Here's a strategy to deal with the use of a microwave on your boat:
Rather than have a large generator on board that can instantly handle the load, install a relatively inexpensive inverter that can supply the higher wattage level from your battery reserves, then use the smaller generator to replenish the battery reserves spent, over a longer recharge period.
Using this idea, one could have a 1200 or 1500 watt microwave powered by a suitably sized inverter, and still get by with the small Honda 1000i (or an even smaller older version) generator.
The small generator plus the inverter are cheaper or no more expensive than the larger generator, and the smaller generator is easier to transport and use, and can more easily be shared between multiple boats and RV units.
You can even use your outboard motor to recharge your batteries, eliminating the generator altogether.
Of course, this won't work if you want to run a water heater instead, as the total power draw over the longer heating period would be too great for the battery reserves.
I use this system on my C-Dory and pontoon boat, using the Honda 1000i or the outboard to recharge on the C-Dory, and only the outboard motor on the pontoon boat. On my Sea Ray, I just use the Honda 1000i plugged into the Shore Power inlet to run the microwave. I'll have to check to see how many watts that unit draws.
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This brings up a whole bunch of issues about how electrical power is developed and used on a boat. Here's my overall strategy and components:
I like plenty of battery reserves and multiple recharge sources and alternatives.
1. The first element is a large battery system with plenty of reserve power.
I prefer not to divide the batteries up for specific functions (engine start, house, special use), and instead just to have one big battery bank of four batteries able to be linked in parallel, using four group 27's with a total capacity of 420 AH. This big combined reserve bank eliminates the need for battery isolators, combiners, voltage sensitive relays, and any other complex and trouble prone systems that few of us understand or can fix!
2. The second element is multiple recharge sources, specifically the outboard engine alternator, a portable generator, and Shore Power combined with a large powerful battery charger.
The engine alternator will be the most commonly use source, with the generator usually coming into play when we have heavier power consumption with the boat at rest, and the Shore Power system is a free lifeline to the good life of electrical fulfillment! The large charger (say 40 amps or so) works both on Shore Power to quickly charge batteries, and also works with the generator to allow the full 120 volt output to be used, as it is about 10 times as powerful as the 12 volt output directly available on the generator. The generator can always be started, of course, and serves at the ultimate backup power generator and battery recharger
3. The next element is the inverter. This allows the creation of 120 volt power without the use of the generator or the Shore Power connection. It's quick, simple, and dirt-free! Plug into it and turn on your appliance! Works with most things you will use on board except a water heater or anything else that draws big amps over a long period. Allows you to use large wattage appliances like a microwave, then replace the charge on the batteries with a smaller generator or the outboard motor. The inverter adds a lot of flexibility to the electrical system.
4. The fourth element is simply a well thought out and installed Shore Power distribution system into which all the above can be integrated. This is a subject in itself, discussed elsewhere, of course.
****The above is my own opinion and a description of how I operate electrical equipment on my boats. YMMV!!! Be careful to think all of this out on your own and be comfortable with whatever you come up with yourself. Different people have different needs and need different solutions. Good Luck with your own system.
Joe. :thup :teeth