Induction coil

“ The condenser is essential to the working of the coil. For complete directions for making induction coils, see Scientific American Supplement No. 160.
(7) J. De F. asks: 1. Knowing the resistance of a wire of given conductivity, length, and diameter, will the resistance of any other wire be in proportion inversely? A. Yes. 2. Is there heat enough developed in the secondary coil of an induction coil to prevent the use of paraffine as an insulating material? A. With proper battery power, no. 3. How high in the list of non-conductors does paraffine stand? A. It is one of the best. ”

“ The induction coil has always been a popular piece of apparatus with those interested in electrical science; the experiments which can be performed with its aid are very numerous. It is of considerable importance, especially in its application to such useful purposes as X ray work, wireless telegraphy and ignition for gas engines. The latter has caused manufacturers to give much attention to the development of the induction coil, resulting in many refinements of design and construction. ”

“ Current Regulator for Induction Coils. Fig. 80. If your coil gives too much of a shock with one cell of App. 3 or 4, you can pull the carbon and zinc partly out of the solution to weaken the shock, or you can use a water regulator. T is an ordinary tin tomato can nearly filled with water, L is a lamp chimney. One wire, A, is fastened to T directly, or by a spring binding-post. The other wire, B, is fastened to a piece of copper, C, which may be raised or lowered inside of L. D is a piece of pasteboard with a small hole in its center. ”

“ A primary coil of length l, having n turns, is wound upon a cylinder made of non-conducting and non-magnetic material, and upon the middle of the primary a secondary or induction coil is closely fitted. When a current of strength i is suddenly interrupted in the primary, the increment of induction through the secondary is sensibly equal to 4πin/l units. All the data required for standardizing the galvanometer can in this way be determined with accuracy. ”

“ When using the ordinary ten-inch induction coil, and when the capacity charged by it does not exceed a small fraction of a microfarad, it is quite sufficient to employ brass or steel balls separated by a certain distance in air, at the ordinary pressure, as the arrangement of the discharger. ”

“ A coil much used for electric baths has a primary winding only, regulated by the sliding in and out of the iron core, which necessitates the use of an independent vibrator, or else by varying the current strength with a rheostat. The general directions given before will answer in the present case, the only data necessary being the size of wire, which should be about six to ten layers of No. 20 B & S. The coil with movable secondaries here comes into service. Strong currents are needed for bath work, and any variety of winding can be used with this make of coil. ”

“ All that is necessary to get a spark is to provide a suitable resistance coil with an iron core, so that the fuse will not be blown and to secure sufficient inductance to get a hot spark. The writer uses an ordinary 50-ohm telephone induction coil, in which the primary and secondary are placed in series by the diagonal connection indicated in the sketch. ”

“ This feature may be easily observed with an ordinary induction coil by taking the primary out, plugging up the end of the tube upon which the secondary is wound, and filling it with some fairly transparent insulator, such as paraffine oil. A primary of a diameter something like six millimetres smaller than the inside of the tube may be inserted in the oil. When the coil is set to work one may see, looking from the top through the oil, many luminous points—air bubbles which are caught by inserting the primary, and which are rendered luminous in consequence of the violent bombardment. ”

“ By means of a large induction coil we can obtain a voltage hundreds or even thousands of times greater than that of the original battery current, but on account of the great resistance of a very long, thin wire, the amperage is much smaller. The induction coil produces a rapid succession of sparks, similar to those obtained from a Wimshurst machine. A coil has been constructed capable of giving sparks 421⁄2 inches in length, and having a secondary coil with 340,000 turns of wire, the total length of the wire being 280 miles. ”

“ As in the simple electromagnet, the proportions of diameter and length of the primary coil and core will determine its rapidity of action. A short fat coil and core will act much quicker than a long thin one. But on a short fat coil the outside turns would be too far removed from the intensest part of the primary field. A good proportion of core length is given in the following table:
The primary coil P consists of two or not more than three layers of insulated copper wire of large diameter, being required to carry a heavy current in a 2-inch spark coil, probably from 8 to 10 amperes. ”

“ There is nothing quite so startling as to receive an electric shock unexpectedly and such a shock may be given to a friend while shaking hands upon meeting. The shock produced is not harmful and the apparatus can be carried in the pocket. It consists of a small induction coil that can be constructed at home.
The core of the coil, A, Fig. 1, is constructed in the usual manner, of small soft-iron wire to make a bundle about 3/16 in. in diameter and 2 in. long. The coil ends are made from cardboard, about 1 in. in diameter, with a 3/16-in. hole in the center. ”

“ The intensely disruptive power of the long spark is readily shown by its power to perforate substances, but great care must be taken that the secondary wires of a coil are led away from the body of the coil. A good plan is to hang two silk cords or stout threads from the ceiling, to which the secondary wires may be attached and kept in sight when experimenting at any distance from the coil. ”

“ Early experimenters describe the display of sparks produced by an ordinary large induction coil upon an insulating plate separating the terminals. Quite recently Siemens performed some experiments in which fine effects were obtained, which were seen by many with interest. No doubt large coils, even if operated with currents of low frequencies, are capable of producing beautiful effects. But the largest coil ever made could not, by far, equal the magnificent display of streams and sparks obtained from such a disruptive discharge coil when properly adjusted. ”

“ In the majority of his experiments Tesla uses alternating currents generated by machinery of his own design, but in a large number of cases his effects can be duplicated with an induction coil suitably energized. In the latter case the apparatus consists of a battery, a Ruhmkorff coil, two condensers, and a second specially constructed induction or disruptive coil, with some few subsidiary implements. The contact-breaker or rheotome must be one giving interruptions of very rapid sequence. ”

