In a Parallel Resonance circuit (C parallel with RL)

[sspj9]

Why does the total supply current increase when the capacitance value is further increased after parallel resonance is reached (where the supply current is minimum) ? I know it has to do with the phase angles but I cannot reason it out.
Thanks

[Ice-Tea]

The resonance occurs for a frequency defined by the L and C. So if you change the C, the frequency changes. Or at the same frequency, you are no longer at the resonance frequency

[sspj9]

What does the frequency has to do with the supply current though?

[rstofer]

http://www.electronics-tutorials.ws/accircuits/parallel-resonance.html

The impedance of a parallel resonant circuit is highest at resonance - thus the lowest current.  The impedance decreases on both sides of resonance - thus a higher current.

The linked page gives a very good discussion of parallel resonant circuits and their analysis.

[danadak]

A pure LC resonant parallel tank at resonance exhibits an infinite
impedance, no matter what the values of L and C, for finite values
of L and C. Therefore no current is drawn by the tank, the energy
simply cycles back and forth between the reactive elements, L & C.

If there is a finite R in parallel with L & C, then the tank exhibits R
as its resonant impedance value.


https://en.wikipedia.org/wiki/LC_circuit


Regards, Dana.

[rstofer]

Perhaps a more intuitive way to look at it is to just consider the reactances in parallel. 

For the inductor, the reactance is Xl = wL where w is omega - 2 pi f.  We can see that the reactance increases with increasing frequency.  Conversely, the reactance decreases with decreasing frequency.  For the parallel circuit operating below resonance, the inductive reactance dominates the circuit.

For the capacitor, the reactance Xc = 1/wC so the reactance decreases with increasing frequency and increases with decreasing frequency.  For the parallel circuit operating above resonance, the capacitive reactance dominates the circuit.

In either case, the farther the circuit is from resonance, the lower the overall impedance and the higher the current flow.

Pick a really big number for w:  Xl will also be a big number and Xc will be a small number.  For a big number, the capacitor dominates the parallel combination.
Pick a really small number for w:  Xl will also be a small number and Xc will be a large number.  For a small number, the inductor dominates the parallel combination.

[w2aew]

Here's a video I did on LC resonant circuits, just in case you were interested: