Modu82+ 625 Power Supply: Enermax to the Forefront

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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. The ATX12V Power Supply Design Guide is the most referenced PSU standard in the computer industry. This guide is part of Intel's Power Supply Design Guide for Desktop Platform Form Factors, now in Revision 1.2, dated Feb 2008.

For a complete rundown of testing equipment and procedures, please refer to SPCR's PSU Test Platform V.4. The testing system is a close simulation of a moderate airflow mid-tower PC optimized for low noise.

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 >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. 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.

Great effort has been made to devise as realistic an operating environment for the PSU as possible, but the thermal and noise 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.

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 3" from the exhaust vent at a 45° angle, outside the airflow turbulence area. The photo below shows the setup (a different PSU is being recorded). All other noise sources in the room were turned off while making the sound recordings.

A TWIST IN FAN SPEED MONITORING

In our usual test methodology, the voltage to the fan is monitored with a multimeter by tapping the fan wires. This was not possible to do with the fan in the Modu82+ 625 because it is controlled with PWM, and thus the voltage would always read as 12V.


4-pin connector indicates PWM fan control.

Another method of fan speed monitoring had to be used. We opted for our optical (laser) tachometer. It requires a reflective piece of tape to be affixed to one of the blades, then counts the rotations to determine RPM.


Reflective tape affixed to one of the blades for RPM monitoring.

This meant we could not monitor the fan speed continuously, as the fan is located on the bottom of the PSU, which faces the inside of our thermal simulation box. The exhaust fan had to be removed from the PSU thermal simulation box in order to gain access to the bottom of the PSU where the fan could be seen. We did a fan speed check just before and right after each power load change.


The only way for the optical tachometer to "see" the blades of the PSU fan.

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 also influence the PSU fan speed. Our PSU test rig is a thermal challenge for a power supply: A portion of the heat generated inside the case must be exhausted through the power supply, which causes a corresponding increase in fan speed. This replicates conditions inside a typical PC.

When examining the 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.



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