SilverStone ST30NF Fanless ATX12V PSU

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ON THE TEST BENCH

For a complete rundown of testing equipment and procedures, please refer to the article SPCR's Revised PSU Testing System. It 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 actual output load, which is exactly the way it is in a real PC environment. But there is the added benefit of a precise 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 loads. It is a very demanding test, as the operating ambient temperature of the PSU often reaches 40°C or more at full power. This is impossible to achieve with an open test bench setup.

Ambient conditions during testing were 26°C and 17 dBA, with input of 119VAC / 60 Hz measured at the AC outlet. The intake temperature was read by a sensor in the testing box positioned about an inch below and behind the PSU; this can be considered the operating ambient temp. The casing temp was measured with a sensor placed in one of the exhaust vents on the back panel.

TEST CUSTOMIZATION FOR ST30NF

The test rig was modified slightly for the fanless operating of the ST30NF, as for the Coolmax Taurus Fanless PSU review. In SPCR's PSU Testing System, there are four medium speed 80mm fans at 5V that blow the heat from the loaded resistors in the PSU load tester into the thermal simulation box. There is a slight positive airflow pressure in the box which actually helps with PSU cooling. An exhaust Panaflo 80M fan at 5V just below the PSU serves to reduce the positive pressure somewhat and to better model a typical low noise system.

  • The sides and top of the ST30NF is open to the outside in the test rig. This allows heat to be radiated directly to the outside air, something that never happen in a normal system setup. So the top and side were blocked off with a piece of cardboard. It's true that close proximity allows some transfer of heat to the top panel of a typical case, but I wanted to err on the stringent or conservative side in testing.
  • Testing was done with the 80mm exhaust fan removed from the test box. Because the PSU has no fan, the amount of air that flows through it depends on convection and the positive pressure in the case. The exhaust fan was removing some of the heat, on the one hand, but also reducing the amount of positive pressure in the case. In an attempt to answer the question, the exhaust fan was removed and the hole for that fan was left open.

After an initial minute or two of temperatures dropping and rising, once things stabilized, there was no change in temperature with the fan blowing out at 5V versus the fan completely removed. This held true for test loads. I believe this means that the airflow produced by the fan is effectively no greater than that created by convection alone, although it does not feel like that -- when I place my hand in front of the hole. Perhaps some cool outside air enters while some hot air exits.

On to the results...

SilverStone ST30NF TEST RESULTS
DC Output (W)
65
90
150
200
250
AC Input (W)
86
117
192
247
312
Efficiency
76%
77%
78%
81%
80%
Intake Temp (°C)
30
34
38
41
44
PSU Casing* (°C)
33
46
52
60
77*
NOTES:
The ambient room temperature during testing varies from review to review.
Please take this into account when comparing PSU test data.
* PSU Exhaust: The unit was accidentally left running at full power load (250W) for nearly two hours.

1. VOLTAGE REGULATION was excellent. Throughout the range of test output levels, the range was as follows:

  • +12V: 11.79 ~ 12.25V
  • +5V: 4.98 ~ 5.11V
  • +3.3V: 3.27 ~ 3.37V

2. EFFICIENCY (AC-to-DC Conversion) was excellent, starting at 76% at the low 65W load test where even high efficiency models tend to drop. The efficiency range was also very tight, varying only from 76% to 81%.

3. POWER FACTOR was excellent, always 0.97~0.99, regardless of power load.

4. NOISE: There was no noise to be heard at all. No whine, no buzz, nothing. It was dead silent. It must be pointed out that rare is the PSU that buzzes with the pure resistive load of the power tester. This is no guarantee that the unit will not hum or buzz when faced with the more complex (though lower power) loads of PC components. Coil buzz is often the result of interactions between components.

3. POWER OUTPUT & TEMPERATURE: Care was taken to ensure than neither the 140W (3.3V + 5V combined) max power nor 30A (5V + 12V combined) max current was exceeded during testing. The unit ran with good stability at all output levels. The full 250W output at 100~120VAC input was confirmed. As the lab is not equipped to provide 200~240VAC, the higher 300W output at this input voltage could not be confirmed.

The ST30NF test sample was accidentally left running at full power (250W) for nearly two hours. As noted in the results table above, the casing temperature reached 77°C and was too hot to be touched for more than an instant. Much of the insulating foam strips on which the PSU rests in the test rig ended up melting due to the high temperature. Yet the sample PSU showed no signs of any distress. Amazingly, there was not even the electronic burning smell that usually results when a PSU is overheated. Finally, a second set of load tests yielded exactly the same results.

Interestingly, neither of the back panel LEDs changed color from green during the lab testing, except once: When the 250W full load test had been running for about 10 minutes, the PSU temp was at 64°C, and the temperature LED had not changed from green. With the casing temp at 77°C two hours later, the temp LED was glowing red. I did not witness exactly when the LED color changed, but obviously the 55°C trigger point mentioned in the manual is not correct, at least for this sample. With the power load reduced to absolute minimum and external fans turn out to help cool off the unit, the temp LED stayed red as the temperature dropped to below 50°C. It was only after the power was turned off for a couple of minutes and turned back on that the temp LED changed back to green.



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