CHAPTER XI.
INDUCTION COILS AND THEIR ATTACHMENTS.
_134. Induction Coils_, or shocking coils, are rather expensive to buy, and altogether too complicated for boys to make by the methods usually given in books. The method here given is simple, the materials are cheap, and if you make them according to directions, you will have an apparatus that will, be able to make your friends dance to a rather lively tune. The amount of shock can be regulated perfectly (App. 103).
Winding. Full instructions have been given for making bolt magnets (App. 88). The winding of our induction coils is done in the same way by the same winder as the bolt magnets (App. 93), or by hand. You will find it a very tiresome and troublesome job, however, to wind on 12 or 15 hundred turns of fine wire by hand. Make a winder.
Several different forms of induction coils are shown. The coil is the most important feature, however, and we shall consider that separately. When you understand the construction of one coil, you can readily apply this to the different forms. Some form of contact breaker, or current interrupter, is needed also. These will be treated by themselves. The connections will be discussed under each form of apparatus.
APPARATUS 96.
_135. Induction Coil; Construction of Coil Proper._ Figs. 73, 74. An induction coil is a peculiar and wonderful apparatus. There are at least two coils to each one. These are both wound upon the same core. They are made of different sizes of wire, are wound separately, and the strangest thing of all is, that these two coils are not connected with each other in any way. If they were not thoroughly insulated from each other, the coil would be of no value. (Study induction.) The winding of the two coils is done as explained in App. 88.
136. The Core is made of a 5/16 machine bolt, 2-1/2 in. long. Leave but 2 or 3 threads at the end, just enough to fasten it solidly to the winder (App. 93). The washers should be about 1-5/8 in. apart inside, and they should be made around a spool (Sec. 119) that is fully 1 in. in diameter.
137. The Inside or Primary Coil could be wound directly upon the bolt; but it is much better to cover the bolt with one or two thicknesses of paraffined paper, I (Index), as shown. A pinhole, H, in the washer is for the inside end (see Sec. 123) of the primary coil, and the hole, J, is for the outside end of it.
The primary coil should be made of 3 layers of wire, which should be coarser than that used for the secondary coil. For our purposes it is best not to use a wire coarser than No. 20, and not finer than No. 24.
Use No. 24 insulated copper wire if you are going to connect ordinary batteries with it. A bichromate cell (App. 4) is best. Put about 6 in. (see Sec. 109) of wire through H, and with App. 93 wind on 3 layers of say No. 24 wire. There being an odd number of layers, the winding will stop at the head end of the bolt, where a half hitch (see Sec. 110) should be taken before passing the wire through the hole, J. Cut the wire 6 in. from the hole. Write down the number of turns of wire to each layer and the total number of turns. You now have a 3-layer coil, and a current passed through this will magnetize the bolt; you have--so far--merely an electro-magnet. Cover the primary coil with 2 layers of paraffined paper, K (Fig. 74), and put some paraffine between the edges of K and the washers, so that the wire of the secondary coil cannot possibly come in contact with that already wound on.
138. The Secondary Coil should be made of a large number of turns of fine wire. Do not use anything coarser than No. 30. This is a good size, as finer wire is very easily broken by unskilled hands. For the size of bolt mentioned put on 13 layers. There will be about 100 turns to each layer, making a total of about 1,300 turns of No. 30 wire. Write down the total number of turns in your coil. To start the secondary coil, make a pinhole, L, just outside of the insulation, K, of the primary coil. Put 6 in. of wire through this, wind the end around the nut (App. 93, Fig. 70), and wind on as evenly as possible 13 layers. If the layers become rough, it is well to put a band of paper around after each 3 or 4. When you have finished take a half hitch (Sec. 110), and leave a 6-in. length free. Cover the secondary coil with strong paper. This coil may be used on any of the forms of shockers given.
APPARATUS 97.
139. Induction Coil. Fig. 75. The base is made of a piece of board, 7 x 5 x 7/8 in. The locations of the different parts are shown in the figure. The coil is explained in detail in App. 96. It is fastened to the base by a thin copper strip, 4, which is bent over the coil and held down by screws, 3. If you haven't any copper you can use a narrow strip of tin. Do not use a wide piece of tin or iron. The coil may be held down firmly by strong twine placed around each end of it. The twine should pass through holes in the base, and be tied on the underside of the base. The binding-posts are like App. 46.
