Mains overvoltage causing Mastervolt unit to shut down

[Lomax]

Since yesterday we've had just over 250 V coming out of the socket on the pontoon, which after our Victron isolation transformer becomes over 260 V The Mastervolt Mass Combi which handles all power on board refuses to work with such a high voltage (I think the cut-off is set to 260 V at the factory), and consequently we have no power on board. The "Master Adjust" software does not expose a setting for max input voltage, only min input voltage - and I wouldn't want to raise it even if it was. What to do?

[Lomax]

I also notice that our Victron 3600 isolation transformer is making more noise than usual, and gets warm to the touch even with no load

[Lomax]

I realised I could get pass-through AC by setting the Mastervolt to "charger only" mode, so managed to get back online. Input voltage is now 247.8 V, 259.3 V after the transformer. The AC LED on the Mass Combi still blinking red and it's refusing to start up.

[SailingHarmonie]

The Victron Isolation transformers are designed to bump up the incoming voltage by 10%. This is done as a deliberate decision to handle the far more common case of low voltage on a heavily loaded dock. Of course nobody ever notices if this works as designed and the power with unusually low voltage is bumped up to a usable range.

As far as I have been able to tell, there is no way around this. The voltage ratio from input to output is fixed by the winding ratio. Small tweaks can’t be done in software. It happened to us on one of the out islands in the Bahamas where the island generator ran at 135V. This was then converted to 247.5V, which would be marginally ok, but that extra 10% moved it to 272 V which our inverter/charger would not accept.

[Lomax]

Originally Posted by SailingHarmonie

As far as I have been able to tell, there is no way around this.

Yeah, my conclusion as well - other than putting a very expensive 16 A 230 V line conditioner/voltage stabiliser before the isolation transformer... Frustrating! It's not a problem I've ever had before though - what's up with the UK grid? 255 V at the outlet surely can't be right for a nominal 230 V supply! I wonder what might happen on other boats in the marina with less sophisticated equipment, perhaps damaged battery chargers - or worse!?