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- To: tesla-at-pupman-dot-com
- Subject: Re: Magnet Design for Tesla Coils
- From: FutureT-at-aol-dot-com
- Date: Mon, 10 Mar 1997 15:01:07 -0500 (EST)
Tim, All, Thanks for the data. Magnetic gap quenching is an intriquing subject, it would be interesting to hear from others who have tried magnetic quenching, or have theoretical viewpoints. How does it compare with other quenching methods; air, gas, etc? John Freau << 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
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