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Power inverter vs. portable generator?

Discussion in 'Boat Electronics' started by Duffer2, Jul 4, 2006.

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  1. Duffer2

    Duffer2 Guest

    Thinking about installing a 2000watt Power Inverter to run a 1000W (1350W @
    120vac consumed) microwave oven and to heat my hot water tank 1200W @
    120vac not at the same time.

    Or to use a 2KW portable generator.

    When heating the water, I estimate that the run time is about 20 minutes to
    achieve max temp.

    I'm wondering if my house batteries could handle the additional load of an

    My boat has a 300HP outboard with 60-70 Amp alternator (i cannot increase or
    change the alternator)

    help is neeed for an old "Duffer"
  2. Larry

    Larry Guest


    1200 watts divided by 12V (just to keep it simple) equals 100 amps, if the
    inverter were 100% efficient, which it's not, but close enough.

    100 amps X 12V for 20 minutes, not seconds like starting a diesel, is
    probably way enough to warp the hell out of the house battery plates,
    wouldn't you say? I would....they have little cooling for long hard pulls,
    even the wetcells will get really hot.

    One good battery explosion should just about convince you this is NOT a
    good idea unless you have a battery rated for 100 amps for most of its
    discharge time, which it's not. (Look under the seat of an electric fork
    lift truck at what will. You probably won't want to float it.)

    Actually, the fork lift batteries aren't a very good example, either. They
    get the current down to a safe level by running 24 or 48 or 96 volts with
    lots of cells in series to higher voltage traction motors. The Toyota
    Prius, for instance, takes this notion even further putting so many cells
    in series to get the current down low they run 400VDC or something like

    Nothing's funnier than watching a boater with a new, $4000, 4KW inverter
    walking down the dock with an electric heater in his hand and a big smile
    on his face.

    The microwave works good for a couple of minutes, though, on an inverter.

    So, you need a generator to do the job at a reasonable weight.

    If it's just 1500 watts, this one will work:
    It's a very quiet 2KW inverter running off a 1 cyl, computer controlled gas
    engine whos actual engine speed has nothing to do with making 60 Hz. The
    alternator in them looks like your outboard motor's high frequency stator
    coils inside the magnet-encrusted engine flywheel. You can't hurt it like
    a regular genset, either. If you overload or short it, its computer simply
    shuts off the load and drops the engine to idle until you shut it off and
    restart the engine after pulling the load off it. It will stand a short
    overload over its rated output, warning you by turning the output light
    from green to yellow to red, when it shuts it down. At only 46 pounds,
    it's very portable and easy to store....

    I have two of them, the EU1000i, the little 1KW brother to the 2KW. But, I
    needed more power for my stepvan electronics shop so I got this one:
    the big brother to the 2KW suitcase.

    There is a BIG difference between the plastic suitcase gensets and the
    3000is, however. The two little gensets have tiny, compact, FAST TURNING
    little engines that, I predict, will wear out quite quickly at your 1350
    watt load, working hard to pull it. The EU3000is, on the other hand, has a
    much BIGGER, stouter, SLOWER TURNING and QUIETER engine with a much lower
    running note. It's just larger, as you can see at 134 pounds. It also has
    a MUCH larger STEEL fuel tank that will pull two 8000 Btu window air
    conditioners and my little bar fridge and soldering equipment for over 8
    hours on ONE tank that's REALLY easy to fill through the HUGE, strainered
    gas cap made of STEEL, not plastic. The whole case is steel, not plastic.
    The EU3000is is the finest genset I ever owned at any price, even the
    diesel ones. One neighbor asked if that was my air conditioner outside
    unit's THAT quiet! Electric start comes from a separate
    internal AGM lead acid battery built right into the case under the control
    panel. Your boat's 30A shore cable plugs right into its twist-lock 30A
    connector. It also puts out 12A from a completely separate winding to
    charge your boat batteries while its running....12V at 12A charging only.

    Because all of these gensets are a really nice, rugged inverter, the
    engines have an Econo mode, switch selectable. I've never figured out why
    they'd want to switch it to full speed...?? Pulling a 1500W electric
    heater and a 1200W calrod hot plate with both thermostats switching these
    big loads on and off don't wiggle an AC voltmeter (not included) monitoring
    its output...the 3000is. Very save for computers and electronics.

