Adding Solar - Victron MPPT to MultiPlus

So I've finally taken the plunge and ordered a Victron SmartSolar 100/30 to pair with my existing MultiPlus 12/1200. Running it on the narrowboat primarily, but the same setup doubles as emergency backup at home when we get those lovely grid outages (cheers, Western Power Distribution 🙄).

My plan is to let the MPPT feed directly into the battery bank and let the MultiPlus sort itself out — seems like the "just works" approach from what I've read. But I'm wondering if I'm missing a trick by not using a Venus GX or Cerbo to tie them together properly?

Few specific questions:

• Is the VE.Direct to USB cable enough to at least get basic monitoring without splashing out on a Cerbo?
• Anyone running this combo on a narrowboat where the panel positioning is... creative (read: shading is a nightmare near locks)?
• Does the MultiPlus charger profile need adjusting once the MPPT is doing most of the heavy lifting, or does it back off automatically?

I've got 200Ah of Fogstar Drift LiFePO4 going in at the same time, so I'm trying to get the charge parameters right from the off rather than bodging it and crying later.

Presumably I'm not the first person to overthink a fairly standard setup — what does everyone reckon? Worth doing the full Victron ecosystem properly, or is that overkill for a two-panel, one-battery situation?

@HollyGaz solid choice pairing those two. One thing worth doing immediately — connect both units via VE.Direct to a Cerbo GX or at minimum a SmartShunt so the MultiPlus knows the actual state of charge rather than guessing from voltage alone. On narrowboats the voltage sag from the inverter load can completely fool the charge algorithm otherwise.

Also check your charge profile settings are identical across both devices. I had a frustrating few weeks where my MultiPlus was set to AGM absorption voltage and the SmartSolar was running a lithium profile — Fogstar cells weren't being charged properly despite VictronConnect showing everything "green."

VE.Smart Networking (Bluetooth mesh) lets the MPPT share temperature and voltage data directly with the MultiPlus without needing a GX device if budget's tight.

@HollyGaz interesting setup — does your MultiPlus have the VE.Bus port available, or are you using the older model? Worth clarifying because the integration options differ slightly.

One practical point nobody's mentioned yet: with a 100/30 you'll want to double-check your battery cable sizing handles the combined charge current properly. If the MultiPlus is also bulk charging from shore/generator at the same time, both chargers push current simultaneously and undersized cables can get warm.

Also — are you planning to set a shared absorption voltage via VE.Configure or just letting each unit do its own thing? I've seen people run into battery stress issues on my static caravan setup when the MPPT and charger weren't coordinated properly. The DVCC function in Venus OS sorts this neatly if you've got a Cerbo, but worth thinking about even without one.

What battery chemistry are you running?

Don't forget to tick "has DC system" in VE.Configure or your MultiPlus will spend its life convinced the solar is phantom load and throw a wobbly — spent three days debugging that exact nonsense on my static van before I realised. Also set your absorption/float voltages consistently across both devices or they'll argue like a pair of seagulls over a chip. @HollyGaz the 100/30 is a decent shout for a narrowboat, Fogstar cells take the charge beautifully if you ever upgrade your bank.

@NotAnElectrician80 that "phantom load" issue nearly drove me mad on my static caravan setup before I figured out what was happening — MultiPlus was absolutely convinced something was draining the batteries overnight like a vampire. Turned out it was just the MPPT doing its thing and the system having an existential crisis about it.

One thing nobody's mentioned