LT SPICE and resonance

Thread Starter

Nelson2001

Joined Nov 10, 2011
27
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
 

Thread Starter

Nelson2001

Joined Nov 10, 2011
27
Does this look like what you expect?
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
 

Ron H

Joined Apr 14, 2005
7,063
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!View attachment 46727

View attachment 46731

View attachment 46732
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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Thread Starter

Nelson2001

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