Quatro control during Cerbo Boot and DVCC external control start

Been wrestling with something similar on my van build that I've since scaled up to a static off-grid setup, and I reckon this deserves more attention than it gets.

Running a Victron Multiplus-II with a Fogstar Drift lithium bank, I noticed that during the Cerbo GX boot sequence, there's a window — maybe 30 to 60 seconds — where DVCC hasn't fully handed control over yet. During that gap, the inverter/charger can behave as if it's operating blind, ignoring the charge current limits the BMS would normally enforce.

For most people this is probably fine. But if your battery bank is already sitting near full SOC when you cycle power, that early uncontrolled charge push could theoretically stress your cells before the BMS gets a word in edgeways.

My questions for the group:

• Has anyone with a multi-unit setup (particularly paralleled or 3-phase Quattros) seen this cause actual problems — voltage spikes, BMS trips, anything logged?
• Is there a reliable way to sequence the boot so the Cerbo is fully initialised before the Quattros start doing anything meaningful?
• Does the DVCC "SVS" or "SCS" mode help here, or does it make the timing issue worse?

I've seen suggestions to use an ESS minimum SOC trick to prevent charging at startup, but that feels like a workaround rather than a proper fix.

Curious whether anyone's dug into the VE.Bus Assistant side of this or set up custom relay logic to handle the sequencing more gracefully. Would love to hear what others have landed on.

@VitoBuild yeah the Cerbo boot sequence is a proper pain point that not many people talk about.

Had this exact issue on my motorhome build - Multiplus-II comes online before the Cerbo has fully established DVCC comms, so you get that brief window where the inverter/charger is effectively running without BMS oversight.

Few things that helped me:

• ESS assistant timing settings are worth digging into
• Check your VE.Can termination resistors are solid - dodgy connections slow the handshake right down
• Victron's keep batteries charged mode during boot can reduce the risk window

The Fogstar Drift cells I'm running have a fairly conservative BMS that handles it ok, but I wouldn't want to be pushing a marginal state of charge during that window.

What BMS are you running? Makes a big difference to how exposed you are during that startup sequence.

@VitoBuild this is something I've been quietly worrying about with my van build before I scale it up like you have.

Quick question — during that window when the Cerbo is still booting and DVCC hasn't taken control yet, what's actually governing the charge parameters? Is the Multiplus just falling back to its own internal settings, or does it essentially operate "blind" until the GX device hands over?

Trying to understand the risk window here, especially with a Fogstar Drift lithium pack that has its own BMS. If the Multiplus briefly pushes incorrect charge voltages before DVCC kicks in, could that actually stress the cells or does the BMS just handle it regardless?

Also — does the boot sequence duration vary depending on Cerbo firmware version? Wondering if a more recent update has tightened that gap at all.

@StuKnight worth stress-testing the boot sequence before you scale up, genuinely. Cost me a few headaches when I moved from van to static.

The bit that catches people out — DVCC doesn't hand control back cleanly if the Cerbo reboots mid-charge cycle. Quattro/Multiplus just sits there waiting for CVL/CCL signals that aren't coming yet.

What sorted it for me was setting a conservative fallback charge voltage directly on the Multi itself, so even if the Cerbo is still booting, you're not flying blind. Fogstar cells aren't particularly fussy but I still wouldn't want unregulated charge hitting them.

Also worth checking your BMS CAN timeout settings if you're running that comms path — some will trip the system entirely which is actually safer than the alternative.

@VitoBuild this is exactly the scenario that exposed a flaw in my own setup about eight months back.

What I found — and it genuinely surprised me — is that during the Cerbo's boot window, the Multiplus falls back to its internal charge parameters rather than waiting for DVCC to assert control. If your battery's BMS hasn't also completed its own initialisation by that point, you've got two systems effectively arguing over who's in charge of nothing.

My fix was adding a startup delay via the VE.Bus assistant — gave the Cerbo enough time to establish comms before the inverter started making autonomous decisions.

Worth checking your DVCC logs in the VRM portal immediately after a cold boot. The timestamps tell the whole story — there's usually a gap where no external control signal is present, and that's your vulnerability window.

@VitoBuild @TorJake this is exactly why I document every boot sequence event in my tiny house setup with a Cerbo GX and a Fogstar Drift 200Ah.

What catches people out is the pre-DVCC window — the Quattro/Multiplus doesn't sit idle during boot, it falls back to its own internal charge algorithm temporarily. If your BMS has a tight over-voltage threshold, that brief uncontrolled period can trigger a protect disconnect.

My fix was setting the charge current limit conservatively in the Multiplus itself (not relying solely on DVCC), so even during that uncontrolled window it can't do damage. Essentially belt-and-braces — DVCC takes over once Cerbo is ready, but the standalone settings act as a hardware floor beneath that.

Worth checking your VE.Configure settings aren't just defaulted from installation and never revisited.