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flies back again, thus re-establishing electrical contact. It will le apparent that the circuit can be broken and re-established many times per second, and as each interruption in current flow induces an impulse in the secondary winding, the greater the number of vibrations of the armature the higher the value of the induced secondary current.
Q. How is the secondary winding made?
A. The secondary winding is composed of a large number of coils or layers of very fine, thread-like insulated wire carefully wound and thoroughly insulated from each other. The greater the number of turns of secondary wire in proportion to the number of layers of primary wire, and the greater the relative difference between the size of primary and secondary wires, the higher the value of the induced secondary current in proportion to the pressure of the primary current. The voltage of the primary current may be increased several thousand times by properly proportioning the primary and secondary windings, and at the same time it will have sufficient heating value to explode the gas as it overcomes the resistance of the air gap between the spark plug electrodes.
Q. What is the condenser and how is it made?
A. The condenser is a simple assembly introduced between the adjusting screw and armature spring in such a way that it is in shunt or parallel connection with the contact points. It is composed of two sets or layers of tin foil insulated from each other by layers of wax paper. Alternate sheets are joined together so there is no electrical connection between one set of tin foil sheets and the other. The function of the condenser is to absorb any excess current present between the platinum points that would tend to produce a spark as they separate. This excess current is the result of selfinduction of one coil of the primary winding upon the neighboring one, and would tend to oppose the passage of the current from the battery if it was not absorbed and stored in the tin foil layers of the condenser. If no condenser is provided, the spark between the points would pit them and burn them to such a degree that prompt vibrator action would be prevented because of the uncertainty of metallic contact when the platinum points came together. This would result in sluggish vibrator action and diminish strength of secondary current.
Q. Describe induction coil action.
A. The diagram at Fig. 85 will assist the reader in obtaining knowledge of induction coil action. Here a solenoid or hollow coil of wire is shown attached to a sensitive form of current indicator. A primary coil, which contains a core of soft iron wire, is depicted as just entering the solenoid. The ends of the primary winding are joined to a simple battery composed of two dry cells. A current of electricity is thus flowing through the primary coil all the time, and the core member is a magnet from which magnetic influence is radiated. When the primary coil assembly is first introduced into the solenoid, the needle of the current indicator will move, thus showing that another current of electricity, other than that flowing through the primary.coil from the battery, has been induced in the secondary winding or solenoid. If the primary coil and core assembly is allowed to remain inside of the solenoid, the current indicator needle comes to rest, showing that there is no current induced in the solenoid. If the primary coil be withdrawn from the interior of the secondary winding, another movement of the current indicator needle in the opposite direction to that which it moves when the primary coil was introduced will show that another impulse or induced current has been produced by withdrawing the primary coil as embly. If the primary coil could be thrust in and out of the secondary coil sufficiently fast, practically a continuous flow of alternating current would be induced in the solenoid.
The induced current is produced by magnetic influence from the core, and obviously if the primary coil was allowed to remain in the secondary coil and the electric current from the battery interrupted and the flow re-established often enough, we would have practically the same effect as though the primary coil was thrust in and out of the secondary coil a number of times corresponding to the making and breaking of the primary circuit at the batteries. It will be apparent that the induction coil assembly outlined at Fig. 84 is practically the same as that shown at Fig. 85, except that the primary coil is a fixed member inside of the secondary winding and the number of current interruptions through the primary coil is obtained by means of a very rapid automatic magnetic circuit breaker or vibrator, the action of which has been previously considered.
Q. Describe timer construction.
A. The usual form of timer as outlined at Fig. 81 is composed of a fiber insulating ring which carries a number of metal contacts which are out of electrical connection with each other and with the metal body of the timer. The rotary contact member revolves in the interior of the insulating fiber ring and makes contact with the segments as it revolves. Each segment communicates with one of
Fig. 85.-How Current is Induced in Secondary Coil by Varying Flow
of Energy Through Primary Coil.
the units of an induction coil and the number of segments and terminals used is determined by the number of cylinders to be fired. The device shown is adapted for a four cylinder motor.
Q. What is the difference between a single cylinder engine timer and one for multiple cylinder ignition?
A. The difference is only in the number of insulated contacts. The timer intended for the multiple cylinder engine having the greater number. A one cylinder timer has but one insulated contact segment and one external primary terminal. As the number of cylinders increase additional contacts are provided, one for each added cylinder.
Q. Are timers used only with primary current?
A. Timers may be used in connection with either primary or secondary current, though when used for distributing the high tension current, they are termed "secondary distributors."
Q. What is the difference between a primary timer and a secondary distributor?
A. In a primary timer the revolving contact element is grounded or attached directly to the metal parts of the engine. In a secondary distributor the revolving brush or contact member is well insulated from the engine and is coupled directly to the source of current or secondary winding of the induction coil. Special care must be taken to insulate the terminals and contacts of a high tension distributor on account of the ease with which the high voltage current overcomes resistances that would effectively bar the progress of the low tension current. Usually a secondary distributor includes a primary timing arrangement as well when used in connection with a battery ignition system.
Q. How are contacts in timers and distributors spaced?
A. In a timer intended for a two cylinder motor the contacts ure spaced according to the arrangement of the cranks on the crank:haft. If the motor is a double opposed form or a two cylinder vertical type with both connecting rods attached to a common crank pin, the contacts are separated by 180 degrees or are spaced on halves of the circle. If the engine is a two cylinder vertical or V type, the contacts are not evenly divided but are separated by spaces of 270 and 90 degrees respectively. The contacts of a three cylinder timer are spaced on thirds of the circle or 120 degrees apart. Those of a four cylinder timer are separated by a space of 90 degrees and
spaced on quarters of the circle. (See Fig. 81.) For a six cylinder engine the contacts are spaced on sixths of the circle, which means that they are 60 degrees apart.
Q. What is the difference between primary and secondary wire and why are they different?
A. Primary wire carries current of low voltage that does not short circuit easily, so the insulation is not nearly as heavy as that on the secondary or high tension current conductors. A primary wire is insulated with but one layer of rubber; whereas a secondary wire has several of insulating compound. A number of wires are shown at Fig. 86. Those at A, B, and C are heavily insulated conductors used to convey high tension energy, while the wires with the lighter insulation, as shown at D and E, are suitable for primary circuits. A number of primary leads are sometimes joined together and though separately insulated, are run through a common conduit, or insulating tube, as shown at F. When used in this manner the inner insulation of the different wires is usually of different colors so they may be easily recognized when making connections.
Q.' How is electricity measured?
A. The strength, quantity, potential and other characteristics of the electric current may be readily determined by simple meters provided with a pointer and a calibrated or graduated scale so the readings can be made easily.
Q. What is the volt?
A. The volt is the unit of pressure and may be taken as corresponding to the head or pressure of water.
Q. What is the ampere?
A. The ampere is the unit of current quantity and corresponds to the amount of electricity flowing through a circuit. A current may have a large amperage, which means that a large volume is flowing, and yet it may have low pressure or voltage. The reverse condition may also obtain and a current of high voltage may not have much amperage.
Q. What is the watt?
A. The watt is the unit indicating the amount of electricity or the value of the current flow. A current of one ampere flowing at a potential or pressure of one volt has a value of one watt. There are 746 watts to the electrical horse-power. In all cases the amount of current consumed by any piece of eiectrical apparatus is indicated in watts, which is always the product of the number of amperes o current times the potential or voltage.