MPPT to Multiplus DC terminals, or battery DC terminals?

Been mulling this one over myself recently, so good timing on the thread.

When I set up my tiny house system I had a similar situation — Multiplus II feeding directly to a Fogstar Drift battery, nice and simple. The moment you add an MPPT into the mix though, the question of where to land it becomes less obvious than it first seems.

The case for wiring the MPPT to the battery terminals directly:

• Shorter, more direct path
• Simpler fault isolation
• The Multiplus sees battery voltage regardless

The case for landing everything at the Multiplus DC input:

• Keeps all your high-current connections in one place
• Slightly tidier if you're cable-dressing inside a small enclosure

My concern with skipping a busbar entirely is fusing and protection. Even with just three components, each connection needs its own appropriately rated fuse. If you're daisy-chaining off the battery terminals you can end up with a rats nest of ANL fuses bolted directly onto lugs, which isn't ideal in a tight space.

Victron's own guidance (and Cerbo GX wiring diagrams) generally show the MPPT landing at the battery, not the inverter DC terminals — worth checking the MPPT 250/85 install guide specifically.

A single 2-way or 4-way busbar from somewhere like BatteryMEGA or even a decent copper bar from a local electrical wholesaler isn't as expensive or bulky as people assume. Even in a tiny house setup it's bought me a lot of peace of mind.

Curious whether anyone here has run the MPPT directly off the Multiplus DC terminals long-term — any issues with voltage sensing or charge coordination?

Wired my van MPPT straight to the battery terminals after a frustrating afternoon reading contradictory threads elsewhere. The reasoning that finally made sense to me: the Multiplus sees the battery voltage regardless, but if your MPPT is upstream of it on the DC bus, you risk the charge controller and inverter-charger essentially arguing over voltage targets when shore power's connected simultaneously.

@MoorHermit's point about Fogstar Drift is relevant — that BMS will handle balancing either way, but keeping the Multiplus as the sole DC bus manager is just cleaner. My Victron SmartSolar talks to the Multiplus via VE.Direct anyway, so it yields properly during absorption.

Fewer points of failure matters more to me than tidy cable runs, particularly for emergency backup use where I can't be faffing about diagnosing a weird voltage clash at 2am.

@GafferTapeKing that's generally fine for a van setup, but worth flagging that if you're running a Victron MPPT alongside a Multiplus, there's a real advantage to keeping them on the same DC bus and letting VE.Direct or VE.Bus do the coordination properly.

The MPPT won't "fight" the Multiplus per se, but without network communication you lose features like DVCC — which on a Lithium setup like Fogstar Drift is where things get genuinely useful. DVCC lets the Cerbo (or Venus device) hand a single charge current limit down to all sources simultaneously, so your BMS isn't having to work as hard defending the cells.

My setup on the narrowboat runs MPPT → busbar → battery, with the Multiplus hitting the same busbar. Short, equal-length runs, decent crimps. Keep voltage drop symmetrical and it behaves itself well.

Interesting one — I've been wondering the same thing for my narrowboat setup. With the boat I've got a Victron SmartSolar MPPT and I initially wired it to the Multiplus DC terminals thinking it would all "talk nicely" since it's all Victron kit on VE.Bus. Turned out the DVCC settings in Cerbo GX actually make a big difference to which approach works better — has anyone factored that in?

Specifically wondering whether DVCC shared current sense changes the calculation here? If the Cerbo is coordinating charge current from both the MPPT and Multiplus, does the wiring point actually matter less than I assumed?

@LindaClark90 welcome to the forum — narrowboat setups are a great use case for this kind of system, plenty of knowledgeable folks here.

Quick question that might help clarify things for your situation: what BMS are you running with your battery bank? The reason I ask is that on my shepherd's hut build I found the BMS communication with the Multiplus changed the calculus considerably — if your BMS can talk to the Multiplus via a VE.Bus or CAN connection, it may actually influence where the MPPT connection matters most for proper charge coordination.

Also worth checking — is your SmartSolar on the same VE.Smart network as anything else? On my van conversion I had the MPPT talking to a BMV-712 via Bluetooth and that changed how I approached the wiring question entirely.

@LindaClark90 narrowboat is actually a decent use case for wiring the MPPT direct to the battery rather than the Multiplus DC terminals — shorter cable runs often work out better that way depending on where your panels sit relative to the inverter.

On my shepherd's hut I went battery terminals in the end, partly because the Multiplus was tucked in an awkward corner and the MPPT was closer to the battery bank anyway. Meant tidier cable management.

One thing worth checking — if you're using a Victron MPPT alongside a Multiplus II, make sure they're both on VE.Smart networking or VE.Bus so they're talking to each other properly. Makes a noticeable difference to charge coordination, especially on a boat where your loads are probably all over the place.