Multiplus II going into passthrough every 10 minutes?!

Been lurking on this one because something similar happened on my boat last winter and it nearly drove me round the bend.

Mine was an MPII 48/5000 paired with a couple of Fogstar Drift 100Ah cells — nowhere near 32kWh, but the pattern sounds identical. Every 8-10 minutes like clockwork, passthrough, then back to inverting. Victron Connect logs looked fine on the surface. No alarms, no fault codes, nothing obvious.

Turned out the culprit was the BMS communication dropping packets intermittently over the VE.Bus cable. The Multiplus was seeing a momentary loss of the battery "ready" signal and being cautious — fair enough, really — but the root cause was a slightly dodgy RJ45 crimp I'd done myself in a hurry. Swapped it for a proper pre-terminated cable and the issue vanished overnight.

A few things worth checking if you haven't already:

• BMS comms cable — reseat both ends, check for corrosion (especially on a boat or van where moisture is a factor)
• Cell voltages under load — is any single cell sagging and triggering a BMS protective event, even briefly?
• ESS assistant settings — specifically the "Minimum SOC" and "Grid setpoint" if you're running ESS; odd interactions there can cause cycling behaviour

What firmware are you on? There was a MPII firmware revision a while back that caused some quirky passthrough behaviour on certain BMS configurations — worth cross-referencing on the Victron Community forum too.

Anyone else on here seen this with the Fogstar 32kWh specifically? Curious whether it's something in how that BMS handles the keep-alive signal.

@OldSailor86 that Fogstar Drift pairing rings a bell — I had almost identical grief with my shepherd's hut setup last autumn. Turned out my BMS was throwing a silent overcurrent flag every time the compressor fridge kicked in, which the Multiplus interpreted as a battery fault and bailed into passthrough. No alarm, no obvious log entry at first glance.

Worth pulling the full VRM history and filtering specifically for "BMS error" events rather than just inverter alarms — they're logged separately and easy to miss. Victron Connect on the MPII itself also showed me a subtle DC input low threshold being breached for maybe 200ms at compressor startup.

Raising the low battery disconnect just slightly on the BMS sorted it completely. Fifteen minutes of head-scratching once I knew where to look.

@OldSailor86 worth checking your DVCC settings in VenusOS before anything else — specifically the CVL and CCL values being pushed from the BMS to the MPII. If the Drift's BMS is sending a charge current limit that's too conservative under cold conditions, the Multiplus can interpret that as a near-fault state and drop to passthrough to protect itself.

On my system (MPII 48/3000, Fogstar Drift 200Ah × 4S2P) I had to manually cap the DVCC voltage limits in Venus rather than letting the BMS dictate them blindly. The Drift BMS can get a bit twitchy around 10°C and starts throttling CCL aggressively.

Check your VRM logs — look for sudden CCL drops right before each passthrough event. That'll confirm it within minutes. If you're not on VenusOS 3.x yet, update first as there were known DVCC stability fixes in that release.

@Spider12 already beat me to DVCC but I'll add — what's your BMS communication set up as? On my garden office build I wasted two weeks convinced it was a config issue before realising the CANbus cable between the BMS and Cerbo had a dodgy crimp at the BMS end. Intermittent connection, so the Cerbo was periodically losing the battery data and the MPII was defaulting to passthrough as a safety measure.

Symptoms were almost identical to what you're describing — regular, almost clockwork intervals.

Worth checking:

• VRM portal → does the battery data disappear for ~30 seconds before each passthrough event?
• Physical inspection of every CANbus connector
• Swap to a known-good cable temporarily if you can

What BMS are you running? That'll narrow it down considerably.

@OldSailor86 oh mate, I lived this saga on my old Ducato motorhome conversion. The culprit in my case was the BMS screaming at the Multiplus via CANbus with a CCL of zero during a brief cell imbalance — Victron interprets that as "right, I'm out" and goes full passthrough faster than you can say "why is everything beeping."

Pulled up VRM remotely from a motorway services car park, watched the CCL nosedive every ten minutes like clockwork.

Key question nobody's asked yet: are you on VenusOS 3.x? There were some spicy DVCC handshake quirks in the earlier 3.x builds that caused exactly this with Fogstar's BMS firmware. Worth checking the Venus changelog before you go poking anything else.