Fig. 179.—Step-Down Transformer.
It is often desirable to have at hand an alternating current of low voltage for experimental purposes. Such a current may be used for operating induction coils, motors, lamps, toy railways, etc., and is quite as satisfactory as direct current for many purposes, with the possible exception of electro-plating and storage-battery charging, for which it cannot be used.
When the supply is drawn from the 110-volt lighting circuit and passed through a small "step-down" transformer, the alternating current is not only cheaper but more convenient. A transformer of about 100 watts capacity, capable of delivering a current of 10 volts and 10 amperes from the secondary will not draw more than approximately one ampere from the 110-volt circuit. This current is only equal to that consumed by two ordinary 16-candle-power lamps or one of 32 candle-power, making it possible to operate the transformer to its full capacity for about one cent an hour. A further advantage is the fact that a "step-down" transformer enables the small boy to use the lighting current for operating electrical toys without danger of receiving a shock.
Fig. 180.—Core Dimensions.
The transformer described in the following pages can be easily built by any boy at all familiar with tools, and should make a valuable addition to his electrical equipment, provided that the directions are carefully followed and pains are taken to make the insulation perfect.
The capacity of the transformer is approximately 100 watts. The dimensions and details of construction described and illustrated are those of a transformer intended for use upon a lighting current of 110 volts and 60-cycles frequency. The frequency of most alternating current systems is 25, 60, or 120 cycles. The most common frequency is 60. Dimensions and particulars of transformers for 25 and 120 cycles will be found in the form of a table farther on.
The frequency of your light circuit may be ascertained by inquiring of the company supplying the power.
