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insure that the ignition spark will always occur at the same time relative to the piston position or at top center in the cylinder about to be fired.
Q. How are dynamos driven?
A. Dynamos may be driven by direct gearing, if desired, though this is not necessary because this instrument delivers a low tension current that must be used in connection with suitable timing and intensifying means that are auxiliaries to the dynamo. A dynamo can be driven by flat or V leather belts and in some forms the armature is rotated by contact of a friction pulley against the engine flywheel periphery.
Fig. 100A.-Outlining Method of “Floating Battery on Line" Generally
Used When Current From Dynamo Type Generator is Employed
for Ignition, Electric Lighting or Self-Starter Service. Q. Describe a combination battery-magneto ignition system?
A. On some forms of engines two practically separate ignition systems are provided, one being by battery, timer and spark coil, while the other system is by magneto, which is another selfcontained system. When used in the manner outlined at Fig. 100, either magneto or battery outfit may be utilized for ignition pur
poses. The change from one to the other is easily accomplished by shifting a switch lever. When a system of this kind is provided the battery group is intended to be used only for starting and emergency service in event of failure of the mechanical generator. The magneto is used regularly in order to conserve the battery energy. Combination systems of this nature are seldom provided at the present time because the improvements made in magneto design and construction have practically eliminated all liability of trouble at this point. Many cars made in previous years are fitted with combination systems so it is well for the reader to become familiar with the arrangement of the parts and their functions.
Q. What is meant by “floating the battery on the line”?
A. A storage battery is said to be “floated on the line” when it is used in connection with a dynamo which keeps it always fully charged as outlined at Fig. 100-A. The dynamo current is first directed to an automatic cut-out arrangement and from thence to the storage battery, the cut-out being used to interrupt the circuit when the dynamo is not generating energy in order to prevent the storage battery from discharging back through the dynamo and converting that into a motor. The current for ignition is taken from the storage battery instead of from the dynamo so that a constant delivery of current is obtained regardless of fluctuations in engine speeds and the changing amounts of current delivered from the battery charger because of these variations in rotative speed of the dynamo armature. When utilized in this manner a storage battery gives very good service, because it is always kept fully charged by the dynamo and is operating at maximum efficiency. This system can be applied to great advantage in connection with electric car lighting and engine starting systems.
LOW TENSION IGNITION SYSTEMS
Q. Name principal parts of low tension ignition system.
A. A low tension ignition system consists essentially of the current generator usually of the magneto form and a series of makeand-break contact plates attached to the cylinder wall is such a way that a pair of contact points extend through into the combustion chamber.
Q. How is the spark produced in the cylinder?
A. The spark is produced in the cylinder by the separation of the contact points at the instant of maximum current generation in the magneto armature. Q. How is the spark timed?
The make-and-break igniter plates are operated by a camshaft, as outlined at Fig. 101, and the points of the igniter plate are only separated by the mechanism at the time a spark is desired in the combustion chamber. The spark time is thus controlled by the position of the operating cam which is usually so timed in relation to the crankshaft travel that it will separate the igniter points in the cylinder about to fire at just the proper time.
Q. Is battery current strong enough to produce low tension spark?
A. Battery current can be utilized in producing a low tension spark though more energy is required than would be needed by a high tension ignition system. The battery current must be intensified to some extent by means of a "kick-coil” which increases the current value at the time contact is broken in the engine cylinder. Dry cells are not suitable for use on low tension igniter plates unless these have been designed especially for use with battery current.
Fig. 101.-Outlining Operation of Low Tension or Make and Break Spark Plates for Four-Cylinder
A storage battery is more suitable because it will maintain a steadier flow of current and is not exhausted so soon as primary cells, especially if the igniter plate construction is based on the use of electrical current supplied by a magneto. An igniter plate intended for use solely with batteries is devised in such a way that contact is established and broken between the points of the igniter plate only when a spark is necessary, whereas on igniter plates that operate with magneto current the points are kept permanently short-circuited or in contact together until the spark is needed in the cylinder. Where the contact points are practically always together it will be seen that the battery current would be permanently short circuited. Therefore, on most forms of low tension ignition systems the battery is supplied Fig. 102.—Low Tension Igniter Plate Used
on Locomobile Cars. only for an emergency use, as it will soon become exhausted if employed for regular ignition service.
Q. How is spark coil made, and what is the difference between low tension "kick coil” and induction coil used in high tension systems?
A. The kick coil consists of a core of soft iron wire around which is wrapped eight or ten windings of coarse magnet wire No. 16 or 18 gauge. Unlike the induction coil the "kick coil” has only one winding of coarse wire and does not employ a vibrator or condenser. It is much simpler than the induction coil, because the secondary winding, the condenser and the vibrator parts are eliminated. It is connected in series with the battery current, i. e. the positive