Brushed DC motor noise

Discussion in 'General Electronics Chat' started by AidanCroft, Nov 28, 2015.

  1. AidanCroft

    Thread Starter New Member

    Jan 7, 2015
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    Hello all,

    At work we have large 277kW brushed DC motors for traction purpose (four per vehicle).

    Under powering and braking (regenerative braking is used) the tone of the motor ascends and descends respectively but is largely silent during coasting. I assumed that the noise came from brush/commutator interaction but I would still expect mechanical interaction, at least, during coasting.

    Can anyone suggest where the noise is coming from?

    Kind regards,

    Aidan.

    Motor brushes (1).JPG Motor gear interface (1).JPG
     
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  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I suspect that they are driven from an AC supply that has a full wave SCR controller, this would account for the switching noise that is common, even in small T.M. motors that use this type of drive.
    Max.
     
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  3. AidanCroft

    Thread Starter New Member

    Jan 7, 2015
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    The overhead is 750V DC using GTO thyristors to supply DC to the motor via brushes.

    Aidan.
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    OK so the Thyristors would be the origin of switching noise in the windings for my guess.
    Max.
     
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  5. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Rapid switching/commutation could possibly introduce noise via magnetostrictive effects, or via current-induced forces between adjacent conductors.
     
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  6. AidanCroft

    Thread Starter New Member

    Jan 7, 2015
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    The GTOs chop on and off at a fixed frequency (250Hz) but altering the width of the pulse. This is smoothed by various devices such as capacitors etc.

    From a standing start the motor makes a very deep rumbling noise that of course increases in tone. At any speed, the noise stops during coasting.

    Thanks,

    Aidan.
     
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
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    That would make sense as the Thyristor switching only takes place during accel and braking.
    Max.
     
  8. AidanCroft

    Thread Starter New Member

    Jan 7, 2015
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    Would this be the case even though the GTO chopping frequency stays the same for the whole Voltage range? Only the width of the pulse itself changes.

    Since my last post, I was also wondering if it might be due to arcing on each commutator bar and/or magnetisation of individual portions of the rotor coils?

    Aidan.
     
  9. RRITESH KAKKAR

    Senior Member

    Jun 29, 2010
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    Hello ,
    what are you building from such big motor, i am sure i will learn something from you.
     
  10. AidanCroft

    Thread Starter New Member

    Jan 7, 2015
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    I'm not building anything unfortunately. They are part of these vehicles -

    Park Grange 22-07-2012 (2).JPG
     
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  11. RRITESH KAKKAR

    Senior Member

    Jun 29, 2010
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    Hello,
    Motor is DC Brushed then from where AC being used?
     
  12. BillB3857

    Senior Member

    Feb 28, 2009
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    DC supply goes to GTO chopping circuit to create PWM to drive motor. Noise can be the result of pulsating torque. During ACCEL and DECELL, current limit may be causing the PWM percentage to change at a non-linear rate and creating a beat frequency with the 250Hz chop rate.
     
  13. AidanCroft

    Thread Starter New Member

    Jan 7, 2015
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    AC is not present anywhere. This is purely a DC arrangement.

    That makes sense. What is causing the pitch to rise during acceleration? It really does start with quite a low rumble and it gets progressively higher. As soon as power is taken off the noises cuts out and when power is applied again the tone starts again at the pitch that it last left off from.

    Aidan.
     
  14. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Without any instrument involvement all is purely conjecture.;)
    Max.
     
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  15. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Google magnetostriction

    It is the same electromechanical effect that makes a transformer Hum. The higher the current, the more noise. You say pure DC but most likely Pulse Width Modulated to avoid abrupt starts/stops and passengers flying ass over tea kettle. PwM can be argued as an AC signal. All in the semantics.
     
  16. BillB3857

    Senior Member

    Feb 28, 2009
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    Here is a current plot for Acceleration, up to speed, and Deceleration based upon a 3 phase full bridge SCR drive. The main difference between the SCR drive and the OPs drive is the GTO drive will provide the effect of commutation that the 3 phase AC accomplishes in the SCR drive
     
  17. RRITESH KAKKAR

    Senior Member

    Jun 29, 2010
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    Then you must be using pwm
     
  18. MaxHeadRoom

    Expert

    Jul 18, 2013
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    See post #6 ;)
    Max.
     
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