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The power supply below is similar in design and construction as the one on the 'Inside the Computer's Case' page but it's of much higher quality and has more features. The other power supply had essentially no features. It was probably the least expensive power supply available at the time. More expensive supplies typicall have more features, higher power output capacity and better efficiency.
Multiple/Adjustable Fans:
This supply has 2 fans instead of one. Using multiple fans allows the same amount of air to be moved at much lower RPMs which results in quieter operation. Some supplies use a single, larger fan. This also provides more air flow and reduced noise (compared to a single, smaller fan that has to be spun at high RPMs to provide sufficient air flow). When/if more air flow is needed (when there is more demand for power from the computer or when the internal case temperature is higher), the fans can increase in speed and keep the internal power supply components from overheating.
Fans Controls:
This fan has several ways to control the fan speed. It can allow the motherboard to influence fan speed. It can control the fan speed based on internal temperatures and there is a fan speed control on the rear of the fan. This fan speed control is a potentiometer that allows precise control. Others that have external controls often simply have a multi-position switch (not to be confused with the power switch or voltage selector). The Enermax supply shown here allows the motherboard to control the rear fan on the supply (one fan on bottom, one on the rear of the supply).
Current Ratings:
The current ratings are simply the maximum current draw that the power supply can sustain.
Multiple Rail Voltage Regulators:
Some power supplies monitor only one power supply rail (output) and other outputs varied in output voltage depending on the current demand from the monitored rail. On older supplies, the 5 volt rail was the only regulated output. In better supplies, multiple rails are monitored and controlled by individual regulators so that the voltage on the various rails is much closer to the rated voltage. In low end power supplies, there is only one rail for each output voltage (3.3v, 5v, 12v...). The newer/better supplies have multiple outputs (particularly for the 12v rails. The following image shows the ratings of one such supply. There are three 12v rails. As you can see, 12v3 is rated slightly higher than the others. Generally it's not important what you use the individual rails for but when you have a high-end graphics card, you will often need to use the highest rated rail for the card.
Universal Power Cable:
Most personal computers use a universal power cable. It's also used on many other types of electronic equipment. I'm sure that everyone's probably seen cable but for those who haven't...
Power Supplies with Modular Connections:
On older power supplies, all of the wires were hard-wired to the power supply circuit board. Many of the newer power supplies have 'modular' connectors. This allows the PC builder to use only the wires/connectors needed which eliminates having to try to keep the unused wires/connectors out of the way. This makes a better looking computer that's easier to work on and has somewhat better air flow.
Common Connectors:
There are many different types of connectors on the power supply wiring harnesses. The most common are the flat 4 pin molex and the 20/24 pin power connector. The flat molex generally supplies power to older hard drives and optical drives but can also be used to feed power to the motherboard. When the 4 pin molex is used to feed power to the motherboard, it's typically used to supply power to the PCI-E sockets. This can supply power to low end graphics cards that use the PCI-E slots.
Most newer motherboards use 24 pin connectors. Older boards used 20 pin connectors. The 4 additional pins provide 1 extra terminal for the 12v, 5v, 3.3v and ground. Most new supplies have a 20+4 pin configuration that makes them backwards-compatible with older boards. The following shows a 20 pin power supply being used with a 24 pin motherboard. This computer had very limited power requirements so this wasn't a problem here but for high-end computers, you should use the proper power supply.
High-end graphics cards need more power than can be supplied through the PCI-E slot so they use other types of power connections. Typically, the high-end graphics cards use either a 6 pin or an 8 pin connector. In the photo below, you can see that the card uses a 6 pin connector but the power supply has provided a second connector that provides the extra 2 pins needed for the cards that use the 8 pin connector.
For quite a while, motherboards have used additional connectors to feed the voltage regulators that supply power to the microprocessor. Earlier boards used 4 pin connectors but now, the higher powered, faster processors require more power so some use 8 pin connectors. To make the power supplies backwards-compatible, they use two 4 pin connectors.
The 4 or 8 pin connector is used to supply power to the switching regulators that ultimately supply power to the CPU. The photo below shows the switching regulator components on a motherboard. The green arrows point to; A: transistors, B: capacitors, C: inductors.
Other Features:
Above, you can see that the supply label indicates it's a universal voltage supply with PFC (power factor correction). Universal voltage means that you can supply any voltage in it's design range and it will work properly. Other supplies have a switch that must be set to 115 or 230 volts for the supply to work properly. Power factor correction is used to compensate for the 'reactive' nature of the power supply. This makes it more efficiently use the mains voltage feeding it.
Dust in the Supplies:
All of the power supplies that I've shown you in this tutorial were essentially new. They had not yet had time to accumulate dust. In time, dust will accumulate on the air intake grill and on the heatsinks inside the power supply. When this happens, it will prevent the power supply from cooling and will possibly lead to premature failure. If you open your computer case and the intake of the power supply is dusty, I recommend that you carefully vacuum it (with the computer unplugged - not simply off). Be sure not to pull any wires loose and don't put undue stress on any components mounted to the motherboard (or any other board). If you're using a vacuum with a brush, you have to be careful. The brush fibers can get under some components and pull them loose. If you're using a low-end computer, vaccuming the grill may be enough. If you're using a computer that draws significant current from the power supply and the grill intake has significant dust on it, you may need to clean the interior of the supply as well (you won't have to disassemble the power supply).This is especially important if you've cleaned the grill several times. To clean the inside of the power supply (after it's been removed from the computer - don't do this with the supply in the computer case), you'll need to use a compressed gas duster or an air compressor with a blow nozzle. If you use an air compressor and live where the humidity is relatively high, the compressor MUST have a water trap on it. It's also important that there is no 'oiler' (used to lubricate air tools) on the compressor. Blowing water (if no water trap) or oil (if there's an oiler) could cause the supply to fail which could cause your computer to be damaged.
When you do this, you want to blow the dust out from every angle possible. Continue until little or no dust is dislodged, no matter the angle you apply the air stream. If you're using an air compressor, you have to be careful not to damage the fans. The velocity of air from a compressor can spin the fans so fast that the blades will break off.
Blow from one end then from the other end or wait until the fans spin down before continuing. Do this outside. Some supplies can have a significant amount of dust in them. If you do it near a computer, there's a good chance that the dust will find it's way back into the computer.
If the computer is old, has a lot of airflow through it or has been in a really dusty environment, you may want to blow the dust out of the case and off of the motherboard. Before you do this, you MUST remove the optical drives and I recommend that you remove the hard drives. If dust gets in the optical drives, it will severely degrade their performance or could render them inoperative. Simply wiping the drives with a dry cloth is good enough.
Again, if you use an air compressor and you live in a humid area, you MUST have a water trap on the compressor to prevent getting water on the motherboard or in the power supply. Water on either could cause them to fail catastrophically.
Power Supplies with Monitor Connections:
The power supply below has a second power connector. This connector used to be on virtually all power supplies. They were used to deliver power to the monitor. There is a special cable that connects between the monitor and the supply. The monitor would only receive power when the power supply was on. These aren't used any more. They were needed when monitors had locking power switches and required that someone push the power switch to turn the monitor off. Now, all monitors have digital controls and the computer can tell the monitor to switch off.
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