    The 3000is turns 1200 RPM in Econo mode until the total load is over about
    1950 watts. That's SLOWER by 1/3 a big 4-pole 60 Hz commercial alternator-
    direct genset. I don't know how long it will last. Mine only has about
    2200 hours on it, estimated, and uses no oil at all. I change the oil at
    around 100 hours, about every other week. It only holds a little more than
    a quart and that's real easy from a little door on the opposite end from
    the control panel. It has a drain plug and a filler with dipstick. It
    also has Oil Alert and will shut itself down if it's low on oil. No oil,
    it won't even start. It has a recoil manual starter to pull, but mine is
    mounted against the back door of the van. Open petcock, pull choke
    (manual) and turn key works every time, even UNDER THE TWO AIR CONDITIONERS
    AND FRIDGE compressors coming on all at once!

    It's a helluva great genset.

  3. Dick Locke

    Dick Locke Guest

    You need to consider the size of your house batteries plus another
    important item.

    Considering inefficiences, you're talking about using maybe 40 amp
    hours to heat the water. A 4D (183 Amp hours and 130 pounds) ) or 8D
    (225 Amp hours and 160 pounds) gel cell would probably be adequate.
    You would need to run the engine almost twice as long as you run the
    microwave to recharge.

    The other item is that unless you spring for some really big bucks,
    inverters do not put out a real sine wave, and microwave ovens seem to
    be sensitive to that. Power output drops off, things overheat.

    By the way, we burned up a coffee grinder and a power tool battery
    charger using the inverter.

    Our seagoing Winnebago has about 1000 Amp hours of house batteries and
    we don't run the microwave on the inverter more than a minute or two.
  4. Al Thomason

    Al Thomason Guest

    For the Microwave, an inverter and a couple of T105, or L16 batteries
    would be just fine. Your existing batteries may or may not be large
    enough. Microwaves use a lot of power when 'on', but their on cycle
    is typically not very long. So overall the total power draw is not
    that great. For heating water though, not too likely... Heating
    uses a lot of energy for a rather long period of time and containing
    that muck energy in batteries is just not too practical.

    Not knowing your boat or needs, there are a few options for heating
    water: As you have an outboard, hooking into the engine cooling loop
    is not an option for you. For dishes, sponge bath: Just use the
    stove or microwave. Same for cooking. There are also instant
    propane water heaters available, again not sure if one would work for
    you or not and there is some controversy about their safety.

    And then there is the idea of a small portable generator. Might be a
    good solution for your situation, get a good quite one, takes little
    room. Or, perhaps both! Use the Inverter to run the Microwave when
    you want, then run the Generator once a day to recharge the batteries
    and make hot water.

  5. Larry

    Larry Guest

    AAAAAAAAAAAAAAAAACK! 100A off a gelcell for 30 minutes?!!


    No cooling!

    Melt it!!

  6. Larry

    Larry Guest

    One wonders why we don't see the obvious solution to this hot water
    problem more often....for free.....

    Australia has lots of water bladder websites. I suppose the simplest
    solution is too simple for us Americans used to advanced technology they
    don't have on the Outback.

    We are sold these rugged inflatable dingys and rafts made of nylon
    materials that can easily withstand more pressure than your 12V water
    pump can generate. So why can't we have a 6 gallon, flat black little
    bladder that hangs off the stern with two black hoses, inlet bottom and
    outlet top that pumps itself up and sits there in the FREE sunshine,
    saving gallons of fuel by getting so hot you can't hold your hand on it
    all day?? Make it with ears like dingy oarlocks to tie it down to a
    wasted deck or even over the stern under the nav light like a big fender.
    Sailboats have a big, wasted deck space on the centerline, under the
    swinging boom, where an even bigger flat bladder heater would nearly boil
    water all day, giving lots of free hot water, while keeping the sun off
    the cabin roof.

    Boaters are used to compromises, like taking showers when conditions
    permit. Sailors will put up with a lot to NOT have to crank that noisy
    diesel just to get hot water. This solution is totally quiet, uses no
    energy from house batteries or fuel tanks, except to run the pump they
    were already going to have to.


    A big ol' Navy fuel bladder made of heavy, flat black neoprene rubber
    makes a HUGE hot water heater! Fresh water washdown? No, HOT water

    Another plus for the flat bladder heater on top of the main cabin of a
    sailboat would be it puts the cabin IN THE SHADE, under the bladder! No
    crazy-looking canvas awning would be necessary! The cabin would be
    "water cooled" until the tank got hot...A thin layer of foam pad under
    the bladder would insulate the "tank" and keep the cabin even cooler!

    Of course, boat manufacturers COULD build us a little flat tank as wide
    and long as the cabin top, about 3" deep, right INTO the cabin's black
    fiberglass top. It would be permanently plumbed to the hot water pipage.

