# Why is the current not ~96A in this simple ckt sim?

Qspice sim shows current through this circuit with an amplituded of 60A --it should be ~96A. What am I doing wrong? What settings can I mess with to improve the accuracy of the simulation?

This is worrisome because in more complex circuits, I wouldn’t necessarily know what ot expect for currents and voltages, and would not be able to vet the sim results.

@jrive I am not sure how you can get anything other than 100 amps peak as shown by @bordodynov above because at resonance the capacitive and inductive reactances cancel out leaving only the 0.1 ohm resistor across your 10V peak voltage source. Your resonant frequency of 84.574 kHz seems also out as if you calculate it from fr = 1/(2Pi SQRT(LC)) gives you 86.314kHz, this may be part of your problem.

If you want simulate ideal RLC series circuit, you can check you collect enough points, so you do not miss maximum value. Also you can make inductor to look like more ideal with GMIN or LFT options. Try following directives, if results agrees better with your expectations:

.tran 0 10.1m 10m 10n
.options lft=1e308

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that’s great…but it still doesn’t explain why my simulation only shows 60A. Run the circuit as I drew it. Do the math by hand,
10/abs(0.1-j0.2) ~= 96A (with phase -15 deg).

Does the circuit as I drew it give you the expected 96A? If so, what are the settings in your simulator?

Thanks,

That’s the point. I’m not asking for help with the circuit (or the math). I’m asking why the circuit doesn’t simulate correctly. Did you try running it as drawn?
I think @frankSh provided the answer I needed.

Thank you.

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This is what I get:

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Thank you. I think not bounding the max step size in the transient simulation is the maiin reason it was not simulating correctly.
thanks again!

Yes I did run the ckt as sown and keep getting 100A peak which is what I would have expected if you feed 84.574kHz into it. Maybe I misunderstood your question but I don’t know why you are expecting 96A instead of 100. I get the point that 60A is not right, way to low. This is what I get:

~96A is correct at 84574Hz for this circuit setup.

If run in .tran, you can get peak current ~96A with one of this .option

• .option maxstep=10n
• .option reltol=1e-6

this is a very high Q circuit and require a tighten error tolerance or smaller time-step to get correct answer. In general, this is not required in spice simulation except extreme case.

Or, run a .ac to get the answer, but you still need a relatively small frequency step for precise answer
The center frequency that yield highest current is ~ 84640Hz.

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