Sarasota PC Monitor
Practicing the Black Art (05/04)
Choosing a Power Supply
by Vinny La Bash, vlabash@home.com
Member of the Sarasota Personal Computer Users Group, Inc.The power supply on your PC is like Rodney Dangerfield. It gets no respect. High powered video and sound cards get all the attention. People get excited about CPU speed, virtually no one gets wound up about a power supply. Even most geeks ignore it nearly all of the time.
The power supply is essentially a device made up of a group of electrical parts that converts 120 volts alternating current into the 12 volt, 5 volt and 3.3 volt power that your motherboard, disk drives, and other components require to operate.
Power supplies are rated by Watts, a measure of the amount of electrical power the unit can deliver. The label should tell you how much power can be delivered at continuous and peak performance levels. You will most likely need a unit that can provide 400 Watts of continuous power without excessive noise or heat. Its peak should be at least 100 Watts above its continuous rating. Think of it like an automobile where you generally drive within the middle range of your speedometer, but you could get more if you need it.
Labels will also give you information about how much current each of the output lines can support. Output lines are the connectors that hang off the unit. Let's say one of them is rated at +3.3 Volts @ 30Amps. That line can handle any device that requires 99 Watts or less to operate. It's not enough that the unit can deliver sufficient power. Take another look at the label to see how much the output tolerance can vary. A good quality power supply will have +/- 3% variance or lower. Insist on this to minimize harmful effects brought about by variations in line voltage. A poorly designed or manufactured power supply will eventually lead to system crashes, application hang-ups, and other assorted failures.
A good power supply unit will have a balanced combination of capacitors and inductors. Working together, these two devices protect your PC from both drops (SAG) and surges in voltage. These surges and drops tend to be brief, but if your power supply can't compensate for them, your PC could be toast.
You still need an external surge protector or a UPS for full protection. If you suffer a power failure, the sag protection in your power supply protects your PC until the UPS can kick-in and give you time to perform an orderly shut-down without losing any data. Surge protection helps to overcome power spikes that could fry your PC's electronics.
Your power supply needs a high quality reliable fan to keep it cool. Get a unit with a ball bearing fan. They are less likely to fail than any other kind of fan, and they offer an additional benefit of running quietly. They cost more than other fans and that's why manufacturers make a point of having this information on the label. Newer models have a connector that allows the motherboard to control the fan using its own temperature sensors.
Some power supplies come with adjustable voltage potentiometers. Slight variations of input voltages are inevitable, and these controls allow fine tuning of these minor differences. They don't do much for the average user, but if you're an over clocking fanatic or hardware nut case, twiddle away.
There is more than one type of power supply and it must comply with your motherboard's form factor. Unless you're putting together a slim line or mini-pc, you will need an ATX form factor compatible unit. Be aware that Intel has recently updated the ATX standard by adding a four-pin 12V connector for the motherboard.
If you are evaluating a unit from a manufacturer you never heard of, pick it up and judge its sturdiness. You're looking for heavy. High quality capacitors and heat sinks weigh a lot for their size. If the unit is light compared to others that have similar ratings, it's probably made by a manufacturer who is using substandard materials to increase profit margins. While everyone loves a bargain, it's wise to stay with reputable manufacturers such as PC Power & Cooling, Antec, and Enermax. :
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Copyright 2004. This article is from the July 2004 issue of the Sarasota PC Monitor, the official monthly publication of the Sarasota Personal Computer Users Group, Inc., P.O. Box 15889, Sarasota, FL 34277-1889. Permission to reprint is granted only to other non-profit computer user groups, provided proper credit is given to the author and our publication. We would appreciate receiving a copy of the publication the reprint appears in, please send to above address, Attn: Editor. For further information about our group, email: admin@spcug.org/ Web: http://www.spcug.org/
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