I'm not sure that I can answer the question that you posed, but I have one.
Seems those statements contain an oxymoron. Can anyone spot it? Sorry, I just
couldn't resist.

Rudy
Briney Bug, Panama City, Fl

On 3/27/2010 5:14 PM, Don Kugle wrote:

Don,

We have small Tappan 700W microwave on board, and regularly run it with
our inverter. Our inverter is a 3Kw Freedom MSW, with 4 AGM golf carts
(380 AH - about 180 usable AH). The microwave is not particularly fond
of the inverter power, for on the inverter it cooks slower, and it
sometimes takes a few seconds to start cooking, I am not real sure, but
I suspect it may be the magnetron warming up? But, it works fine.

I can't say if a full sine wave inverter will do better, there are
others on the list who are better qualified to speak to that than I, but
I can tell you how our real-life installation works.

Steve Sipe
Solo 4303 "Maerin"
Ft. Myers Yacht Basin

"Don Kugle" dkugle@comcast.net writes:

Don,

A couple of answers to the actual questions, instead of random editorializing:

1. For your application, the battery bank is more or less irrelevant. Group
   31, golf cart, whatever. All that matters is whether you can pull about 200
   amps out for a few minutes. Your batteries will be fine.

2. Similarly, your alternator is fine. Cooking a cheeseburger, even if it
   takes 5 minutes, will pull out about 20 amp-hours. No problem. Just don't
   cook 10 in a row.

3. What is VERY important is the wiring from the battery to the inverter.
   This has to be as BIG and as SHORT as possible. Remember, 200 amps is more
   than most welders put out, and the idea is to keep all the smoke inside the
   cables!

4. If you don't have it, I would HIGHY recommend putting in a separate,
   dedicated start battery. Hook it up using this Blue Sea switch and combiner
   (http://bluesea.com/category/2/productline/overview/329). This way you can
   cook all the cheeseburgers you want and the engine will still start.

Now, the grey area: for reasons that are not worth going into, microwaves are
very complex loads electrically. I've got a 4000 watt 24 volt inverter on my
boat, and the microwave creates more DC current draw than any other load.
Plus, as you have noticed, the output power rating of a microwave ("600
watts") is not the same as the input current draw. So, you want to go with a
relatively high powered inverter. As for sine-wave vs. modified sine-wave,
that is completely dependent on the microwave. However my Panasonic works
fine with my MSW Xantrex.

If this were my boat, here would be my choices:

1. A new dedicated group 27 starting battery.

2. The Blue Sea switch and combiner.

3. An inverter or inverter/charger with built-in transfer switch. This means
   that when you are at the dock there's no futzing around with plugs. Something
   like this will do the job, or you an go up to the HF series and get a charger
   as well:
   http://www.defender.com/product.jsp?path=-1|328|936|613742&id=674814

4. Do not skimp on the wiring. 1800 watts at 110 volts = 150 amps at 12
   volts, plus another 20% for inefficiency equals a MINIMUM of 180 amps.
   Looking at the wiring chart from Ancor
   (http://www.marinco.com/page/conductor-sizes) our MINIMUM conductor size is
   #1 cable, but for a 10 foot run and low voltage drop I'd be using #0. Don't
   forget to protect it with a properly-sized fuse such as this:
   http://bluesea.com/category/5/21/productline/128 (choose the next fuse size
   DOWN from the rated ampacity of the cable).

5. Finally, a small-but high-quality microwave. I'd pick one without a
   turntable, especially on a sailboat.

All in all a nice weekend project, and when you're not cooking a burger you
can also use it to power a TV. About 1 Boat Unit all in.

Scott Welch
Chief Evangelist, Open Text Social Media Group
www.opentext.com
905 762 6101

"Things turn out best for people who make the best of the way things turn
out." - John Wooden

REPLY
A friend who built a sailboat for single handed cruising didn't even
bother with a stove top. His reasoning was  as follows.
A sailboat usually heels when underway. A pot on a stove pot is  a
potential spill of hot liquid onto the cook. Especially in boisterous
weather.
A microwave is faster  and with  the door closed  will not dump hot
liquids over the cook. Being single handed he did not like to spend too
much time below in the galley when under way and a quick  cup of noodle
heated in microwave was easier than cooking on a stove top. He used the
space normally occupied by a stove to install a tool makers lathe.
When in port he did on many occasions cook gourmet quality meals on a
portable 2 burner camping stove.

On the subject of efficiency. I have recently begun measuring the amount
of electrical energy used by various counter-top appliances to cook meals.
In most cases they use less energy than the electric stove. If you equip
the galley with three outlets each  fed by a sepearat breaker you have
greater flexibility than with a fixed stove. These  counter-top appliances
can often be stowed away in a locker or closet that would not be
convenient to place a stove in.
And look at the amount of counter-top space you have  when you are not
cooking hot meals.

Arild

A pot on a stove

Okay, I forgot that some folks like more than crackers while underway. When I
start whining about eating the same thing, day after day, Jill whips up a
sandwich for me. You are suggesting that some folks cook underway??

Interesting Arild, can you expand on that, particulary which types of
applicances and energy consumption notices. I guess that I just assumed that a
1500 watt stove element would require as much energy to, let's say boil water,
as would a 1500 element in a hot plate. You've got my attention.

Rudy
Briney Bug, Panama City, Fl

It's all a question of heat transfer.  On a typical spiral heat element
the pot never matches the diameter perfectly. If its a thin skinned pot it
may not even be flat to completely mate up with the heat element. Both of
these factors contribute to heat loss around the edges.

Countertop appliances are designed to direct heat into the food in the
best possible manner. Being a 120V plug-in in it is limited to 1800 watts
or 1650 if it only gets 110V supply.
Many of them have less than 1000 watt elements. For example I can defrost
and grill a steak in 9 minutes ( according to stopwatch) using a George
forman grill  but for a typical lunch consisting of grilled prawns  served
with a california salad  it only takes 7 minutes  from freezer to plate
and my stomach.  <smile>

Crackers??  Only when served with hummus( roasted red pepper flavor)  some
smoked oysters or mussels. Oh yes  also goes well with old cheddar or
Monterey jack cheese. But for a real treat  Brie or  some good German
Butter cheese is better.
Rudy you obviously have not been told the main purpose of having a trawler
is to avoid dumping the canapes on the floor during a cruise. And good
crystal stemware is so tippy on a sailboat.

Now  moving right along to rough weather cooking. Forget the pot holder
rails on a regular stove. In any case the pot lid seldom stays connected
to the pot.
A crock pot has a lid that sits in a groove and under extreme angles of
heel in excess of 15 degrees from horizontal can be restrained with a
bungy cord across the top and under the bottom. Kind of hard to do if the
bottom is sitting on the heat elements of a stove. <smile>

We can place a frozen chicken in a crock pot  and depending on size/weight
it is ready to serve  in 3 - 4 hours. Just the thing to finish off a
passage from noon to dinner time.  Stews,  chili, seafood chowder, and
cooked chicken are just a few of the meals you can prepare in a crock pot
driven by an inverter and even a modest size alternator. As long as the
engine is turning, battery size doesn't matter so much.
I outfitted a friends long haul truck with a 1750 watt Xantrex inverter
powered from his start battery and in 5 years he never once had a flat
battery. He ran a microwave oven, a bar fridge, an electric frying pan, a
tea kettle and a coffee maker, and a Forman grill not to mention his TV
and radio. No room to install a stove in his sleeper rig.
Items not in use got stowed in the jockey box which only had access from
the outside of the cab.

Arild

Arild