Dont hang me

Discussion in 'Propulsion' started by Manie B, Apr 4, 2008.

  1. Manie B
    Joined: Sep 2006
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    Location: Cape Town South Africa

    Manie B Senior Member

    Gents i dont understand how it works and that is why i ask.

    Inverters are expensive and problematic at times (stepped - full sine etc.)

    Is it not possible to drive a 12 or 24 volt dc motor off the batteries which in turn then belt? drives a generator to produce 110 / 220 v AC.


    My small petrol generator does that - all i am wanting to do is take out the petrol motor and replace that with a dc motor. Just a thought - can it work - we could talk about efficiency vs inverters later
     
  2. alan white
    Joined: Mar 2007
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    alan white Senior Member

    The answer is yes. The driven generator cares not a whit what's driving it.
    So now on to the efficiency of that system. The more complicated system has the lower efficiency and the higher initial cash outlay.
    And of course the question arises, where is the prime source of your power? A shore-based battery charger or yet another generator?


    Alan
     
  3. Fanie
    Joined: Oct 2007
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    Location: Colonial "Sick Africa"

    Fanie Fanie

    Hi Manie, as Alan said, it's all about efficiencies. Pertol motors are VERY inefficient, and so are electric motors unfortunately.

    There are actually very few power items that are efficient, non are 100% since there are always losses. To generate power from 12/24/36/48V you have about 25% losses, then if you drive the electric motor there are again losses, so you could easily get to 50% losses before anything is moving .

    Best way to drive a 12V motor is with 12V, same for any other voltage motor.
    If you want to generate 230V to compensate for the power cuts, petrol is EXPENSIVE to do it with.
     
  4. Landlubber
    Joined: Jun 2007
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    Landlubber Senior Member

    Manie B,

    First question mate is how much AC do you really want.

    If it is only light loads or for occassional use, it is very hard to go past an inverter.

    Used correctly they can reduce the size of the prime genset and save a lot of money.

    What is your expected usage?
     
  5. the1much
    Joined: Jul 2007
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    the1much hippie dreams

    o.k.,,,,only cause i know Manie is a little used to it,,,but,,Wow i would love to turn my whole house into 12 volts system hehe ;) ,,kinda like opposite huh hehe ;)
    sorry fer the off topic Manie ;)
     
  6. Mikefleetwood
    Joined: Jul 2006
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    Location: Cornwall, UK

    Mikefleetwood Junior Member

    You say "inverters are expensive" - but I would have thought a motor + generator + frame/belt/etc. would be even more so!

    It does depend on the power rating you are looking for. As the power increases, the efficiency of motors and generators also increases. I am sure there reaches a point where motor/generator becomes more cost-effective than an inverter. But this is likely to be in the region of a couple of kW, at which point the current draw from the low voltage DC becomes so high as to render the whole exercise impractical!

    Small inverters are very cheap these days.
     
  7. Pericles
    Joined: Sep 2006
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    Location: Heights of High Wycombe, not far from River Thames

    Pericles Senior Member

    Manie B

    Read the article on page 74 in

    http://www.proboat-digital.com/proboat/20080405/

    The Synchronising Inverter plus a battery bank will give you peaceful nights at anchor with A/C running and no sweaty bedding. The smaller generator, efficiently loaded, will also save oddles of dosh, in fuel and maintenance.

    Regards,

    Perry
     
  8. lazeyjack

    lazeyjack Guest

    Consider this Mans
    for the best and most reliable, I have had one of my yachts running a 4000 watt TRACE, pure sine wave for nine years, because it is 120 ac, and our vac down here is 220 it takes the ships load it runs all day off a big batt bank
    i can nor speak highly enough of Trace
    import to you from FISHERIES SUPPLY SEATTLE avail in 120-230, charges batts 12--36 dc, can even sell power back into the grid!!
     
  9. FAST FRED
    Joined: Oct 2002
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    FAST FRED Senior Member

    Wow i would love to turn my whole house into 12 volts system hehe

    Sure would be expensive tho to pull all the wiring , and install wires 10X heavier!

    FF
     

  10. masalai
    Joined: Oct 2007
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    Location: cruising, Australia

    masalai masalai

    Naaaah Fred, 12v is the batteries, put in serial to meet your inverter demand & parallel the banks to meet your needs.. Charge by air turbine, solar panels, or diesel generator charging direct at the voltage your batteries need.

    I set up a system on a 500,000 acre farm in the NW of Western Australia (just a bit south of "Gascoyne Junction" - we ended up running the genset for 1.5 hr per day to give full 24x7 power - even to the walk in freezer/chiller rooms and shearing shed (to shear 40,000 sheep each year) - previously the genset used to be run twice a day for 4 hours each time...
     
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