LtSpice does not support resonance?!?

Discussion in 'General Electronics Chat' started by Hypatia's Protege, Dec 30, 2015.

  1. Hypatia's Protege

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    Kind friends -- Pursuant to my attempted assistance of another member with his studies, I wished to present a simulation illustrative of resonance phenomena -- unfortunately Ltspice is averse:(;) -- Despite the series LCR circuit's resonance at the selected frequency and highly precise component specification, I(R) peaks at less than 2 nA:confused::confused::confused:

    Any assistance/insight will be greatly appreciated!:):):)

    Edit -- So I discovered that Ltspice interprets 'M' and 'MHz' as millihertz (go figure!?)...

    That said, with the proper frequency specification (i.e. "100e6" Hertz) -- I(R) is peaking at ~20mA when a correct value would approach 10A...:(

    Very best regards
    HP:)
     
    Last edited: Dec 30, 2015
  2. Hypatia's Protege

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    Please see edit to the OP -- Again any and all assistance will be much appreciated!!!:):):):)
     
  3. OBW0549

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    No, Spice is NOT averse to resonance; it handles it quite nicely, in fact.

    For those of us who use some other Spice package in stead of LTSpice, it would help if you would post a screen cap showing your schematic complete with Spice statements, plus any relevant plots; I have no way of reading a .asc file.

    (Use "Meg" to indicate 10^6; "m" or "M" indicate 10^-3.)
     
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  4. crutschow

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    As OB implied, Spice is case insensitive so M and m are the same (milli in both cases) so you use meg or MEG for mega.

    Spice is simulating the circuit as configured since you have a 253pf cap internally in parallel with the inductor in the inductor definition.
    Was that intentional?
    That means the inductor is looking like a high-impedance parallel tank, giving the small external current you see
    If you remove that, then you get the 10A you expected.
    And what's with the 11 numbers to the right of the decimal for the capacitance value? :confused:
     
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  5. Hypatia's Protege

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    Many thanks for your response!:) -- A (would be) instructor likes to be certain she knows what she's talking about!:eek::oops:

    You can have no idea how relived I am to hear that!:cool: --- I will be genuinely pleased to learn the error of my ways!:):):)

    Attached is the schematic and a 'sample' of the output...
    Clearly I(R) should approach 10A in a 'perfect world'...

    Very best regards
    HP:)

    SLCCAP.jpg
     
  6. Hypatia's Protege

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    There seems to be some misunderstanding -- The reactors are in series:)

    Many thanks for your reply
    HP:)
     
  7. Hypatia's Protege

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    All I intended is what's visually apparent on the schematic???:confused:
     
  8. Hypatia's Protege

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    Am I to understand that I somehow managed to inadvertantly alter the inductor's model?:eek::confused:
     
  9. crutschow

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    Right click on the inductor. You will see an added 253pF parallel capacitor. That value is normally for small parasitic elements of the inductor.

    Generally if LTspice is giving you values you don't expect then there's something wrong with the circuit, not with LTspice. ;)
    I've found few exceptions to that in my many years of using Spice.
     
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  10. Hypatia's Protege

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    Lemme check that out --- Back in a trice:D
     
  11. OBW0549

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    Why is the inductor labeled "10nF"?
     
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  12. crutschow

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    He corrected that in his later post.
    But the letter after the n is simply for clarity. Spice ignores it.
     
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  13. Hypatia's Protege

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    10 nano Farad

    Well hey! All's working as expected now I've corrected the inductor's model!!!:):):)

    Apparently I muddled the reactor property screens:oops: --- And here I was poised to render yet another diatribe Re: Spice:oops::oops::oops: --- Jeeeze am I glad I kept my alligator mouth shut! --- Lessons -- even in humility -- are always a good thing!!!:):):)

    Many, many thanks!
    HP:):cool:
     
  14. Hypatia's Protege

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    A sentiment/lesson worthy of framing!:cool:
     
  15. OBW0549

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    Uhhh... what? I thought Spice interprets "n" as nano.
     
  16. OBW0549

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    The unit of inductance is the Henry, not the Farad.
     
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  17. crutschow

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    True. I stated that it's the letter after the n (or any of the recognized suffixes) that is ignored.
     
    Last edited: Dec 30, 2015
  18. Hypatia's Protege

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    While troubleshooting the 'difficulty', I wished to make certain the circuit was as near resonance as possible:D:D:D
     
  19. OBW0549

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    Memo to self: read posts carefully before replying...:oops:
     
  20. Hypatia's Protege

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    Yikes!!!:eek::eek::eek: --- To much 'multitasking' -- too little sleep!:oops::oops::oops: --- Time I proofread my proofreading!:rolleyes::rolleyes::rolleyes:

    With marked abashment
    HPo_O
     
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