Anyone else running a Victron Orion-Tr Smart in absorption without a proper alternator health check first?

Pulled a classic "just plug it in and see" move in the motorhome last week — Orion-Tr Smart 30A, leisure bank is 200Ah Fogstar Drift LiFePO4, and the alternator is a bog-standard 90A unit on a 2006 Fiat Ducato. Worked fine for about 40 minutes then the Ducato started running rough as a badger's backside.

Turns out the Orion was happily pulling a sustained 30A with zero engine load sensing configured, so the alternator was cooking itself trying to keep up alongside the cab electrics. Switched on the engine load assist delay in the Victron Connect app and dropped the charge current to 20A — night and day difference, no more unhappy Ducato noises.

Anyone found a sensible rule of thumb for sizing DC-DC charge current against alternator output on older vans? Seen some folk say 25% of rated alternator amps maximum, which would put me at ~22A on a 90A unit — seems roughly right based on my accidental experiment.

@PanelRob this is a genuinely risky setup that deserves proper scrutiny before you proceed.

A 90A alternator under sustained DC-DC load on a 2006 engine is asking for trouble — those older units weren't designed for continuous near-maximum draw. The Orion at 30A is pulling roughly 35-40A from the starter side once you account for efficiency losses.

Run the alternator for 20-30 minutes under load and check housing temperature with an IR thermometer. Anything above 90°C and you're shortening its life considerably.

I've got a similar arrangement on my boat — 95A Iskra alternator feeding a Victron Orion-Tr Smart 12/12-18A — and I deliberately undersized the DC-DC specifically to protect the alternator. Worth considering whether dropping to the 18A model buys you longevity.

Also check your alternator's duty cycle rating if you can find the datasheet.

@PanelRob worth checking what your alternator is actually outputting at idle and cruise before you commit to absorption mode on the Orion. The Fogstar Drift will happily accept as much as you throw at it, which is exactly the problem — the alternator becomes the weak point, not the battery.

One thing @DougPearce probably touched on is that older 2006 alternators often have tired diodes and worn brushes, so rated 90A on paper might be delivering considerably less in practice. Grab a clamp meter on the B+ cable while running accessories and see what you're actually working with before you stress it further.

I'd also check whether you've got engine load compensation enabled in the Victron Connect app — the input current limit setting is your friend here. Start conservative, maybe 20A input, and work up gradually while monitoring alternator temperature.

@PanelRob I had a similar worry when I was setting up DC-DC charging on my narrowboat — older alternator, new LiFePO4 bank, and no idea how stressed the alternator actually was under load.

What made the difference for me was fitting a clamp meter on the alternator output wire and logging the current at different RPMs over a proper run. Gave me actual numbers rather than guessing from the nameplate rating.

Have you checked whether your 2006 engine has any thermal protection on the alternator itself? Some older units just cook quietly rather than tripping anything obvious. The Orion-Tr Smart is brilliant for protecting the battery side, but it can't see what's happening upstream on the alternator.

Worth doing that health check before running sustained absorption — a replacement alternator will cost considerably more than half an hour with a multimeter.

@PanelRob one thing nobody's mentioned yet — the Orion-Tr Smart's input current limit is your friend here. Drop it to 50-60% initially and monitor your alternator casing temperature with a cheap IR thermometer during a proper run. My 2.1-litre setup was pulling the alternator into thermal shutdown before I'd even hit absorption phase on the leisure bank.

Also worth enabling the engine shutdown detection feature properly — if your alternator voltage dips below threshold when you kill the engine, you want that Orion isolating cleanly rather than back-feeding.

The absorption concern is valid but the transition into absorption is often where the real stress occurs — bulk current is still near-maximum whilst the alternator is already warm from motorway running.

@PanelRob ran something similar on my static — older alternator feeding a Fogstar bank via the Orion-Tr Smart. The thing that saved me was enabling the engine shutdown detection properly in VictronConnect before I ever let it hit absorption.

Worth checking your alternator's actual duty cycle rating too — a 90A unit doesn't mean 90A continuous. Most aren't rated for that sustained load, especially on older vehicles.

One thing nobody's mentioned yet: watch your battery temp during charging. LiFePO4 handles heat differently and if your Fogstar doesn't have a proper BMS temp sensor feeding back to the Orion, you're flying blind.

The Orion-Tr Smart's adaptive algorithm is decent but it's not a miracle worker — garbage in, garbage out really.

@SprinterProject makes a good point about the input current limit — that's probably your best first line of defence here. One thing I'd add though: keep an eye on your alternator casing temperature during longer runs. A cheap infrared thermometer does the job nicely. On a 90A unit that's already a few years old, you want to catch any thermal stress early rather than waiting for symptoms. I'd also check your alternator belt tension while you're at it — increased DC-DC load can expose slack you'd never have noticed before. If the belt's original to the vehicle I'd just replace it as a precaution, honestly. Not expensive and saves a potentially horrible roadside situation. What engine is it — Fiat Ducato by any chance? If so there's loads of documented experience with those alternators in the van conversion community worth digging into.

Good shout from @SprinterProject and @Liam1998 on the input limit — worth also keeping an eye on alternator temperature if you can. A cheap CHT sensor cable-tied near the alternator body will tell you a lot more than guessing. Older units on pre-Euro 5 engines often run hotter than you'd expect anyway, and once you add sustained DC-DC load it can creep up surprisingly quickly. If you notice the alternator casing getting uncomfortably hot to touch after a run, that's your cue to dial back further regardless of what the settings say.

Good points all round. One thing I'd add — don't overlook the age and condition of your drive belt while you're at it. A tired belt slipping under sustained high load from the alternator is a sneaky failure mode that often gets ignored until it's too late. @PanelRob, if that 2006 unit hasn't had the belt inspected recently, worth a quick visual check before you commit to longer charging runs. Glazing and minor cracking are easy to miss but can cause real grief. Cheap insurance before trusting the whole setup.

Worth adding that the alternator's age matters as much as its rating here. A 90A unit on a 2006 vehicle likely has worn brushes and degraded output — you might only be seeing 60-70A effective capacity under load. I ran diagnostics on a similar-vintage alternator feeding my shepherd's hut build's charging circuit and actual measured output was well below nameplate.

Before trusting the Orion's input limit setting alone, I'd log actual alternator voltage under sustained charge load using a Victron SmartShunt or even a basic clamp meter on the alternator output wire. Voltage sag below ~13.2V under load is your early warning that something's struggling upstream of the Orion.

Really good point from @AndyGraham there — age and condition are often overlooked. One thing I'd add is that the Orion-Tr Smart's engine running detection via the input voltage threshold is worth fine-tuning in the app if you haven't already. The default threshold can sometimes kick the charger in before the alternator has properly stabilised after startup, which puts unnecessary strain on an older unit right when it's already working hardest. Give it a slightly higher trigger voltage and you'll get a gentler relationship between the two.

Jumping in to echo what @LochStu and @AndyGraham have said — and @PanelRob, the thing that catches people out with LiFePO4 specifically is how flat the charge acceptance curve is. A flooded or AGM bank will naturally taper the current draw as voltage rises, giving your alternator a bit of a breather. Lithium just keeps pulling hard right through bulk. Your Orion's input current limit setting is your friend here — definitely worth dialling it back to something like 20A initially and monitoring alternator temperature over a decent run before pushing it harder.