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After years of endless diatribes from tech sites of all stripes, it would seem that the Power Supply has finally begun to recieve its proper due as a key core component to any computer system. With the dawn of the Dual Core, Dual Video Card (or quad even) CPU, users basically had no choice but to re-evaluate their power supply requirements.
Today we will be looking at a multitude of different power supplies each with a unique set of specifications. The big question is: have we moved from under appreciating the importance of a good Power Supply to the other extreme, where we now have companies pushing outlandishly powerful units that are surely more than anyone but the most hardcore will ever need. We will be staying away from the 700W+ units today as it is our belief that they're a bit of overkill, at least for now. With the next generation of video cards projected to consume upwards of 300W, Kilowatt PSU units may soon become a necessity. Don't believe that it's true? Read on and see how these sub 700W units perform!
In order to understand just how much juice is really needed to power todays high end systems we will push each of the power supplies to their limits using a dual core, dual video card setup. We will also be checking out the questions of power efficiency and rail stability across all models along with unit noise levels. There is, or course, always the aesthetics factor as well.
Here's a list of the power supplies we're looking at today:
All of the units range between 430W and 650W, with a median of 556W. Prices are as low as $75 for the Antec True Power 2.0 480W and as high as $155 for the 680W Thermaltake PurePower.
All of the units we're looking at today are at least ATX12V 2.0 compliant, with a couple that are 2.01 and 2.2 compliant. Four of them feature the 8-pin EPS12V adapter required by many dual core motherboards (note that they are the only ones that are over $100 in price).
Each PSU has its own features and perks that make them stand out from each other. First we'll look at how their connectivity specs contrast to each other, then look at each unit individually:
Before we get to the good stuff though, let's take a moment for some quick background information and buzzword explanations.
All electricity supplied to your house by your power company is in the form of alternating current (AC). Since a PC runs using Direct Current (DC), the primary responsibility of any PC Power Supply is to convert your homes AC power to DC power that your PC can use.
Many other devices also use DC power (eg. telephone answering machine, printers, speakers) however their power converters are much less complex. These devices use AC Adapters, which are linear power supplies. This means that they constantly provide the same amount of power no matter the load on the device. Because of this there is a tremendous amount of waste (50% or more) which results in the excess energy being removed from the power supply in the form of heat.
A PC Power Supply is more complex in that it uses what is called a swtiching power supply. Basically a switching power uses a closed feedback loop to provide DC power. This loop helps to regulate the amount of DC power produced regardless of the load on it so that it only draws the amount of AC power needed to produce the DC power required at any given time. As with everything else in this world however, nothing is perfect. How efficient your Power Supply is in regulating this load can determine both how much heat it produces (the less efficient the more heat produced from wasted power), as well as how much power it draws from the wall socket.
Power Factor Correction
The Power Factor of a Power Supply refers to the ratio of power used by the device to the current times voltage supplied to it. Traditionally power supplies came with a power factor of about 0.6 to 0.7 however many new units now have power factor correction (PFC) built in which allow for a power factor of or near 1.0.
So what does this mean to you? In short a power supply with a power factor less than 1.0, although utilizing the same amount of power, will draw more current or amperage than one at or near 1.0. This means that your could run twice as many computers with Power Supplies that had a power factor of 1.0 on a typical 15 amp circuit than you could computers with Power Supplies having a power factor of 0.5.
This can have serious implications if you are into the LAN party scene as distribution capacity is almost always limited. It also has ramifications on the size of UPS battery backup sytem one would need.
The real winner from having units with PFC builtin hower is the utility provider. A unit with a lower power factor uses more of the distribution system's capacity than the same wattage unit with a higher power factor. Since you're billed only by Wattage as a home user the utility would obviously like to minimize the amount of capacity it needs to expend in order to supply a given amount of wattage.
Watts the Deal
Whenver a manufacturer's marketing machine pushes a power supply, typically the firstÂ and sometimes only number that is thrown at you is the power supply's output in terms of Watts which is both convenient to remember and sufficiently vague to confuse the consumer. Buying a power supply based solely on its wattage rating is akin to purchasing a car based solely on it's horsepower production.
A great example of how a Wattage rating can be distorted is seen in many "el cheapo" power supply. These values are taken from an actual 400W ATX PSU
Output Voltage Level - Maximum Current (Amps) - Maximum Power (Watts)
+3.3V -> 26 - 3.3 * 26 = 85.8
+5V -> 28 - 5 * 28 = 140
+3.3V / +5V Limit = 150
+12V -> 14 - 12 * 14 = 160
-5v -> 0.3 - 5 * 0.3 = 1.5
-12V -> 0.5 - 12 * 0.5 = 6
+5VSB -> 1.5 - 5 * 1.5 = 7.5
Total = 150 + 160 + 1.5 + 6 + 7.5 = 325
Now you'll notice that if you go through and simply add up all of the max power ratings for each seperate rail you will get a total of 400.8W which is where the company gets the gall to put 400W on the packaging. The fact of the matter is that with the +3.3V/+5V limit of 150W the absolute maximum power the above unit will be able to put out is 325W.
Tricky, but not illegal. If we don't pay attention to the combination limit (it's usually written in smaller letters below the rail information) it would be easy for someone to be decieved by numbers that might make a unit look much more impressive on paper than it acutally is.
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