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7. TEMPERATURE, COOLING & NOISE
An infrared temperature sensor was used to scan the entire exterior of the PSU. The hottest points, usually atop the large heatsink, were recorded. (See main results tables on previous page for the recorded load temperatures.)
The only real noise that a fanless power supply can make is directly related to the mechanical vibration of transformers and other electronic components that ring or oscillate audibly. A worst case scenario would be the whistling, whining cacophony that often emanates from the back of a big CRT TV, though this is not to say similar noises don't also come from modern big flat panel TVs. What's more normal for a computer PSU is occasional buzzing or whining under certain load conditions.
Kingwin STR-500 at typical idle load for a modern PC. Note absence of any spikes in the curve other than the one at 600Hz, which is in the ambient. This show the complete absence of any buzzing or high pitched whining noise. It is nearly identical to the Seasonic X-460, whose frequency spectrum was captured the same way.
Seasonic X460 shows a similarly clean acoustic profile.
The Silverstone ST50NF shows some high frequency tonal peaks, at 9kHz, and in the band 10~20 kHz. These are too low in level to be considered audible for most people.
At full power load, the Kingwin shows some buzzing centered at 300Hz, and a couple of ultrasonic spikes. The total SPL is still just 12.7 dBA@1m.
The Silverstone at 300W had a surprisingly
high SPL of 14.6 dBA@1m, and its frequency spectrum was quite complex, with multiple peaks at lower frequencies, as well as in the high frequencies. All of these peaks were audible from ~3'.
At full power, the level rose by about 2 dBA; this was not captured, unfortunately.
STR-500: We had mentioned that the fan-cooled LZP-550 emitted a bit of high pitched noise audible from very close distance (under 2-3 feet) at very low loads, a noise that disappeared at higher loads. With our fanless STR-500 sample, there was no buzz or whine at almost any distance, under almost any load. The touch of whine or buzz heard from under 1 foot distance at mid-load was so slight that its presence was difficult to be sure of. It certainly could not be measured; the level was too low to be accurately measured. At full load, turning off the cooling fans in the PSU tester revealed a touch of buzzing, and the SPL was measured at 12.8 dBA@1m, but it was so mild as to be dismissible.
The unit is so efficient that it cannot help but run cool, even without any forced air. Even at full tilt, 500W output, the dissipated heat of the PSU barely amounts to 50W. It's no wonder that the maximum temperature of the exterior after more than half an hour at full power load was just 60°C.
No testing was done with the PSU in the hotbox. The Kingwin STR-500 should do fine with a modicum of airflow, as well as any of the Seasonic X-series 80 Plus Gold fanless models, given its even higher efficiency. It simply has less heat to dissipate.
ST50NF: The Silverstone was also silent at modest loads, although it exhibited some high frequency tonal peaks that people with highly sensitive hearing might be able to hear, at least from up close. As the load increased, these tonal sounds (buzzing, whining) increased in level, so that by 300W, the SPL measured a surprisngly high 14.6 dBA@1m. At full load, the buzzing became a bit more audible, by perhaps 2 dBA overall. In normal use, most of this noise would not be audible for most users, but it definitely wasn't as quiet as the Kingwin or previously tested Seasonic fanless X series samples.
There was also a lot more heat to be dissipated in the ST50NF. As mentioned earlier, the amount of power lost at heat in the STNF was roughly double that of the STR-500 at any given power level. While this had no serious impact at low loads, as load increased, the ST50NF ran increasingly hotter. The recorded temperatures of 60°C and 67°C at full power are not that far apart, but under hotter ambient conditions or more prolonged high load, that difference will increase. A little more care has to be taken to ensure the heat from the ST50NF does not add to the thermal load of your PC, and in the long term, the hotter running temperature of the components within the PSU means higher possibility of earlier failure.
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