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Computer Power Supply

Power Supply Schematics Will Help The Install

Choose the right computer power supply for your system; use power supply reviews to choose from the many computer power supplies and suppliers available. Understand power supply schematics for installation and troubleshooting.

This supply component, yes, you guessed it, supplies power to the computer. The power supply converts 100V - 120V or 200V - 220V power to low voltage DC power that is usable by a computer.

Power supplies typically supply three voltages to the computer: 3.3, 5, and 12 volts. These voltage values are known as "rails".

The 3.3 and 5 volt rails are used normally to power digital circuits, while the 12V rail will normally power internal or external hard drives, fans, and graphic cards.

Power supplies have pretty much standardized to conform with the ATX form factor. This allows power units to be interchangable between computers. So when you decide to upgrade that old Dell computer, you don't have to worry about the power supply not fitting.

The power supply for computers is measured in watts, abbreviated "W". Their rating is based on the maximum power output, which typically ranges from 300W for lower end desktops, to 2000W for multiple core servers.

There are a number of good power supply reviews that can help when selecting. You want to make sure that you match up your power needs with your power supply. Using a power supply that outputs too much power is a waste of energy, while using one that does not output enough power will cause problems with your computer.


Power Supply Connections

A power supply will normally have multiple types of connections...

  • Main Power Connection: this is the connection that provides the main power connection to your motherboard. This used to be a 20 pin power connection, but has been upgraded to a 24 pin connection. You may also encounter power supplies with a 20 pin connector in addition to a 4 pin connector that can be used side by side on a 24 pin motherboard connection.
  • ATX12V: this is a 4 pin power connector, also known as the P4 power connection. Don't get this confused with the one that goes along with the 20 pin connector - they are two separate connectors. This is a second connection for power on the motherboard.
  • 4 Pin Peripheral: also known as a Molex connection (named after the company that created it), these are multiple use power connections that are used for case fans, hard drive, DVD drives and more. They are the general-use power connections.
  • Serial ATA: these are the computer power supply connections that are used for SATA drives, both hard drives and CD/DVD drives.
  • 6 or 8 Pin Connector: a recent addition to computer power supplies. The 6 pin connections are used for PCI-E graphics cards but are being replaced by the 8 pin power connector for high end graphics cards.


Buying Considerations

When you are looking to purchase a power supply for your computer, there are a few things to take into consideration.

Power Needs

It is important to strike a good balance between your computer's power needs and the output of the power supply. Too much power from the power supply, and you are wasting power and money. Too little power output, and your computer will start acting weird.

How to tell if your power supply just isn't cutting it:

  • Failure to power on
  • System instability
  • Random rebooting, especially during peak power usage
  • Failure to boot, even though fans and lights are on

For the majority of PCs, a quality 450W power supply will be sufficient. The only time you will need more power than that is if you are running a higher end graphics card, such as the latest Nvidia and Radeon cards. When looking at power supplies, there are a few technical specs to keep your eye on:

  • PCI-E 6 Pin Connectors: depending on whether or not you are using a graphics card, or more than one graphics cards, make sure you have enough 12V rails for all cards.
  • Efficiency (for green computers): the higher rating, the better. A higher rating in the category means that less power is lost to heat dissipation, and less power is wasted.
  • MTBF: (Mean Time Between Failures) this rating measures the lifespan of the power supply in hours. Quality construction will increase this value, and in today's computer power supplies, 120,000 hours is a good rating.
  • Miscellaneous Features: keep an eye out for different features such as modular power cables that allow you to only use the ones you need and remove the others or SLI and ATI Crossfire support.

Computer power supplies are often reasonably priced and easy to find. Look for a supply unit that is well built, will not quickly over-heat (which is a primary cause of failure) and that will last.


Read more about Power Supply Reviews.

Find out more about External Hard Drives.

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Thanks for
Clear Guide

"Putting the parts together was relatively straightforward. The only snag we hit (my son & I) was getting the CPU fan aligned properly. We had 3 pins in, then noticed when we turned the board over that one wasn't through.

After struggling (carefully!) for 10 minutes, we loosened the other pins, aligned all the pins and we were away again.

The hardest part, I thought, was the wiring. And here your guide really shined.

Most of the other guides ignore it, or just say 'connect all the wires properly'. So thanks for the details (because the devil really is in those wiring details)."

Don, the Netherlands



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