DC stands for direct current. AC stands for alternating current. But what exactly do those two terms mean? Basically, with direct current, the electrons or particles that carry the electric charge flow or move in only one direction, and that direction stays the same all the time. With alternating current, the flow of electric charge periodically reverses direction.
When a magnetic field is placed near a wire, electrons are repelled by the negative side and attracted to the positive side of the magnet. This causes them to flow in one direction along the wire, producing direct current. This DC form of electricity was developed for more widespread use by Thomas Edison, although the work of earlier inventors was also instrumental. In contrast, systems that generate alternating current, or AC, use a rotating magnet. As the magnet flips direction, so do the electrons. Nikola Tesla was the inventor of this form of electricity, which was then popularized by George Westinghouse.
AC or DC? Which Is Best?
It depends on what you're doing. AC is much easier to produce and to convert to higher or lower voltages than direct current, and this was what enabled electric power to be widely distributed. AC is the best way to transmit electricity over large distances because the voltage can be increased, or stepped up, for transmission and distribution, which is more efficient. Then a transformer is used to convert that electricity to a suitable voltage for household use and other everyday applications.
DC can be stored in a battery, which is then used to power something. Cordless tools, vehicles, and virtually all computers and electronic devices all operate on direct current. AC cannot be stored, but it can be converted to DC by means of an adapter, which is why the charging cord for your laptop or drill has that big box at the plug or along the cord.
(Team Edison or Team Tesla? Read more about the “War of the Currents” HERE.)
So How Does This Apply to Motors?
AC motors are more efficient than DC motors because they need lower current to operate and have a faster start-up speed than a DC motor that requires more voltage to push it. However, you can better control the speed of a DC motor, which is why they are often used when a slow steady speed is required under load.