Articles: Cases/PSU
 

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Recently we’ve published a roundup of six system cases from Antec, ranging from the tiny NSK1380 to the colossal P182 and Nine Hundred. That article brought us some feedback. Particularly, we were asked how advanced a configuration could be assembled in the compact cases. Yes, it is all clear about the Nine Hundred which can easily accommodate a 1000K PSU but what about the NSK1380? Can its 350W PSU power up a serious graphics card? Will it be working at its limit or perhaps won’t cope at all?

To give an exhaustive answer to this question I carried out a test of power consumption of the configuration I use in my tests. Namely:

  • ASUS P5E mainboard
  • Intel Core 2 Duo E6850 CPU
  • Zalman CNPS9500 AT cooler
  • Four HDDs (Western Digital Raptor WD740GD)
  • HIS Radeon HD 3870 graphics card
  • 2x2GB DDR2-800 SDRAM (Patriot PDC24G6400LLK)
  • DVD-RW drive
  • Microsoft Windows XP Professional SP2

I performed the measurement by means of a Gigabyte Odin GT GE-S550A-D1 power supply. This PSU features a system of monitoring of the currents and voltages, and a USB interface into the bargain. I connected the latter to a nearby PC and launched the Power Tuner tool on it. Thanks to this program I could keep track of the power consumption of my testbed continuously, right from the moment I turned it on. The Odin GT is sufficiently accurate, especially at high loads. Of course, I could arrange a set of shunts and measure the currents in a more honest way but it would improve the precision but slightly (within 10-20W) while making the whole test much more difficult to perform.

I’d like to give you my opinion about two myths, by the way.

Myth One: increasing the number of fans or USB devices raises the PSU load greatly. As a matter of fact, you can just look at the consumption of both to see this is untrue. USB is limited to 2.5W (a current of 500mA at a voltage of 5V) while a regular fan consumes no more than 3-4W. You’ll need some two dozen fans to beat the consumption of a single graphics card!

Well, if your system is on the verge of becoming unstable (due to lack of power or low quality of the PSU), even one fan may be enough to get it beyond that verge. But in this case you should think about the adequacy of the PSU at large rather than about the power consumption of your fans. A stable system, which has a reasonable reserve of power, just cannot be affected by USB devices and fans.

Myth Two: a PC with a large number of hard disks needs a lot of power to start up. In fact, a modern HDD has modest power requirements, about 12-15W under load. The spinning-up of its platters at system start-up requires far less power than a modern graphics card is consuming in 3D mode. In fact, it is in games which simultaneously load both the graphics card and the CPU (these are the two main consumers in modern PCs) that your system may feel a lack of power. If your system with a 400W PSU refuses to start up when you add a fifth or sixth hard disk, you should blame the quality of the PSU rather than its wattage.

So, I performed the test in four modes: 1) Idle, 2) full load on both CPU cores by means of Prime95, 3) full load on all the four HDDs by means of IOMeter, and 4) 3DMark06, the most interesting mode from a practical point of view. In every mode I noted the highest peak of power consumption.

The table below shows the power consumption of my configuration from the PSU (not from the wall outlet, so you don’t have to take the PSU efficiency into account).

As you can see, a system with an advanced CPU, a top-end graphics card, and four fast HDDs has a peak power consumption of only 210W! Well, I was not surprised at the results at all as we had previously measured the consumption of individual CPUs, graphics cards and hard disk drives in our reviews, but the overall consumption numbers make it all even clearer.

Most customers have overestimated notions about the power requirements of their PCs. I won’t discuss that further. I will just mark the points corresponding to these values in the cross-load diagrams of the tested PSUs.

Testing Methodology

Click the following link for a description of our testing methodology, the equipment we use, and a brief explanation of what the specified and tested parameters of power supplies mean. The article is called X-bit Labs Presents: Power Supply Unit Testing Methodology In-Depth. If you feel overwhelmed with the numbers and terms this article abounds in, check out an appropriate section of the mentioned article for an explanation.

 
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