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Degenerative Breaking

  1. Apr 7, 2005 #1

    liv

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    Another one of those holiday assignments we all love.

    would just like some genreal info on degenerative breaking... and why the electrical power that is generated is dissapated as heat into the resistors instead of being fed back into the electrical supply.....?
    thank you!!!

    Liv

    nec hostium timete
    nec amicum reusate
     
  2. jcsd
  3. Apr 7, 2005 #2

    brewnog

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    Sorry, I couldn't help laugh at this one.

    Liv, you might have more success if you look for regenerative braking. Good luck :smile:
     
  4. Apr 7, 2005 #3

    Ivan Seeking

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    This is typically done using variable frequency drives [VFDs], which are an electronic motor control device. These can generate specific waveforms over a range of frequencies, and they control the flow of current using, in addition to other components like diodes, IGBTs, or isolated gate bipolar transistors. Also, about 20% of the rated power of the motor can be dissipated in the motor itself, and any additional braking can be accomplished by adding braking resistors. Of course, the total braking capacity is limited by the size of the motor.
     
  5. Apr 7, 2005 #4

    Danger

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    Hi Ivan;
    You're talking about the kind of brake you find on power saws and whatnot, right? Not vehicles, which usually do regenerate. If so, thanks for the info. I never knew how they work.
     
  6. Apr 7, 2005 #5

    Ivan Seeking

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    This is used throughout industry for most motor applications that require speed control or braking; not for a handheld saw, but say for a large saw in a mill, a press, conveyor, fan etc in a factory, and for applications ranging from fractional to 5000 Hp. Regeneration of power for braking in electric cars should work about the same. In standard industrial motors, the power is dissipated as heat in the motor and braking resistors. In an automobile, the power would be used to recharge the batteries.

    Edit: Note also that even in a car where the braking power is used to charge batteries, the I2R losses in the motor are unavoidable.
     
    Last edited: Apr 7, 2005
  7. Apr 7, 2005 #6

    Stingray

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    The simple answer is that there is a limit to how quickly a battery can be safely charged. In hybrid cars, my understanding is that the energy that could be recovered from braking is usually generated too quickly for all of it to go into charging.
     
  8. Apr 8, 2005 #7

    Ivan Seeking

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    I know there were shuttle busses using this pretty effectively at LAX. I don't know how efficient they were, but the operating costs were reduced enough to justify the investement.

    New battery technology promises to improve the situation in one respect, but obviously this won't work with fuel cells.
     
  9. Apr 12, 2005 #8

    liv

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    thanks for that brewnog! lol

    and for ivan seeking, would you mind dumbing down what you said by about 10 fold cause I'm no that bright and struggle to get the intial concept. What u said kinda just messed with my head....sorry,

    Liv

    Nec Hostium Timete
    Nec Amicum Reusate
     
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