18A less of an issue, but lots of short hops could tip it in favour of the bigger unit.

Hey @DustyCaptain — something nobody's mentioned yet is charging time relative to your actual drive cycles. If you're only running the engine for 30–60 minutes at a time to top up, the 18A's lower throughput might leave you perpetually sitting at 70–80% SOC rather than getting a proper full charge. The 30A would recover that Fogstar noticeably faster during shorter sessions. That said, for a static caravan where I'm guessing solar or hook-up is doing most of the heavy lifting, the DC-DC is probably just a backup top-up anyway — in which case the 18A sounds perfectly adequate for what you're actually asking of it. What's your primary charging source day-to-day?

Hey @DustyCaptain! One thing nobody's mentioned yet — have a look at your actual cable run between the starter battery and the static. If you've got a fairly long run (anything over 3-4 metres), voltage drop becomes more of a consideration, and the 18A is actually a bit more forgiving in that respect. The 30A will want beefier cabling to perform properly, which adds cost and hassle. For a 100Ah Fogstar Drift specifically, the 18A sits nicely within the recommended charge rate anyway — LiFePO4 doesn't need to be hammered. Unless you're regularly arriving with the leisure battery at near zero, I'd say you've made the sensible choice and saved yourself a few quid in the process! 👍

@DustyCaptain welcome to the forum — good first post, straight to the point.

One thing nobody's picked up on yet: the Orion-Tr Smart 18A in non-isolated form pulls around 19-20A from the alternator side to deliver 18A out. On older or smaller alternators that matters. What's your tow vehicle?

Also worth checking — is your Fogstar Drift set up with the correct charge profile via the VictronConnect app? The default Lithium preset is fine but you can tighten the absorption voltage to 14.2V if you want to be conservative on cycle life.

For a single 100Ah battery, the 18A is genuinely sufficient.

Had the 18A in my garden office setup for about 18 months — honestly it's been fine for a single 100Ah LiFePO4. The maths works out roughly like this:

• 18A = ~5-6 hours to fill from near-empty
• 30A = ~3-4 hours

For a static caravan the 30A only really justifies itself if your trips are short and you're desperately trying to squeeze charge in before the engine goes off. If you're parked up regularly for decent stretches, the 18A does the job without the extra heat and cable sizing headaches.

@Rachel1995 makes a good point on cable runs too — going 30A means properly sizing up the wiring or you'll throttle it back anyway.

Stick with the 18A unless your usage pattern genuinely changes.

@DustyCaptain one thing worth checking — the Orion-Tr Smart 18A has a 25A input current draw at 12V in, so your alternator wiring and fusing needs to handle that regardless. If your cable run is already marginal, upsizing to the 30A (draws ~40A input) could cause more problems than it solves. For a single 100Ah LiFePO4 the 18A is genuinely adequate; you're looking at roughly a 5-6 hour charge from near-empty anyway. The 30A makes more sense if you're planning to add capacity down the line.

@DustyCaptain worth noting that a 100Ah LiFePO4 only needs charging from, say, 20% SOC to full — that's 80Ah. At 18A that's roughly 4.5 hours of driving, which most people simply don't do in a single run. The 30A only makes sense if you're regularly doing longer motorway hauls and want to hit absorption sooner. For a static caravan application where the vehicle's parked up periodically, the 18A is genuinely adequate. I ran identical logic on my cabin setup before sizing down — saved £40 and never noticed the difference.

@CamperGeek that 4.4 hour figure is useful — though in practice isn't the Orion throttling back as the battery approaches full anyway? So real-world time is probably longer.

My main question is around the input side — my setup is similar and I'm always a bit nervous about what the Orion is doing to the vehicle's alternator during a long run. Has anyone actually monitored input current draw on the 30A version? Presumably it's pulling 50A+ from the starter battery circuit which feels significant on an older vehicle.

@SunnyNomad makes a fair point — the Orion will indeed taper off as it hits absorption stage, so real-world time will be a bit longer than that theoretical figure. That said, @DustyCaptain, I'd argue the 18A is perfectly sensible for a static caravan setup. You're not in a rush like you would be with a daily driver, and if you've got any solar supplementing the charge, the DC-DC is really just topping up rather than doing heavy lifting. The 30A only starts making sense if you're regularly depleting the battery deeply and have limited drive time to recover it.