Nikola Tesla Books
WELDING TRANSFORMER 213 under its proper heading. The transformer is designed for operation on a 110-volt, 60-cycle alternating current circuit and when the load is applied, the current in the primary is approximately 26 amperes. The secondary current at 11 volts is in the neighborhood of 250 amperes and this is sufficiently large to make quite a display. The Core. The core of the transformer is of laminated iron or preferably silicon steel .017 inch thick and cut into pieces as indicated in Fig. 1. From the diagram the reader will note that two sizes are required, i. e., 3 by 6 inches and 3 by 8 inches, respectively, and 340 pieces of each size will be needed. The steel for the core may be obtained cut to size and ready to assemble from certain transformer manufacturers who buy the material in large quantities and cut it with a gate shear. Fig. 3 shows how the 3 by 8 inch pieces are assembled with the ends projecting alternately three inches first on one and then on the other side. The strips are divided into two piles of 170 pieces each and each pile is then built up as shown in Fig. 3 to make two cores, each three inches thick. A generous wrapping of tape and three layers of press board make the cores ready for the windings. Primary and Secondary Winding.-The secondary is wound over the primary on each leg of the transformer. For this reason the primary winding will be considered first. As mentioned before, the winding described is for use on a 110-volt circuit; if the builder desires to wind for a 220volt circuit, he should substitute twice as many turns of a wire three sizes smaller in the primary only. The windings here mentioned are figured at but 500 circular mils per ampere, but in view of the fact that the transformer is used for only a few minutes at a time, the heating will not be excessive. The primary consists of 120 turns in all and so arranged
