TKO Electric / Solar Concept

Discussion in 'Boat Design' started by TKOUSA, Jul 16, 2012.

  1. Red Dwarf
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    Red Dwarf Senior Member

    I have been following this thread and I am lost. Either TKOUSA is not a native English speaker so we are losing something in the translation or TKOUSA has no engineering background. If you want any usable input from people on this forum, please put ALL the details down on one page.
     
  2. TKOUSA
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    TKOUSA Junior Member

    Okay so what we really want to argue here is torque. A gasoline motor has a peak torque value for a given RPM (3600). It’s easy to peg that as a HP rating – measured torque at a fixed RPM.

    An electric motor produces torque in response to load. You load it, the RPM drops, and it draws more current and produces more torque. It’s more of a moving target, so you have to rate it, rather than the actual horsepower it produces, the horsepower it can produce at a given load.

    That being said the torque produced by this motor is equal to a 48 HP Diesel according to their use on Mars, as well as here on earth in sailboats ...
     
  3. Jeremy Harris
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    Jeremy Harris Senior Member

    Torque is irrelevant, I'm afraid, as the propeller torque load is very low at low rpm. Propeller power absorption follows a cube law relationship with rpm; double the rpm and the power required increases by eight times.

    I've lost count of the number of times I've heard the torque argument applied to justify the false claim that electric hp is greater than gasoline engine hp on a boat. The bottom line is that a low torque gasoline engine, like a two stroke, is a reasonably good match to a propeller's torque requirement, whereas an PM electric motor is capable of producing far more torque than the propeller can absorb, meaning that, in practice, it ends up delivering exactly the same torque at any given propeller rpm as any other engine would. It's simple physics, in that no matter what the engine driving it, the propeller torque requirement will be exactly the same at any given rpm.

    This is unlike land vehicles, BTW, where the high torque at low rpm characteristic of a PM electric motor does indeed make a vehicle feel more powerful, by allowing more hp to be produced at low rpm. Unfortunately propellers don't behave the same way at all.

    Getting back to your boat again, if you let us know the total primary energy source you intend using then we can try and help when it comes to performance, component sizing etc.
     
  4. TKOUSA
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    TKOUSA Junior Member

    Attached Files:

  5. Jeremy Harris
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    Jeremy Harris Senior Member

    Sorry if I've misunderstood, but that diagram looks like the only energy source is the small stored charge in the battery.

    If the PMAs are being driven by battery power, what are they feeding, and why are they there? Clearly they cannot charge the battery, as that would be a futile attempt at creating a partial perpetual motion machine, and defy the law of conservation of energy.

    If you want to put charge into the batteries that exceeds the power being drawn by the system from the batteries, then you need another source of energy. It's this missing energy source that has me puzzled.
     
  6. TKOUSA
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    TKOUSA Junior Member

    The PMAs create 12 volts each 1000 Watts each. How long would it take 6 of these to charge the batteries?
     
  7. daiquiri
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    daiquiri Engineering and Design

    Ok, you want to charge the batteries with the PMAs.

    Now comes a question, please give us an answer:

    What or who drives the PMAs?
     
  8. TKOUSA
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    TKOUSA Junior Member

    Porsche and many other car companies are engaging on line generators to extend range... the design follows their proven concepts. As far as your comment about torque and water, that brings us to the prop. In larger catamarans the same group who makes this motor recommends the following ... Our Cherubini 44 installation carries a 20 inch diameter 16 pitch prop. Our Saga 43 installation has an 18x18 prop, as does our recent 51’ Gold Coast cat installation. Our 35’ Tektron cat installation sports an even more aggressive 16x20 prop.
     
  9. FMS
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    FMS Senior Member

    Most "wasted" energy recovery concepts which work for cars do not apply to boats. Cars have regenerative braking and spend most of their time idling. Boats need constant power. There is no downhill and no braking. The concept of generating power at anchor has been discussed.
     
  10. Stumble
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    Stumble Senior Member

    If the power to operate the PTO is from the batteries, it will never charge them, but drain them instead.

    You cannot draw power from the batteries to operate an alternator to charge the batteries. Well you can, but it will slowely drain power from the batteries, and cannot add more than it drains. Otherwise you would have a perpetual motion machine.

    If the alternators are being driven by a gas/diesel engine then would depend on the charging efficiency of the charger, the voltage of the output, and the size of the batteries as well as the output from the alternator.
     
