An alternating current may be represented by a wavy line drawn above and below a straight line. Every time that the wavy line crosses the straight line it represents an alternation or a reversal of the direction in which the current flows.
[Illustration: FIG. 53.—A Diagram showing how a Rectifier cuts off one-half of the Alternating Current Wave and changes it into Pulsating Direct Current.]
The direct current from an electrolytic rectifier working under proper conditions is practically one-half of the alternating current wave and may be represented by the series of waves marked by "C" in the lower part of the illustration in Figure 53.
It will be noticed that these lines do not cross the straight line and the current therefore does not reverse but flows in one direction only.
When a single cell of rectifier is used on the 110 volt current supply, it should be placed in series with a lamp bank or a step-down transformer so that the current is reduced to lower voltage.
Figure 54 shows how to connect a storage cell in series with a single cell of rectifier and a lamp bank so that the storage cell may be recharged from the alternating current. A step-down transformer will be found more efficient and not quite so wasteful of current as a lamp bank. The rectifier and the storage cell are simply connected in series with the secondary of the step-down transformer in order to secure this result.
[Illustration: FIG. 54.—Circuit showing how a Single Cell of Rectifier should be connected in series with a Lamp Bank to Recharge a Storage Cell. A is the Aluminum Plate and L the Lead or Iron Plate.]
[Illustration: FIG. 55.—Diagram showing the Difference in Current after it has been passed through a Single Cell or Rectifier and after passing through a Four-Cell Rectifier.]
The negative pole of the storage cell must always be connected to the aluminum electrode of the rectifier.
The series of little curved lines at the bottom of Figure 53 which represent the alternating current after it has been changed into direct current by the action of the rectifier, have a space between each two, showing that there are periods during which no current flows but that the current is intermittent and made up of a number of short impulses. One-half of the alternating current is therefore really wasted.