# Non Zero Voltage Across LC Series Resonance Circuit

I'm simulating a series resonance RLC circuit using the TINA-TI. The resonance frequency for the circuit is 85 kHz. I did notice that when measuring the voltage across the capacitor, the voltage is higher than the source voltage which what is expected. The problem is when I measure across both the combination of L+C, the voltage is not zero. I expected that at resonance the voltage across L is the same as the voltage across C just with 180 degree phase difference. Below is an image of my simulation:

The source voltage is 5 V amplitude or 10 V peak to peak. I did notice that if I increase the series resistor to a high value like 20 Ω, the voltage across L+C becomes almost zero. Also, If I ran that same exact circuit at a very low resonance frequency like 100 Hz, with changing the capacitor value of course, the voltage across L+C becomes almost zero even though the series resistor is still 0.032 Ω. Is this a normal behavior?

The resonance frequency for the circuit is 85KHz

In detail: -

The resonant frequency is actually 85.0962 kHz.

That small difference is usually enough to produce this type of error.

Also, If I ran that same exact circuit at a very low resonance frequency like 100Hz, with changing the capacitor value of course, the voltage across L+C becomes almost zero even though the series resistor is still 0.032 ohm. Is this a normal behaviour?

The devil will be in the detail and you need to provide values of capacitor and exact frequency applied. At the true resonant frequency the impedance of L and C in series will be zero.

• Also, note that the Q factor is extremely high (sqrt(L/C) / R ~= 885) so not only will the frequency need to be very precise, but numerical errors likely dominate (RELTOL needs to be 0.1m or maybe even less, or, whatever equivalent parameters TINA uses, I don't recall). And the sim will take as many (i.e. thousands of) cycles to stabilize Commented Dec 1, 2022 at 21:58