Popular Science Monthhj 



283 



Rectifying Alternating Current 



ANEW machine designed to rectify 

 alternating current at li' ^^ voltage 

 into direct current at arc voltage has 

 been placed on the market. It involves a 

 radical departure from ail former prac- 



Ingenious machine changes alternating 

 current into direct current without per- 

 ceptibly decreasing the light 



tice in motor generator sets, as applied 

 to motion picture projection. The 

 armature sets in vertical position, or 

 stands on end, and is carried or supported 

 on hall bearings. The direct current 

 generator is of the inter-pole type, there 

 being four inter-poles and four main 

 poles. '.The inter-pole feature is an im- 

 portant one since it makes possible the 

 handling of heavy fluctuations in current 

 without si)arking at the brush, or with 

 sparking reduced to a minimum. It acts 

 as an aid to commutation, and at the 

 same time produces a constant current 

 characteristic which is most desirable for 

 projection work. 



In order to reduce vibration and noise 

 the vertical type of construction is used. 

 The ball bearings greatly reduce the 

 friction load, which |)artly accounts for 

 the high cfticiency. In order to secure a 

 perfect armature l)alancc the manu- 

 facturers test each machine in a dynamic 

 balance at a speed of seven thousand 

 revolutions a minute, which is appro.xi- 

 mately four times full load speed. The 

 forced ventilation produced by the fan 

 between the motor and the armature 

 keeps the machine cool. 



()ne of the important features of the 

 eciui[)ment is the ability to dissolve 

 from one lamp to the other without a 

 perceptible decrease in the light. The 



machine is so arranged that the operator 

 can change from one lamp to the other 

 before it is possible to heat up the carbons 

 of one lamp with say, fifteen amperes, 

 while operating the other lamp at fifty 

 amperes. While the machine is only 

 rated for constant duty as a fifty ampere 

 equipment, yet it is designed to stand 

 eighty amperes during the change, pro- 

 viding that change does not occupy 

 more than fi\-e minutes. 



The construction of the upper bearing 

 is shown in the accompanying illustra- 

 tion, in which 4 and 5 form the inner 

 and outer shell of the ball-race carrying- 

 balls 6. The inner race 5 is locked to 

 armature shaft 9 by nut 2 and revolves 

 therewith. The outer race 4 sets in a 

 recess in the main frame casting and is 

 stationary. Ten is an oil-well, and 7 is 

 an oil-thrower, which is locked to the 

 shoulder of shaft 9 under inner ball race 

 5 by nut 2, and revolves at armature 

 speed. The action is that the oil is, by 

 centrifugal force, thrown up through pas- 

 sage 3, whence it descends through and 

 around balls 6 by gravity, thus flooding 

 the entire bearing with a constant stream 

 of oil. Thirteen is the plug which closes 

 the upper end of passage 11 through 

 which oil-well 10 is filled. Twelve is a 

 plug througii which oil-well 10 may be 

 drained and washed out with kerosene. 



Adjusting Handles 



THE composi- 

 tion tops of 

 drawing -ink bot- 

 tles may be con- 

 veniently used for 

 insulated handles 

 for many instru- 

 ments by drilling a 

 hole in the center 

 and inserting a 

 brass screw. 

 These look like 

 hard rubber and 

 are \ery servicea- 

 ble, lender con- 

 stant use they will 

 wear as well as 

 most insulators 

 now in use and 

 when broken can 

 be thrown away as 

 useless. 



From ink-bottle top 

 to insulator 



