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Coil electrodynamics

Discussion in 'Electronic Design' started by Karl Roberts, Oct 28, 2011.

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  1. Karl Roberts

    Karl Roberts Guest

    Can anyone please clarify the following for me?

    Two part question:

    If I take a solenoid and feed a positive DC offset sinewave (ie. 6V
    max 2V min) into one end and an inverted copy with a similar negative
    offset (ie -2V max -6V min) into the opposite, what, in terms of
    electrodynamics, occurs within the coil?

    If I now split the coil in half and ground the center point, what
    happens now?

    Karl Roberts
     
  2. Phil Allison

    Phil Allison Guest

    "Karl Roberts"
    ** The voltage across the coil varies from 4 to 12 volts in a sine wave
    fashion - IOW an 8 volt p-p sine wave with a DC component of 8 volts. So
    a current will flow in the coil that depends on it's impedance at the
    frequency of the sine wave AND it's DC resistance.

    The mag field inside the solenoid will be in proportion to the instantaneous
    value of the combined currents.


    ** This is ambiguous.

    What does '"split the coil in half " mean ?

    Grounding the center point has no effect, on it's own.

    Good enough for homework ??



    .... Phil
     
  3. Karl Roberts

    Karl Roberts Guest

    But don't two identical waves 180 degrees out of phase cancel to zero?
    Or does the symetrical DC component change this?

    I gather from your kind reply, the answer to the last question is
    "yes".

    This is what I am trying to visulaize/understand.

    Karl Roberts
     
  4. mike

    mike Guest

    It melts.
     
  5. Phil Allison

    Phil Allison Guest

    "Karl Roberts"


    ** Only if they are summed.

    In your example the coil sees the * difference *.

    As any load connected between two terminals does.

    Very basic stuff.

    Try " sci.electronics.basics " - next time.





    .... Phil
     
  6. DonMack

    DonMack Guest

    "Karl Roberts" wrote in message
    Can anyone please clarify the following for me?

    Two part question:

    If I take a solenoid and feed a positive DC offset sinewave (ie. 6V
    max 2V min) into one end and an inverted copy with a similar negative
    offset (ie -2V max -6V min) into the opposite, what, in terms of
    electrodynamics, occurs within the coil?

    If I now split the coil in half and ground the center point, what
    happens now?

    -----------

    Do you realize that voltage is relative? You can add any voltage to one
    point as long as you add it to any other and the "physics" will not change.

    So, your first case is identical to setting one side to 0 volts and the
    other side to (2sin(wt) + 4) + (-4 - 2sin(wt)) = 0. So both ends of the coil
    are at the same voltage. I could have set one end to Zeta(wt)^w +
    cos(wsinw(wt))^t and wouldn't have changed anything.

    In the second case when you ground the center you end up with two coils. You
    can separate them mentally or even physically since you know(or forced) the
    center(or even some other point) to be a certain value. It is exactly the
    same when we know(force or decide) that something is "ground".

    Note that this is distinctly different from the first case. In the first
    case we have one coil and the second case we have two... but each one
    similar to the others.

    Anyways, if you think about it a bit you shouldn't have any issues. Use
    resistors instead of coils. The only difference with coils is that the
    voltage drop across the coil may not be linear due to self and mutual
    electromagnetic effects and fringe effects.
     
  7. Karl Roberts

    Karl Roberts Guest

    What? ... and get answers from more people like me.

    Karl
     
  8. Phil Allison

    Phil Allison Guest

    "Don Mack"

    " If I take a solenoid and feed a positive DC offset sinewave (ie. 6V
    max 2V min) into one end and an inverted copy with a similar negative
    offset (ie -2V max -6V min) into the opposite, what, in terms of
    electrodynamics, occurs within the coil? "

    ** That is completely absurd.

    The two voltage sources are summed in series, so the total is 8 + 4sin(wt).

    ** Drivel.


    ** More absolute drivel.


    ** Take your own advice - fool.


    .... Phil
     
  9. Karl Roberts

    Karl Roberts Guest

    In that case, given my original example of a + and - 2VDC offset for
    each idendtcal sinewave, there would be a residual DC current flow at
    4V from one end of the coil to the other.

    Going back to having one sinewave inverted from the other, I
    understand (now) the voltages add to 12 and the composite signal is
    riding on the same 4V current.

    Is that all correct?

    OK, that's my last follow-up.

    Karl Roberts
     
  10. Phil Allison

    Phil Allison Guest

    "Karl Roberts"
    " J.A. Legris"

    ** FFS pal - you just contradicted yourself.

    The new case is VERY DIFFERENT from yuor example !!.



    ** Thick as a plank.

    The offset voltage is 8 volts - cos that is the AVERAGE value of 8 +
    4sin(wt)

    The sine wave both adds to and subtracts from the DC offset - giving 4 and
    12 as the min and max values.


    .... Phil
     
  11. Phil Allison

    Phil Allison Guest

    "Karl Roberts"
    "Phil Allison"

    ** Hey dickhead.

    Have a look and see who is supplying most of the answers.

    The NG is about basic electronics, like your question.



    .... Phil
     
  12. MrTallyman

    MrTallyman Guest

    Where do see the application here being that of a solenoid? He did not
    mention one.
    Since you seem to think he is referring to a solenoid maybe?
     
  13. MrTallyman

    MrTallyman Guest


    IOW, you react with: "When slapped, I dance like a little girl..."

    Now, you tell us that you cannot even grasp a 100% *BASIC* netlist.

    Logic 2
    John G 0
     
  14. John S

    John S Guest


    Always wrong as usual. Look in the first sentence following the "Two
    part question:" above, AlwaysWrong. Damn, you're stupid.

    Since you couldn't find your ass with both hands, AlwaysWrong.
     
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