  11. daiquiri
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    daiquiri Engineering and Design

    I've been given an info through a private message about the manufacturer of the motor. I don't see anything wrong in sharing that info, because it is a company with a public website which advertises their marine electric drives. It is the Ikanos Technologies (www.ikanostech.com), and the motor is presumably the ST 74 model: http://www.ikanostech.com/index.php/electric-motor-drives/st-74-electric-motor

    Now, I don't see that they are explicitly saying that 12 HP electric equals 48 HP diesel in their website (a hint about it is visible at the end of this page: http://www.ikanostech.com/index.php/propeller-size), but some articles in the sailing magazines do, and they must have taken that info from someone, so... Examples: http://www.masteryachting.com/files/lagoon_elec.pdf and http://www.electricmarinepropulsion.org/Newsabout/CWMarch05.PDF

    So where does that claim comes from? It comes from considerations on torque only. Yes, the 12 HP ST74 electric motor will indeed give a torque equal to a 48 HP diesel (like a BUKH model DV48 ME: http://www.kalundborgbaadebyggeri.dk/documents/bukh/bukh_marine.pdf). The ST74 gives a constant torque of 74 lb ft (around 10 kgm) over the whole RPM range, whilst a BUKH DV48 gives a torque between 8 and 10 kgm in it's operating range.

    So... where is the catch? It is in the RPM range. The ST74 works between 0 and 900 RPMs, while a DV48 works between 1200 and 3600 RPMs - 4 times higher revs. Hence, a same prop shaft connected to the output shafts of, respectively, an electric and a diesel engine will work in extremely different conditions in two cases.

    Now, remember that:
    1) Power is directly proportional to the Torque times RPMs
    2) Torque is directly proportional to Power divided by RPMs
    .

    So if you attach a, say, 4:1 reduction gear to the output shaft of a diesel engine, then both engines will deliver their power to the prop shaft at the same RPMs. However, by reducing the diesels RPMs by a factor of 4, the torque will be multiplied by the same factor, because the output power remains constant 48 HP and the mathematical relationship n.2 is valid.

    The above situations are well visible in these comparative graphs: View attachment 12 HP Electric vs. 48 HP Diesel.pdf
    The first one shows the RPM-power and RPM-torque curves for the ST74 and the DV48 engines. Essentially, the diesel carries on where the operational range of the electric motor stops.
    The second graph shows what happens when a 4:1 reductor is attached to the diesels output shaft. Here the 48 HP diesel clearly shows its bigger muscles over the 12 HP electric motor, and is superior over it both in power and in torque.

    So the claim "12 HP electric motor is equal to a 48 HP diesel" is only true if just the torque is considered and there is no reduction gear at the diesel's output shaft.

    For curiosity, let's see it from another point of view. What happens if we compare the ST74 motor to a 12 HP diesel engine, like this one: http://www.dek.co.nz/diesel-engines?
    Here come the two graphs showing that situation: View attachment 12 HP Electric vs. 12 HP Diesel.pdf
    The first one shows again the different RPM range for the motors, and a clearly inferior torque value of a diesel (at high RPMs).
    The second one shows the same diesel with a 4:1 reductor. A miracle! The two curves now look almost identical, except for the low-RPM (below 400) zone, where diesel cannot work.

    So, clearly, a 12 HP electric gives the same power and torque as a 12 HP diesel, at the same RPMs.

    It is a physical banality which can be deduced directly from the two mathematical relationships previously written in bold letters, and it says nothing different from what Jeremy Harris wrote in his post #48. However, I think it might be even better understandable through colored graphs like the ones shown here.

    Hope it helps making it clear once for all.

    Cheers
     
  12. masalai
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    masalai masalai

    A total waste of time... All other posters have ably demonstrated that TKO is officially trying to create a perpetual motion machine and "missed the boat"... I move the motion, that he be awarded a "Technical Knock Out"...
     
  13. daiquiri
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    daiquiri Engineering and Design

    :D Nice one.

    My post was not about this particular boat. It is an effort to try to dismantle the myth about HPs from an electric motor being different from HPs from a diesel engine.

    Cheers
     
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  14. TKOUSA
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    TKOUSA Junior Member

    We considered both designs at first, and we are talking now through that discovery - trying to bring others up to speed
     

  15. TKOUSA
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    TKOUSA Junior Member

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