Swapping between two inverters

[MapisM]

Overloading an inverter usually is not as dramatic as overloading a battery system so most decent inverters will just trip on overcurrent and shut down to protect themselves. The real danger is repeated or sustained overloads, since the thermal stress can shorten lifespan or, in a worst case, damage components if protections lag. That’s why people lean toward the separate outlets approach you mention it keeps the wiring dead simple and ensures you’re always in control of what runs where

That's well and good theoretically, but the elephant in the room for using these separate outlets is that I have yet to find a boat whose AC circuit is designed for splitting AC equipment with high current absorption (airco, cooktop, etc.) from other "lighter" stuff than can be ran through an inverter.
So, using the "passthrough" AC outlet of the inverter for the former and the DC-powered AC outlet for the latter requires a rewiring that, depending on the boat, is anywhere between a massive headache and brain surgery.

That's the reason why in my boat, whose AC system can potentially draw up to 50A when running all onboard equipment, I connected my 3kW inverter to the general AC circuit, and when I'm neither on shore power nor genset, the instrument I use for limiting AC absorption is the good old common sense.
BUT, since I don't fancy the idea of stressing the inverter/batteries whenever the wife may turn the cooktop on forgetting that we are running on inverter, rather than rely on the fact that the Multiplus will eventually trip and shut down for protection, I wired a 10A breaker in between the AC outlet and the onboard AC circuit.
Which is more than enough to power the AC outlets for charging mobiles, keep the 5G router running, and also occasionally make an espresso - which covers our needs for 95% of the time we spend at anchor, while still remaining well below the max inverter capacity.
And if the wife forgets to turn the genset on before using the cooktop, it's a simple matter of rearming the breaker...

 

[geem]

That's well and good theoretically, but the elephant in the room for using these separate outlets is that I have yet to find a boat whose AC circuit is designed for splitting AC equipment with high current absorption (airco, cooktop, etc.) from other "lighter" stuff than can be ran through an inverter.
So, using the "passthrough" AC outlet of the inverter for the former and the DC-powered AC outlet for the latter requires a rewiring that, depending on the boat, is anywhere between a massive headache and brain surgery.

That's the reason why in my boat, whose AC system can potentially draw up to 50A when running all onboard equipment, I connected my 3kW inverter to the general AC circuit, and when I'm neither on shore power nor genset, the instrument I use for limiting AC absorption is the good old common sense.
BUT, since I don't fancy the idea of stressing the inverter/batteries whenever the wife may turn the cooktop on forgetting that we are running on inverter, rather than rely on the fact that the Multiplus will eventually trip and shut down for protection, I wired a 10A breaker in between the AC outlet and the onboard AC circuit.
Which is more than enough to power the AC outlets for charging mobiles, keep the 5G router running, and also occasionally make an espresso - which covers our needs for 95% of the time we spend at anchor, while still remaining well below the max inverter capacity.
And if the wife forgets to turn the genset on before using the cooktop, it's a simple matter of rearming the breaker...

My 3kw inverter will allow 6kw for short durations. Over 3kw load, it has a loud buzzer to warn you that it's in overload territory. The Mrs understands that. She is also happy to plug here sewing machine into the 800w inverter dedicated to the nav station double socket.

 

[Beneteau381]

Well, my late mate Glyn used two flicking needles, one for each genset, mounted next to each other. As they were rising and falling, he made minute adjustments to what I imagine was a govenor. When he was happy, the needles rising and falling in perfect unison, a very large antique switch was thrown, connecting the two outputs.
When it connected, a collective sigh of relief. When it did not, a bloody great bang and a sore hand. What the needles measured was never explained any further than "I've got to get 'em in phase together, or it wont connect. So, IF these needles were measuring the phasing/frequency, your first premise is clearly wrong. I saw the Alderney kit synchronised, plus the Moravany water wheel syncronised, both, 30 - 35 years ago, using antique kit. A pleasure to see master of what was clearly a 'black art' at work.

Some of the boat chief engineers used to do that as well.
My 3306 Cats for the camp were sent set up for 50hz and 240v phase neutral. The camp sent knocked down, was a Porta Kabin? USA version so wired for 110v - 60 hz.
The gen sets were set up for 1500 rpm to give the 50hz, a function of their speed. I adjusted the pumps to give 1800 rpm and 60 hz and Stan the man the electrician fixed the output at about 210v which was all we could get out of them. They worked fine for 5 years or so and I overhauled the bottom ends, the rear main seals started leaking a bit. There were 3, we did a week on in turns with them.
So a bit of old fashioned common sense and knowledge allowed them to function ok!
We did use the hz meter offshore to sync them. There was some mechanical stuff in the panel, no fancy electronics in those days and it worked.

 

[Beneteau381]

My 3kw inverter will allow 6kw for short durations. Over 3kw load, it has a loud buzzer to warn you that it's in overload territory. The Mrs understands that. She is also happy to plug here sewing machine into the 800w inverter dedicated to the nav station double socket.

My 500 watt invertor drives our 201k Singer easily, the 301k bought on Geems recommendation