The recent trend of building high performance entertainment and gaming PCs for the modern living room is compelling manufacturers to reduce their systems' dimensional proportions, slowly but steadily increasing the popularity and market of small form factor (SFF) products. With PC case and system manufacturers trying to compete with both each other and gaming consoles, the selection of SFF cases increases with each passing day.

Yet despite the increasing popularity of SFF cases/systems, there is still a rather limited selection of SFX PSUs available, with most manufacturers shyly releasing a unit or two. SilverStone, thankfully, is an exception to this rule, as they are one the few companies that is almost entirely focused on the SFF/SFX market and offer a very wide range of products. For SFX PSUs alone, we have reviewed their mainstream ST30SF and ST45SF units, as well as the exceedingly powerful SX700-LPT and SX800-LTI.

In today's review, we are taking a look at another SFX PSU from SilverStone, the Nightjar NJ450-SXL. A quick glance at its electrical specifications reveals that it is a highly efficient design with an 80Plus Platinum efficiency certification. But what makes the Nightjar NJ450-SXL really unique is that the PSU is entirely passively cooled. Passive PSUs are as rare as hen’s teeth and this is a scarce chance to see what a reputable company has managed to develop for a passive power supply in an SFX form factor.

Packaging and Bundle

SilverStone has us used to practical and aesthetically simple packaging. The packaging of the Nightjar NJ450-SXL is no exception, with a mostly black cardboard box that is focused on highlighting the product’s features and protecting it during shipping.

Despite the class of the PSU, SilverStone only supplies the absolute minimum items required. Inside the box, we found only the four typical black mounting screws, an AC power cable, and a thorough manual. There are no cable ties, straps, adapters, or any other accessories included in the Nightjar’s bundle.

The SilverStone Nightjar NJ450-SXL is a fully modular PSU and every cable can be detached, including the 24-pin ATX cable. All of the cables are ribbon-like, “flat” type, and relatively short when compared to typical ATX products. The shortened cables are the reasonable choice considering that the PSU may be installed in very confined spaces where every millimeter matters. Plus, since SilverStone does not supply an SFX-to-ATX adapter, they probably expect that users will not be installing this PSU in an ATX case anyway.

External Appearance

SilverStone’s Nightjar NJ450-SXL definitely is a unique PSU in both practical and aesthetic terms. Its chassis is essentially a large heatsink and there are no air vents anywhere to be found. The chassis is 130 mm long, which does not fit the standard 125 × 63.5 × 100 mm / 4.92 × 2.5 × 3.94 in (W×H×D) SFX form factor dimensions. SilverStone designates these PSUs as “SFX-L” units and caution is advised as they could be incompatible with compact cases designed to just fit a regular SFX PSU. It also tips the scales at slightly over 1.5 kg, making it significantly heavier than any similarly-sized conventional PSU.

As the PSU relies on natural convection for cooling, the designer had to convert its sides, top, and bottom into aluminum heatsinks with adequate mass and surface area. Instead of using a fan to remove thermal energy from the unit’s internal heatsinks and transfer it to the outside of the case, the internal heatsinks are now attached to the comparatively massive chassis heatsink and the energy is being dissipated directly to the surrounding air - this air, however, will still be inside the system’s case.

In order to leave the heatsinks unobstructed, the designer moved the sticker with the unit’s electrical specifications and certifications at the rear side of the PSU, next to the on/off switch and the AC cable receptacle, on the area that is normally used for the air exhaust vents. The front side holds the connectors for the modular cables. Most of the connectors are black, with the exception of the PCI Express device connectors, which are blue. SilverStone also placed small plastic caps on most of the connectors, excepting the 24-pin cable connector that will always be populated anyway. A small legend on a sticker below the connectors indicates where each connector goes. An interesting observation here is that the NJ450-SXL offers four PCI Express device connectors, suggesting that it can be used to power multi-GPU systems, even though it clearly is unwise to try and power two top-tier graphics chipsets with such a low power output.

