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crankshaft. When the device is working as a generator the current that is developed goes to the storage battery, and from that member to the various current consuming units.
Sometimes the motor and generator are combined in one casing and the system so provided is erroneously called a "one unit” system. This construction is shown at the right of Fig. 141. In reality such a system is a two unit system, because the electrical machines are uni-functional instead of performing a dual function as does the combined-motor-generator at the right of the illus
Fig. 141.—Simplified Diagram Showing Operation of One Unit System at
A and Two Armature One Unit System at B.
tration. The wiring of the one unit system is shown in simplified form and should be easily followed by any repairman. The parts of a two unit starting and lighting system are shown at Fig. 142. This system is sometimes called a “three unit”' system, on account of having a source of independent current supply for ignition purposes. This is shown as fitted to the Overland six-cylinder engine at Fig. 143. As will be observed, the generator in the diagram is driven from the motor crankshaft by silent chain connections, one of the terminals passing through the cut-out device
and to the storage battery, the other terminal running directly to the storage battery terminal having a short by-pass or shunt wire attached to the cut-out. All the time that the engine is running the generator is delivering electricity to the storage battery.
It will be seen that the storage battery is also coupled to the lighting circuits which are shown in a group at the right of the illustration, and to the electric starting motor as indicated. One of the storage battery terminals is joined directly to the switch
terminal by a suitable conductor, the other goes to one of the terminals on the starting motor, while the remaining terminal of the starting motor goes to the switch. In this system, when the small sliding pinion is meshed with the flywheel gear, the switch is thrown on simultaneously, and the current that flows from the storage battery through the windings of the starting motor rotates the engine crankshaft by means of reduction gears shown. As soon as the engine starts the foot is released and a spring pulls the switch out of contact, and also disengages the sliding pinion from the flywheel gear.
Fig. 143.—Illustration Showing Location of Starting, Lighting and Igni
tion Units on the Overland Six Cylinder Engine.
The actual appearance of a motor fitted with a two unit motor starting ignition and lighting system is shown at Fig. 144. It will be observed that the generator is driven from the pumpshaft extension by a leather universal joint, while the starting motor is mounted at the back end of the crankshaft in such a position that the automatic sliding pinion may be brought into engagement with
Fig. 144.—Moline-Knight Power Plant Showing Application of Starting
Motor with Automatic Pinion Shift and Method of Driving Generator.
the flywheel driving gear. Electrical starting systems are usually operated on either six- or twelve-volt current, the former being generally favored because the six-volt lamps use heavier filaments than those of high voltage, and are not so likely to break, due to vibration. It is also easier to install a six-volt battery, as this is the standard voltage that has been used for several years for ignition and electric lighting purposes before the starting motors were applied.
In referring to a system as a one unit system of lighting, starting and ignition, one means that all of these functions are incorporated in one device, as in the Delco system. If one unit is used for generating the lighting and starting current, and also is reversible to act as a motor, but a separate ignition means is provided such as a high tension magneto, the system is called a "two unit” system. The same designation applies to a system when the current generating and ignition functions are performed by one appliance, and where a separate starting motor is used. The three unit system is that in which a magneto is employed for ignition, a generator for supplying the lighting and starting current, and a motor for turning over the engine crankshaft. Before describing the individual systems it would be well to review briefly the various components common to all systems.
The generator, as is apparent from its name, is utilized for producing current. This is usually a miniature dynamo patterned largely after those that have received wide application for generating current for electric lighting of our homes and factories. The generators of the different systems vary in construction. Some have a permanent magnetic field, while others have an excited field. In the former case permanent horseshoe magnets are used as in a magneto. In the other construction the field magnets, as well as the armature, are wound with coils of wire. In all cases the dynamo or generator should be mechanically driven from the engine crankshaft either by means of a direct drive, by silent chain, or through the medium of the timing or magneto operating gears. Belts are apt to slip and are not reliable.
All the current produced by the generator and not utilized by the various current consuming units such as the lamps, ignition system, electric horn, etc., is accumulated or stored in the storage battery, and kept in reserve for starting or lighting when the engine is not running or for lighting and ignition when the car is being run at such low speed that the generator is not supplying current. Storage batteries used in starting systems must be of special design in order to stand the high discharge and to perform efficiently under the severe vibration and operating conditions incidental to automobile service. The storage battery may be in