Help Litio system RV

Anyone else running lithium on a newer Sprinter-based motorhome with a smart alternator? Curious what solutions people have landed on.

Had similar headaches on my static van setup — obviously no smart alternator issue there — but I've helped a mate sort his Hymer on a Euro 6 Sprinter and it was a proper pain. The smart alternator basically throttles charge voltage all over the place, so your lithium bank thinks something's wrong half the time.

The fix we went with was a Victron Orion-Tr Smart DC-DC charger isolated version. Sits between the alternator and the lithium bank, regulates everything properly. Works a treat. Fogstar drift cells behind it, Victron BMV-712 keeping an eye on state of charge.

Few things worth checking if you're in this situation:

• Don't just wire lithium direct to a smart alternator output — you'll likely confuse the BMS and possibly cook something
• DC-DC isolating charger is almost always the answer on modern Euro 6/Euro 7 base vehicles
• Size the charger properly — a 30A unit sounds fine until you realise you're barely tickling a 200Ah bank

What size battery bank are you running? And are you on 12V or 24V? Makes a difference to which Orion you'd want.

Also worth knowing if the Carthago already has any factory leisure battery management — some of the fancier continental vans have their own systems that can complicate things further.

Not an expert on Carthago specifically but the underlying Sprinter issue is pretty universal these days. Others on here will have done this exact job, sure someone'll chime in.

@ZFS_OffGrid smart alternators are a right pain — variable voltage output confuses standard B2B chargers something rotten.

On my boat I ended up going with a Victron Orion-Tr Smart DC-DC charger, isolated version. Takes whatever nonsense the alternator throws at it and outputs a proper lithium charge profile. Non-negotiable in my view.

Worth noting the Sprinter's ECU can also throttle alternator output based on engine load and battery state readings — so even if you bodge around the voltage issue, you might still get pathetic charge current. The Orion handles this gracefully because it's drawing a controlled load rather than just lumping everything across the system.

What battery chemistry are you running? Some of the cheaper LiFePO4 packs (Fogstar Drift etc.) have BMS comms that can integrate properly with Victron kit via Cerbo GX, which helps enormously.

@ZFS_OffGrid Victron Orion-Tr Smart DC-DC is the weapon of choice here — it doesn't care what the alternator's doing because it actively regulates its own input, so your lithium bank gets a proper absorption charge rather than whatever voltage the ECU fancies sending today.

Worth noting the isolated version is essential on modern Sprinters where chassis and habitation grounds aren't truly common — learned that one the hard way when my Fogstar cells started behaving mysteriously.

Size it properly too: a 30A unit sounds generous until you realise you're only getting ~360W and your 200Ah bank is laughing at you after a cloudy week.

@OldSailor beat me to the Orion-Tr but I'll add — don't cheap out and grab a dodgy Amazon unit thinking it's the same thing, learned that one the hard way in my van before the Victron arrived and saved the day 🔥

Great points all round. One thing worth adding — on newer Sprinters specifically, make sure you're going into the leisure battery side of the vehicle's split charge relay, not directly off the starter battery terminals. Some folks wire straight to the starter and wonder why they're getting weird readings or the van's BCM starts throwing faults.

Also worth checking your Orion-Tr sizing carefully — the 30A unit is popular but if you're running a decent lithium bank you might find the 12/12-30 feels a bit underwhelming on longer runs. The 18A models suit smaller setups fine though.

@ZFS_OffGrid what size bank are you working with? That'll help narrow down the right spec. And are you planning any solar alongside it, or purely alternator charging? Makes a difference to how you'd configure the charge profile.