# Protecting capacitor from high voltage impulse spikes

The purpose of the circuit below is to produce an extremely high voltage impulse over the inductor so that I can place a spark gap in parallel to it and create a very large spark. According to simulation this should work as designed, but I am concerned about protecting the capacitor. The highest voltage rated cap I could find was 30k, but the simulation predicts spikes of -220 kV. I tried placing a diode in parallel to the inductor, but that drastically reduces the voltage spikes. The source controlling the switch is just a simple pulse function switching every 1.2 seconds.

• You don't need a capacitor, just use the back emf. You will need to take care that the relay (or whatever else you have) can take the voltage. The contacts don't just jump to the open position, they take the whole way from contact to open, which means there will be an air gap that will have a finite amount of resistance, and that resistance is variable. Commented May 14, 2021 at 15:52
• You could put capacitors in series, with balancing resistors to share the voltage across them. Commented May 14, 2021 at 15:52
• You won't get 220kV. To accurately simulate this you need to ensure the parasitic capacitance of the components, especially the inductor are included. The voltage in any practical circuit will be much, much less. It will also be limited by breakdown in the switch. Commented May 14, 2021 at 16:43
• If using the cap to charge the inductor (with voltage) to make a spark, instead think in terms of charging the inductor (with current), then interrupting that current. For that is what creates the spark (the near-instantaneous collapse of the inductor's magnetic field.) Commented May 14, 2021 at 16:49
• The simplest solution is a dry contact relay switch to an energized L with low Parasitic C and rapid velocity to delay ionization breakdown at 3kV/mm. ESR and DCR with switch and wiring R’s will limit current. But a spark plug between two step up transformers will create the Tesla corona Commented May 14, 2021 at 17:39