Efficient Use of Efficiency

摘要

In the september issue of electrical contractor, there was an Industry Watch story titled "Efficiency from the Wall to the PC," about an organization that is campaigning for more efficient power "cords." There was a reference to a quote indicating only 50 percent of the power that leaves the outlet reaches the PC because energy "leaks" out of inefficient power cords. However, a typical PC line cord has 0.3 ohms of resistance. If the computer consumes 720W, that is 6A on 120V circuit. The power loss in the cord is 6A~＾2~*0.3 ohm = 7.8W. Relative to the computer itself, that is approximately a 1 percent loss of power delivered from the outlet, a 99 percent efficiency rating.