Alternating current (AC) and direct current (DC) are two types of electrical currents. AC-DC power supplies are very different. A DC current moves in only one direction, providing power only a short distance. Typical items producing a DC current include fuel cells, batteries, and solar cells. AC can move in two directions and can switch from one to the other very quickly. AC is produced by power plants and is the type of current found in wall sockets in American homes.
DC was first discovered by Thomas Edison and was in use for many years. It had limitations, however since DC power plants could only transmit current about a mile. When George Westinghouse developed his high-voltage AC system, it could transmit electrical current many hundreds of miles.
Today, both types of current are used frequently. For example, a laptop computer uses both AC and DC to operate. The laptop is plugged into the wall where it receives AC electricity. This provides power to the plug that inserts into the laptop which is delivering a DC charge to the battery of the laptop. There is a transformer located on the laptop’s power cord which converts the AC electricity into DC.
Electric companies use a similar type of transformer (although much larger) to change the power voltage from the local power plant. Power companies will use this transformer to convert the AC power produced by the power plant to very high voltages while it is being transmitted. The power voltage is then reduced until it is safe for use in the home.
There are significant differences between the two types of current. AC is safe over long distances and provides more power at the end of the line. DC is best for short distances and will lose power over a long distance. The frequency of AC is usually 50Hz or 60Hz. This depends on the country. DC frequency is 0. AC current can reverse and go in the other direction, while DC current only flows one way.
AC current is produced by power plants and generators. DC current is produced by cells or batteries. AC current can be converted to DC with the use of an adaptor or converter. DC may be changed to AC by using an inverter. You can use an inverter to create 120 volt AC from the 12 volt DC if you want to run a small device.
AC and DC power supplies are used for different purposes. AC power can be transmitted longer distances and DC power will operate batteries and fuel cells.