# Capacitor Voltage Rating

#### p75213

Joined May 24, 2011
70
I am wondering what voltage rating I need for the capacitor in the attached circuit. Its basically the front end of a Tesla coil. The voltage source is a neon sign transformer 3kV open circuit at up to 15ma short circuit (2kV 10ma under load), 30K Hz. This is what I understand about the circuit. The voltage is rectified to pulsed DC via the full wave rectifier bridge. The capacitor acts like a short circuit so the nst effectively pumps the capacitor up to the breakdown voltage of the 2nd neon lamp (90V). When the breakdown voltage is breached the capacitor releases a 90V spike into the inductor. I'm not sure what roll the first neon lamp (spark gap) plays other than delivering a current rush to the capacitor.

If the AC from the nst is a sinewave the capacitor would collect about 0.182V in one pulsed DC period (t=0 to t=16.6 uS) (disregarding the effect of the first neon lamp). I'm thinking a capacitor with a voltage rating of at least 200V?
Two Questions:
1. What is the purpose of the first neon (spark gap)?
2. Would a capacitor with a voltage rating of around 200V suffice?

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