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Thread: Voltage Drop??

  1. #11
    Join Date
    Sep 2008
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    All aspects are consistent with very minimal variables. In this case there are two other motors present at about one quarter of the distance to the furthest motor and all appear to start and reach full load/RPM within the same amount of time. What would be considered a marginal difference to start and get the motor to full RPM? Is the time exposed to the start in rush extremely minimal...say .5 seconds etc? Motors and motor loads seem to have so many variables that it's interesting to learn and understand more. I appreciate every ones time and I encourage any additional feedback or recommendations in regards to this thread.

  2. #12
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    191109-1014 EST

    jahilliard:

    You need to study a lot of basic theory --- physics and electrical.

    I suggest that motors for the most part do not exhibit inrush current, but rather what many call inrush is really motor starting current. Motor starting current can last for a substantial amount of time, like many seconds. Its duration is a function of available torque and mechanical load. Inrush for the most part would occur for about 1/2 cycle.

    .

  3. #13
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    Quote Originally Posted by gar View Post
    191109-1014 EST

    jahilliard:

    You need to study a lot of basic theory --- physics and electrical.

    I suggest that motors for the most part do not exhibit inrush current, but rather what many call inrush is really motor starting current. Motor starting current can last for a substantial amount of time, like many seconds. Its duration is a function of available torque and mechanical load. Inrush for the most part would occur for about 1/2 cycle.

    .
    I would suggest that the instantaneous starting current at T=0 is indeed inrush and is independent of load.
    Once rotation begins, assuming it does begin to rotate, I would term as starting current and it is very load-dependent both in magnitude and duration.

  4. #14
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    181109-1535 EST

    retirede:

    Can you instantaneously change the current in an inductor? No. If the current in a motor at t=0- is zero, then is there an inrush current at t=0+? Where t=0 is when voltage is applied to the motor?

    In the first half cycle of applied power to a motor is there any large peak current into the motor other than defined by the torque load? I have not observed any. Residual flux in a motor core is not generally much, and thus core saturation at startup isn't much, and thus, not much inrush current.

    See my thread at
    http://forums.mikeholt.com/showthrea...tartup+current
    for plots of motor starting currents.

    .

  5. #15
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    Voltage Drop??

    Quote Originally Posted by gar View Post
    181109-1535 EST

    retirede:

    Can you instantaneously change the current in an inductor? No. If the current in a motor at t=0- is zero, then is there an inrush current at t=0+? Where t=0 is when voltage is applied to the motor?

    In the first half cycle of applied power to a motor is there any large peak current into the motor other than defined by the torque load? I have not observed any. Residual flux in a motor core is not generally much, and thus core saturation at startup isn't much, and thus, not much inrush current.

    See my thread at
    http://forums.mikeholt.com/showthrea...tartup+current
    for plots of motor starting currents.

    .
    I’m good with that....

    What I should have said was that until the motor starts rotating, it draws locked rotor current regardless of the shaft load.

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