Circuit.—Electricity will not flow unless there is a circuit or ground return to its original source.
Low Tension Current.—Low tension current is generated in the primary winding or coil by placing it in a magnetic field. It will flow from one point to another but has very little strength and will not jump the gap at the spark plug. It is used for lighting purposes, or conducted to an induction coil which transforms it into a high tension alternating current.
High Tension Current.—High tension current is generated in the secondary coil by interruption of the primary current or by the rapid magnetization and demagnetization of the core and primary coil.
Direct Current.—Direct current is produced by placing a coil or wire in a magnetic field. 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; a primary and secondary winding, and a set of platinum points. The primary winding is wound directly over the core and consists of a few turns of thick wire. The secondary wire is wound over the primary and consists of a great many turns of thin wire. [Fig. 54] shows the functional action of an induction coil. Both of the coils are wound on the soft iron core A-B. The primary current which is supplied in this case by a cell or number of cells, C and D, is broken at frequent intervals of time. The method of doing this is as follows: One terminal of the primary coil is connected to the fixed platinum stud D, the other terminal to a spring which carries a piece of soft iron, E. When the spring is unbent it touches the stud D, and a current passes in the primary. The core of soft iron becomes magnetized and attracts the soft iron disc, E, thus breaking contact at D. The current is stopped and the core immediately becomes unmagnetized, the spring flies back and the contact is again made. The process is then repeated. When the contact in the primary is broken the current flows in one direction in the secondary coil, when it is made the current flows in the opposite direction in the secondary. Thus an alternating current is set up in the secondary current of great frequency.
Commutator.—The commutator or timer as it is commonly called is used only in connection with the induction coil to complete the circuit when a spark is required at the plug in the cylinder.
Insulation.—Insulating is the act of covering a conductor with a non-conducting substance to prevent the spark from jumping or seeking ground.