Articles: Cases/PSU

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Power Consumption

Before we proceed to our tests, we’d like to discuss the power consumption issue. You can hear all manner of opinions about how much watts a particular PC configuration needs and most of those opinions are going to be obviously exaggerated. Many people doubt that 120- and 160-watt power supplies typical of such compact systems can handle a computer with anything more than an entry-level CPU. And when a graphics card like ours is added, a 500W power supply is considered necessary because the basic 250-300 watts won’t be enough. Well, let’s just check this out. That’s not difficult. We just took our test configuration (with one hard disk) and connected it to our tool we described thoroughly in our special article on the power consumption of modern computers called PC Power Consumption: How Many Watts Do We Need?.

First, let’s see how much power a system without a discrete graphics card needs in idle mode and under high load. The high load is provided by Prime95 running in In-Place Large FFTs mode. We do not additionally load the mainboard’s integrated core as its power consumption is very low.

The numbers in the last column are most expressive, we guess. The system needs no more than 42 watts when idle, its average power draw being a mere 30 watts.

When the CPU is heavily loaded, the system begins to consume more from the +12V rail: the peak power draw is almost as high as 6A, the average increasing from 1.8A to 4.5A. What about the system’s total power consumption? The average is about 64 watts and the peak value is 80 watts. The numbers are higher than in the idle mode but even notebooks’ power adapters can provide that much power. The power supplies of our system cases are going to cope easily with that load.

And now let’s add a graphics card. A Radeon HD 3870 comes first.

We are interested in the peaks of power consumption although you should keep it in mind that the average is going to be lower.

The overall consumption of the system under the hardest load possible (FurMark fully loads the graphics card and Prime95 does the same for the CPU) is just a little higher than 160 watts. Compare this to the previous results and you can see what a difference the discrete graphics card makes. Yet we can also see that even a 300W power supply is going to cope with this load. The peak power draw is 10W lower under 3DMark 2006 which is closer to real-life games than the synthetic FurMark.

Next, let’s replace the card with a newer and faster Radeon HD 4850. Is it going to be hungrier as well?

The new card is far more voracious indeed. It adds 25W to the system’s overall consumption in both test modes. Anyway, the total power draw of the system is never higher than 200W, which means that a 300W power supply would ensure a large margin of safety.

So, do the bundled power supplies suffice? Yes. They are all right unless you are going to overclock your CPU or graphics card (in which case the computer’s power draw may easily double). The power supply just has to comply with its specs. And we will check this compliance out in this review, too.

We will also mark the peak power consumption of the configuration assembled in each system case in the cross-load diagrams.

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