Problemas en la puesta en marcha instalación Victron-Fronius

Has anyone managed to get a Fronius inverter working on the AC-OUT of a Victron Multiplus II without constant headaches?

I've got a cabin setup with a Multiplus II 48/5000 and was planning to add a Fronius Symo on the AC-coupled side rather than go full DC-coupled with more MPPT controllers. Seemed like the tidier solution at the time.

The problem I'm running into (or anticipating, based on what I've been reading) is the frequency shifting during high solar production. When the batteries are full and the Fronius is pumping out near its maximum, the Multiplus starts shifting frequency to curtail it — but apparently the Fronius can behave erratically and doesn't always back off smoothly. Some people report it dropping off entirely and needing a restart.

My specific questions:

• Is this more of a firmware issue on the Fronius side, or is it a config problem in the Victron settings?
• Does the MG50 grid code on the Fronius actually help stabilise things, or is it a red herring?
• Would I be better off just sticking with a couple of Victron SmartSolar MPPTs and keeping everything DC-coupled to avoid this mess altogether?

The cabin isn't my primary residence so I need the system to be as hands-off as possible — can't be driving out there to reset inverters every other week.

Running Fogstar Drift 48V batteries if that's relevant. Any experience with this combo appreciated.

@OffGridFreak yes, done exactly this on my garden office setup. The Fronius on AC-OUT config is genuinely solid once you nail a few things:

• Make sure your Fronius is on Victron's compatible inverter list — not all models are
• Set the Fronius to MG50 or MG60 frequency shifting mode (critical, this is how the Multiplus curtails it)
• In VEConfigure, enable AC coupled on output and set the feed-in limit properly

The frequency shifting is where most people trip up — without it the Multiplus can't tell the Fronius to back off when the batteries are full and you'll get overvoltage shutdowns.

What Fronius model are you using? Some of the older Primo units need a firmware update before they'll play nicely. Also worth joining the Victron Community forum — their official docs on this are actually decent.

Done this on my static caravan — Fronius on AC-OUT-2 of a Multiplus II 48/5000, works a treat once you set the Fronius to MG50 grid profile and enable the ESS assistant properly in VEConfigure.

The bit that catches everyone out: make sure PowerControl is enabled in the Victron and set the Fronius AC input current limit lower than you think you need — otherwise the Multiplus throws a wobbly trying to manage the feed-in.

Also worth checking your VE.Bus firmware is current; older versions had proper grief with Fronius frequency-shift comms. Victron's ESS design guide actually covers the Fronius pairing in decent detail — read it before touching anything, not after like most people do. 🙄

Hey @OffGridFreak — worth adding to what @SmartSolar_Geek and @Rob1963 have said: make sure you've got the MicroGrid frequency shifting properly configured on the Fronius side. The Victron shifts frequency to tell the Fronius to back off when the batteries are full, and if the Fronius frequency tolerance settings aren't dialled in correctly, it'll just keep pushing and you'll get all sorts of grief.

Also double-check your AC-OUT transfer switch settings in VEConfigure — the default overload behaviour can catch people out with a PV inverter on that output.

What size Fronius are you running? The Fronius Primo range tends to play nicest in my experience. What's the rest of your setup — battery bank, BMS type? Might help narrow down where the headaches are coming from. 👍

Done this on the boat — one thing nobody's mentioned yet: make sure your Fronius is on the supported devices list for the specific Victron firmware you're running. Caught me out badly when I updated the Multiplus II firmware and the Fronius integration went haywire overnight.

Also worth checking the AC-OUT-2 current limit is set correctly in VEConfigure — easy to overlook and causes weird behaviour under load.

@Rob1963 and @SmartSolar_Geek have covered the main bits, but the Victron community forum has a solid thread specifically on Fronius compatibility that's saved me hours of head-scratching. Worth a read before you start pulling cables.

Spent three weeks wrestling with this exact setup in my motorhome before realising I'd forgotten to enable PowerControl in VEConfigure — felt like a right numpty, I can tell you.

Also worth knowing: the Fronius must see a stable grid frequency from the Multiplus before it'll even think about playing nicely — if your battery state of charge drops and the Multiplus starts wobbling, the Fronius throws a tantrum and shuts down faster than I used to dodge difficult patients on night shifts.

Check your ESS assistant is properly configured too; without it the whole lot argues like a dysfunctional family at Christmas.