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dc motor vs ac motor

Discussion in 'Electric Vehicles' started by franzellin, May 6, 2016.

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  1. franzellin

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    I am future tesla3 driver but I am also an old electric scooter driver, with more than 35.000 km

    The main difference between an electric scooter with 80V and 4.8 Kwh batteries and 150 A controller with DC brushless motor on the rear wheel and a Tesla, is the AC motor in the rear transmission with till 700V

    Speaking with the scooter producer in China , mr.Chen, he tells me that the last DC controllers are able to support till 500A and an E scooter could easely increase the installed batteries over 100 V with always 5kwh capacity and could be also an insane e-scooter
    My e-scooter has a consumption of 62W/km with my way of riding and streets, a TESLA I read has an average of 250W/km, but in Singapur 450W/km

    The questions that I would like to ask and receive an answer is:

    1?) There must be a reason why all EV car producers use AC motors, it sounds illogical because the energy is DC,

    somebody tells me that AC motors are standard in the industry and are easier to purchase but sounds illogical

    2?) what is the transformation loss from DC to AC? 1%? if it is so small makes only 4km range


    thanks - renato
     
  2. garsh

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  3. franzellin

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    thanks, the link was perfect to begin my short quest for explanations:

    I understood that a "Tesla" motor, is cheaper, no risks of rare earths embargos, once the electronics is programmed, you do not need other investments and it is perfect for high powers, the only disadvantage seems to be the increased heat production that has to be controlled.
    Independently that this motor was the first one used by Tesla, seems that it is still the best choice
     
  4. TitanG

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    I remember hearing about Porsche's new Mission E electric sedan would be using permanent magnet (PM) synchronous motors, so they will be using DC brushless motors. Seems like Porsche thinks they have the best method -- something I disagree with because of how bad PM's are for the health of people, and the towns, that mine them.

    According to this article (http://www.gizmag.com/porsche-mission-e-production/40786/) though, even this health tradeoff does not seem worth it from a performance standpoint as it does not accelerate as fast as a Model S P90D, but it will have slightly more range than a Model S 90D. This may be due to the increased thermodynamic efficiency of the brushless DC vs induction; however, it could also be due to a more aerodynamic car shape or bigger/better battery, so the health/danger tradeoff is not worth it.
     
  5. franzellin

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    and 800V working tension
     
  6. TitanG

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    Yeah, well I guess VW (Porsche's parent company) has to make amends for the whole diesel scandal. Only problem is that they'll create another one with these PM's....
     
  7. franzellin

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    by the way I read that VW decided to build a Battery Gigafactory in Germany, in the neighborhood of one of their Motor plants, to prevent the closing of the factory in the future due to evolution to e-motors
     
  8. TitanG

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    Yeah I think I heard about that. It's great to hear but my blood still boils over their whole diesel scandal.
     
  9. John

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    Choosing an AC motor is smart if you think that electronics and software will get cheaper and can be easily enough developed. Although AC motors require more "smarts" to work well in a wide range of conditions, once you have those smarts you have more control over power and efficiency. You can do things like "field weakening" in various conditions to control losses that you can't do with magnets, which always produce the same fields.

    History has shown that the cost of electronics and software drop faster than just about anything else. (Maybe music is the exception to that.)

    But if you and I were cobbling together something, we might choose a DC motor because it simpler to develop.
     
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  10. garsh

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    I should also mention.

    1) Actual DC motors have a huge problem. They require brushes that wear out and need to be replaced periodically. It also results in a lot of sparking as the brushes cannot always be in good contact with the rotor, which results in poorer efficiency and a smell of ozone.

    2) Brushless DC motors are similar to AC motors, in that some type of inverter circuitry is used to generate the rotating magnetic field. So they have the same conversion inefficiencies as AC induction motors.
     
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  11. Kizzy

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    I decided to look up the difference for myself. The film on this page filled in a lot of gaps in my knowledge.
     
  12. Badback

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    Brushless DC motors require permanent magnets in the rotor, this adds cost and weight.
     
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