ESS Betrieb bei Netzausfall - keine Frequenzerhöhung durch MP 2 bei geladenen Akkus

Been thinking about this after a neighbour's generator caused some grief on a shared rural supply last winter — running at slightly elevated frequency and causing all sorts of odd behaviour with my Multiplus II.

Specifically curious whether anyone's experienced the MP2 not ramping up frequency when the grid drops and batteries are already full? The whole point of ESS frequency shifting is to signal connected inverters/chargers to back off, but if the system transitions to island mode with a full battery and doesn't raise freq above 50Hz, you've got no headroom to shed load or dump excess solar.

My setup is a Multiplus II 48/3000 with a Fogstar Drift 48V pack and a couple of Renogy panels feeding in via a SmartSolar MPPT. Works brilliantly 95% of the time, but I've had at least two occasions after grid outages where the logs showed the battery sitting at 100% SOC with PV still producing and the frequency barely nudging.

Questions for the thread:

• Is this a VE.Configure assistant setting issue, or something deeper in the ESS assistant logic?
• Does anyone use an external frequency relay as a belt-and-braces measure?
• Worth raising with Victron's community forum, or is there a known workaround already documented?

Feels like one of those edge cases that only bites you during an actual outage — exactly when you don't want surprises. Would be interested to know if this is a firmware version thing too, as I'm not always on the bleeding edge with updates.

What are others running in terms of ESS config for island/backup scenarios?

Classic Victron ESS quirk this. When the MP2 is in island/ESS mode and batteries are full, it can't export the excess so it should raise frequency to signal connected inverters to back off — but if the BMS is capping charge at 100% and not communicating state properly, the frequency shift never triggers.

Worth checking your DVCC settings and whether your BMS is actually talking to the Cerbo properly. Also look at the ESS assistant config — there's a "sustain voltage" threshold that sometimes confuses things when SOC sits at 100%.

On the generator frequency issue specifically — MP2 is supposed to tolerate ±4Hz but misbehaves when it drifts above 50Hz unexpectedly. A cheap power meter on the genny output would confirm if that's your culprit rather than the ESS logic itself.

@Wardy the MP2 won't raise frequency to signal "back off" to connected devices if it's still seeing the grid — it only does that frequency-shifting trick in true island mode, which is why your full batteries had nowhere to put the excess and things got grumpy.

Worth checking your ESS settings: "Keep batteries charged" mode vs "Optimised" makes a big difference here. Also, if you've got a Victron MPPT in the loop, enabling DVCC properly lets the whole system talk sensibly rather than everyone doing their own thing.

Had similar chaos on my narrowboat when a marina's dodgy shore power wandered in frequency — sorted it by tightening the AC input voltage/frequency acceptance window in VEConfigure. Narrower tolerance = MP2 drops to island mode sooner and then does the frequency dance properly.

@Wardy this is the crux of it — when the MP2 is grid-tied it defers frequency control to the grid itself, so the frequency-shift mechanism for curtailing MPPT output simply doesn't activate. It's only in genuine island mode that you'll see it push frequency up toward 52–53Hz to signal connected Victron MPPTs to back off.

Worth checking your ESS assistant settings — specifically the "minimum SOC" and "feed-in excess solar" options in VEConfigure. If the batteries are sitting at 100% and feed-in is disabled or grid doesn't accept it, you'll get that exact stalemate.

On my shepherd's hut setup I had a similar puzzle until I realised the grid code settings (EN50549 for UK) were constraining behaviour in ways I hadn't anticipated. What firmware is your MP2 running? Some of the earlier builds handled this edge case poorly.

@RetiredChef and @LiamFrost70 have nailed the core issue, so I'll add the practical bit nobody's mentioned yet — this is exactly why the AC-out-1 vs AC-out-2 distinction matters when you're planning loads.

In my garden office setup I've got non-critical stuff on AC-out-2 (drops on grid failure) and the important kit on AC-out-1. When the batteries are stuffed full and the MP2 can't frequency-shift because the grid is holding frequency, your only real lever is load management via the DVCC settings or a proper Cerbo-controlled relay to dump excess somewhere useful — immersion heater, etc.

The frequency-raise trick only kicks in properly during genuine island mode. Grid present = grid wins the frequency argument, full stop. Victron's own ESS documentation buries this rather quietly, which catches a lot of people out.