PC Power Supply Efficiency

How The Efficiency Rating of A Power Supply Can Save You Money
Introduction

Personal computers use a tremendous amount of power these days. As the processors and components get more powerful, so does the amount of energy they need to consume. Some desktop systems now can consume almost as much power as a microwave oven. The problem is that even though your PC may have a 500W power supply, the amount of power that it actually pulls from the wall could be much higher than this. This articles takes a look at how much energy a power supply uses and what consumers can do when making a purchase to try and reduce that consumption.
Power In Versus Power Out

The electrical power that is supplied to your house runs at fairly high voltages. When you plug your computer system into the wall for power, this voltage does not flow directly to the components within the computer. The electrical circuits and chips run at much lower voltages than the current coming from the wall outlet. This is where the power supply comes in. It converts the 110/220V incoming power down to the 3.3, 5 and 12V levels for the various internal circuits.

Changing the voltages from one level to another requires various circuits that will lose energy as it gets converted. This means that the amount of power in watts used by the power supply will be greater than the amount of watts of energy that is supplied to the internal components. This energy loss is generally transferred as heat to the power supply and is why most power supplies contain various fans to cool the components.

The big thing to remember is that if you computer uses 300W of power on the inside, it is using more power from the wall outlet. The question is, how much more?
High Efficiency Power Supplies

The efficiency rating of a power supply determines how much energy is wasted or lost when it converts the wall outlet power to the internal power components. For example, a 75% efficiency power supply that generates 300W of internal power would draw roughly 400W of power from the wall. The important thing to note about a power supply is that the efficiency rate will vary depending upon the load amount on the circuits as well as the condition of the of the circuits.

Many power supply manufacturers are beginning to label units as high efficiency or HE. This is really a marketing term that can vary between manufacturers and even models. One high efficiency model might reach 80% efficiency levels while another might reach 85% efficiency. In addition, that 85% efficiency unit may only reach that percentage when it is at a 50% power load. When the unit is at 25 or 75% power loads, it may only have a 70% or lower level of efficiency.

Some manufacturers are now listing the power supply efficiency ratings. It should be noted that many of these still list the optimal efficiency level. Only a few will list the efficiency levels for various load levels on the power supply. Be sure to look for these numbers before buying any PC power supplies.
ENERGY STAR And Power Supplies

The Enery Star program was originally established by the EPA as a voluntary labeling program designed to indicate energy efficient products. It was initially established for computer products to help corporations and individuals mitigate energy expenditures. A lot has changed in the computer market since the program was initially established back in 1992.

Early ENERGY STAR products did not have to meet very strict energy efficiency levels because they didn't use as much power as they do now. Because of these increasing levels of power consumption, the ENERGY STAR program has been modified multiple times. The latest revision takes effect in July of 2007 and makes a very specific standard for the ENERGY STAR label for computer power supplies.

In order for new power supplies and PCs to meet the ENERGY STAR requirements, they must meet an 80% efficiency rating across all rated power output. This means that if the computer is running at 1%, 100% or any level in between, the power supply must reach a minimum 80% efficiency rating in order to get the label. This means that many high efficiency labeled power supplies will not meet this requirement. After all, if it only has 75% at a one quarter load, it fails to meet the guidelines.

These new ENERGY STAR guidelines should help users in finding a power supply that will help meet the needs of their computer systems yet still provide cost savings thanks to the efficiencies. Eventually, the ENERGY STAR group will look to increase the requirements from the 80% efficiency to a higher 85% at some future date.

When looking for a power supply, look for one that carries the 80 PLUS logo on it. This means that the power supply efficiency has been tested and approved to meet the ENERGY STAR GUIDELINES. The 80 PLUS Program provides a list of power supplies that have meet the requirements. This list is updated periodically and provides downloads of PDF's with their test results to let you see exactly how efficient they were.
Conclusions

The amount of power that we consume has become a major issue. Personal computers are becoming a standard item in the home similar to TVs and stereos. Because of this, it is important to try and select equipment that is as energy efficient as possible. By knowing what it really means for a power supply to be efficient, consumers can help reduce their power consumption and make some difference with the environment at the same time.