“ They involve no machinery with moving parts, but simply coils of wire placed in such relation to each other that the currents passing in one induce similar currents in the other. The practical value of this system arose with the discovery that the induction coil, like the dynamo, is reversible. This coil had long been used to transform a current of considerable volume and low pressure into one of very great pressure and small volume. ”

“ The first thing, then, in operating the induction coil is to combine capacity with the secondary to overcome the self-induction. If the frequencies and potentials are very high, gaseous matter should be carefully kept away from the charged surfaces. If Leyden jars are used, they should be immersed in oil, as otherwise considerable dissipation may occur if the jars are greatly strained. When high frequencies are used, it is of equal importance to combine a condenser with the primary. ”

“ When the space is filled up to the level of the paper disks and the paraffin is hard, loosen the set screw, and removing the outside disk, the coil can be slipped off, or a slight warming will loosen it. Any number of these coils can be made, and there are the advantages in this mode of construction that a bad coil will not spoil the whole secondary, and that the wire can be obtained in comparatively small quantities. ”

“ It is usually conducted to an induction coil where it is transformed into a high tension alternating current.
Alternating Currents.—Alternating currents are produced by the rapid breaking down and building up of the primary current. An alternating current flows forward from zero to its highest point of strength and back again to zero. The alternating action takes place so rapidly that a light can be connected in this circuit and it will burn steadily without any noticeable fluctuation.
Fig. 54. Coil Diagram
Induction Coil.—An induction coil consists of a soft iron core ”

“ The decomposition of water, which consists of oxygen and hydrogen in the formula H2O, is readily accomplished by the secondary current, and the greatest volume of gas (hydrogen) will be evolved at the negative pole. For ready reference a summary of these facts is given 45below:
Although it is customary to use bundles of fine, soft iron wire for coil cores, very excellent results have been obtained with cores made up of soft iron filings. ”

“ Thus one coil may be in
parallel with the other, and the action on the plunger will then depend
on the relative currents passing through the coils.
Coil, Choking.
A coil of high self-induction, used to resist the intensity of or
"choke" alternating currents. Any coil of insulated wire wound around
upon a laminated or divided iron core forms a choking coil. The iron
coil is usually so shaped as to afford a closed magnetic circuit.
A converter or transformer acts as a choking coil as long as its
secondary is left open. ”

“ When the current is thus interrupted, the spring flies up by its elasticity and again establishes the circuit at e. This interruption was originally invented by P. Wagner. secondary coil are the Faradic or induced currents. They last only a minute fraction of a second of time. An induction coil, then, consists of a primary coil, with which a galvanic cell is connected, and a secondary coil. ”

“ The line being connected to the ground, all the wires could be handled with perfect impunity, no matter how high the potential at the terminals of the condenser. In these experiments a high tension induction coil, operated from a battery or from an alternate current machine, was employed to charge the condenser; but the induction coil might be replaced by an apparatus of a different kind, capable of giving electricity of such high tension. In this manner, direct or alternating currents may be converted, and in both cases the current-impulses may be of any desired frequency. ”

“ In operating large coils, it is convenient to be able to vary the capacity of the condenser on the primary circuit. To make an adjustable condenser presents no more difficulty than a non-adjustable one, simply more labor. For example, the large condenser used with the 6-inch spark coil might be divided into four sections, containing 2000 square inches, 500 square inches, 300 square inches, and 200 square inches of surface (see Fig. 34) . ”

“ It is absolutely essential that the diameter of contacts for all contact breakers should be as large as possible and their faces filed truly parallel to enable them to easily carry all the current required. One of the main causes of failure of coil is burning of the platinum point and platinum burr, the current being then materially reduced. Large sparks at point of rupture are often indications that the condenser is not working properly—perhaps has broken down or is not large enough. ”

“ In coils with independent circuit breakers, sliding both core and primary coil out of the secondary together or independently. (b) Moving a metal tube over or off the primary coil or core or both. Many combinations of these methods are practised. Attempts have been made to regulate battery current by rheostat,52 but it is not feasible, except in large stationary outfits. Cheap medical coils are wound with bare wire, with layers of thread between adjacent turns, or even only bedding the wire turns in paraffined paper. ”

“ In automobile work, where a heavy strain is made upon the engine, as in climbing heavy grades, it has been found that a stronger spark gives surer results. This would indicate more battery current through the coil, and it is a wise precaution to have a few extra cells attached that can be 40switched on if necessary.
In constructing spark coils for gas engines particular care must be given to the contact breaker. In most types of gas or oil vapor engines it is absolutely necessary to have the spark pass with uniform regularity, and immediately and surely when required. ”

“ As the connections of the coil will probably be under the base, a sufficient space must intervene between the base and the top of the condenser. It is a good plan to lay the condenser at least one half inch below the top of this box, and fill up to, say, one eighth of an inch with melted paraffin, leaving the condenser wires projecting for attachment. The connections of the primary coil and contact breaker should by all means be soldered, not simply wires held under screw nuts. ”

“ Four to eight large cells of dry battery are used, or eight cells Edison-Lalande—iron-clad type. Number of cells varies with size of coil needed, some classes of engines require a heavier spark than others to ignite the vapor.
When a primary and secondary are used, the primary should be made of two or three layers No. 14 B & S magnet wire, and a secondary of one pound No. 34 B & S magnet wire. There can be an independent contact breaker or the coil can be made up similar to a one-half inch spark Ruhmkorff coil (see Chapter I.) .
Fig. 12. ”