Making a high efficency 3 Kw DC Generator

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

  1. apex1

    apex1 Guest

    EDITED for links
    Thats a wasting of energy too, just leave the EL.part, or do it proper if you MUST do it.

    Hello mudman,
    have a look here:

    download "achieving the impossible" read the article and understand that there are different ways to come to different solutions. And there is a clever one too.
    And again, and again, and again:

    goto "content" then page 82 "Hybrid Marine Power" read the article in the following issues too.
    there are solutions, yes, but even the promoter of such system comes to the conclusion "its not worth"

  2. mudman
    Joined: Mar 2007
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    mudman Junior Member

    I believe the law of conservation of energy. Sorry about the energy loss thing. I meant energy converted to heat, rendering it unusable in an electrical system.

    I cant see what is being achieved as impossible except that there is no wasted energy from heat through the inverter. This machine is just an inverter/battery charger with a switch. Not enough amps, pull from battery, too many amps put some to the battery. Nothing impossible here, unless I'm missing something. It is a neat little package and can be useful to aid in an situation where there is too much energy than needed, where all extra energy is stored a potential energy in the battery bank. Depends on the price of this deal. A $500 dollar genset and a $300 inverter, with a $40 battery charger may be more cost effective, even though there is more energy than required from the genset.

    I think that what is trying to be obtained by kistinie is acheivable, but I can't understand why. I guess that kistinie already has an electric setup, and needs power to recharge the battery bank as cost effective as possible, I'd probably do the same and get a small diesel engine with a car alternator and let it run run run while I was trying to hear nothing while at sea. On the other hand, I probably never would have had a electric motor in my boat because I know that it would be impossible to run it without an elaborate mess of batteries, chargers, alternators, etc. Even the hybrids have a hydrocarbon powered engine to assist. Just put an engine on the driveshaft and be done with it. I haven't seen the numbers, but I'd have to think that a gas or diesel engine would be more energy friendly than any electric/battery/diesel setup.

    If energy can' be created or destroyed, then 5 hp generator could not possibly run a 5 hp electric motor, due to heat loss. So you would need a 6 hp generator to acheive power for the 5 hp motor. This generator would run all of the time, even when the motor is not running. Green technology is just not economical, yet. Am I wrong or something here?
  3. apex1

    apex1 Guest

    Right with you!

    So, where is the reason, one´s throwing his small Diesel engine(which he did), then installing crap for twice the money, to end up at the same (or higher) weight, and with less efficiency???
    On top of that..... asking us for recommendations of a system he only dreams about?
    Do we agree, that a El.propulsion that lets you escape a lee shore or strong tide current is at least twice the weight, twice the cost, twice the hassle, than a simple Diesel propulsion?
    Are we of the same opinion, that a Propeller driven generator of sufficient size to feed a battery for such El. propulsion, acts almost like a prop in reverse gear on a boat of 2 tonnes displ.?
    So, whats our conclusion?
    Electric propulsion in a manner our French friend is dreaming about, is the plain nonsense.

    The Victron thoughts I recommended to read, just give the novice a deeper insight in some not so easy to understand correlations.
    For old salts it is a helpful hint to rethink the usual Genny installations, and therefore to save some bucks and have more convenient El. system aboard.
    I agree there is nothing close to impossible.
  4. mudman
    Joined: Mar 2007
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    Location: Madisonville, LA

    mudman Junior Member

    Right on my friend.

    Generator on the prop is going to slow the boat down plenty. I'm not sure about acting in reverse, but it sure is alot of drag for such small electrical gain. Don't most sailboats have collapsable props while under wind power to minimize drag?

    Yeah, Frenchie is dreaming. After all of this stuff is installed the boat will displace 5 tons.

