be sufficiently large to pass a current of from 40 to 200 amperes, depending upon the voltage of the starting system and the size of the engine to be turned over. If the contact points were not of large area they would be very soon burnt. There are two types of starting switches in common use, one has only a single contact and is used on those systems in which the motor is connected at once directly to the battery terminal. The other type of switch has two sets of contacts, the first one completing a circuit through a resistance, the second one cutting out this resistance and permitting the maximum current to flow. The Gray & Davis laminated switch, shown at Fig. 166, A, is a two-contact form. A movement of the switch actuator first engages the blades with the contacts E E, then the arched contact piece L makes a connection with the pieces C C to allow the maximum current to pass. With the switch shown at D, which is also of Gray & Davis manufacture, there are no starting gears, and the only necessary operation is to direct the current directly from the battery into the starting motor winding. The switch is set in the floor boards of the car and is operated by the push rod P, which terminates with a button. The contacts C and O are circular in form and their free ends are turned away from each other so they may slip down over the members R and S, which are set in the insulating piece B. As soon as the pressure of the foot is released a spring returns the push button P and the electric circuit is broken. The switch used on some of the Delco systems is shown at C. In the latest form the motor generator has two independent windings, both on the field and the armature. If the current from the battery is directed into the generator end the machine acts as a shunt motor and the armature rotates at a moderate speed. If the starting gearing will not mesh immediately when brought together a starting button on the dashboard enables the operator to pass the current through the generator winding, this causing the armature to turn over and facilitating meshing of the gearing. The main starting switch has only two points. In the off position the starter is connected directly to the battery terminal. An auxiliary contact on the starting switch breaks the circuit through the generator end and stops the current flowing when the device is used as a starting motor. A heavy copper bar is moved across the face of the contacts B, E and F, the switch normally connects E and F, a feature which is necessary because of the dual functions of the combined motor generator. When the copper bar is moved to the left contacts B and F are brought into full electrical connection with one another and the entire battery current then flows to the motor. The contact pieces are molded into a piece of insulating material. The contact bar is pressed against them by means of springs. Another form of laminated spring switch, which is known as the harpoon type, is shown at B. This is of Ward Leonard design. It is designed for use with a starter having flywheel gear drive, there fore it provides two contact points. The first contact with resist ance in circuit is secured when the fingers C contact or make connection with the plugs E and F. Further movement of the switch short circuits the resistance by closing the main laminated contacts M M. These allow for considerable latitude of movement. The entire switch is built up on a piece of slate as a base and the resistance coils of wire are placed in the back of this base piece. The switches shown may be considered representative design, though the construction varies with practically every starting system. The writer is indebted to the Horseless Age for the illustrations at Figs. 165 and 166. |