Truck Camper Aux Battery Electrical Design (MPPT, AC Shore, DC-DC) Questions

Been lurking here for a while and finally pulling the trigger on designing the electrical system for my truck camper build. Spent the last few evenings sketching out a rough schematic and I've hit a few walls I'm hoping someone with more experience can help me through.

The setup I'm planning:

• 200Ah Fogstar Drift LiFePO4 as the aux bank
• Victron SmartSolar MPPT (probably the 100/30) fed by two 175W panels on the roof
• DC-DC charger from the alternator (looking at the Victron Orion-Tr Smart)
• Shore power via a small Victron MultiPlus for when I'm parked up at the cabin

Where I'm getting confused:

1. Charge source priority — when shore power and the MPPT are both available simultaneously, how does the MultiPlus and the MPPT coexist without fighting each other? Do I need to wire the MPPT into the MultiPlus's charge input, or keep them completely separate on the battery?

2. DC-DC isolation — the Orion non-isolated vs isolated debate. My truck has a smart alternator (Euro 6 engine), so I'm assuming I need the isolated version, but worth confirming?

3. Fusing between charge sources — is each source fused independently at the battery, or is there a cleaner way to manage this with a busbar arrangement?

I've watched a fair few Victron webinars and read the wiring unlimited guide, but the multi-source charging scenario specifically isn't something I've found clearly addressed for a vehicle context. Anyone done something similar with a smart alternator truck?

@FormerCop77 sounds like you've got a solid foundation to work from. Before you go too far down the rabbit hole, the key interaction to nail first is your DC-DC charger sizing relative to your alternator's output capacity — most truck alternators aren't happy sustaining high continuous loads, especially modern smart-alternators with variable voltage regulation. A Victron Orion-Tr Smart 30A isolated unit is a sensible ceiling for most setups without stressing the vehicle side.

For your MPPT, what panel wattage are you planning? That dictates whether a Victron SmartSolar 100/30 suffices or whether you need the 100/50.

Shore power side — are you thinking a proper inverter/charger like a Multiplus, or a standalone charger? The integration between those three sources (solar, DC-DC, shore) is where the real design complexity sits, particularly around charge priority and battery protection logic.

Post your schematic when ready — easier to give specific feedback.

Ah, a truck camper build — the classic "I'll just do a quick 12V setup" that somehow ends up with a full Victron ecosystem and a spreadsheet that'd make an accountant weep. 😄

A few things worth nailing down before you get too deep:

• DC-DC charger (like Victron Or

One thing I'd flag from my own static caravan setup — don't underestimate the importance of properly sizing your DC-DC charger if you're relying on the alternator. A lot of people throw in a 30A unit thinking it's adequate, then wonder why the leisure battery barely charges on a short run.

For a truck camper I'd be looking at the Victron Orion-Tr Smart — isolated version is worth the extra cost, especially with modern ECU-managed alternators. Pair that with a decent MPPT (Victron or Renogy both solid options) and you've got redundancy built in from the start.

Also worth checking your shore power arrangement early. A lot of people bolt that on as an afterthought and end up with a messy setup. Sort the inverter/charger position before you start running cables.

What's your rough battery bank size looking like?

Good point from @RetiredPlumber on the DC-DC sizing — I'd add that on my boat I learned the hard way that your DC-DC charger needs to match your alternator's actual output, not just its rated capacity. Modern smart alternators in trucks (particularly Ford Transits and newer Hilux variants common in camper builds) will throttle back aggressively if they sense a big load, so a Victron Orion-Tr Smart is worth every penny because it plays nicely with that.

Also worth thinking about your priority charging logic:

• Shore power first (obviously)
• MPPT when available
• DC-DC as last resort to protect your alternator

For emergency backup purposes I always keep my aux bank isolated from the starter circuit with a proper battery protect relay. Saved me once when the aux developed a fault.

What alternator is your truck running?