    Thanks for the links and info.
  5. alan white
    Joined: Mar 2007
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    alan white Senior Member

    kistanie, if the propellor is not a folding type, the drag induced from the open blades will slow the boat. Another reason to go with an outboard motor. The electric hybrid system cannot be made efficient unless the generator runs constantly during operation. Imagine you wanted to go for 6 hours (not unusual) at 10 knots. If your power requirement were 6 hp, you'd need a battery bank that weighed 2 1/2 tons to do the job.
  6. mydauphin
    Joined: Apr 2007
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    Location: Florida

    mydauphin Senior Member

    I have a pertual motion machine to attach to prop, it generates electricity, sends it via inverter, heats water for showers and then drive prop to go forward... NOT....

    Newton 25 law of Motion, The more you mess with energy/motion- the more you lose by friction, heat and other losses...
  7. kb1one
    Joined: Feb 2009
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    Location: Alfred, Maine

    kb1one KB1ONE

    Truck alternators can be had up to 12VDC/300 amp. Any Freightliner dealer will do. I prefer the Leech-Neville over the Delco, as the cooling fins are more efficient, but either will work. Leeches have to reach a certain minimum rpm (on as truck engine) before they start putting out, t6hen will put out constant even at an idle. You just have to tap the trottle after initial start up. That's just in my 12 years of OTR use. Make it turn with whatever power plant you desire. Run two on the same belt? A pair of at a lower amp rating might give you better overall service in the long run. Charge your batteries in two seperate smaller banks, instead of one big one. Then, when you experience that inevitable electrical system breakdown, you still have half of your full power reserve at your disposal. It's just truck experience. But, for what it's worth, I never lacked power for my accesories -- way too much heavy HAM radio gear, and enough halogen load lights to light up Japan from a field in Kansas.
  8. Landlubber
    Joined: Jun 2007
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    Landlubber Senior Member


    yeah mate and a 500hp engine under the bonnet producing the power too, evan at idle....she is still putting out enormous power compared to a little motor.

    300 amps at 12VDC is 3600 watts, 5 hp without any just did not feel the engine grunting to power the alternators.
  9. kb1one
    Joined: Feb 2009
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    Location: Alfred, Maine

    kb1one KB1ONE

    landlubber -- you are right there. I did not feel it. I feel it now though. I feel it every day, even at idle. In fact, I feel it right now, and I haven't even had a cup of coffee yet. I was only suggesting a possible powerhead, readily available. I still have one on the truck (which has gone nowhere for years now), and two spares in my closet.

    I beleive the original question was a home built generator alternative. How to turn it over is not something I was offering. If you will excuse me, I am going to go find that cup of coffee now, and my oversized jug of ibuprofen. Might just be time to find a cortizone shot...

    Godspeede to one and all.
  10. M-Sasha

    M-Sasha Guest

    And I believe the original question was not much more than a schoolboys dream.
    The following statements have shown that very clear.

  11. kroberts
    Joined: Mar 2009
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    kroberts Senior Member

    Sorry for stepping in when the discussion already is so lively, but I have a couple questions.

    First, I failed to find a complete and concise definition of the problem. The first-glance application is for a low powered series-hybrid electric with batteries. I agree that this would be expensive to the point of being prohibitive, especially when you add the phrase "high efficiency."

    An internal combustion engine of automotive scale tops out at about 40% efficiency. A small 5 kw engine is going to be much, much worse. No matter how efficient your generator and (electric) motor, you have already lost a huge amount of power, and that power was lost at the initial phase of power generation. You start with the potential energy of your fuel, then multiply that energy by the efficiency at each stage. Each step takes the number coming out of the previous step as input, multiply by efficiency and you get a number out. Efficiency of a component is usually measured as peak/best efficiency at an ideal speed and is lower for most conditions. By the time you get through the engine, generator, charger, batteries (loss in charging), batteries (loss in discharging), speed controller and motor, you have a small amount left no matter what. Then you figure your prop is 70% efficient.

    However, from the OP's posts I wonder if this is a secondary drive like a trolling motor? Or, perhaps a motor for a sailboat? I missed the part where he said it was the primary drive.

    If this is were a drive for tight maneuvering of a larger boat, to be used for an hour or less and then stowed, then the problem becomes much simpler doesn't it?

