Flow of electric charge that does not change direction. Direct current is produced by batteries, fuel cells, rectifiers, and generators with commutators. Direct current was supplanted by alternating current (AC) for common commercial power in the late 1880s because it was then uneconomical to transform it to the high voltages needed for long-distance transmission. Techniques developed in the 1960s overcame this obstacle, and direct current is now transmitted over very long distances, though it must ordinarily be converted to alternating current for final distribution. For some uses, such as electroplating, direct current is essential.
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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
