Making a high efficency 3 Kw DC Generator

Discussion in 'DIY Marinizing' started by kistinie, Mar 8, 2009.

  1. kistinie
    Joined: Aug 2007
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    Location: france

    kistinie Hybrid corsair

    A good 90/95% efficiency Permanent magnet brushless motor (so in fact bare alternator ) is 15 Kg and 450 to 1000$ for 3 or 4 KW under 50 volts (a German PERM or MARS motor by example)

    A good 5 Kw air cooled engine is 7 to 30 Kg, price ? 300$ gas, 1000 diesel ?

    A water injected muffler exhaust fed by an electric water pump, is 3 Kg and 300$ i guess


    For what god dammed reason is this kind of generator for outside use absent of manufacturer's offer ?
    Inboard groups are 4 to 6000$ without the very efficient water injection to improve exhaust flow gas expulsion and cancel noise. Cost arm and legs !!!

    Such a product is a peace of cake to sell to any light hybrid sailing boat under 40 feet for 1500 to 2500$ it seems ?

    Why is the product missing ?
    Can we make one of our own till it comes on market ?

    Do you see major drawback to the outside, rain protected, air cooled, water exhaust injected light generator choice ?
     
  2. marshmat
    Joined: Apr 2005
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    Location: Ontario

    marshmat Senior Member

    Does the motor you're talking about require a controller of some kind? Most BLDCs do, and it's sometimes an expensive part. 4 kW at 12 VDC is 333 amps. A pair of truck alternators would give you this, and they shouldn't be too hard to find.

    Also, are the prices you suggest in Euros, and do you have suppliers that can get you those prices? $300 here will get you a 5 hp lawnmower engine, single cylinder, loud and prone to misfiring, and without a bunch of stuff (flame arrestor, exhaust system, fuel system, etc.) that would be needed if you put it in a boat.

    With proper safety precautions, it shouldn't be too hard to hook up a small diesel engine to a couple of beefy alternators to get a functional DC genset. Whether it would last long in salty air is another question, though.
     
  3. alan white
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    alan white Senior Member

    A B&S Etek or Etek RT should run a continuous 6 hp I think, at around $500, but the controller (as it is with the German Perm) is vital, at $450, making close to a grand for the combo.
    The batteries should put out 72vdc to get this kind of power (and more--- maybe 19hp for a short burst), so a bank of six batteries (at maybe $200 apiece = $1200, so $3000 plus cabling, switches, panel/guage, etc..
    The generator would be rated for continuous use, and so would likely be a diesel, and should be a good sized unit as that will ensure longevity and shorter operating cycles. A 10 kw unit ($8000?) would probably be about right.
    Cost? Well, my guess is 6 hp continuous is fine for up to 4 tons as long as the reserve hp is as high as 30 hp for short bursts, but an extra motor and a bigger controller (maybe 600 amp) should be added, adding another $1000, so---
    $13,000?
    Maybe some of my figures are a ways off. The setup described (12 hp continuous, 38 hp for short periods) might provide enough power to push a 36footer at 8 tons. The 6 batteries wouldn't be enough to last more than an hour or so, so more would be required, maybe 6 more, so add $1200.
    None of this is researched but just off the top of my head, but you see it isn't a simple or cheap venture.
    Run time could be continuous so long as the generator is constantly running, or the generator could be up-sized, but you can see the system is problematic in terms of space, cost, complexity, and usefulness. The few percent of gains in efficiency work much better on very large boats daily-use that benefit from savings over time. Pleasure boats don't get used enough to make electric hybrid drive cost effective.
     
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  4. kistinie
    Joined: Aug 2007
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    kistinie Hybrid corsair

    I was really thinking to a small 3Kw solution
    my boat is razor sharp and light. need nothing to move

    Rather gas than diesel, for occasional use
    Typical use, going up river, day with o wind

    Wind cooled except exhaust

    Easy to get in and out
    used outside in a box you open, with noise directed behind stern with a clever acoustical panel design

    No controller, just rectifier and regulator, in fact a 48V alternator

    The same thing than 220w groups but 48V DC and modified exhaust.
    I really need this for my trimaran, the light emergency outboard i keep is too difficult to use when i sail single handed
     
  5. Frosty

    Frosty Previous Member

    What the hell do you want DC for?

    An industrial unit made by Yanmar in deisel can be bought for much less than the marine component. Electric start etc with 3Kw output glassed in with air cooling is not difficult, no water cooling or heat exchangers. The best bit of kit on the boat,--- when I am beached.
     
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  6. TeddyDiver
    Joined: Dec 2007
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    Location: Finland/Norway

    TeddyDiver Gollywobbler

    Cheap..

    (Hz) 50
    (V) 230
    (A) 12,2
    continous(kW) 2,8
    max(kW) 3,0
    DC : 12V / 8,3A
    599,00 €
     

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  7. kistinie
    Joined: Aug 2007
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    kistinie Hybrid corsair


    Yes perfect !

