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AC adapter
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==Efficiency== The issue of inefficiency of some power supplies has become well known, with U.S. president [[George W. Bush]] referring in 2001 to such devices as "Energy Vampires".<ref>[http://www.extremetech.com/article2/0,1697,87100,00.asp Bush Takes Aim at "Wall Warts"] {{webarchive|url=https://web.archive.org/web/20071113123837/http://www.extremetech.com/article2/0%2C1697%2C87100%2C00.asp |date=2007-11-13 }}{{snd}} Extreme Tech article</ref> Legislation is being enacted in the EU and a number of U.S. states to reduce the level of energy wasted by some of these devices. Such initiatives include [[standby power]] and the [[One Watt Initiative]]. But others {{who|date=November 2017}} have argued that these inefficient devices are low-powered, e.g., devices that are used for small [[battery charger]]s, so even if they have a low efficiency, the amount of energy they waste is less than 1% of household consumption of electric energy.{{citation needed|date=March 2011}} Considering the total efficiency of power supplies for small electronic equipment, the older mains-frequency linear transformer-based power supply was found in a 2002 report to have efficiencies from 20 to 75%, and have considerable energy loss even when powered up but not supplying power. [[switched-mode power supply|Switched-mode power supplies]] (SMPSs) are much more efficient; a good design can be 80β90% efficient, and is also much smaller and lighter. In 2002 most external plug-in "wall wart" power adapters commonly used for low-power [[consumer electronics]] devices were of linear design, as well as supplies built into some equipment.{{citation needed|date=February 2021}} External supplies are usually left plugged in even when not in use, and consume from a few watts to 35 watts of power in that state. The report concluded that about 32 billion [[kilowatt-hours]] (kWh) per year, about 1% of total electrical energy consumption, could be saved in the United States by replacing all linear power supplies (average efficiency 40β50%) with advanced switching designs (efficiency 80β90%), by replacing older switching supplies (efficiencies of less than 70%) with advanced designs (efficiency of at least 80%), and by reducing standby consumption of supplies to not more than 1 watt.<ref>[https://www.nrdc.org/sites/default/files/app2.pdf Calwell, Chris and Travis Reeder (2002), ''Power Supplies: A Hidden Opportunity for Energy Savings''], [[Natural Resources Defense Council]], pp. 4β9. Retrieved 2010-02-19.</ref> Since the report was published, SMPSs have indeed replaced linear supplies to a great extent, even in wall warts. The 2002 report estimated that 6% of electrical energy used in the U.S. "flows through" power supplies (not counting only the wall warts). The website where the report was published said in 2010 that despite the spread of SMPSs, "today's power supplies consume at least 2% of all U.S. electricity production. More efficient power supply designs could cut that usage in half".<ref>{{usurped|1=[https://web.archive.org/web/20030925181328/http://www.efficientpowersupplies.org/ Efficiency of Power Supplies in the Active Mode]}}</ref> Since wasted electrical energy is released as [[heat]], an inefficient power supply is hot to the touch, as is one that wastes power without an electrical load. This waste heat is itself a problem in warm weather, since it may require additional air conditioning to prevent overheating, and even to remove the unwanted heat from large supplies.
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