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 maxi

mum 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

View at Right

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

Fig. 148.-Internal Wiring of the North East Motor Generator.

very large when the battery is in a discharged condition and of low value when the battery is fully charged. The voltage is independent of the speed and the amount of lighting load. The regulator consists of a vibrating armature that intermittently short-circuits a high resistance in series with the shunt field winding of the generator, the length of the short-circuit period depending on the load on the generator. A machine working on this principle is shown at the top of Fig. 150 partially dismantled and

at the right of Fig. 149 as it appears when viewed from the commutator end.

In practically all systems an amperemeter (Fig. 145) is mounted on the dash so that it can be readily inspected by the driver, this indicating at all times the amount of current being produced by the dynamo or drawn from the battery. If the indicating needle of the amperemeter points to the left of the zero point on the scale, it means that the battery is furnishing current to the lights or other current consuming units or discharging. When the needle points to the other side of the scale, it means that the

Fig. 150.-Westinghouse Current Generators Dismantled to Show Interior Construction.

generator is delivering current to the battery which is charging it, the amount of charge or discharge at any time can be read from the scale on the face of the amperemeter. Some of these instruments have the words "charge" and "discharge" under the scale in order to enable the operator to read the instrument correctly.

Another important element is the lighting switch, which is