Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!lll-crg!ames!ucbcad!ucbvax!hplabs!tektronix!teklds!midas!jeffw From: jeffw@midas.UUCP (Jeff Winslow) Newsgroups: sci.electronics Subject: Re: Tesla Coil Message-ID: <922@midas.UUCP> Date: Fri, 12-Dec-86 16:16:07 EST Article-I.D.: midas.922 Posted: Fri Dec 12 16:16:07 1986 Date-Received: Tue, 16-Dec-86 00:29:19 EST References: <4815@reed.UUCP> <823@A60.UUCP> <824@A60.UUCP> <904@sfsup.UUCP> Reply-To: jeffw@midas.UUCP (Jeff Winslow) Organization: Tektronix, Inc., Beaverton, OR. Lines: 39 In article <904@sfsup.UUCP> dcm@sfsup.UUCP (David C. Miller, consultant) writes: >In article <824@A60.UUCP> ron@A60.UUCP (Ron Burns) writes: >> >>Gene did forget one very important item. As a series resonant LC circuit, >>you need a capacitor. this is placed in series with the neon sign xfmr >>secondary, the spark gap, and the Tesle coil primary. > >Not necessarily. In fact, I would hazzard a guess that Gene could have >omitted the spark gap as well and it would have still worked. > >Spark gaps and capacitors are there to accumulate a charge, then release >it through the primary in one large burst; much like the capacitor and >point in a car. The difference is that the circuit that Ron is >referring to is strictly for DC power, Genes is for AC. Yes, those >neon sign transformers put out AC, so you really don't even need the >sparkgap. I have some serious questions about this! First, neither circuit, with or without capacitor, is DC, since as you said, the power "source" (sign transformer) puts out AC. Now, I was under the impression that neon sign transformers work on 60Hz. Also that a Tesla coil uses much higher frequencies. The primary of the Tesla coil as described would have far too low an impedance at 60Hz to allow even a 1kW sign transformer to develop anywhere near its full secondary voltage. A spark gap is a great generator of wideband noise. That gets you the high frequency. The capacitor, in combination with the primary inductance of the Tesla coil and the leakage inductance of the sign transformer, makes a high-frequency resonant circuit which, among other things, keeps the sign transformer from being effectively shorted out by lower frequency currents which would otherwise flow through the spark gap. I suspect both the spark gap and capacitor are quite necessary. Corrections welcomed... Jeff Winslow