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- To: Tesla List <tesla-at-pupman-dot-com>
- Subject: Re: Magnet Design for Tesla Coils
- From: Bert Hickman <bert.hickman-at-aquila-dot-com>
- Date: Sun, 09 Mar 1997 16:42:48 -0800
- References: <33231061.26E2-at-stic-dot-net>
Tesla List wrote: > > Subject: Magnet Design for Tesla Coils > Date: Sun, 9 Mar 1997 10:01:57 -0500 (EST) > From: TimRaney-at-aol-dot-com > To: tesla-at-pupman-dot-com > > Folks: > > Just some notes on electromagnet design and references. Building a cyclotron > is undoubtedly a very challenging project. However, designing electromagnets > to magnetically quench a spark gap in a disruptive Tesla Coil is not nearly > as difficult. > > Some folks will debate the utility of magnetic quenching applied to small > Tesla Coils, but I think it has good possibilities. Tesla used magnetically > quenched gaps in some of his designs and those details are covered in "The > Inventions, Researches and Writings of Nikola Tesla," by T.C. Martin (1894) > and reprinted by Barnes & Noble Books. This book contains a lot of other > great information and has been mentioned before on the Tesla List. > > To put things in perspective, I built a "large" (everything's relative!) > electromagnet and will relate some of the design features and problems. This > particular magnet was not used to quench spark gaps, but the design > principles are the same. This magnet used two coils mounted opposite each > other on a mild steel frame and this configuration is known as a "Weiss > Electromagnet' (Bleaney, et al, 1957). > > Each coil consisted of 6 lbs. of #18 magnet wire, "scramble-wound" on 2 1/8" > diameter cold rolled steel (mild steel) pole pieces. The pole piece faces > were machined at a 60 degree angle so the face was 1" across. Magnet gap > width was adjusted with steel washers as spacers. Power supply was either a > filament tranformer with rectifier or a Variac-rectifier combination. Magnet > coil resistance was apprx. 15 ohms at 70 degrees F (resistance obviously will > increase as coils warm up). > > With the magnets' gap set at 2 cm, a 6 ampere current at approx. 100 VDC, > produced a 10K Gauss magnetic flux in the center of the gap. Measurements > were taken with a Bell Gaussmeter (expensive item, but not if you can borrow > one!). This is not bad and would probably be higher if the coils were not > scramble-wound. However, at this current, the coils heat up rather quickly > and that's not good (can use larger gauge wire). And yes, you can calculate > the magnetic flux: that's easy for an air-core solenoid, but gets tedious > with electromagnets. At lower currents, this particular magnet serves its > purpose of producing moderately strong fields from 1K to 5K Gauss without any > dangerous rise in operating temperature. > > So, in that regard the magnet was successful. Again, this is not really a > big magnet by many standards, but similar designs can be used to quench spark > gaps in disruptive Tesla Coils. An important difference in this application > is insulating the spark gap from the magnet pole pieces (whether you use a > permanent gap magnet or electromagnet). This is not as easy as it sounds, > especially when you don't have exactly what you need and must "improvise" > (we're all kind of used to that!). > > Applicable references follow and are certainly not all inclusive. Original > publication dates included; these references are still available, except for > Bleaney (that's why it's a good idea to "cruise" used book shops). These are > useful references that cover many facets of magnet design. Other resources > include most electrical engineering texts (especially the older ones) and > physics text books. > > Underhill, C.N. Solenoids, Electromagnets and Electromagnetic Windings. > Reprinted by Lindsey Pubs., 1921. > > Lee, E.W. Magnetism - An Introductory Survey. Dover Pubs. (and Lindsey Pubs, > I believe), 1970. > > Bleaney, B.I. Electricity and Magnetism. Oxford University Presss, London, > 1957. > > Montgomery, T.B. Design of Magnets and Electromagnets. Reprinted by Lindsey > Pubs., 1948. > > Chabay, R. and Sherwood, B. Electric and Magnetic Interactions. John Wiley > & Sons, Inc., New York, 1995. > > Fretter, W.B. Introduction to Experimental Physics. Prentice-Hall, Inc., > New York, 1954. > > Gingery, D.J. How to Build a Magneto Magnetizer. Self-published, available > through Lindsey Pubs., 1994. > > Martin, T.C. The Inventions, Researches and Writings of Nikola Tesla. > Reprinted by Barnes & Noble, 1894. > > Hope this helps! Good luck experimenting! > > // S // > > TIMOTHY RANEY, TCBOR Timothy, Duh... After re-reading your post, I found that you didn't use the big magnet to quench a gap... my other post ASSumed you did... Sorry 'bout that! :^] -- Bert --
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