Silverstone Nightjar ST45NF: 450W Fanless Power Supply

A higher power, more efficient version of a model released back in 2004, the ST45NF has the good looks associated with Silverstone PC cases. It’s also one of a very few fanless power supplies in the computer marketplace. The assured, silent performance is commensurate with its top dollar price tag.

Dec 28, 2008 by Mike Chin

The Silverstone ST30NF power supply is one of the most enduring power products in silent computing. We reviewed a sample all the way back in September 2004, and found it then to be the most capable fanless PSU reviewed to date: “The features alone are impressive enough, but more importantly, real performance was exemplary throughout bench and in-system testing.” Amazingly, nearly five years later, this model continues to be in production. It is still the model most often mentioned when anyone inquires about a fanless PSU in the SPCR forums. In fact, one of them is powering the new silent PC that processes the digital audio measurements and recordings from SPCR’s anechoic chamber.

The ST45NF is a higher power version of this popular fanless power supply and this 450W model has at least one significant improvement over the original 300W model: It is certified 80 Plus Bronze, which means its efficiency is at least 82% for all loads from 20% upward. The ST30NF, in contrast, is not 80 Plus approved at all, which means even 80% efficiency is not assured. (In our 2004 testing, the ST30NF efficiency ranged 76%~81% at 65W~250W.) Why this pair of fanless PSUs is called Nightjar is a mystery… although the entry in Wikipedia about this European bird may be a hint:

During the day it lies silent upon the ground, often on a heap of stones, concealed by its plumage; it is difficult to detect, looking like a bit of lichen-covered twig or a fragment of bark. With eyes almost closed it watches through tiny slits, rising suddenly, sometimes with a croak of alarm, but usually silently, when almost stepped on.

FEATURES, SPECIFICATIONS

Silverstone has focused mostly on the performance-oriented sector of the market with its power supply lines, of which there are many. For company which began and still has a primary identity as an aluminum case specialist, Silverstone offers a huge range of power supply models, made for them by several different manufacturers. The ST30NF and ST45NF are both made by Etasis Electronics.

A silver cardboard retail box proclaims Zero dBA in red. The contents include the PSU, paper manual and spec sheet, two AC cord for different regions, plastic and velcro cable ties, plus screws and thumbscrews for mounting. A bracket for additional support on the back of the PSU is also provided (for those cases which allow this).

Note that there’s no claims about multiple 12V lines, which is generally a good thing. The details of the power rating deserve a little more attention, because it is not normal for a PSU to have different ratings for different AC input voltages. Silverstone goes so far as to list two complete output spec tables, one for 180VAC~264VAC and another for 110VAC~180VAC. This oddity will be discussed in detail in the test analysis section.

VISUAL TOUR

The ST450NF appears similar to the ST300NF, but not identical. Its exterior is silver in color, made of meshed aluminum panels on four sides, extruded aluminum with very short fins on the bottom, and a thinner solid panel on top. It is actually a bit different from the ST300NF in that there are more open vents all around the unit. In fact, only the top panel (which has the label) is without vent holes.

All four sides are vented with meshed aluminum panels. The bottom is vented… …but not the top.

When compared to the ST300NF, the casing of this model has fewer external fins. It appears to rely more on airflow through it — rather than conduction of heat to the external panels and convection from there on. The latter is the most common approach to cooling in fanless PSUs. The assumption with the ST45NF is that there will always be some peripheral airflow from other fans in the system, and the vents are meant to take advantage of that airflow. We’ll see later what this design does to overall airflow in a typical quiet PC.

OUTPUT CABLES are all sleeved. Note the existence of both dual PCIe connectors and an 8-pin EPS12V connector. This PSU is equipped for some heavy duty work with a modern computer.

1 x 550mm cable 24 / 20-Pin Motherboard connector
1 x 550mm cable 8 / 4-Pin EPS / ATX 12V connector
1 x 550mm cable 6-Pin PCIe connector
1 x 550mm cable 8 / 6-Pin PCIe connector
2 x 500mm cables, each with 3 x SATA connectors
2 x 500mm cables, each with 3 x 4-Pin Peripheral connectors and one 4-Pin Floppy connector

INSIDE

The removal of eight screws allows the extruded bottom panel to come off. It is tightly affixed to the flat tops of the internal heatsinks for good transfer of heat from the components to the external panel.

High quality capacitors are used throughout: For the primary section, there are three Nippon Chemi-Con units rated for 105°C. The secondary section uses smaller NC-C, Teapo and solid polymers. As with the original ST30NF, the impression is very positive. It’s a tidy, well-made PSU using high quality components.

TESTING

For a fuller understanding of ATX power supplies, please read
the reference article Power Supply Fundamentals.
Those who seek source materials can find Intel’s various PSU design guides at
Form Factors.

