Choking Coil.—A choking coil in simple form consists of a coil and iron core to increase self-induction. It is used to reduce currents of high pressure and is commonly called a bucking coil.
Fuse.—A fuse is used to prevent conductors or coils from being damaged by heat generated from high pressure currents. It consists of a metal and glass tube which contains a fine wire. This wire being much thinner than the wire of the cable, the heat naturally develops faster at this point, and is soon high enough to melt the wire and break or open the circuit, and thus any further damage to the insulation is prevented.
Condenser.—A condenser usually consists of a few strips of folded tin foil insulated from each other with paraffined or oiled paper. It absorbs, restricts and distributes high pressure currents and also prevents excessive sparking at the contact points.
Fig. 55. Dynamo—Diagram of Action
Dynamo.—A dynamo is a machine which converts mechanical energy into electric energy, and must consist of at least two separate parts; the field magnets to create the magnetic field, and the armature or conductor in which the current is generated. One or the other of these must be in motion in order to cut the lines of magnetic force crossing the field. [Fig. 55] shows the operation of the most common or simplest type of alternating current producing machine, which is similar and conforms in action to the high tension magneto and generator. Field pieces magnetize the pole pieces N and S. A wire coil is placed in the field at right angles to the magnetic lines of force turned to the right. It takes up the position of the dotted lines and no lines of force are cut, whereas in its original position, as many lines of force as possible are cut. Turning the coil on its axles, a-b, causes the lines of force cut by c-d, and e-f to vary from the highest number of lines that it is possible to cut to zero and back again, thus constantly changing the flowing direction of the current. The reversal of the current takes place at the instant that the coil passes the point where it cuts the greatest number of lines of force. The ends of the coil are connected to a commutator on the shaft a, b. Steel insulated brushes pick the current from the commutator ring and conduct it to the brush post; an insulated wire conductor is attached to this post and conducts the current to the place of use or storage.
Voltaic Cell.—The source of energy of a voltaic cell is the chemical action. (See [accumulator]).
Accumulator.—The standard accumulator or storage battery is composed of three cells or hard rubber jars in which a number of lead plates are immersed in a solution of sulphuric acid and water known as electrolyte. The plates are stiff lead grids which hold a paste made of various oxides of lead. Six plates in each cell are joined to the positive terminal, and seven plates in each cell are joined to the negative terminal. Thin wooden separators are inserted between the plates to prevent them from touching one another. In the forming process the material on the positive plates becomes converted into brown peroxide of lead; the negative plates assume the form of gray metallic lead. The material on both plates is known as active material. When current is taken from the cells the sulphuric acid in the electrolyte combines with the active material of the plates to form sulphate of lead, and when the battery is recharged the lead sulphate is again converted into the original active material and the acid set free in the solution.
Storage Battery.—For construction and action see [Accumulator]. For care see chapter on [storage batteries].
Electrolyte.—A chemical solution used in voltaic cells consisting of two parts sulphuric acid added to five to seven parts of water by volume.