Charging current in dvcc, and ESS

Been running a similar setup on my narrowboat for a couple of seasons now — twin Multiplus-II 3000s with a pair of SmartSolar MPPTs feeding a 48V flooded lead-acid bank (about 560Ah, Rolls Surrette). Mostly off-grid, occasional shore power when I moor near a marina.

Something that's been nagging at me lately: DVCC charge current behaviour when the system is under mixed load conditions.

When I'm running heavy loads mid-afternoon — induction hob, inverter AC loads, the lot — I've noticed the total charge current being pushed to the batteries seems to get a bit unpredictable. The DVCC shared current limit should be coordinating everything neatly across the MPPTs and the Multis, but I'm occasionally seeing the bank getting hammered slightly above what I'd expect from the configured limits.

It's not catastrophic, but with flooded LA you really don't want to be consistently over-gassing, and I'm already watching water levels carefully.

A few things I'm curious about, and would love to hear others' experience:

• Does ESS mode fundamentally change how DVCC enforces the charge current ceiling compared to a straight off-grid profile?
• Are the Multiplus charger and MPPT currents truly summed and capped, or is there a coordination lag?
• Anyone running Victron with a third-party BMS on wet cells where this has caused grief?

I've got a Cerbo GX doing the talking between everything, firmware all reasonably current. Wondering if it's worth digging deeper into the VRM logs to spot a pattern.

Anyone else wrestled with this on a boat or off-grid cabin setup?

@FZ_Builds that Rolls Surrette bank will be thirsty for absorption current — have you found DVCC's BMS_CVL / BMS_CCL limits playing nicely with flooded batteries, or are you having to manually cap things in VE.Configure?

On my shepherd's hut build I ran into a similar headache — the MPPTs kept backing off earlier than expected because the system-wide charge current limit was being divided awkwardly across both controllers. Turned out I needed to enable Shared Current Sense properly rather than just Shared Voltage Sense. Night-and-day difference once sorted.

Worth also checking whether ESS is actually using DVCC override or just politely ignoring it — the VRM dashboard logs will tell you pretty quickly if the CVL is being respected.

@FZ_Builds with flooded LA you probably don't even want DVCC's BMS_CCL capping your charge current too aggressively — those Rolls cells genuinely need a decent absorption phase to gas a bit and mix the electrolyte.

On my setup I've got DVCC enabled but with SVS and SCS switched off, letting the battery sensor handle voltage sensing directly. Made a noticeable difference to charge acceptance.

Worth checking your Max charge current in the CCGX/Cerbo — that's your real ceiling regardless of what the MPPTs are trying to do. If that's set too conservative your bank will chronically undercharge over winter.

@FZ_Builds worth knowing that with flooded LA and no actual BMS talking to DVCC, the BMS_CCL limit just defaults to whatever you've set manually anyway — so you're not really losing anything by having DVCC on.

Main gotcha I'd watch with Rolls Surrettes is making sure your absorption time is generous enough. DVCC controls the voltage ceiling fine, but if your MPPTs are cutting to float too early the big bank never fully tops off.

Had something vaguely similar sorting out my shepherd's hut setup — not flooded LA, but the DVCC interaction with multiple charge sources was less scary than the Victron docs make it sound once you just dig in and test it. 🔧

@GazAllen that's the bit worth expanding on — if there's no BMS actively talking on the VE.Can or VE.Direct bus, DVCC won't magically invent a BMS_CCL value. It'll just fall back to whatever you've set manually in the MPPT and Multiplus charge profiles. So @FZ_Builds your Rolls bank should still get its full absorption current from the individual device settings.

The place I'd actually watch is the SVS (Shared Voltage Sense) behaviour under DVCC — with flooded LA on a boat, voltage drop across cabling can be significant and SVS will average readings across devices, which occasionally causes odd absorption timing on my setup.

@ExBrickie so just to clarify my understanding — if there's no BMS on the bus, DVCC is essentially just coordinating the charge sources without applying any BMS_CCL cap at all?

I'm curious what happens in that scenario if you do set a manual charge current limit in the Multiplus-II itself via VEConfigure — does DVCC respect that, or does it override it with its own shared voltage/current logic?

Asking because I'm looking at eventually swapping my flooded bank for a Fogstar Drift lithium setup, and I want to understand the control hierarchy before I make the jump rather than after something goes sideways. Would the Fogstar BMS actually communicate over VE.Can or would I need a separate CANbus adapter?

@Cleggy pretty much, yeah. DVCC without a BMS is basically just traffic control — keeps your MPPTs and Multiplus playing nicely together so they're not fighting over charge current. Still useful, don't get me wrong.

The bit people miss with flooded LA is you want your absorb/float params set properly in VEConfigure, not just relying on DVCC to save you. Had a mate bodge this on his setup and wondered why his bank was sulphating.

With Rolls Surrette specifically — decent batteries but they want a proper charge profile. Set your DVCC - SVS (shared voltage sense) on if you've got a SmartShunt on the bank, that at least gives all your kit the same voltage reference. Makes a real difference with longer cable runs.