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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
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 instru- . ments 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
usually mounted at some point within convenient reach of the car driver. This is often placed on an instrument board on the back of the cowl in connection with other registering instruments. As ordinarily constructed, the switches are made up of a number of units, and the wiring is such that the head, side and tail lamps may be controlled independently of each other. For simplicity and convenience of installation, the switch is usually arranged so that all circuits are wired to parallel connecting members or “busbars" placed at the rear of the switch. In some cars, as the latest Overland and the White models, the switch units are placed on the steering column. As but little current passes through the lighting switch the contacts are not heavy in construction as are those of the starting switch.
The function of the starting switch is to permit the current to flow from the storage battery to the starting motor, when it is necessary to start the car. It is arranged usually so as to be readily operated by the foot and is nearly always installed at some convenient position on the toe board of the car. have previously shown, the starting switch is often interlocked with the starting motor gearing so that the operation of engaging the gear with the flywheel and of turning on the current to the starting motor are accomplished simultaneously. The lighting and motor starting wiring systems are independent of each other, and may be easily found as that used to convey the high amperage starting current is of heavy round single conductor cable, while the lighting wiring is usually a light multiple strand cable. In order to prevent chafing and depreciation of the insulation the wiring is often protected by conduits of a flexible metal tubing, and the terminals are extremely heavy and well adapted to resist the vibration which is unavoidable in automobiles.
In a paper read by Benj. F. Bailey, of Michigan State University, before the Detroit section of the A. I. E. E., some interesting deductions are presented showing the influence of voltage desired on the electrical equipment, also reasons why the Edison storage battery, which is so well adapted for lighting or ignition is not equally suitable for starting purposes.
On account of the somewhat fragile nature of the filament of
an electric lamp it is not advisable to attempt to operate small lamps at a high voltage, since a high voltage lamp requires a long, slender filament. Practice in this country has practically standardized the six-volt lamp, and there seems to be no valid reason for making a change. This being the case the total voltage of the battery is always some multiple of six, usually 6, 12, 18 and 24 volts.
As far as the battery is concerned the smaller the number of cells the better. A certain minimum of stored energy is necessary and this can be provided with less weight and at a lower cost in a few large cells than in a greater number of small ones. The smallest possible cell using a certain size of plate would have three plates, one positive and two negatives. A cell of double this capacity would require only five plates, two positives and three negatives. The weight of the container would be only slightly greater, and the whole cell would weigh decidedly less than twice as much as the small one. Thus it happens that a battery capable of supplying a certain amount of energy at 12 volts will weigh approximately 35 per cent. more than a battery of the same capacity at 6 volts. The cost of the 12-volt battery will also be about 35 per cent. more. The labor of caring for the battery and the chance of trouble due to a broken battery jar are about doubled.
Good starting motors may be built for any voltage from 6 to 24. Comparing a 6-volt motor with a 12-volt, the commutator of the former would have to be much larger than that of the latter. This means not only added cost of construction but the loss in the larger commutator is approximately twice as much as in the smaller. As this loss is large in any event the efficiency of the 6-volt motor is perhaps 1 or 2 per cent. lower than that of the 12-volt. The designer of the 6-volt motor is also seriously hampered in his choice of windings, and frequently cannot get just the combination needed to give the exact characteristics desired. For example, the calculation might show that 142 turns per coil were desirable. He would be forced to use either 1 or 2. With the same characteristics the proper number for the 12-volt machine would be 3, and we should have a good chance to vary the characteristics by using 2 or 4 turns. In spite of these facts the 6