LtSpice does not support resonance?!?

Thread Starter

Hypatia's Protege

Joined Mar 1, 2015
3,203
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:)
 

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OBW0549

Joined Mar 2, 2015
3,148
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.)
 

crutschow

Joined Mar 14, 2008
24,122
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:
 

Thread Starter

Hypatia's Protege

Joined Mar 1, 2015
3,203
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.)
Many thanks for your response!:) -- A (would be) instructor likes to be certain she knows what she's talking about!:eek::oops:

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

Thread Starter

Hypatia's Protege

Joined Mar 1, 2015
3,203
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:
There seems to be some misunderstanding -- The reactors are in series:)

Many thanks for your reply
HP:)
 

crutschow

Joined Mar 14, 2008
24,122
There seems to be some misunderstanding -- The reactors are in series:)

Am I to understand that I somehow managed to inadvertantly alter the inductor's model?
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.
 

Thread Starter

Hypatia's Protege

Joined Mar 1, 2015
3,203
Why is the inductor labeled "10nF"?
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:
 
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