Victron 24V/1200VA inverter's toroidal transformer specifications

Been running a 24V/1200VA in my motorhome for about three years now and the toroidal transformer is genuinely one of the better bits of engineering in the unit. From what I've been able to measure and cross-reference against Victron's service documentation, the primary winding is wound for the 24V DC input stage (operating roughly 20–30V) with the secondary optimised for 230V AC output at 50Hz — fairly standard for UK/EU spec units.

What's interesting is the core sizing. Victron appear to use a relatively high-flux-density design to keep the transformer compact, which is why these units run noticeably warm under sustained load. Not a problem, just physics.

A few things worth noting from my own experience:

• No-load current draw on mine sits around 11W, which aligns with the transformer's magnetising current characteristics
• Efficiency peaks somewhere in the 75–85% load range — pushing it to full 1200VA you start seeing thermal losses climb
• The toroidal design specifically reduces stray magnetic flux, which matters if you're running sensitive electronics nearby (I run a Fogstar battery bank and Victron MPPT in a tight locker)

What I've never managed to find is the exact wire gauge, core material spec (grain-oriented silicon steel presumably), or the turns ratio with any confidence. Victron don't publish those figures publicly as far as I can tell.

Has anyone pulled one apart for repair or modification? I'm particularly curious whether the winding insulation class is F or H — relevant if you're running it in a hot climate or a poorly ventilated bay.

Would be good to build a proper reference thread on this.

@MasterCamper three years of running it and you're pulling out the measuring tape on the toroidal transformer 😄 Most of us are still arguing about cable sizing...

But genuinely — the toroidal design is part of why these units are so efficient at idle. Low magnetising current, less core loss, and they don't hum like a angry wa

@MasterCamper three years in and you've gone full engineer mode — meanwhile I'm still just grateful mine hasn't set the motorhome on fire.

@MasterCamper three years and you've not once just left it alone — some of us are busy watching our Fogstar cells slowly age in a static caravan and haven't prodded a single toroidal since 2021, which is precisely why mine still works.

@MasterCamper curious what you've actually measured — the toroidal design in these units is why the no-load draw is so impressively low compared to older EI-core inverters I've used. My Phoenix 24/1200 sits around 11W idle which for a motorhome or static off-grid setup makes a real difference over 24 hours.

The winding ratio and core cross-section directly affect that efficiency curve — would be interested if your measurements line up with what Victron publish in the datasheet. They're not always forthcoming with the full transformer specs so anything empirical is useful.

@ForestDaz watching Fogstar cells age is a legitimate hobby, to be fair.