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120V from both legs

Discussion in 'Electrical Engineering' started by John Doe, Oct 4, 2004.

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  1. Don Kelly

    Don Kelly Guest

    Power transferred to the mechanical side will be Eg*I* cos( angle between I
    and Eg)
    That old power factor thing again.
    This gross mechanical power is equal to Dv^2 where v is the velocity
    D is the combination of mechanical and acoustic resistance of the speaker
    system. To separate the acoustic output from the mechanical loss requires a
    more detialed model. Again Beranek shows this but Kinsler has a clearer
  2. Don Kelly

    Don Kelly Guest

    Sort of: The angle referred to is not the difference in direction as you
    have implied but the difference in time phase- that is a power factor angle.
    If Eg and I are treated as phasors, then force and velocity can also be
    treated as phasors.

    Force and velocity in a speaker are in the same direction but need not be in
    time phase. If the force and velocity were not in the same direction, then
    the physical difference in direction would have to be taken into account as
    well as the power factor angle.

    Note that the frequency response curves are generally done on a rms basis
    with a single sinusoidal input whose frequency is varied over a range.
  3. Don Kelly

    Don Kelly Guest

    1) Yes (also phase difference between rms velocity and force)
    2)Yes. Note that it is the same magnitude as the angle between Eg and I on
    the electrical side
    3) Yes -analogous to the electrical case.

    Note that mechanical "impedance" F/V appears as an admittance I/Eg as seen
    from the electrical side
    Note also that Eg*I*cos (angle) =V*F*cos (angle) gives the total power
    transferred - not the output power.

    PS I called K spring compliance this should be stiffness (1/compliance).
  4. Tom Grayson

    Tom Grayson Guest

    The professional Engineers you so quickly denigrate here, have been
    posting here for a long time and have contributed selflessly to many an
    honest request for help. As a professional engineer myself, I go over what
    they write and suggest, Partly to see if there is something more for me to
    learn but also to see if they are correct and not bullshititng. ( I have yet
    to find an instance where they have seriously mislead or missinformed an
    honest question) Needless to say The arguments and advice they put forward
    are almost always based on Solid Electrical Engineering Theory and practice.

    Remember that the profession of Electrical Engineering is based on the
    professional work and publications recognized and recomended by the
    various institutes of Electrical Engineers around the world.
    I think very little of it is based on what you can find with a "google
    Search" of the internet or the marketing material published in the Various
    electrical trades magazines.

    The fact that most of us choose to ignore these long and tedious threads you
    create does not, in anyway, endorse what you say.

    Without having the full benefit of the deleted history of these threads, I
    can only go on what appears today, and looking through the threads I see
    very true things written by Don, Charles, and Daestrom and a confusing
    mixture of engineering terms, Miss-quoted physics terms, gut feelings and
    "Buzz words" from yourself.

    My suggestion to you is that you stay away from Electrical Engineering as
    your knowledge is embarrassingly deficient in this field. Maybe you should
    stick to quoting Electrical codes and leave the real engineering to those
    who are clearly Qualaified to do so.

  5. WRONG again! Dang you should learn to read. You really should look up back
    EMF and find out what that term really means.

    Reactive current is not back EMF, harmonics from adjustable speed drives is
    not back EMF. All of the math that was shown was done so to prove you
    wrong. Get over it.

    Charles Perry P.E
  6. Tom Grayson

    Tom Grayson Guest

    I'm with you charles, It is just this guy seems to have his own
    beliefs regardless of what the majoritory of main stream Engineering has to

    Tom Grayson
  7. daestrom

    daestrom Guest

    You're right Charles, of course. The poor guy, doesn't even recognize which
    side of the argument so many of the posters are on. Doesn't realize when a
    person's post refutes his arguments. Would rather just stick his head in
    the sand and pretend he has supporters.

  8. Tom Grayson

    Tom Grayson Guest

    You're right Charles, of course. The poor guy, doesn't even recognize
    Or pretends he has knowledge
  9. When in doubt, IEEE STD 100. All of your questions regarding the
    definitions of electrical engineering terms will be answered. And to answer
    your question, no, emf still means what it always has.

    Charles Perry P.E.
  10. Tom Grayson

    Tom Grayson Guest

    Maybe you are right Phil,
    From my experience, the changes from "recent" innovations in Electronics are
    mainly applied in the "Control" side of things, not just motion control but
    also in power monitoring and analysis.

    One of the points I emphasise when teaching electricians and engineers about
    the more advanced control systems we now supply to customers, is that OHMS
    LAW is still valid and that equations for AC and DC motors are still 100%

    I Do and say this because, these days, the young as well as the older (or
    should I say "Experienced") electricians seem to want to Blame the recent
    technology thingo's first and then go looking at the traditional things
    secondly when trying to find something that has gone wrong.
    From Experience it is the same old things that go wrong now that did 25
    years ago. The art of "Card Swapping" seems to have evolved in place of
    good solid analytical Deduction.

    I am not saying that AC and DC Drives, or PLC's do not fail, They Do, But
    mostly the problems in the industrial applications that I am involved with
    are outside of the control system.

    I know I am geting "off Subject" a little here, but I firmly stick to the
    traditional theories of Counter EMF, Harmonic Current content, Power factor
    and Motor Theory and they are yet to be proven wrong.
  11. Don Kelly

    Don Kelly Guest

    My two bits worth-
    Faraday and Lenz's Laws give e=-d(N*phi)/dt in an N turn coil with flux
    This can be broken into two terms:
    a) a transformer voltage
    b) a speed voltage
    In a motor or generator (b) is the dominant mechanism and the voltage so
    produced is the generated voltage in the generator and, in the motor, this
    is what is called the "counter" or "back" emf. It is still simply a speed
    "generated" voltage. It is "counter" or "back" in that it is of the same
    polarity as the applied voltage and opposes it.

    The only essential difference between a motor and a generator is in the
    direction of power flow.
    Yes, Tom's old fashioned motor concepts still apply
  12. daestrom

    daestrom Guest

    Quite right. We used a style of motor-generator consisting of an AC
    synchronous motor driving a DC generator to charge ship's battery. Whenever
    we needed to reduce the load on the ship's normal AC generators, we just
    decreased the DC generator field currently slightly. The DC generator power
    flow would drop to zero and reverse. The AC synchronous motor's power angle
    would smoothly drop to zero and rise on the other side of the bus voltage
    and power would begin flowing from the ship's battery to the AC busses. No
    relay contacts, switching, or anything. Just a slight reduction in the
    field current on the DC machine and it smoothly transitions power flow from
    one direction to the other.

    And the problems today of harmonics are not because of some mystical
    'sending back' to the generating station the harmonics of non-linear loads.
    They are quite easily explained and analyzed by studying the non-linear
    current flows and the impedance in the supply. The lower the supply
    impedance, the less a distorted voltage drop is created by a non-linear
    load's non-sinusoidal current.

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