LT SPICE and resonance

Discussion in 'Homework Help' started by Nelson2001, Sep 26, 2012.

  1. Nelson2001

    Thread Starter Member

    Nov 10, 2011
    27
    0
    Hi, I'm trying to graph the series in LT SPICEresonance, making a AC sweep analysis.


    SIMPLE RCL circuit in series
    *
    VS 1 0 SIN(0 10 166.81) AC 100
    *
    RESISTOR 1 2 4
    CAPACITOR 2 3 10uF
    Linduc 3 0 100mh
    *
    * ANALYSIS
    .AC DEC 9 10 1MEG
    *.TRAN 10s 10.02s 10s
    * VIEW RESULTS
    *.PRINT VP(2) vm(1,2)
    *.PLOT AC VM(2) VP(2)
    *.PRINT TRAN V(1) V(2)
    *.PLOT TRAN V(1) V(2)
    #autoplot 1 v(1,2) v(2,3) v(3)
    #autoplot 2 i(RESISTOR) i(VS)*-1
    #autoplot 3 vp(1,2) vp(2,3) vp(3)
    .probe
    .END
    rlc resonance.JPG

    res2.JPG
    My question is : at resonance the current must be of I=100v/4Ω≈25A. So the voltage in resistance= 25A*4Ω=100volts, capacitor or inductor should be ≈3900 Volts.
    The resistor is not at 0° so there is no 100Volts.
    The link example is below, and I would aprecciate your help. Guess LT SPICE have a bug?. Don`t think so.
    Below is the link with example the example. I make the math again & is correct!. SO why lt spice is not showing the correct graph?.
    THANK YOU VERY MUCH
    http://www.electronics-tutorials.ws/accircuits/series-resonance.html
     
  2. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    657
    Does this look like what you expect?
     
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  3. Nelson2001

    Thread Starter Member

    Nov 10, 2011
    27
    0
    Thanks a lot, so I have another problem with LTSPICE when performing transient analisys. In your example transient analisys works very well, the sin function I put works (the 25A mirros in both analisys)- But in this example (new resonance circuit), the sweep analisys shows 25A in resonance, when in transient analisys it shows only 15A.
    I send you all-
    THANK YOU VERY MUCH AGAIN! resonance 2.jpg

    View attachment resonance2.asc

    View attachment resonance at 50hz.zip
     
  4. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    657
    I didn't open the zip file, but I modified your simulation. Run the .asc file.
    Note that the sim runs for 2.5 sec, because the Q of the circuit (XL/R) prevents the current from reaching full amplitude immediately.
    Also note that the maximum timestep is 10uS. This gives more accuracy.
    I also ran your .AC sim over a single octave, because I was too lazy to calculate the resonant frequency. I modified your transient sine wave frequency to 49.96Hz.
     
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  5. Nelson2001

    Thread Starter Member

    Nov 10, 2011
    27
    0
    excellent!, very clear, thank you very much
     
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