Internal Design

There is no fan to talk about in the NJ450-SXL, so we jump right to the OEM of the platform, which is Enhance Electronics. Enhance is not particularly popular amongst enthusiasts because their top-tier designs are frequently outperformed (or outpriced) by other OEMs but their products undeniably are of high quality and reliable.

Internally, the SilverStone Nightjar NJ450-SXL is not in any way special when compared to typical PSUs, with the exception of the strange-looking heatsinks. Unlike the heatsinks we normally find in regular air-cooled PSUs, the internal heatsinks of the Nightjar NJ450-SXL are thin and designed so as to have ample contact surface with the exterior heatsinks of the power supply. As they have very little mass, the internal heatsinks store very little thermal energy and quickly transfer it to the greatly larger exterior of the PSU, acting much like solid heat pipes.

The filtering stage is found on a daughterboard that is placed against the rear wall of the unit, where the sticker with its electrical specifications is. Enhance is a bit generous when it comes to filtering, as we counted two more X capacitors than usual, i.e. four Y capacitors, four X capacitors, and two filtering inductors. There are two rectifying bridges, both attached to a small heatsink that is in contact with the chassis. The rectifying bridges are greatly oversized and can handle the load of even >1 kW PSUs, so it is highly unlikely they will be getting even lukewarm inside the Nightjar NJ450-SXL.

Enhance took a slightly wild approach with the positioning of the two primary inversion MOSFETs that form the unit’s half-bridge primary stage. The designer moved them on a vertical daughterboard near the edge of the unit, in direct contact with the unit’s side cover. As these are perhaps the hottest part inside modern PSUs, the designer most probably wanted to ensure the best possible heat transfer from them to the unit’s exterior. The primary APFC capacitor is rated at 450V/390μF and made by Hitachi.

All of the secondary side MOSFETs that generate the 12V line are placed on the underside of the main PCB, in direct contact (via a thermal pad, of course) with the large heatsink cover of the PSU. A vertical PCB near the left edge of the PSU holds the DC-to-DC converters for the 5V and 3.3V voltage line. The few electrolytic capacitors on the secondary side are made by Unicon, a Japanese company that we rarely see supplying products for PC PSUs. The solid-state capacitors are supplied by Nichicon.

Cold Test Results (Room Ambient Temperature)

For the testing of PSUs, we are using high precision electronic loads with a maximum power draw of 2700 Watts, a Rigol DS5042M 40 MHz oscilloscope, an Extech 380803 power analyzer, two high precision UNI-T UT-325 digital thermometers, an Extech HD600 SPL meter, a self-designed hotbox and various other bits and parts. For a thorough explanation of our testing methodology and more details on our equipment, please refer to our How We Test PSUs - 2014 Pipeline post.

Due to the unique thermal design of the Nightjar NJ450-SXL, we had to change our testing methodology quite a bit. As there is no airflow to assess, we placed a sensor on the bottom side of the chassis and measure its surface temperature instead. Note that these thermal results are not directly comparable with those obtained by testing regular air-cooled products.

The SilverStone Nightjar NJ450-SXL easily honors its 80Plus Platinum efficiency certification, significantly surpassing the minimum requirements of 92%/94%/90% efficiency at 20%/50%/100% load respectively (230V AC input). It has an average efficiency of 92.9% across its nominal load range, a relatively high figure even for an 80Plus Platinum certified unit. The efficiency drop when the unit is powered from a 115V AC source is small, reducing its average efficiency across the nominal load range down to 92.5%. Note that the efficiency drop is more severe at higher loads but negligible, or even negative, when the unit is very lightly loaded.

As expected from a well-designed passively cooled device, the surface temperature of its heatsink increases almost linearly and in near-perfect alignment with the unit’s thermal losses. It does reach over 40°C when the power supply is heavily loaded but that is a perfectly safe figure for an advanced PSU. The internal temperatures of the PSU over its primary and secondary side MOSFETs are acceptable, with the primary side getting a little bit hotter than the secondary side.

Hot Test Results (~45°C Ambient Temperature)

Early SFX PSU designs displayed relatively poor power quality figures but we are constantly getting better and better performance figures from newer designs, indicating that manufacturers are now placing more resources on their design and development. The Nightjar NJ450-SXL feels eons ahead of the units that we reviewed merely a couple of years ago, displaying outstanding power quality figures that easily compare to those obtained from top-tier ATX units. However, we could not operate the unit stably inside our hotbox at 100% load, as the PSU would randomly shut down, therefore we were forced to limit our testing up to 90% load. SilverStone clearly states that this unit is rated for operation up to 40 °C and the high ambient temperature greatly impacts the unit’s ability to dissipate its thermal losses, so the behavior of its safety mechanism is both expected and welcome.

SilverStone’s unit uniquely hits its best performance at 50% load, with the power quality figures worsening when the PSU is very lightly loaded. We recorded a maximum voltage ripple of 26 mV on the 12V line at 90% load, an impressive figure for any SFX PSU. Voltage regulation is very tight on the 12V line, at lower than 0.6% across the nominal output range. The secondary lines are not as tightly regulated, at 1.2% and 1.6% for the 3.3V and 5V lines respectively, yet these figures still are excellent by any measure.

The energy conversion efficiency of the SilverStone Nightjar NJ450-SXL takes a significant hit with the unit operating in our hotbox, a natural phenomenon considering the high internal temperatures of the unit under these operating conditions. The average efficiency reduction is 2%, equally distributed across the entire load range, suggesting that the efficiency drop is not due to the overstressing of a particular component but merely due to the high operating temperatures. Albeit the Nightjar NJ450-SXL is clearly not designed to withstand such operating conditions, it remains operable and it recovers safely from overloading/overheating conditions.

Conclusion

SilverStone's PSU division places a lot of their R&D efforts into the advancement of small form factor systems, and the Nightjar NJ450-SXL is testament to that fact. The Nightjar NJ450-SXL is the first (and currently only) advanced fully passively cooled PSU in SFX form factor, designed to power truly quiet SFF PCs.

The electrical performance of the Nightjar NJ450-SXL is impressive, especially for a passively cooled PSU of this size. We recorded excellent power quality figures, with the PSU showing outstanding voltage line stability. There is very low voltage ripple on all lines, with Enhance designing the platform so as to perform best when it's normally loaded. The PSU easily meets its 80Plus Platinum efficiency requirements at both common input voltages and, as we expected from a passively cooled unit, it is measurably more efficient than the average 80Plus Platinum-certified PSU.

SilverStone backs the NJ450-SXL with a three-year warranty, which is acceptable but not really impressive by today’s standards. Nevertheless, the design and overall quality of the PSU appears to be excellent. Enhance did not cut any corners, performing an exceptional assembly job and using top quality parts all around. We do not foresee any quality-related issues, except perhaps from cases where the PSU may remain significantly and continuously loaded for long periods of time at high ambient temperatures.

When using a passively cooled PSU, there are certain implications. The major point that requires consideration is the fact that the heat generated by the PSU (i.e. its thermal losses) will be released inside the system itself, whereas typical PSUs would actively vent most of that heat to the outside of the case. This means that the system itself will get hotter and may require better cooling in order to sustain its overall performance. Even the PSU’s overall performance will degrade if the ambient temperatures inside the case rise, impacting its own efficiency and longevity. This will probably not be a problem with modern systems that are built with efficiency in mind, but the specifics of this must be considered and weighted by the system’s builder in building a balanced system. After all, it would not make any sense to use a passively cooled PSU only to replace it by another noise source, such as additional case fans.

With the Nightjar NJ450-SXL SilverStone is seeking to satisfy the craving of those who are obsessed with absolute silence, allowing experts to design truly tranquil living room entertainment systems. The performance of the Nightjar NJ450-SXL is excellent and will leave nobody disappointed. However, the design of a truly silent PC requires expertise and the PSU alone is but a small factor. For example, the noise coming from typical gaming GPU will greatly exceed that of the PSU, making its purchase pointless to begin with. The Nightjar NJ450-SXL is a specialized product meant to offer advanced users and experts the ability to design near or fully silent systems, but buyers will want to keep in mind that making the most of the passive PSU will require a bit more than a basic level of user/builder experience.