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Perfect Load Distribution: 3.3, 5 And 12 Volt

Inadequate and Deceptive Product Labeling: Comparison of 21 Power Supplies
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The most important starting point prior to buying a new power supply is to check how high the required power output of the computer actually is. To this end, the user has to calculate the computer system's energy requirements. For drives and components, the power demand can be determined relatively easily. In most cases, the manufacturers specify the power demand either on the product or in the user manual. Things get more complicated when it comes to calculating the power requirement for the motherboard, the memory and the CPU. In this case, it is useful to have a table with the average consumption of the individual components of a system.

AMD provides example tables in the Builders Guide for Desktop/Tower Systems . To calculate the minimum output of a power supply, AMD offers the following formula: start with the power demands of the CPU, plus 80% of the total output of all the other components. It is also important to make allowances for a power reserve for future upgrades. In the table, we have listed the power demand for a high-end system, which constitutes the basis of our test. In addition to the total power, the combined outputs play a significant role. The +3.3 Volt, +5 Volt and +12-Volt voltages cannot be exposed simultaneously to any randomly chosen loads. By way of example, with a 300-watt power supply, the maximum power rating of the +3 Volt line in conjunction with the +5.5 Volt line is approximately 180 watts. The key data relating to the power supply can be found on the label and, if available, in the user's manual. Frequently, however, the combined output is not specified.

Important Equipment Features

Further important criteria when deciding on a power supply include computer features, such as the connection facilities for hard disks and drives, plus the length of the connecting leads. In a typical system, there are four power-consumers: the DVD and CD-RW recorder, hard drives and the disk drive, which all require HDD/FDD connections. Depending on the type of case, it may also be necessary to select the lead length. The difference in the length of lead required between a Desktop case and a full Tower case is 20 centimeters, on average. It is also important to consider whether the computer is to be sold internationally. Power supplies are available with both a fixed input voltage of 230 Volts and with a variable input voltage. It is advisable to choose a model with an automatic voltage selection facility. When installing a power supply that uses a switch to select the voltage, prior to switching it on for the first time, it is essential to check the fixed input setting for your country is selected. If you do not check this, the power supply will be instantly destroyed.

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