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Oct 30, 2006 by Mike Chin
** POSTSCRIPT on page 7 added Dec 22, 2006: v4.1 or Bonefish edition **
A little over a year after our last major update, we've made a series of changes extensive enough to consider this the fourth iteration of SPCR's power supply testing system. PSU reviews have been popular bread-and-butter articles at SPCR for years. This is partly because of our close attention to detail, fundamentally sound test procedures, good test gear and thorough acoustic analysis. It is also because there were very few serious PSU reviews done by other hardware web sites. In this context, SPCR PSU reviews really stand out.
Recently, some worthy competitors have emerged. These include extremeoverclocking, xbitlabs, pcperspective, and the latest, johnnyguru. We welcome these serious PSU reviewers to the field. There are still too few sane voices trying to cut through the raucous babble of hyper-marketing that surrounds power supplies for computers these days. Our worthy colleagues have also helped us to reexamine and improve our own test resources and techniques, and we thank them for the impetus.
The changes in our system add several new items to our long list of tested parameters:
- AC ripple, measured with the benefit of a digital oscilloscope.
- Effects of crossloading on output voltage regulation and AC ripple.
- The effects of low AC input voltage on output voltage regulation and AC ripple to examine performance during AC voltage sags and brownouts.
Other changes include:
- Dedicated 120VAC/15A and 240VAC/15A line for power supply testing.
- Added 350W loading capacity on 12V lines to stress test the highest rated power supplies (>1,000W)
- 120mm fan in the thermal simulation box replaces the previous 80mm exhaust fan, which more closely reflects today's best cool and quiet cases.
For the benefit of new readers, this article covers our entire PSU testing system as it stands today. You do not have to refer back to articles describing the earlier versions... unless you want to.
For the record, we first began testing power supplies because they are one of the major sources of noise in a PC, the others being hard drives and fans. The PSU is also a major source of heat; in converting AC voltage from the wall to DC for the computer components, the power supply generates heat as a "waste" byproduct. In most systems, fans are required to remove the heat produced by various computer parts, such as the power supply. The greater the heat, the faster the fans need to spin in order to remove the heat. The relationship between fan noise and fan speed is almost linear. Our PSU test procedure began by examining noise primarily, but quickly expanded to include efficiency, power delivery, voltage regulation, temperatures and many other parameters that describe the electrical, thermal and acoustic characteristics of a power supply.
The photo below shows all the components of our power supply testing system except for the silent PC that runs the audio and oscilloscope software, the microphone preamp and the external digital sound box. Unlike commercial power supply testing systems that can often be fully automated, our customized system is completely manual, with fans that can be completely turned off/on at will to serve our particular needs, one of which is very low ambient noise. There's no way to measure a quiet power supply if the automated power supply tester is whirring, whooshing and whining away with multiple fans. As far as we know, all automated power supply testers have built in fans that are non-defeatable. This makes them useless for us.
From the left: Sennheiser ME 66 shotgun microphone, custom built wood PC thermal simulation box with Nexus 120 fan and internal 21A loading resistors for the 12V2 line, digital thermometer to monitor in/out temperatures of the power supply, a test power supply in the "hot seat", digital multimeter to monitor the PSU fan voltage, DBS-2100 PSU load tester integrated with PC thermal simulation box, B&K 2203 sound level meter in front, 120/240 VAC dedicated outlets, high accuracy Extech 560 digital multimeter to measure output voltage and current, Extech 380803 AC power analyzer/datalogger, 20A 0~140VAC variac, USB Instruments DS1M12 digital oscilloscope to measure / display AC ripple, LCD monitor for silent PC running sound and oscilloscope software, along with spreadsheet software to calculate PSU settings and tabulate measurements. For more details on all of our test gear, please check pages 5 and 6.
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