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red-hot thermal / acoustic torture test shootout last year established the
Seasonic X400 and X460 as the only serious options among fanless ATX power supplies.
The single overwhelming factor was the high 80 Plus Gold efficiency of the Seasonics,
at >90%, head and shoulders better than even the nearest competitor. The
high efficiency means much lower heat generated in the PSU, which makes cooling
so much easier.
For example, the Seasonic X-400, with 91% efficiency at 250W
DC output, produced only 24.7W of heat. Compare that to the runner-up in efficiency,
the Silverstone ST40NF, which at 86% efficiency, produced over 40W of heat at
the same power load. Especially as the load increases, the rising temperature
has a further deleterious effect on less efficient PSUs, which increases the
advantage of the most efficient PSUs. The X400 and X460 signaled clearly that the days of lower efficiency fanless PSUs
cooled by massive external heatsinks are over.
In the year since that roundup, there has been talk of a few
more fanless, high efficiency PSUs. Since 80 Gold efficiency models are now
fairly common, and even 80 Plus Platinum models are coming on stream, this is no
surprise, technically speaking. If you start with a higher efficiency circuit design, it's so much easier to achieve fanless power conversion.
Of course, technical feasibility often has little to do with marketability
or profitability. The consensus of industry sources mostly big online retailers consulted for last year's roundup
was that the market for fanless PSUs has always been small. Whether
the Seasonic X-400 and X-460 grew demand by their availability is difficult
to judge. Still, there are rumours that the Seasonics inspired other brands
to get back into the fanless act.
What is most revealing is that at ascendent US computer hardware e-tailer Newegg, there are only two fanless
PSUs other than Seasonic. Both are examined in this review.
The Kingwin above and Silverstone below both exhibit "classic" fanless PSU design.
This photo of the Silverstone ST50NF shows how the internal
heatsinks are mechanically/thermally joined with the top external
plate for heat conduction.
The Kingwin STR-500 is clearly the more exceptional. It is the first fanless model under the Kingwin or Super Flower brand names. The latter is the actual manufacturer. Not only is it fanless,
the STR-500 offers 80 Plus Platinum efficiency, >92% at midpower. A previous
Kingwin, the LZP-550,
was the first Platinum efficiency model we tested, and possibly the first Platinum on the
market. Like the Seasonic X-series, this Kingwin features detachable cables,
though unlike the X-series whose cables are all detachable, several main output cables are permanently soldered on the STR-500.
The Silverstone ST50NF, in contrast, is not quite as new, offers 80 Plus
Silver efficiency, and has no detachable cables. Still 80 Plus Silver means >88% peak efficiency, which is nothing to scoff at. The last Silverstone we reviewed, the ST40NF, was made by Fortron-Source; for the ST50NF, Silverstone went back to Etasis, the supplier of their earlier fanless models, the ST45NF and ST30NF. These earlier Etasis-built models were the most reliable fanless PSUs until the Seasonic X series.
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