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MANAGERS AND PROJECTIONISTS 599
S, as shown. The ratio of secondary voltage to primary voltage will depend upon the ratio of the number of turns in the primary as compared to the number of turns in the secondary, just as in the ordinary transformer.
If connection T were made in such way that the number of turns in the primary would be two-thirds the total number of coils in the primary and secondary combined, then the secondary voltage would be about one-third the primary voltage, and the secondary amperage will be about three times that taken from the supply lines. The auto transformer may be, and frequently is, so made that the secondary terminals may be, by means of proper switches, connected to points located anywhere along the length of practically the entire winding. There is at least one auto transformer which is designed for projection work. It is the product of a western coast manufacturer. It is reported as giving satisfaction. .
EFFICIENCY.— Assuming a 100 per Cent, efficiency, the watts consumed in the primary coil will equal the wattage output of the secondary coil. Like all other devices, however, the transformer is not 100 per cent, efficient, though if well designed it should have an efficiency of better than 90 per cent. The losses in the transformer consist in what is known as core and copper losses, the percentage of loss depending upon the construction of the device. If a transformer which is in good order operates at high temperature, it is evidence of lack of efficiency, as core and copper losses appear in the form of heat.
TRANSFORMER CORE.— The core of a transformer consists of thin sheets of sheet-steel, technically known as "electrical steel." The sheets are painted on either side with an insulating compound and then clamped together into a solid ma§s. The thickness of the sheets of metal necessary for best performance is dependent on the cycle of the current the device is to operate on.
RATIO OF TRANSFORMATION.— A transformer may either be a "step up" or a "step down" transformer. A step down transformer is one in which the secondary voltage is lower than the voltage impressed upon the primary, and the amperage correspondingly greater. For instance, if a transformer were 100 per cent, efficient and ten amperes at 100 volts (10 x 100 = 1,000 watts) were taken from the supply lines, and in the process of transformation the voltage was lowered to 50, then the secondary amperage would be 20.