Motors and generators are the exact same device, but motors convert electrical energy into mechanical energy if the shaft on a motor is spun, a voltage is generated at the terminals! This is useful for many large appliances like dishwashers, refrigerators, and so on, which run on AC.
Direct current is a bit easier to understand than alternating current. Rather than oscillating back and forth, DC provides a constant voltage or current. The tank can only push water one way: out the hose. Similar to our DC-producing battery, once the tank is empty, water no longer flows through the pipes. DC is defined as the "unidirectional" flow of current; current only flows in one direction.
Voltage and current can vary over time so long as the direction of flow does not change. To simplify things, we will assume that voltage is a constant. For example, we assume that a AA battery provides 1.
What does this mean? It means that we can count on most DC sources to provide a constant voltage over time. In reality, a battery will slowly lose its charge, meaning that the voltage will drop as the battery is used.
For most purposes, we can assume that the voltage is constant. Almost all electronics projects and parts for sale on SparkFun run on DC. Examples of DC electronics include:. Almost every home and business is wired for AC. However, this was not an overnight decision. In the late s, a variety of inventions across the United States and Europe led to a full-scale battle between alternating current and direct current distribution.
Thomas Edison, on the other hand, had constructed DC power stations in the United States by A turning point in the battle came when George Westinghouse, a famous industrialist from Pittsburgh, purchased Nikola Tesla's patents for AC motors and transmission the next year. Thomas Edison Image courtesy of biography. In the late s, DC could not be easily converted to high voltages.
As a result, Edison proposed a system of small, local power plants that would power individual neighborhoods or city sections. Even though the voltage drop across the power lines was accounted for, power plants needed to be located within 1 mile of the end user. This limitation made power distribution in rural areas extremely difficult, if not impossible. With Tesla's patents, Westinghouse worked to perfect the AC distribution system.
Transformers provided an inexpensive method to step up the voltage of AC to several thousand volts and back down to usable levels. At higher voltages, the same power could be transmitted at much lower current, which meant less power lost due to resistance in the wires. As a result, large power plants could be located many miles away and service a greater number of people and buildings.
Over the next few years, Edison ran a campaign to highly discourage the use of AC in the United States, which included lobbying state legislatures and spreading disinformation about AC. Edison also directed several technicians to publicly electrocute animals with AC in an attempt to show that AC was more dangerous than DC. In attempt to display these dangers, Harold P. In , the International Electro-Technical Exhibition was held in Frankfurt, Germany and displayed the first long distance transmission of three-phase AC, which powered lights and motors at the exhibition.
Several representatives from what would become General Electric were present and were subsequently impressed by the display. The following year, General Electric formed and began to invest in AC technology. Westinghouse won a contract in to build a hydroelectric dam to harness the power of Niagara falls and transmit AC to Buffalo, NY.
The project was completed on November 16, and AC power began to power industries in Buffalo. This milestone marked the decline of DC in the United States. However, due to the high cost and maintenance of the Thury systems, HVDC was never adopted for almost a century.
With the invention of semiconductor electronics in the s, economically transforming between AC and DC became possible. Specialized equipment could be used to generate high voltage DC power some reaching kV. In the end, Edison, Tesla, and Westinghouse may have their wishes come true. AC and DC can coexist and each serve a purpose. Another way to transmit it would be to send 1 amp at 1 million volts. Sending 1 amp requires only a thin wire, and not much of the power is lost to heat during transmission.
Sending 1 million amps would require a huge wire. So power companies convert alternating current to very high voltages for transmission such as 1 million volts , then drop it back down to lower voltages for distribution such as 1, volts , and finally down to volts inside the house for safety. As you might imagine, it's a lot harder to kill someone with volts than with 1 million volts and most electrical deaths are prevented altogether today using GFCI outlets.
To learn more, read How Power Grids Work. A bitter rivalry between electricity-savvy inventors may sound fictional, but the tension between Thomas Edison and Nikola Tesla was real. Tesla championed alternating current, while Edison insisted that it was too dangerous. The only casualties in this "war of currents" were the animals Edison publicly electrocuted with Tesla's high voltage system to prove his point.
The early victims were dogs and cats, but Edison eventually electrocuted an elephant named Topsy [source: Ruddick ]. Sign up for our Newsletter! Alternating current AC is an electric current that periodically reverses its direction, in contrast to direct current DC which only flows in a single direction which cannot change sporadically.
Most students of electrical engineering and related subjects begin their studies by learning about direct current DC.
This is because most of the digital electronics these students will build will use DC. However, it is important to understand alternating currents AC and its concepts too, because it has many useful properties and use cases.
Alternating current green curve. The horizontal axis measures time; the vertical, current or voltage. Source: Public Domain. Both AC and DC describe types of current that flow in a circuit.
Many sources of electricity, most notably electromechanical generators, produce AC current with voltages that alternate in polarity, reversing between positive and negative over time. An alternator can also be used to purposely generate AC current. In an alternator, a loop of wire is spun rapidly inside of a magnetic field.
This produces an electric current along the wire. As the wire spins and periodically enters a different magnetic polarity, the voltage and current alternate on the wire. This current can change direction periodically, and the voltage in an AC circuit also periodically reverses because the current changes direction. AC comes in several forms, as long as the voltage and current are alternating.
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