Overview

Selecting a power supply is one of the most important aspects to consider when preparing a SoftXpand host computer. The Power Supply Unit (PSU) may greatly affect the stability, reliability and longevity of the host.

SoftXpand software, being an application, does not increase the power consumption. However, a multi workstation SoftXpand host computer will probably utilize more than one video card and will strain the CPU more than a standard one user PC.

The process of selecting a suitable power supply has several important factors to consider. The standard power rating label may be misleading. This guide covers the major factors that you should be aware of when planning the hardware purchase.

Calculating the real power capacity

The PSU rated electrical power is represented in Watts. This rating shows the maximum total power output of the PSU in Watts. The power rating can be misleading at times, because the power inside a computer system is not drawn from one single line. The power consumption is divided between several voltage lines, referred to as rails.

The most important rail is the 12V rail. The components that draw their power from the 12V rail are: CPU, Motherboard, RAM and Video cards.

There may be more than one 12V rail in a PSU. Power stability increases as the rail number grows.

The power capacity (in Watts) available on the 12V rail(s) may be calculated by multiplying the voltage (V) by the current (A) available on the rail(s): W = V X A

The power rating of a typical PSU (the number specified in big letters on the label) may be 500W, however, it does not necessarily mean that the 12V rail is capable of even half of that.

Checking the fine letters on the label of a typical 500W power supply will probably reveal that the number of amps the rail supplies is 18A.

Therefore, the real available power supply on the 12V rail is: 12V X18A = 216W which is actually less than half of the rated power.

Example: How much 12V power will your SoftXpand host computer need?

It is important to have a rough assessment of the power consumption of the computer components. After you have the total, select a PSU that will be able to handle the power demands, while taking note of the 12V rail(s) and not the total power rating.

The following example will demonstrate the anticipated 12V power consumption when planning a six workstation SoftXpand cluster:

Hardware specification

The total 12V power demand should be: 65 + 70 + 80 + 48 = 263W

The total available current on the 12V rail(s) must be not less than: 263W/12V=21.92A (22A)

The suggested solution for this particular case is to use a power supply that has two 18A 12V rails.

Click here for additional information concerning computer power supplies: http://en.wikipedia.org/wiki/Computer_power_supply