Most of the electrical power used aboard aircraft is AC, which makes the AC generator the most important means of producing electrical power. AC generators, generally called generators, vary greatly in size depending upon the load to which they supply power. For example, the generators in use at hydroelectric plants, such as Hoover Dam, are tremendous in size, generating thousands of kilowatts at very high voltage levels. Another example is the generator in a typical automobile, which is very small by comparison. It weighs only a few pounds and produces between 100 and 200 watts of power, usually at a potential of 12 volts.