battery and generator may be made without regard to polarity, a very valuable feature. Even if wrong connections are made, the generator will reverse and assume the correct polarity to charge the battery. Each machine is provided with a fuse in the field curcuit to prevent injury in case the circuit and the battery is opened. Running the generator under these conditions would result in an abnormal rise in voltage which would damage the field windings except for the protection offered by the fuse. The

application of the constant current machine is shown in the wiring diagram of the Appearson system at Fig. 216.

The constant voltage generators are also shunt wound and regulation is effected by varying the excitation in this winding. The principal circuits for the regulating mechanism are shown in wiring diagrams at Fig. 217. The method of operation is as follows: In series with the shunt regulation is obtained

winding 11 is a fixed resistance 12, and by short circuiting this resistance when the generator voltage falls below normal and removing the short circuit when the generator voltage rises above normal. The regulator for performing this operation consists of an iron core 14 with a single winding 13, this winding being connected across the generator brushes. The current in this winding and the resultant pull or magnetic attraction of the core depends, therefore, upon the voltage of the generator. The vibrating armature 15 is pulled away from the core by a spring. When the spring pull predominates, the

Fig. 219.-Battery Charging Curve of Bijur Generator with Voltage Regulator.

armature moves away from the core, closes contacts 17 and 18, and provides a low resistance path around the resistance 12. The field current increases and the generator voltage builds up; when it exceeds its normal value the magnetic pull of the core predominates and the armature is attracted to the core, thus

again inserting the resistance in the field circuit. One of the main features of this regulator (Fig. 218) is that the contacts which shunt the resistance in series with the field winding in and out of circuit are continually shifting, and do not regularly make contact at the same point. Each contact is mounted on a thin, straight spring which is fixed at the end opposite the contact.

The reeds carrying top and bottom contacts are mounted at a 90 degree angle so that the point of contact continually shifts because of vibration and resulting oscillation of the contact. Continuous vibration is obtained because one of the contact reeds is mounted on a regulator armature which vibrates at a high rate of speed. The shifting of the contacts prevents the formation of minute projections on the negative contact and corresponding re

cesses in the positive contact, with the result that the contacts never stick.

Wear manifests itself by the positive contact becoming thinner and the negative growing thicker. Periodically, a disconnecting plug is turned in its socket which reverses the polarity of the

Fig. 221.-View Showing Construction of Bijur Automatic Current

Regulator.

contact so that metal which has been deposited from one contact to the other is returned. The regulator vibrations do not take place at irregular or haphazard intervals, but in the order of something like 100 to 150 times per second. The resulting voltage is the resultant of a series of fine ripples above and below the mean value for which the regulator is adjusted. The amplitude