Motion Picture News (Sept-Oct 1916)

2078 ACCESSORY NEWS SECTION Vol. 14. No. U A B C of the Motion Picture Operating Room Long Ago Majority of Exhibitors Discarded the Rheostat as a Means of Resistance on Alternating Current, a.s Toe Much Power Is Wasted in Heat and the Projection Current Is Not as Satisfactory as That Which Is Obtained by Use of Economizers and Rectifiers THE majority of exhibitors long ago discarded the rheostat as a means of resistance on alternating current, for the reason that too much power is wasted in heat and the projection current is not as satisfactory as that which is obtained by the use of Economizers, Rectifiers and so forth, which are nothing more or less than low voltage transformers. Manufacturers of these devices make all kinds of claims for their product as to the saving which will be efTected through their use. These claims are in many cases overdrawn, but it is a well known fact that these devices can be operated more economically than can a rheostat. There is, however, a great difference in the construction of the various devices of this kind, and the exhibitor should carefully investigate the claims made by the manufacturer before purchasing, as the first cost is a big factor. Then, too, it is not practicable to carry one of these devices for use on the road, owing to the fact that the electrical current A.C.Une Connecting Transformer with Arc supplied by the various lighting companies varies, and while we might start out with a sixty cycle 110 volt machine the very first town we visit might prove to be our Waterloo, for the current might be thirty-three cycles, 220 volts. This would make it necessary to carry several of these devices which, as I said before, would be impracticable, for their weight, which is considerable, would make them costly to carry around. A transformer should only be used on the current and cycle for which it has been designed and exhibitors ordering one of these devices should be very careful to state the number of cycles which it is to be used on. A good transformer used properly, and by that I mean on the current cycle for which it is designed, will operate noiselessly and it should be possible for you to lay your hand on it anywhere without feeling an appreciable degree of heat. A transformer consists essentially of: 1. A primary winding ; 2. A secondary winding; 3. An iron core. Primary and Secondary Coils Within a soft iron core made up of laminated plates of soft iron, there are four coils of insulated wire, two of which are called the primary and two the secondary coils. The two secondary coils are connected to the projection lamp, and the two primary wires are connected to the operating room switch, or source of supply. The number of turns and size of wire tc be used is determined by the pressure at the line and the amount of current you desire at the arc. The secondary coils will have a lesser number of turns ol larger wire than will the primary. If this were not so, and th« conditions reversed, the transformer would be what is knowr as a " step-up," and would furnish current at the arc of highei voltage than that at the line. And this is exactly the conditior you would have if you were to connect your wires to the wronj set of binding posts, with the result that you would soon have a " Fourth of July celebration " of your own with all of th< attending " fireworks." It will only be necessary for me to say that the action of : transformer is as follows : When your switch is thrown into position you have a current in the primary wires which magnetize; the iron plates and induces a current in the secondary coils tc which the lamp is connected. This might be elaborated upon anc continued for some time, but I do not believe that the average operator would care to go into any great detail as to the iror or core losses, copper losses, hysteresis, etc., therefore, I will make this as brief as possible and yet enable the operator to form some idea as to the modus operandi. Those who care to go into thi! more deeply can do so by consulting any of the standard book; on electricity, which may be found in any public library. On nearly all of the transformers used in the operating roon the binding posts are plainly marked " line " and " lamp." Con nect one wire marked lamp to one binding post on the lamp anc the other to the other lamp binding post. Those marked Urn connect directly to the operating room switch. Transformers are usually adjustable, that is they are so constructed as to give three or more different amperages, ranging from 30 to 60 amperes depending upon the make of the machine One thing that should be borne in mind is that a transformei cannot be used on direct current, they are purely and simply al ternating current machines, but it is possible for an operator whc is always "on the job" to get as good a light on the screen will one of these transformers as it is with the use of direct current The accompanying diagram shows the method of connecting j transformer in circuit. The A. C. line is taken to the cut out or fuse block, Fig. 1 from there to operating room switch. Fig. 2. A-A are the line; from switch to transformer; Fig. 3 is the transformer; B-B are the lines from the transformer secondary to fuse block at 4. anc C-C are the lines from secondary fuses to machine switch. Fig 5; and D-D the line from machine switch to arc. Fig. 6. Things to Avoid There are a number of things to remember when using eithei an inductor, transformer, or compensarc. and the operator shoulc never overload his machine beyond its normal capacity, for there is danger of its heating to such an extent that there will be c smoking or burning of the insulation that is not only objectionable to the operator but may give the audience a false impressior of danger, and that is what we want to try and overcome. Sometimes, though, it is possible that the machine itself is insulated improperly wdiich will also cause this smoking to occur When it does you should immediately shut down until the machine has had its coil removed and rewound. The operatoi should never attempt to do this, as it is a job for the manufacturer. Many operators have continued to operate their machine,' under conditions such as this with the result that they have succeeded in injuring the other coils to such an extent as to make their machine absolutely worthless, and caused their employei unnecessary expense that could have been avoided, if the operatoi had used a little more care. A transformer as well as a rheostat should always be placec in such a position as to have it entirely insulated from any par of the operating room, if the operating room is of metal con (Continued on page 2088)