Kohler 10EOZD High Voltage

Well, what is the output voltage of the generator? What do the meters on the main panel show?

this is why I like having digital meters with alarms visible from the salon. You can see right away what’s going on and many like Blue Seas have audible alarms

it sounds like a voltage regulator problem although I m not familiar with Kohlers. Last year I had a similar issue with my Norpro 18, running around 250v. It was the regulator. To make things worst at first I could only find a Chinese knock off to the original Marathon electric. Cheap but only lasted a couple of hours before it started failing. Was able to find another one made in the US. No more issue

I would replace it right away. These faults don’t cure themselves and while you inverter may shut down on over voltage other things may get damage of it gets any worst

A few points I would like to present.

Having studied the wave out put of a few marine gen-sets with the help of an oscilloscope, I can tell you it is amazing that anything works at all.
Unlike the pretty sinuous signal that can be observed at home, office or dock outlets, that is one ugly, noisy signal with protruding spikes denoting 60 (or close) Htz, coming from a small gen-set.

Better voltage regulators make better signals, some regulators you can make adjustments to the wave shape and amplitude. After this, it is still an ugly signal.

Then, an inverter, built also under a budget, is not going to be able to detect and identify every signal error that it receives. "High Voltage" may mean just that or I can imagine a few other things.
Oh, while charging "High Voltage",, Is that ACv or DCv?

The OP has not an idea of what his gen set output is producing when operating.
Has no idea of the wave form, load or not.
Has no idea of the frequency the gen-set is producing, load or not.
No idea of what other error conditions can cause a "high voltage" error, could be a battery issue. Or, if any Magnum options are installed causing this error.

The fault may very well be the regulator. The regulator may be the only easily replaceable part on a 10KW set.
There may only be 4 or 6 wires going to the regulator and easily replaced by a non technical person.

But I sure wish I knew more of what was going on before replacing anything.
And for the non-technical operator, I would recommend a proper tech with a scope, DVM and maybe a power analyzer (with a spare regulator in his truck).

Heck, an adjustment from 245 to 235Vac or speed from 64 to 60Htz (a few RPM) may be all that is needed.
A set-up parameter on the inverter could be the fix also.

And, are there other charging devices on the batteries?

400 hours?? Under warranties??

I ll say it again… good meters that are easy to see are a must. Long tim me ago I removed the solid doors on an electrical panel of a Johnson 70 I ran back there and replaced them with smoked Lexan so the meters and bilge pump lights could be seen from the salon. This is why when I redid the entire electrical on my boat I moved the panel from the ER to the salon. The blue seas meters are visible from the lower helm, the couch and the galley, well from the galley I have my glasses on . They cycle thru voltage, amp and Freq. when I turn on the cooktop, I can see the freq dipping by half a hertz

monitoring genset output is a must and easy to do

I have a Magnum PAE inverter with advanced remote display, battery monitor and gen-set controller. None of these 4 books have a high voltage error.
What model inverter do you have?
What did the tech recommend?
10KW is not much, How much of a load?
Was the problem there before battery replacement?
What is the ACv out put then?

So far, not.

Yes, some clocks look for that 60htz to keep time. On a boat, you can still read 60htz but the noise can alter the clock a bit +/-.
I have a clock that does not even like my Magnum inverter. Again a sinuous signal (true sine, Ha) on a budget.
But I like the clock (shuzbut), so I deal with it.

Please keep us up on your results.
Take pictures of every wire and connector and jumper before unplugging anything.
Do you have access to a quality DVM and O Scope? Would be interesting of readings and wave form before and after replacing the AVR.

One last thought. The AVR uses low voltage to excite the windings to create the output voltage.
Done differently from model to model but some do use 12Vdc to start this event. Others use some noise generated from built in exciter windings.
Please check all connects from B+ or exciter leads to the AVR and ensure all are clean and solid.

Are you getting alarms or seeing issues anywhere else on the boat other than just the inverter? Your gen has to be feeding more things than just supplying a single leg of 120v to the inverter. 150v is very high. I’m surprised your not getting issues elsewhere if this is real. Wondering if the input voltage sensor on the inverter isn’t the culprit? Magnum is a pretty good quality inverter but nothing is fool proof.

Magnum has pretty good customer support and tech help. Would be worth a call to them to see if they have seen this before on your model.
Lastly, I believe you can get a data logger to monitor the voltage fairly inexpensively. Might be worth it to try to nail down which device is the culprit.

When you talk to Magnum Support and they go over your inverter set-up, Ask them what trips the High Vac error.
Ask them how to filter it out.
The only line I find in my Magnum ARC manual is:
• High VAC In Fault – The AC input voltage is above 275 VAC.
Remedy: This fault automatically clears once AC input voltage falls below 260 VAC.

I need to ask a question about the Kohler visit; Did the tech look at the Vac signal with a scope? Is there any noise above 275 Vac?
Please re-read my #5 post above.