140. The Current Interrupter consists of a tin or copper strip, R, 6 in. long and 1/2 or 3/4 in. wide. At one end of R is a screw, S, which is used as a binding-post for the outside end, B, of the primary coil. (See Sec. 137.) Along the center line of the strip, R, are driven 1-in. wire nails, Q. These are placed 1/4 in. apart, and they should go into the wood enough only to make them solid. (See Fig. 81.) Do not drive them in so far that they will split the base. A stout wire, P, fastened at one end only completes the interrupter.
141. The Connections. The binding-posts, W and X, should be connected with the wires leading from a battery. Use the bichromate batteries of App. 3 or 4. A dry battery will do. If the current enters at X, it will pass around the primary coil (Sec. 137) and out through B into R. It can go no farther until the free end of P is made to touch R, or one of the nails, Q, when the circuit will be closed. The current will fly around and around through the battery, primary coil, and interrupter as long as the end of P touches a nail. The battery current does not get into the secondary coil at all. You can see, then, that the primary circuit, that is, the one passing through the coarse wire, will be rapidly opened and closed by bumping the free end of P along upon the row of nails.
The wires, C and D, coming from the secondary coil (Sec. 138) are in connection with Y and Z, to which are connected the wires leading from the handles (App. 101) held by the person receiving the shock.
142. To use the coil, arrange as explained. Let your friend hold the handles (App. 101) while you scrape the end of P back and forth along the row of nails. For those who cannot stand much of a shock, use a regulator (App. 103).
APPARATUS 98.
_143. Induction Coil._ Fig. 76. In case you wish to make the interrupter as a separate piece of apparatus, as App. 104, this arrangement will be found good. The base is 5 x 4 x 7/8 in. The coil is explained in App. 96, and the methods of holding it to the base are given in App. 97. The binding-posts are like App. 46.
The Connections. We shall suppose that you have the interrupter of App. 104, Fig. 81. The ends of the primary coil (Sec. 137) are fastened under the screws of X and W, and those of the secondary coil to Y and Z. Connect one battery wire with X and the other battery wire to the interrupter at S, Fig. 81. Fasten the end of a stout wire to W, and leave the other end free to scrape along on the nails, Q, of the interrupter. This will then open and close the primary circuit. The handles (App. 101) are connected with Y and Z, as explained in App. 97. Use the battery of App. 3 or 4.
APPARATUS 99.
_144. Induction Coil._ Fig. 77. If you wish to fasten your coil in an upright position the apparatus will look like Fig. 77. The base may be 5 x 4 x 7/8 in. The binding-posts are like App. 46. The coil is made as explained in App. 96; but to have all the ends of the coils come out at the bottom, as shown, an even number of layers of wire will be necessary. It will be just as well to have an odd number of layers as before, and to bring the wire ends down the side of the coil. The coil is fastened to the base with screws, S, passing through a tin strip, T, which has a hole punched for the bolt. T is squeezed between the regular nut on the bolt and an extra one on the underside of it. See Fig. 61 for suggestion of another method of holding bolts upright. The connections should be made with an outside interrupter, battery, and handles, as explained in App. 98.
APPARATUS 100.
_145. Induction Coil._ Fig. 78, 78-A, 78-B. In case you wish to make a larger coil than those already described, the following will be found practical. It is made in the same general way as before, an automatic interrupter, however, being added.
The Core is a machine-bolt, 4-1/2 in. long and 5/16 in. in diameter. You may use a carriage-bolt of the same dimensions, if you file away the square shoulder at the head end, so that it will be the same size as the body of the bolt. Paste a piece of thick paper upon the head, so that A will strike the paper instead of the iron. The Washers should be made around a spool that is fully 1 in. in diameter. (See Sec. 119.) The core should be insulated with paraffine paper before winding on the primary coil. (See App. 88.) The washers are 3-7/8 in. apart, inside. The winding of the coils should be done with App. 93, or some other winder. The winder-nut, W N, Fig. 70, must hold the long core perfectly tight, to avoid wobbling. The base is 8 x 5 x 7/8 in. The different parts are placed as shown. The coil is fastened to the base as in App. 97. For binding-posts see App. 46.
