RECTIFYING DEVICES 391 



rectifier is small and simple to operate and should prove 

 very useful. The battery cannot be connected improp- 

 erly to the rectifier and cannot discharge if the alternating 

 voltage fails; this makes the rectifier a very reliable piece 

 of apparatus. 



Another scheme for obtaining a small amount of c-c. 

 power employs a commutator which is rotated by a small 

 synchronous motor. The commutator has as many seg- 

 ments as the motor has poles and every other segment is 

 connected together. Then each set of segments is connected 



FIG. 257. A Small Vibrating Rectifier, for Charging Storage Batteries 

 from an a-c. line. Westinghouse Elec. and Mfg. Co. 



through slip rings and brushes to the a-c. supply line. 

 Brushes are placed on the commutator and the battery 

 to be charged is connected to these brushes. Careful 

 adjustment of the brush position is necessary to eliminate 

 sparking to this rectifying device. 



123. Mercury Arc Rectifier. Neither of the devices 

 just described will operate well on circuits where much 

 c-c. power is desired because sparking would take place at 

 the contacts and the device would require constant atten- 

 tion when in operation. 



