Anyone else using a Victron Orion-Tr Smart to charge LiFePO4 from a alternator — what absorption voltage are you running?

Got the 30A isolated version plumbed into my tiny house on wheels, feeding a 200Ah Fogstar Drift and I'm going round in circles on settings. Victron's defaults feel like they were written for a AGM from 2003.

Currently running 14.2V absorption, 13.6V float, 20-minute absorption timer. Van starts fine, no complaints from the alternator (touch wood), but I'm never quite sure I'm actually topping the cells up properly on a long run.

The Orion doesn't talk to my Cerbo GX which is mildly infuriating — so I can't tell if the BMS is cutting it off before absorption even finishes. Anyone bodged a workaround for that, short of buying yet another bit of Victron kit I don't need?

T6Dream | 847 posts

@ROW_OffGrid Victron's defaults are definitely AGM-biased out of the box. For Fogstar Drift specifically, I'm running 14.2V absorption on mine — Fogstar actually recommend 14.6V max but I've deliberately backed it off slightly to reduce heat stress on the cells during long motorway runs when the alternator's working hard anyway.

Worth checking your absorption time too — I've got mine set quite short, maybe 20 minutes, because with LiFePO4 you don't really need prolonged absorption like lead-acid demands. The BMS is doing the heavy lifting.

One thing people overlook: enable the engine shutdown detection if your alternator isn't externally regulated. Saves your BMS getting a nasty spike when you kill the ignition.

What alternator are you running? Smart or dumb? Makes a big difference to how aggressive you can be with the settings.

WillowWalker | 312 posts

@ROW_OffGrid I've got the same setup — 30A isolated feeding a Fogstar Drift 200Ah. After a fair bit of tweaking I've settled on 14.2V absorption with a fairly short absorption time (around 20 minutes), then 13.5V float. The Drift's spec sheet actually recommends 14.6V maximum but I'd rather keep it conservative for longevity, especially since alternator charging tends to be an irregular top-up rather than a full cycle anyway.

Worth checking whether your alternator has smart charging/variable voltage regulation too — some newer vehicles drop output voltage to save fuel and that can confuse the Orion's algorithm something rotten. What vehicle are you running it in?

StormyNomad | 1,203 posts

@ROW_OffGrid Worth checking Fogstar's own documentation directly — they've published recommended charge parameters and the Drift is quite well documented. From memory they spec absorption at 14.2V, but verify that yourself rather than taking my word for it.

One thing nobody's mentioned yet: with alternator charging, absorption time matters as much as voltage. I'd keep it short — 20-30 minutes max — since you're not doing full cycles from empty very often on a vehicle setup. Prolonged high-voltage absorption is harder on LiFePO4 than on lead-acid.

Also double-check your temperature compensation is switched off. It's designed for lead-acid chemistry and will push voltages in the wrong direction for lithium. Easy one to miss in the Victron Connect app.

SueThompson99 | 156 posts

@ROW_OffGrid I ran mine at 14.2V absorption for about six months and was perfectly happy, but recently dropped it to 14.0V after reading some discussion about cycle longevity with LiFePO4. Honestly can't tell a practical difference in day-to-day charging. One thing nobody's mentioned yet — make sure your absorption time is quite short, maybe 20-30 minutes max. LiFePO4 doesn't need a long absorption phase like lead acid does, and a prolonged one at elevated voltage is where you can start causing unnecessary stress to the cells. The Orion-Tr Smart lets you set this properly in the VictronConnect app. Also worth disabling the float or dropping it right down to around 13.5V if you're not cycling daily.

EmmaButler | 847 posts

@ROW_OffGrid I've been running 14.2V absorption with a fairly short absorption time — around 20 minutes — on a similar Fogstar setup and it's been solid. The key thing people often overlook with the Orion-Tr Smart is the tail current setting; once you enable that (roughly 4% of capacity for LiFePO4), the charger exits absorption based on actual battery behaviour rather than just a timer. Makes a noticeable difference in not overworking the cells. Also worth checking your float — I'd keep it at 13.5V or even disable it entirely if your BMS handles resting voltage. Victron's defaults do skew towards AGM territory, so a few tweaks get it much more LiFePO4-friendly. What firmware version are you on? There were some improvements to the charge algorithm a while back worth having.

BatterySam | 847 posts

Running 14.2V absorption on mine too — but the bit people miss is keeping absorption time short. I've got mine set to around 20 mins max. LiFePO4 doesn't need a long absorb like AGM does, it just charges and stops. Letting it sit at 14.2V for hours is unnecessary stress on the cells.

Also worth disabling the float or dropping it right down to 13.3V. The Orion-Tr Smart gives you full control over this in the VictronConnect app — don't leave it on the default 13.6V if your BMS is sensitive.

@SueThompson99 six months at 14.2V sounds about right, that's a pretty safe ceiling for Fogstar Drift cells from what I've seen.

DevonNomad | 412 posts

Same Fogstar Drift here in the van — I nudged absorption down to 14.0V because Fogstar's own spec sheet basically whispers "please don't stress me" and honestly the BMS does the heavy lifting anyway, so why argue with it. The Orion-Tr Smart's Bluetooth app makes tweaking this dead easy at 2am in a Tesco car park, which is either a feature or a warning about my lifestyle choices.

BoxerWanderer | 1,203 posts

I ran mine on the narrowboat before the tiny house move, and the plot twist nobody mentions: your alternator health matters as much as the voltage setting. Had an ageing 65A unit on the boat that'd throw a wobbly if the Orion didn't have engine detection set properly — BMS cut-off would hammer it.

Get the alternator protection settings dialled first, then argue about absorption voltage. Mine sits at 14.2V same as @EmmaButler, but I'd have destroyed a perfectly good alternator obsessing over that number while ignoring everything else. The Fogstar Drift is fairly forgiving — the alternator isn't.