146. The Primary Coil (Sec. 137) is made by winding 3 layers of No. 24 insulated copper wire upon the insulated core. One end, 6, is fastened to W (See Sec. 109), and the other end, 5, is held under the screw-head, R. Wind at least two layers of paraffined paper around this coil before winding on the secondary coil.
147. The Secondary Coil (Sec. 138) is made of No. 30 insulated copper wire, there being 11 or 13 layers, each having about 200 turns. This makes, in all, about 2,500 turns of fine wire. If your winder works properly and the long core is strongly held by the winder-nut, you will have no trouble, although it takes a little time to wind on so many turns. The ends of this coil, 7 and 8, are fastened to Y and Z, which are made like App. 46. It will be found best to wrap a piece of thin paper around the coil after every 3 or 4 layers are wound on. This makes better insulation, and makes the winding easier. Protect the coil by covering it with thick paper. The whole coil, when completed, is about 1 in. in diameter.
148. The Automatic Interrupter (Figs. 78, 78-A, 78-B) consists of several parts. B, E, C is a piece of thin tin, all in one piece. The part, B, is 1/4 in. wide and 1-3/4 in. long. Its exact height above the base will depend upon the diameter of your coil. For the coil here described, 1 in. in diameter, the top edge of B is 5/8 in. above the base. See Fig. 78-B for shape of B, E, C before bending it, and for its dimensions. Around the end of B are tightly wound several turns of tin, making the armature or hammer, A, which should not be allowed to strike against the head of the bolt on account of residual magnetism. (See text-book.) A piece of thick paper pasted on the head for A to strike upon is best. A will probably not get near enough to the bolt to strike it, but this will depend upon how you arrange the parts.
D is a wooden piece, 1 in. high, 1 in. wide, and 3/8 or 1/2 in. thick; it is nailed to the base. Through its center is a hole for the screw-eye, S I, which is the regulating-screw. F is a piece of copper, brass, or tin, 5/8 x 1-3/4 in. It is held to the base by the screw, S, and is bent so that it presses tightly against S I. Through F is a screw, R, to hold one end of the primary coil.
149. Adjustment and Use. The battery wires should be joined to W and X, and the handles to the secondary coil at Y and Z, unless a regulator (App. 103) is used. Let us consider the primary circuit. If the current enters at W it will pass through the primary coil and out at X, after going through 5, R, F, S I, B, E, and C. The instant that the current passes, the bolt becomes magnetized; this attracts A, which pulls B away from the end of S I, thus automatically opening the circuit. B at once springs back to its former position against S I, as A is no longer attracted; the circuit is closed and the operation is rapidly repeated. B should press gently against S I, which must be screwed back and forth, until the best results are obtained. While not in use A should be about 1/8 or 3/16 in. from the bolt-head. The armature, A, should vibrate back and forth very rapidly. If this coil gives too much shock with one cell of App. 3 or 4, put a regulator (App. 103) between Y and one of the handles (App. 101).
APPARATUS 101.
_150. Handles for Shocking Coils._ Fig. 79. Ordinary sheet-tin makes good handles. Cut 2 pieces, each 6 x 4-1/2 in., and connect a stout copper wire to each. This may be done as suggested in Fig. 79, where the tin laps tightly over the bare end of the wire, or by punching 4 or 5 holes through the tin, and weaving the wire back and forth through the holes. Be sure that a tight and permanent connection is made. The wires joined to the handles should be about No. 20, and be 4 or 5 feet long. Roll the tin into a cylinder, so that the connection will be on the inside.
APPARATUS 102.
_151. Handles for Shocking Coils._ Very neat handles may be made from 4-in. lengths of brass tubing that is about 3/4 in. in diameter. The wires leading to the coil may be soldered to the handles.
APPARATUS 103.
_152. 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.
153. Use. If this apparatus be put anywhere in the primary circuit, the amount of shock can be regulated by raising or lowering C. When C is raised, the current has to pass through a longer column of water than it does when C is near the bottom of L. When C touches T, the current passes easily. If it were not for the chimney, the current would pass to the sides of T.