There is no way to make DC motors smaller

Discussion in 'General Electronics Chat' started by strantor, Oct 22, 2013.

  1. strantor

    Thread Starter AAC Fanatic!

    Oct 3, 2010
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    When using induction motors, we can scale down the physical size by increasing the rated frequency. Take for instance this 200hp 60HZ induction motor at 2127lbs, vs this 200hp 400hz induction motor at 85lbs. So for weight sensitive applications like aeronautics or EVs, the 400hz motor is the clear winner.

    But what if we want to use a separately excited would field DC motor? We have no recourse to downsize the motor by anywhere near the same degree.
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    If room temperature superconductors were ever invented then it would happen. Tech moves on.
     
  3. MaxHeadRoom

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    You are probably not going to get a large DC brushed motor that would reach 12,000 rpm anyway.
    The motor in the second link is most likely PM rotor, the same way DC wound field brushed motor have been replaced by the smaller AC PM traction motors in locomotives.
    Max.
     
  4. THE_RB

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    A wound field series DC motor should have MUCH higher torque per package size compared to an induction motor anyway (so it's already smaller).

    Speaking of small DC motors, have you pulled apart a digital camera lately? They use TINY little DC motors for the focus assembly, I'm talking about a DC motor so small you can put it on your fingernail and see a lot of fingernail still showing! :)
     
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  5. PackratKing

    Well-Known Member

    Jul 13, 2008
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    Yessir, I know what you mean... I have several !
    They serve as conversation pieces that have garnered more work for me than I can handle...[ Oh wow !... you can do that stuff:eek: ? ]
    I get to Pick and choose profitable work, and leave the potential disasters slide :)
     
  6. strantor

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    It's an induction motor. I queried the manufacturer. I have lots of info about it now, if you're interested.
     
  7. strantor

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    Yes, but torque is only half the equation. Have you seen a 200 hp wound field DC motor anywhere close to 85lbs?
     
  8. MaxHeadRoom

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    No, but the construction requirements prevents this for this technology?

    But most likely the same condition occurs with the other high frequency induction motors, which are unable to be ran at below 120Hz due to construction which amounts to the Induction value below this frequency.
    Max.
     
  9. strantor

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    Your unorthodox use of question marks has finally gotten me; are you agreeing with my original statement that it's impossible, or are you asking a rhetorical question?

    The chart in the datasheet from the manufacturer suggests otherwise. Upon closer examination of the datasheet, it appears that the 200hp rating might be optimistic to the point of fiction. a "peak" of a "peak" rating, not continuous. If rated in the same way that NEMA requires, it might not even pass as a 50 hp motor. I wish I could upload the datasheet, but I'm on my phone now.

    EDIT: datasheet attached.
     
    Last edited: Oct 23, 2013
  10. THE_RB

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    Maybe the induction motor is more powerful (per pound) in a specific fixed speed high-RPM situation, but DC motors come in plenty large packages and generally offer higher performance.

    AC motors to save money, DC motors for best performance. At least that's the way the industry WAS. :)
     
  11. strantor

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    You imply that your perception of the industry is outdated; how recently were you last on the cutting edge? My perception is that AC has all but ran DC out of the industry. DC is almost never considered for any application higher than 5hp. AC is cheaper, and has become as good or better than the best DC can offer. Even servos are AC now.

    I am interested in DC for EVs because I am convinced that they are much better at regenerating than AC induction.
     
  12. THE_RB

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    I was last working with heavy industry motors (seriously large motors) in 1984. :)

    These days VFD electronics are so small and cheap they can get great performance from "AC" or BLDC motors (the lines are blurring).
     
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