Power Supply Facts

Power Supply Facts

You should know the following facts about power supplies:

• The least expensive way to purchase a power supply is usually when it is included with a system case.
• Power supplies range from 200 watts to 600 watts.
• The power supply converts AC current to DC current.
• The more devices you have in your computer, the more wattage you will require.
• You can calculate wattage requirements using the following method:
• Find the wattage requirements of each circuit by multiplying volts by amps (W = V X A)
• Add the circuit wattage requirements together to find the total system wattage requirement
• Newer processors, like the Pentium 4, have greater power needs.
• Liquid cooling is more effective than air cooling.
• A computer that won't turn on indicates a power supply failure.
• When starting up, the power supply fan should activate first.
• Power supplies store dangerous voltages. Never open a power supply.
• Never ground yourself when working on a power supply.
• Desktop power supplies provide +/- 5 and +/- 12 volts of power (ATX power supplies also provide 3 volts).

·         Protecting Power

·         Computers can experience a variety of power problems, many of the due to external conditions. This table lists power conditions you should be familiar with.

Problem	Description
Surge	Over voltage that lasts seconds
Spike	Over voltage that lasts milliseconds
Sag	Under voltage that lasts milliseconds
Brownout	Under voltage that lasts seconds (lights dim)
Blackout	Complete power failure

·         The following is a description of devices used to prevent power problems. Consider unplugging computers during electrical storms.

Device	Description
Surge Protector	Protects against over voltages. A power strip is not necessarily a surge protector. Also, surge protectors can be destroyed by surges and lose their ability to protect. Consider using a surge protector with an indicator light to show whether it is working correctly.
Line Conditioner	Conditions the power signal to remove noise and create a smooth alternating current (AC) signal.
Standby Power Supply (SPS)	An offline device that switches over to provide power when an under voltage occurs. If the switchover is not fast enough, the computer loses power.
Uninterruptible Power Supply (UPS)	An online device that is constantly providing battery power to the computer and being recharged by the wall outlet. The quality of the electrical signal provided by a UPS battery is not as good as the AC power from the wall outlet. Therefore, UPS devices often have built-in line conditioners. A UPS device is designed to provide enough power to shut a system down safely during an extended power outage. A UPS often connects to a computer with an RS-232 connector. UPS size is measured by the volt-amp (VA) rating. A UPS device generally will not check for software updates itself.