    Another stupid idea like the Coleman RV air conditioner.....(c;
  7. Well, maybe in Georgia it will work, us Europeans will get luke warm
    water for 99% of the time. Oops, I mean -- it will stay *COLD* !

    Admittedly, it is 30 degrees Celsius right now where I am typing this,
    but that's not what we usually get. And with this steaming tropical
    weather, hot water is not high on our priority list :)
  8. Dick Locke

    Dick Locke Guest

    Hmmm, maybe I've overlooked something...heating of the battery should
    be 100 amps times the internal resistance. I don't have a clue what
    that is. Educate me!
  9. Mika

    Mika Guest

    Not hopeless, though. Have used them in Finland couple of times and I
    tell you water can get real warm if you leave the black water bag in
    sunshine for whole day. It has more to do with black plastic
    absorbing sunshine than outdoor temperature.


    A bad day on the water is better than a great day on land.

    Lähetätkö e-mailia? Vaihda osoitteen eka (vai oliko se toka?)
    kahdeksikko numeroksi viisi.
  10. Sun? Where?

    You can always tell when people are from an area where the sun doesn't
    shine normally: they'll be the ones that are tanned from catching those
    precious rare rays; people from sunny places stay out of it at all costs...

    And yes, I have severe sunburn from last weekend's very rare combination
    of sunshine with warm weather :) here in the Netherlands.

    I saw on the news that it was nice in Finland as well?
  11. Keith Hughes

    Keith Hughes Guest

    30C is "steaming tropical weather"? We've hit 45C already, and summer is
    just starting! Probably won't hit 50C this year (although we have a few
    times). Enjoy the lovely winter you're having :=)

    As for solar heating, I don't know what the suns' intensity is at your
    latitude (when you see the sun, that is), but in the summer here (34°
    latitude) it can be as high as 375 BTU/ft^2/hr (10WattHr/M^2/hr) with
    the absorbing surface normal to the sunlight. So there's energy to be had.

    Keith Hughes
    (reclining in sunny Arizona)
  12. Larry

    Larry Guest

    100A squared times internal resistance PLUS the heat generated by the
    CHEMICAL REACTION of Sulphuric Acid eating into Lead to create Lead

    And, with Gellcells or AGM, there's NO INTERNAL CONVECTIVE COOLING in the
    gel or guaze between the plates.

    Case in point is my little dock electric scooter:

    It runs 8 miles at 16 mph, wide open, but its 12AH, 12V (2 in series for
    the 24V motor) will trip the overheat breaker wedged between the
    batteries long before you do 3 miles, especially if there is any uphill
    driving. The little AGM batteries, freshly charged just before you left
    home, get HOT really FAST driving the 450 watt motor continuously for any
    distance....too hot to touch!

    450W divided by 24V = 18.75A, far more than a reasonable 10% of capacity
    AH for these batteries. The idiots also put them in this "hot
    swappable" carry bag, exacerbating the heating problem. I got rid of the
    bag and they do run cooler, but not cooler enough for a full-power, 8
    mile run. I'm considering a 24VDC cooling fan with a thermostat switch
    that vents the battery/electronics compartment at 100-110F or so to help

    The chemical reaction happening this fast gets quite hot, too!

    (It's a great scooter for long marina docks, folding flat into your trunk
    or lazarette). Chain drive, smooth power from pulse-width modulation
    electronic throttle. Electric braking also has dynamic braking switch
    that drags on the PM motor on deceleration....small recharging going down
  13. Larry

    Larry Guest

    Fear not, Gentlemen! I watched a BBC documentary on Global Warming and
    London temperatures will soon be 38C dropping to only 24C all Summer by
    2015 if the supercomputers NEC sold them gets it right. The BBC
    documentary included a "future weather forcast" by the BBC's weather girl.
    London will be in the desert and always sunny, an average temp 6C higher
    than now.

    You'll have to splash North Sea water on the bag to keep it from boiling
  14. Larry

    Larry Guest

    You can cook eggs on the cabin top, here at 32N 80W in Charleston, SC, this
    afternoon. The bank clock read 102F as I turned into the
    neighborhood....whew! Unlike AZ, our humidity hovers around 90%....

    here by the OCEAN...(C;
  15. Keith Hughes

    Keith Hughes Guest

    What a wuss! A little humidity never hurt no one. I spent a year in
    Orlando, a year in Augusta GA, and over a year in Raleigh, so I know of
    what you speak. I'll take 115/7 over 97/97 anytime :)

    Keith Hughes
  16. Larry

    Larry Guest

    Yeah, but no OCEAN to play in....(d^:)

    I gotta have ocean....
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