Capacitor in Parallel with Primary Coil

[FPS]

I've seen a few times that adding "resonant capacitor" in parallel with the primary coil will result in improved performance. Now I don't know what is meaned by "improved", be it more efficient or higher voltage etc. I don't understand the physics of it but I ran a test anyway.

Nothing of practical interest was obtained, I plugged the inductance and frequency into an online tank circuit calculator 16kHz, 100uH = 1uF capacitor. Well, it definitely had an effect just nothing useful.

The transformer was just a 1:1 ratio on a small ferrite core. Driver was a 12V variable duty 16kHz square wave.

12V 16kHz 5% duty turned into low voltage low current sine wave. Interesting but with a 0.08A short circuit not good for much.

12V 16kHz 80% duty gave a drop in voltage and very high current draw, it killed 2 caps before I could photograph it. FETs and caps got very hot quick.

Is there any actual purpose to adding a capacitor to the primary input?

[Mads Barnkob]

It is called a tuned circuit, a resonant LC circuit or a tank circuit, many different names for the properties of pumping energy into a self-oscillating LC circuit.

You do need something to transfer that energy to, so a secondary tuned circuit, with a different LC ratio needs to be added. This is how a DRSSTC Tesla coil works.

A induction heater / stove / cooker works without a secondary LC circuit, that is purely a pan load (which represents some complex load) that gets the energy transferred.

Resonant circuits can ring up to very high currents, as you discovered, so you can transfer a lot of energy with short on-times.

[FPS]

OK, thankyou Mads.

So for the simple purpose of pulling arcs, one would say it doesn't have much purpose? or would it increase the output current?