    Why not, if it's a sailboat, throw a couple solar panels in a safe spot and have a battery charging circuit maintain your batteries? Silent, fairly reliable and the only costs are start-up purchase and the replacement of the batteries every so often.

    Or, if it's a power boat, charge your batteries with the engine when that is running, or a battery maintainer when possible, and then use batteries when you need to go slow?

    I saw a lot of stuff about a pure solar boat, but these are renderings and I think this boat has never been built or probably even simulated.

    Propeller-driven generator: Hogwash. A propeller being used in regenerative mode in aircraft is around 10% efficient or less, depending on propeller. In my understanding of thermodynamics, you will do no better with a water prop. You would need an impeller such as is used in a hydroelectric dam, which is designed to get power from the fluid to turn a shaft. At that point you get the same efficiency statistics, figure 70% for a good impeller, then you have your generator again.

    Also note that you are trading drag for power. The thrust you get out of the propeller will be a tiny fraction of the drag induced by the impeller, after all the losses are taken into account.

    Now consider that in order to do the best possible, you need to pull in the motor and propeller before using your regenerative system, and vice versa. I know of no boat where you could chop power and then lower a regenerative system into the water in time to get any useful energy out of it.

    If you want to extract electricity from a main drive engine, then put the generator on the engine.
  12. apex1

    apex1 Guest


    thank you for the effort made. But it was wasted. The guy who opened this thread is just a unmature dreamer, he messed up several threads here with unrealistic estimations, thoughts and, as said, dreams. But the worse, he did not like any advice, hint, link etc. if it did not fit his phantasy. At the end he was telling the old salts how deep the ocean.
    Fortunately he noticed eventually, this was not his platform.

  13. Jimbo1490
    Joined: Jun 2005
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    Jimbo1490 Senior Member

    There have been several of these discussions over the last few months, with 'youthful' posters believing that electric motor/generator sets can ALWAYS directly replace a simple engine driving a propeller and improve efficiency. We know that in some cases, this is viable but in most cases, it is not.

    The simple test is to assess the losses in the transmission of the simple 'engine driving shaft' type installation. If these losses are high, then an electric transmission may be viable. If these losses are not great, then there is virtually no hope of viability.

    The key thing to remember about electric vs mechanical power transmission systems is that as size increases, mechanical power transmission becomes dramatically less efficient, while the efficiency of electric transmission increases with increasing size, or at worst, does not fall.

    Thus the electric transmission makes the most sense when the power requirements are very large, such as with a rail locomotive or large cruise or cargo vessel

  14. mark775

    mark775 Guest

    When you were a kid and the others had Schwinn "Sting-Rays"...or, in Germany, an accordian because everybody was doing didn't have to make sense. This person wanted it and asked for help.
    Many know more than I about this stuff, and it is easy to Google an argument for one's viewpoint, so it would be foolish to weigh in at this point on efficiency, practicality, cost-effectiveness, or even design...Maybe not THIS sailboat, but a cruising sailboat is a perfect prospect for regeneration. Another circumstance that comes to mind is a river commuter, tied to the dock in a current (or anchored out) run a half hour upstream to the office, anchor in current again, and run ten minutes home. There was a guy posting about fast commuters here somewhere for which this would be ideal if his distances were less.
    One more aspect that doesn't get much attention is the PR factor. It doesn't have to actually be green to garner green bonus points and maybe, just maybe, the guy IS just curious and maybe a touch naive. Shouln't he still get CONSTRUCTIVE critisism?
    I've tried the crashed Prius route before. The only ones had cheap have been under water. Polka on!

  15. apex1

    apex1 Guest

    He got much more than that, assistance, advice, help, and the like. But was´nt willing or able, even to improve his knowledge to a basic level, during some two weeks. He refused to read two simple articles he was pointed to, but argued if we referred to the results, given there.
    Then on top he claimed to be an engineer, but did not accept some basic physics. Read his posts if you need some entertainment.
    So, let him dream a stone can fly
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