Page:Popular Science Monthly Volume 89.djvu/297

 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

�� �