How Two Boys Made Their Own Electrical Apparatus Part 10

[Ill.u.s.tration: Fig. 76.]

The Connections. We shall suppose that you have the interrupter of App.

104, Fig. 81. The ends of the primary coil (-- 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 sc.r.a.pe 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 4 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, pa.s.sing 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.

[Ill.u.s.tration: Fig. 77.]

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 -- 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 5 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.

[Ill.u.s.tration: Fig. 78.]

146. The Primary Coil (-- 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 -- 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 (-- 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.

[Ill.u.s.tration: Fig. 78-A.]

[Ill.u.s.tration: Fig. 78-B.]

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, bra.s.s, or tin, 5/8 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 pa.s.s 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 pa.s.ses, 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 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.

[Ill.u.s.tration: Fig. 79.]

APPARATUS 102.

_151. Handles for Shocking Coils._ Very neat handles may be made from 4-in. lengths of bra.s.s 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 pa.s.s through a longer column of water than it does when C is near the bottom of L. When C touches T, the current pa.s.ses easily. If it were not for the chimney, the current would pa.s.s to the sides of T.

[Ill.u.s.tration: Fig. 80.]

CHAPTER XII.

CONTACT BREAKERS AND CURRENT INTERRUPTERS.

_154. Contact Breakers; Current Interrupters._ It is often necessary to make and break the electric current at frequent intervals. This can be done by an ordinary key (App. 118) by rapidly raising and lowering it.

It is more convenient, however, to use some other form of apparatus. The current may be interrupted automatically; that is, it may be made to do the work itself (App. 100), or each make and break in it may be governed by the student.

APPARATUS 104.

[Ill.u.s.tration: Fig. 81.]

_155. Interrupter._ Fig. 81. The body of this consists of a strip of wood, 6 or 7 in. long, 1-1/2 in. wide, and 7/8 in. thick. Cut a strip of tin 1 in. wide and long enough to bend down over the ends of the wood.

Fasten the tin to the wood with small wire nails, driving the nails into the ends as well as into the top of the strip. Make a "center line"

along the tin as a guide, and then drive 1-in. wire nails through the tin into the wood, so that they will make a row the length of the wood, and stand about 1/4 in. apart. On one end make a hole through the tin, and put in a screw-eye binding-post (App. 45). It is evident that if a wire from one pole of a battery be connected with the binding-post, it will also be electrically connected with the tin strip and nails. By touching the wire from the other battery-pole to the tin or to any nail, the circuit will be closed. If this last-mentioned wire be drawn along entirely above the tin, so that its end can b.u.mp along from one nail to another, you can see that the current will be closed every time a nail is touched, and be opened every time it jumps through the air. This apparatus can be connected with shocking coils, induction apparatus, etc., etc. Its use will be more clearly shown in connection with such apparatus.

APPARATUS 105.

[Ill.u.s.tration: Fig. 82.]

_156. Interrupter._ Fig. 82. The nails in this apparatus are placed in a circle about 4 in. in diameter. They are electrically connected to each other by a bare copper wire, which is wound around each nail several times, and then led out to one of the binding-posts. In the center of the circle is a nail, or screw, which is connected by a wire to the other binding-post, care being taken not to allow the two wires to touch each other. Around the central screw is wound one end of a stout wire, the other end of which reaches out from the screw far enough to touch the nails. When this stout wire touches any nail, a current entering one binding-post can pa.s.s through nails, screw, etc., and out at the other binding-post. When the end of the stout wire is between two nails, the current cannot flow. By placing the finger against this stout wire and turning it around rapidly, the current can be interrupted as desired.

The base should be about 5 6 7/8 in.

APPARATUS 106.

_157. Interrupter._ Wind the end of the wire from one pole of the battery around the handle of the file. Sc.r.a.pe the other wire along the rough file. As it jumps from one ridge to another the current will be rapidly interrupted.

APPARATUS 107.

_158. Interrupter._ Hold the end of the wire from one pole of a battery upon a saw-blade. Draw the other wire along over the teeth of the saw.

As the wire jumps from one tooth to the next the current will be broken.