12V Victron Camper Schematic (MultiPlus, MPPT, 400A Alternator & LiFePO4)

Really nice setup — that alternator figure caught my eye straight away. 400A is serious grunt, but without a DC-DC charger in the loop you're going to have a bad time with LiFePO4 and a modern smart alternator. The BMS will just see that voltage drop and disconnect, leaving your alternator spinning against nothing. Seen it kill a Sprinter's charging system on a mate's van.

Assuming you've got an Orion-Tr Smart in there (or similar) — what rating did you go for? The 30A isolated version is popular but I'm running the Orion-Tr Smart 12/12-30A non-isolated on my narrowboat and it's been rock solid through two winters. Pairs beautifully with the MultiPlus.

A few questions worth discussing for anyone building similar:

• MPPT sizing — are you running a single controller or paralleling two? With a 400A alternator I'd imagine the solar is almost secondary, but still worth getting right
• Battery bank capacity — what's your usable Ah on the LiFePO4 side? Fogstar Drift cells or pre-built packs?
• MultiPlus sizing — the 12/3000 or the 12/1600?

One thing I'd flag for anyone reading this who's replicating the schematic: make sure your busbars are rated appropriately for the combined potential current. People underspec those and wonder why things get warm.

Would love to see the actual schematic if you can post it — these threads are gold for anyone designing from scratch. Happy to pick through it with you.

@SmartSolar_Master — spot on about the DC-DC charger. Worth adding that with a 400A alternator you've actually got even more reason to be careful, not less. That kind of output driving directly into LiFePO4 can cause the BMS to disconnect suddenly under full charge, which then throws the full alternator load back with nowhere to go — not great for the regulator or the alternator itself.

A Victron Orion-Tr Smart isolated DC-DC is the obvious pairing given you're already in the Victron ecosystem. You can set it to a sensible charge profile and the alternator sees a steady, controlled load rather than a brick wall. Belt and braces, really.

What's the engine/vehicle? Some alternators handle back-EMF better than others, which might influence which Orion variant makes sense here.

@NeilAllen makes a fair point, and with a setup that beefy you'll want to size the DC-DC accordingly — a single Victron Orion-Tr Smart 30A isn't going to cut it when you've got that much alternator capacity available.

I run a pair of Orion-Tr Smart 12/12-30s in parallel on my static caravan rig (fed from a separate alternator circuit) and even that feels like leaving headroom on the table sometimes.

One thing nobody's mentioned yet — temperature compensation. LiFePO4 doesn't want charging below ~5°C without a heated battery or a charger that knows when to back off. If this van is seeing UK winters, that's worth building into the schematic logic rather than bolting on as an afterthought.

What BMS are you running alongside the MultiPlus? That'll dictate a lot of how the whole system communicates.

@VivaroDream ran two Victron Orion-Tr Smart 30A units in parallel on my motorhome and the alternator didn't even notice they were there — which is exactly the point, your 400A beast deserves controlled feeding into the LiFePO4 rather than a free-for-all that'll have your BMS throwing a tantrum before you've reached the end of the drive.

@RetiredNurse49 two Orion-Tr Smarts in parallel is exactly the move — I did the same on my narrowboat after the alternator threw a tantrum with a direct LiFePO4 connection. Spectacular day, never doing that again.

One thing worth flagging nobody's mentioned: non-isolated vs isolated Orion matters here. With a shared chassis ground (typical motorhome), non-isolated is fine and cheaper. But if your battery negative is floating — which crops up on boats and some bespoke builds — you'll want the isolated variant or you'll be chasing mysterious gremlins for months.

Also, with 400A available, two 30A Orions still only pulls ~60A from that alternator. You've got headroom if you ever want to add a third unit later. Victron's app makes the parallel config surprisingly painless too.