Nexus NX-8060 ATX power supply

Power
Viewing page 4 of 6 pages. Previous 1 2 3 4 5 6 Next

TESTING

For a fuller understanding of ATX power supplies, please read the reference article Power Supply Fundamentals & Recommended Units. Those who seek source materials can find Intel's various PSU design guides at Form Factors.

For a complete rundown of testing equipment and procedures, please refer to SPCR's PSU Test Platform V.4.1. The testing system is a close simulation of a moderate airflow mid-tower PC optimized for low noise.


The current incarnation of SPCR's PSU test system.

In the test rig, the ambient temperature of the PSU varies proportionately with its output load, which is exactly the way it is in a real PC environment. But there is the added benefit of a high power load tester which allows incremental load testing all the way to full power for any non-industrial PC power supply. Both fan noise and voltage are measured at various standard loads. It is, in general, a very demanding test, as the operating ambient temperature of the PSU often reaches well beyond 40°C at full power. This is impossible to achieve with an open test bench setup.

The 120mm fan responsible for "case airflow" is deliberately run at a steady low level (~6-7V) when the system is run at "low" loads. Its measured SPL is <20 dBA@1m. When the test loads become greater, the 120mm fan is turned up to a higher speed, but one that doesn't affect the noise level of the overall system. Anyone who is running a system that draws 400W or more would definitely want more than 20CFM of airflow through their case, and at this point, the noise level of the exhaust fan is typically not the greatest concern. This fan is turned off whenever noise measurements or recordings are made.

While great effort has been made to devise as realistic an operating environment for the PSU as possible, the results obtained here still cannot be considered absolute. There are too many variables in PCs and too many possible combinations of components for any single test environment to provide infallible results. And there is always the bugaboo of sample variance. These results are akin to a resume, a few detailed photographs, and some short sound bites of someone you've never met. You'll probably get a pretty good overall representation, but it is not quite the same as an extended meeting in person.

REAL SYSTEM POWER NEEDS: While our testing loads the PSU to full output (even 1.1 kW!) in order to verify the manufacturer's claims, real desktop PCs simply do not require anywhere near this level of power. The most pertinent range of DC output power is between about 50W and 250W, because it is the power range where most systems work most of the time. To illustrate this point, we conducted system tests to measure the maximum power draw that an actual system can draw under worst-case conditions. Our most power-hungry, overclocked Intel Pentium D950 Presler dual-core processor rig with ATI X1950-XTX video card drew 256W DC from the power supply under full load — well within the capabilities of any modern power supply. Please follow the link provided above to see the details. It is possible that very elaborate systems with the most power hungry components overclocked to the limits could draw a bit more power, but the total would still remain well under 400W. As for high end, dual video card gaming rigs... well, they have no place in quiet computing today.

SPCR's high fidelity sound recording system was used to create MP3 sound files of this PSU. As with the setup for recording fans, the position of the mic was one meter from the exhaust vent at a 45° angle, outside the airflow turbulence area. We also recorded at 30cm distance when the sound was difficult to hear from 1m. All other noise sources in the room were turned off while recording.

INTERPRETING TEMPERATURE DATA

It important to keep in mind that fan speed varies with temperature, not output load. A power supply generates more heat as output increases, but is not the only the only factor that affects fan speed. Ambient temperature and case airflow have almost as much effect. Our test rig represents a challenging thermal situation for a power supply: A large portion of the heat generated inside the case must be exhausted through the power supply, which causes a corresponding increase in fan speed.

When examining thermal data, the most important indicator of cooling efficiency is the difference between intake and exhaust. Because the heat generated in the PSU loader by the output of the PSU is always the same for a given power level, the intake temperature should be roughly the same between different tests. The only external variable is the ambient room temperature. The temperature of the exhaust air from the PSU is affected by several factors:

  • Intake temperature (determined by ambient temperature and power output level)
  • Efficiency of the PSU (how much heat it generates while producing the required output)
  • The effectiveness of the PSU's cooling system, which is comprised of:
    • Overall mechanical and airflow design
    • Size, shape and overall surface area of heatsinks
    • Fan(s) and fan speed control circuit

The thermal rise in the power supply is really the only indicator we have about all of the above. This is why the intake temperature is important: It represents the ambient temperature around the power supply itself. Subtracting the intake temperature from the exhaust temperature gives a reasonable gauge of the effectiveness of the power supply's cooling system. This is the only temperature number that is comparable between different reviews, as it is unaffected by the ambient temperature.



Previous 1 2 3 4 5 6 Next

Power - Article Index
Help support this site, buy from one of our affiliate retailers!
Search: