Fanless PSU Torture Test Roundup

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Fanless ATX Power Supplies
Seasonic X-400 Fanless, Silverstone ST40NF, Silentmaxx MX-560, SilenX Luxurae 460 (FSP Zen 400W), Coolmax CF-480B
Sample Origin
Online purchase, except for Seasonic

A computer with no moving parts remains the Holy Grail of silent computing. There are only two types of moving parts in a computer: Disk drives and fans. The transition from mechanically spinning drives to solid state drives has clearly begun, but there is still no practical substitute for the axial fan in its role as a cheap, efficient mover of air for cooling. Devices that rely on fans for cooling airflow include the power supply, although the latest high efficiency models run so quietly that they might as well be fanless at lower power loads. Still, there's always been a trickle demand, somewhat frustrated by lack of choice, for fanless PSUs.

Silent computing's Holy Grail is still a computer with no moving parts.

Seasonic has always been extremely conservative in its approach to long-term and high-stress reliability, which easily explains why there has never been a fanless model in their lineup, until now. Seasonic's announcement to introduce fanless power supplies actually came as a bit of a surprise to SPCR. The best of Seasonic's own fan-cooled models are now so quiet that there seemed little point going fanless — with the added cooling and reliability challenges. The higher power X-series models feature an effective hybrid cooling design in which the fan simply does not spin below ~200W load.

Perhaps Seasonic's marketing team recognized the dearth of serious fanless PSUs, and made a calculated risk that a PSU which only needs to dissipate 10% of its input power as heat could, in fact, run cool enough and be reliable enough to wear the Seasonic badge, a mark of serious quality in power supplies in recent years. Our recent X-400 Fanless review review confirmed that the new PSU is a marvel of advanced technology, intelligent engineering and quality manufacturing which combine to deliver what Seasonic promises: Silent, utterly stable DC output, all the way to full rated power.

In direct discussions, company reps were brimming with confidence that their new fanless baby could not only perform just like a fan-cooled unit of the same rating, but even deliver full power under extremely low airflow conditions, as one might find in a fanless (or single fan) silent PC. This is the claim that led to the 15-hour long, full-power test without at exhaust fan on the SPCR PSU load tester in our review — an extreme torture test that the SS-400FL passed with flying colors. It is a test that we'd never performed before with any other power supply, fan-cooled or not. As far as we know, no other review web site has published any articles of fanless PSUs under such test conditions.

The question that arose naturally was, "How would other fanless power supplies fare in such a test?"

The question was the genesis of a two-week project that culminates with this article. It is a roundup review of fanless power supplies, in a test setting that can only be described as torturous. Admittedly, the test is not representative of practical usage; few users would push their PSUs to steady-state maximum load for 15 hours in red-hot conditions. The reality is that most people who buy and use a fanless power supply are not looking to push the power or thermal envelope of their PC — usually they're looking to build a silent computer, most often with less-than ultra-power-hungry components. The issue this roundup addresses is just how close to the rated power of a fanless PSU you can run before the cooling requirements of the PSU itself makes the system noisier than just running a good fan-equipped PSU.


Fanless power supplies for DIY computers began appearing in significant numbers some half a dozen years ago. Silent computing was only just beginning to scratch at mainstream tech consciousness, but there was a burst of activity among power supply providers to capture early adopters' disposable cash. They were invariably much higher priced than conventional fan-cooled models. Not coincidentally, a scan of the fanless PSU's history in computing is a stroll through SPCR's review archives. Our focus on quiet/silent PC products means we've examined almost every fanless PSU that made it to market in the past decade. This hands-on experience puts us in a unique position.

SPCR's first close look at a fanless PSU came in June 2003, when the TK Power 300 was examined in an article about a fanless VIA C3 PC built by reader John Coyle. That was a real DIY effort, as the TKPower 300 was not an ATX form factor device. Our own sample proved only marginally reliable, and we never posted an official review.

The Silentmaxx ProSilence PCS-350W, also reviewed that month, was an ATX form factor PSU with a hefty external heatsink fins sticking out the back. It was a massive fanless unit that set the pattern for the breed. The basic concept was to take a standard ATX power supply and rebuild it with massive heatsinks, often turning the casing into an extension of the internal heatsink. The general assumption is that there will be some peripheral airflow in the case/PC; most DIY systems have at least one case fan, and a fan on the CPU heatsink. Sometimes a higher power model was used and derated for hotter operating conditions; the components from a 500W model, for example, might be used in a fanless PSU rated at 350W. This was to try to ameliorate the higher failure rate that surely prevailed at a time when power supply efficiency rarely went much past 70%. This meant that to deliver 200W to the components in a PC, a power supply had to draw nearly 300W, and nearly 100W of waste heat had to be safely dissipated from the power supply. Without a fan, that's a challenging task. Not surprisingly, there were reports in the SPCR forums of many failures with the ProSilence PCS-350W.

Coolmax Taurus CF-300, reviewed in 2004, also used the heatsink-case concept, but in a lighter build altogether, perhaps with more modern circuitry. The efficiency ran a bit higher, climbing up into the high 70s, and overall performance was not bad. Lots of vents allowed air from peripheral devices to flow through it. Unfortunately, our sample began showing glitches toward the end our testing, and we could not recommend it in good faith. Coolmax is still offering fanless PSUs today, however.

The SilverStone ST30NF ATX12V PSU entered the fray in 2004. Manufactured by Etasis, this 300W PSU was the first to employ much higher efficiency (80%) circuitry, the obvious route to making practical fanless power supplies. It was of a much higher quality than the Silentmaxx, with the entire extruded aluminum casing acting as a heatsink and heatpipes used to conduct the internal heat to the casing. It also featured modern auto-range AC input, APFC for very high power factor, and even a thermal indicator LED on the back panel. A fair amount of vent holes allowed some airflow, but the interior of the unit was quite tightly packed. Silverstone claimed that the circuitry and components were from a 450W fan-cooled design, which is credible. Our ST30NF sample became a permanent fixture in the lab, called to perform silent duties for many applications for years. This is the longest-lived fanless PSU, still offered in the market today, along with a higher power, more efficient 400W model, the ST40NF. We reviewed another variant, the ST45NF, in late 2008. That model oddly had a maximum power rating of 450W with 220VAC input and 400W with 110VAC input. The ST40NF may simply be a derated, re-tagged version of the ST45NF model we reviewed.

Antec, one of the biggest case/PSU brands, introduced the Phantom 350 in the fall of 2004. This was another heatsink casing design at least cosmetically similar to the Silverstone ST30NF, with similarly high efficiency (in the low 80s). While it, too, offered much higher build quality than earlier fanless efforts, it must have failed at a higher than normal rate, for Antec introduced a variant a year later, the Phantom 500, the same basic design, but with a fan that turned on beyond a certain internal temperature. Neither of these models is offered in the market today.

Fortron-Source Power (FSP) came to the game in late 2005 with the 300W Zen, which deviated from the previous heatsink-casing models. The top was an extruded aluminum fin piece typical of the fanless breed, but the rest of the casing was mostly open mesh. The mesh cover allowed greater airflow through the Zen, which meant that an exhaust fan mounted on the back panel of a case would tend to pull outside air through the PSU, helping to cool it in the process. It also featured high efficiency, reaching near mid-80s, the highest seen to that point, and modern features such as APFC and auto-range AC voltage input. . The next year, a virtually identical version with upgraded components for 400W rated power appeared rebadged as the Silentmaxx Fanless 400W MX460-PFL01 power supply. Silentmaxx had abandoned its earlier fins-out-the-back design for the more integrated and modern Zen. This 400W fanless model is also sold under the FSP badge, as well as Amacrox.

There were also fanless PSUs built into the now-discontinued, massive fanless TNN-500 and TNN-300 "heatsink cases" by Zalman, as well as the fanless Hush mini-ITX and Hush ATX HTPC cases/systems made by Hush Technologies. These power devices were integral to the cases, however, not in standard ATX form factor, nor availble for separate purchase.

One fanless power supply we never reviewed was the SilenX Luxurae series. These PSUs appeared some time around 2004-5, but they were largely ignored by the SPCR community due to the dubious marketing tactics of the brand's founder. It's unclear whether SilenX is actively selling or promoting the series, as the Luxurae line does not appear on the current product pages, yet they are listed at steep prices at two SilenX online sales sites, as well as one or two other online retailers.

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