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Fig. 145.—Principal Components of Gray & Davis Two Unit Starting stalled on the running board of the automobile, under the body, or under the front or rear seat, the location depending upon the design of the car and the degree of accessibility desired. The best practice is to set the storage battery in a substantial carrying case held by rigid braces attached to the frame side and cross members. If the battery should be set under the tonneau floor boards, a door must be provided in these to give ready access to the battery.
and Lighting System.
The starting motor, which takes the place of the common hand crank, is operated by current from the storage battery, and the high speed armature rotation is reduced to the proper cranking speed by reduction gears of the different forms to be described in proper sequence. The construction of the starting motor is practically the same as that of the dynamo, and it operates on the same principle, except that one instrument is a reversal of the other.
In order to secure automatic operation of a lighting and starting system several mechanical and electrical controls are needed, these including the circuit breaker, the governor, which may be either mechanical or electrical, and the operating switches. The circuit breaker is a device to retain current in the storage battery under such conditions that the battery current is stronger than that delivered from the generator. If no circuit breaker was provided the storage battery could discharge back through the generator winding. The circuit breaker is sometimes called a "cutout." The circuit breaker is usually operated by an electro magnet, and may be located either on the generator itself or any other convenient place on the car, though in many cases the circuit breakers are usually mounted on the back of the dashboard. This device is absolutely automatic in action and requires but little attention.
The governors are intended to prevent an excessive output of current from the generator when the engine runs at extremely high speed. Two types are used: one mechanical, operated by centrifugal force as at Fig. 146, and the other electrical as depicted at Fig. 148. The former is usually a friction drive mechanism mounted in the generator shaft which automatically limits the speed of the dynamo armature to a definite predetermined number of revolutions per minute. The maximum current output is thus held to the required amount independently of the speed at which the car is being driven. The use of this device minimizes the possibility of overheating the generator or overcharging the battery
at high car speeds. The electrical system of governing does not affect the speed of the armature, but controls the output of the generator by means of armature reaction, a reversed series field winding or weakening the magnetic field in some way when the engine speed is excessive. The governors usually permit a maximum generator output of from ten to twelve amperes, though the normal charging current is less than this figure.
The Westinghouse generators for example, with inherent regulation have a compound field winding. The battery charging current passes through the series winding in such direction that any increase in the battery charging current tends to reduce the voltage generated, so that the battery is never charged at an excessive rate. When the lights are burning, however, current flows through this series, winding in the reverse direction, increasing the output
of the generator and causing it to assist the battery in carrying the load. With the usual lamp equipment, this increase in generator output is sufficient to operate the lamps without any demand on the battery at ordinary running speeds. At low speeds the battery supplies a certain proportion of the lighting current, and when the engine is not running, the battery supplies the entire demand. This type of generator is shown at the left of Fig. 149 and at the bottom of Fig. 150.
The generators with automatic potential regulators maintain constant voltage regardless of whether the battery is connected to the system or not. The characteristics are such that the batterycharging current tapers off as the battery charge increases, being