diesel electric

Discussion in 'Hybrid' started by whitepointer23, Oct 4, 2015.

  1. WestVanHan
    Joined: Aug 2009
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    Location: Vancouver

    WestVanHan Not a Senior Member

    A 93% motor,hooked to assuming a 93% generator and assuming 99% control efficiency still equals only 85% efficiency.....

    Anyways to find efficiencies you should be able to find fuel use at rated loads for diesel gen set.
     
  2. pdwiley
    Joined: Jun 2008
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    Location: Hobart

    pdwiley Senior Member

    Soooo..... you're telling me that you can put 7 kW continuous through an 8mm diameter shaft???? Because I'd really like to see it and that's the claim on their web page......

    PDW
     
  3. groper
    Joined: Jun 2011
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    Location: australia

    groper Senior Member

    It happens routinely in their intended usage - which is high perfomance radio controlled helicopters, if you havnt seen what they can do you should look them up and watch the videos online, they are very impressive performers. Search out "3D RC heli" and have a browse... If full size military aircraft could perform anywhere near what they can, they would be impossible to shoot down...

    They can only sustain this rating for 3 mins before heat builds up and risks cooking the windings however, after 3 mins, the motors and batteries will burn your hand if you touch them... Obviously, i was not suggesting these types of motors to be used in yacht propulsion, it was simple to show that the technology can be scaled down. Much progress has occured with electric motors and their drive controllers over the last decade or 2, and if your prepared to do the homework, a reasonably efficient DE system could be realised provided the system is carefully designed.

    My point has always been, if you just chuck a cheap diesel genset in and run any old electric motor off it, then you will invaribaly end up with poor efficiency. The reason for this was as i showed eariler, and that is you end up with poor power factor. The poor power factor has a direct bearing on the efficiency of the generator. The reactive power compoent of an inductive motor (VAR) causes a back EMF in the armature of the generator which distorts its magnetic field from where it can operate efficiently. The prime mover has to work harder to yeild the same electrical kw output. Reactive power does no useful work, however it still must be generated in the first place. Poor power factor is caused by the current lagging the voltage, as the peak current does not occur at the peak voltage on the sine wave, you need more current to account for the lag or slight phaze shift, and so the cable must carry more current, generate more heat, and generate more current in the first place for the same amount of useful power. This occurs no matter what type of generator you are using, so to correct it you must use power factor correction or a motor which does not cause excessive lagging power factor - such as a synchronous AC motor - which is what they use in larger ships for this reason. A simple small capacitor system could be employed on a small scale system for a yacht, or better yet a combination of generator, charger, and VSD with low speed DC motor such as those available from evdrive.com

    The reason you see so many failed attempts at DE is because many people simply dont understand enough about it to design the system properly and acheive a reasonable efficiency, it has nothing to do with scalability or some such, just good electrical design which results from proper training and education in this field...
     
  4. whitepointer23

    whitepointer23 Previous Member

    If you look up fixed wing rc aerobatics. Some of the electric models produce bursts of up to 60 horsepower not bad for a motor you can hold in one hand.
     

  5. Joakim
    Joined: Apr 2004
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    Location: Finland

    Joakim Senior Member

    Actually they have a 6 mm diameter option for the same power. 15 000 rpm and 7 kW leads to 4.5 Nm torque.

    Using the formulas from http://www.engineeringtoolbox.com/torsion-shafts-d_947.html

    You get that the maximum shear stress with 4.5 Nm and 6 mm will be about 100 MPa, which isn't really much for high quality steel.
     
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