Tesla Coil - Construction Details

Tesla Coil. — "P. B. P." will find all he wants in "The Inventions, Researches, and Writings of Nikola Tesla," by T. C. Martin, published by the Electrical Engineer, New York; but in case he has not access to one of the large public libraries, I give some extracts from the book.

In his lecture before the Royal Institution of Civil Engineers (Feb., 1892), Mr. Tesla thus described his coil:—

"The coil consists of two spools of hard rubber, R R, held apart at a distance of 10cm. by bolts, c, and nuts, n, likewise of hard rubber. Each spool comprises a tube, T, of approximately 8cm. inside diameter, and 3mm, thick, upon which are screwed two flanges, F F, 24cm. square, the space between the flanges being about 3cm. The secondary, S S, of the best guttapercha-covered wire, has 26 layers, 10 turns in each, giving for each half a total of 260 turns. The two halves are wound oppositely, and connected in series, the connection between both being made over the primary.

This disposition, besides being convenient, has the advantage that when the coil is well balanced — that is, when both of its terminals, T₁ T₁, are connected to bodies or devices of equal capacity — there is not much danger of breaking through to the primary, and the insulation between the primary and the secondary need not be thick. The primary PP is wound in two parts, and oppositely, upon a wooden spool, W, and the four ends are led out of the oil through the hard rubber tubes t t. The ends of the secondary T₁ T₁, are also led out of the oil through rubber tubes, t₁ t₁, of great thickness.

The primary and secondary layers are insulated by cotton cloth, the thickness of the insulation, of course, bearing some proportion to the difference of potential between the turns of the different layers. Each half of the primary has four layers, 24 turns in each, giving a total of 96 turns. The coil is held in position in the oil on wooden supports, there being about 5cm. thickness of oil all round. The whole coil is immersed in boiled-out oil, contained in a box, B, of thick boards of hard wood, covered on the out- side with a zine sheet, Z, which is carefully soldered all round.

The coil should be placed symmetrically to the metal cover, and the space between should not be too small; especially the two sides of the box, which are at right angles to the axis of the coil, should be sufficiently remote. from the latter. Once the coil has been immersed, it should never be taken out of the oil for more than a few hours, else the guttapercha will crack up.

The primary is No. 12, Brown and Sharpe gauge, ordinary line wire, with a thick cotton coating; the secondary is No. 24 Brown and Sharpe gauge wire, but the sections may be varied considerably. The kind of guttapercha wire in which the insulation sticks to the metal should be used, unless a special method is followed to expel all air. The coil is wound within an oil-tank, so that all interstices are filled up with oil. Paraffin or linseed oil may be used."

W. C. PEAKE.