    But ....how do i feed the 48V batteries ?
    My aim is to feed batteries to run the 48 V motor

    And rather than adding a charger, i prefer direct DC with rectifier and regulator. Safer also

    And i insist on water injection for exhaust
    This is simple, gives efficiency by exhaust gas temperature reduction, that increase torque, and also as a bonus, cancel noise. This trick is used for racing with great success as well as on pantone motors
    This will be used on stock 2010 Renault car too, with additional water heating before injection in exhaust gas
    here application would be easy as speed of motor is constant

    a basic version
    http://www.pg-si.fr/index.php?option=com_content&task=view&id=10&Itemid=33.

    Picture : water injection for race car

    My need : In between


    Of course this works also with your big propulsion engine... :))
     

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  8. alan white
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    alan white Senior Member

    I see, you mean direct, simple and not for constant use. I think the concept is a good one, for occasional use. Light in weight, not so expensive.
    I'd think the exhaust could be as supplied, i.e., not water cooled, so further simplify, with the entire unit being removable for easy maintainence. AC power might be the best solution for cost and efficiancy. A pair of 2500w AC generators would be cheap and redundant, where one could be used normally unless real speed was desired. Light enough to carry with one in each hand!
     
  9. kistinie
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    kistinie Hybrid corsair

    Alan

    i like the idea of two low cost plus 2 chargers

    But efficiency of low cost product is poor, KW per gallon disastrous !

    On another hand, salt will destroy it so fast, why put a lot of money inside ?


    I do not give up with water injection i like the concept !
     
  10. alan white
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    alan white Senior Member

    You like the electric drive, but why if a 4 stroke outboard of 5 hp would do?
     
  11. kistinie
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    kistinie Hybrid corsair

    For noise
    For trust when wavy conditions
    For electric power i get when sailing up to 2KW produced i hope... and i need a lot for PC and other lecombe et schmitt things
    For ergonomic reason ...

    With the 3.5 HP (yes !) motor i have to stand on the stern using the direct emergency rudder. Alone it is hell to keep a correct language.
     
  12. alan white
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    alan white Senior Member

    Pardon your French!
    How do you plan to position the motor? Through the tri transom?
    By the way, I like the self-generating prop idea. I think you might combine a small air-cooled diesel with an efficient generator. Seal it's box well from salt spray. As far as silence goes, you need some serious battery weight to get silence for long. Can your multihull deal with that kind of weight? Each battery will weigh 25 kilos, have maybe 60 AH, store 720 watt hours, about one hp for one hour, so 5 hp or so will deplete the batteries in little over an hour. The bank of say, 6 batteries will weigh 150 kilos. That's an hour top speed for every 150 kilos of batteries, or two hours at normal cruising speed, perhaps. Then the generator kicks in. A water cooled exhaust makes sense for reasons of noise because you will not want to listen to an air exhaust for long. Also a good reason to find a water-cooled diesel )(much quieter and more marinizable). Something like a small tractor engine, probably Chinese. Many are available cheap, but reliability? I don't know.
     
  13. kistinie
    Joined: Aug 2007
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    kistinie Hybrid corsair

    Yes France !

    Glad you like regeneration, make really sense on fast light sailing boats
    We can even do much better than hybrid sailing boat
    http://www.planetsolar.org/bateau.en.php

    Outboard is on the side on 2 rails close to rudder. Works only when water flat
    150 kg of lead is less than on hour high speed, but i think 6 low speed as i am very efficient with very small wet area, and very narrow, therefore drag is not linear
    how do you get heat out of the box for generator ?
    A radiator to salt water inside box ?

    i already have two yanmar IGM and no
    Too big for me
    Too heavy close to 60 kg.

    i will use the generator once a month i guess, not more

    Some like APEX, do not want to accept that this works fine for years on charter boats equipped with Agni or Lynch motors...Read, ask and you will see it is true ! Regenerating at 6 knts for one hour gives 10 minutes motoring 5 knts on a light boat. at 12 knts you will get 3 times this.
    you do not go as long as fast than with ic engine but you refuel in silence, for nothing.
    And once again this is impossible (poorly efficient) with an heavy boat
     
  14. apex1

    apex1 Guest

    Alan, the idea might attract at a first glimpse, you soon give up on a second. The induced drag of a prop genny is incredible, you might as well plow an anchor. Its a contadiction to a multihulls advantages. Adding the weight of a sufficient battery (to escape a lee shore at full throttle for example) adds noteciable weight (and cost) too. I cannot see any advantage of such system.

    A cheap (Chinese, Indian) Tractor Diesel, is a possible choice to run your genny at your off grid retreat, if it fails, drive home. But such metal chunk is never a choice aboard.

    Regards
    Richard
     

  15. kistinie
    Joined: Aug 2007
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    kistinie Hybrid corsair

    incredible drag of propeller ? An anchor !
    Can you be more precise ?...and if possible shall we return for this, to prop subject please, not here it is for a 3 kw air cooled generator with water injected exhaust Thanks !
     
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