Fanless PSU Torture Test Roundup

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We've been running a complete set of tests for PSUs for many years with minor adjustments here and there. You can read all the details the tests in SPCR Power Supply Test Rig, v.4.1. It can be summarized thus:

  • A PSU load tester customized to provide up to ~1,000W loading, with three separate load circuits for 12V lines.
  • Both current and voltage are monitored on each output line and manually summed to obtain the power load.
  • We employ the same loading formula that Intel and 80 Plus uses for PSU testing, and multiple load test points are checked from a low of 20W to full rated power, with 15~20 minutes of operation at each test point.
  • Voltage regulation, power factor, noise & ripple, efficiency, low AC input performance are tested at every test point. Efficiency at 220~240VAC is also checked for a few test points.
  • Noise and temperature are closely monitored, the latter with the enture test rig in a 10~11 dBA ambient anechoic chamber.
  • The heat from the load is in the box where the PSU is mounted, with a single 120mm fan used for cooling exhaust.

For this roundup, the test has been modified:

  • Low power tests (under 250W) conducted quickly to establish efficiency, power factor, electronic noise, voltage regulation and other parameters. Only 120VAC input used.
  • 250W load test run for 15 hours continuously while monitoring all parameters periodically, with no exhaust fan in the hot box. The basic rationale for this test is that any fanless PSU rated for 400W or higher maximum load should be able to handle 250W indefinitely. 250W is a fairly typical maximum peak demand for the kind of system most DIY builders would use with a 400W PSU.
  • Full load test run for 15 hours continuously while monitoring all parameters periodically, with no exhaust fan in the hot box.
  • If Over Temperature Protection (OTP) shutdown occurs, wait till the power supply can be powered up again, then run the test with the Nexus 120 exhaust fan, starting at 800 RPM. If OTP shutdown recurs, retry with exhaust fan at 1060 RPM (maximum speed of Nexus 120). If OTP shutdown still occurs, then try a Scythe Gentle Typhoon 120mm fan at full speed (rated for 1450 RPM and more than double the airflow of Nexus 120). If OTP shutdown, stop test.
  • Don't run the test in the anechoic chamber, which is not ventilated, but in the open adjacent room to ensure some air circulation.
  • Place the PSU for best airflow/cooling, ie, either right side up or upside down. The Seasonic has an advantage with its open vented side facing up here, so let's give all the others a bit of an edge by optimizing cooling for them in our test setup, even if the PSU does not have the screw mount holes to allow upside down mounting. Remember, this is not a realistic test anyway, it's plain torture.

The OTP function in the tested PSUs could be critical to successful completion of the torture test, one measure of which is to survive it, at least. If the components in the power supply get too high, failure can occur. Hopefully, without drama, explosions, sparks or flames. OTP is supposed to halt operation before excessively high temperature is reached. In modern PSUs, normal operation is usually restored after OTP shutdown when the internal temperature drops to a safe level, and the power switch is reset. One simple reason for the seemingly arbitrary 15 hour testing time: Safety. It's about as long as we could stand to be hovering near the test rig to ensure that some catastrophic failure would not occur unwitnessed.

The SPCR PSU tester is a Frankenstein mix of a commercial load tester and a home-brew hotbox. The box simulates a typical ATX tower case, with the PSU positioned just above the rear panel exhaust vent. The bottom, back and one side of the PSU is exposed to the heat generated in the box, which comes from banks of loading resistors in the box and in the commercial load tester. The PSU has the thermal benefit of being open to the outside air on the top and one side, unlike in a case. With no exhaust fan at the exhaust vent, the air temperature directly below the PSU can exceed 60°C at 400W load. This is hotter than any computer enthusiasts would tolerate in their own PCs.

Four 80mm fans running slowly at 5V keep the DBS-2100 commercial load tester cooled; they also blow the heat into the hotbox. Resistor banks in the hotbox account for more than 50% of the heat when the test load is at or above ~400W.

Vancouver's climate is relatively mild, and over the years, most PSU tests have been conducted in 20~22°C ambient temperature. July and August were hot in 2010, with just trace amounts of rain and peak temperature on most days reaching 25~32°C. That meant the ambient temperature in the test room was typically 23-24°C, and often several degrees warmer. It also made OTP shutdown much more likely than at lower ambient temperatures. No tests were run when the ambient temperature in the room (at several points around the load tester) was higher than 24°C... which is one of the reasons this project took a couple of weeks. The ambient noise in the room measured 14~15 dBA — quiet enough to hear any excessive electronic squealing, buzzing or whine (from the PSU under test) worth measuring or recording in the anechoic chamber.

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