For a complete rundown of testing equipment and procedures, please
refer to SPCR’s
PSU Test Platform V4.1. The testing system is a close simulation of
a moderate airflow mid-tower PC optimized for low noise.

Acoustic measurements are now performed in our anechoic chamber with ambient level of 11 dBA or lower, with a PC-based spectrum analyzer comprised of SpectraPLUS software with ACO Pacific microphone and M-Audio digital audio interfaces.

In the test rig, the ambient temperature of the PSU varies proportionately
with its output load, which is exactly the way it is in a real PC environment.
But there is the added benefit of a 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 standard loads. It is, in
general, a very demanding test, as the operating ambient temperature of the
PSU often reaches >40°C at full power. This is impossible to achieve
with an open test bench setup.

The 120mm fan responsible for “case airflow” is deliberately
run at a steady low level (6~7V) when the system is run at “low”
loads. When the test loads become greater, the 120mm fan is turned up to a higher
speed, but one that doesn’t affect the noise level of the overall system. Anyone
who is running a system that draws 400W or more would definitely want more than
20CFM of airflow through their case, and at this point, the noise level of the
exhaust fan is typically not the greatest concern.

Great effort has been made to devise as realistic
an operating environment for the PSU as possible, but the thermal and noise
results obtained here still cannot be considered absolute. There are too many
variables in PCs and too many possible combinations of components for any single
test environment to provide infallible results. And there is always the bugaboo
of sample variance. These results are akin to a resume, a few detailed photographs,
and some short sound bites of someone you’ve never met. You’ll probably get
a pretty good overall representation, but it is not quite the same as an extended
meeting in person.

REAL SYSTEM POWER NEEDS: While we test the PSU to full
output in order to verify the manufacturer’s claims, real desktop PCs simply
do not require anywhere near this level of power. The most pertinent range of
DC output power is between about 40W and 300W, because it is the power range
where most systems will be working most of the time. To illustrate this point,
we conducted system tests to
measure the power draw of several actual systems under idle and
worst-case conditions. Our most power-hungry overclocked 130W TDP processor
rig with an ATI Radeon X1950XTX-512 graphics card drew ~256W DC peak from the
power supply under full load — well within the capabilities of any modern power
supply. Please follow the link provided above to see the details. It is true
that very elaborate systems with the most power hungry dual video cards today
might draw as much as another 150~200W, but the total should remain under 500W
in extrapolations of our real world measurements.

INTERPRETING TEMPERATURE DATA

The airflow in our PC simulation box relies on a single 120mm fan blowing air out just below the CPU. When a normal fan-cooled PSU is in place, there are two hot air exhaust paths, one through the case fan, and the other through the PSU. When a fanless PSU is used, any vents in the PSU become an intake path for the case fan: Cooler outside air is sucked in through the ST45NF’s vent openings, then gets blown out through the case fan.

The standard position of the two thermal sensors in our test setup was not changed: One monitored the internal air temperature at the DC output side of the PSU, about an inch below. This is close to the position of the CPU heatsink in a typical mid-tower system. The other senor was placed at the center of the external grill of the PSU. Neither of these sensors can correctly be described as intake or exhaust. Instead, it makes more sense to consider the sensor on the grill (normally exhaust) as PSU, and the sensor inside the box (normally intake) as BOX.

MORE TEST COMPLICATIONS

Issue #1 – An extra step had to be taken during testing. Normally, the PSU simply sits in the “cradle” of the PC simulator box. With the ST45NF, the vented side then is exposed to the outside air, which gives it cooling advantage that it would not when installed in a normal case. So that side was blocked off with a piece of cardboard.

Issue #2 – Power Rating

Another question that had to be resolved was whether to treat the ST45NF as a 400W or a 450W model. Silverstone classifies it as 400W at 110~180VAC input and 450W at 180~264VAC.

Why the difference? If the unit is 3~4%
more efficient at 230VAC compared to 115VAC, as is typical, the difference in the heat generated at 400~450W could be big enough to cause a reduction in maximum power delivery. Assuming a 82% efficiency with 230VAC at 450W, the total heat generated in the PSU would be 99W. If 115VAC input reduced efficiency to say 78% at 450W load, then the heat generated in the PSU would be 127W. That 28W of heat might be enough under most circumstances to push internal temperatures beyond safe operating range, which is especially important given that this is a fanless PSU.

Choosing to test the unit as a 400W or 450W rated model dictates the precise combination of loads applied for each power setting. It also has relevance to the 80 Plus Bronze rating, which apparently found the ST45NF reached 82% efficiency at 20% load, 85% efficiency at 50% load, and 82% efficiency at 100% load. The point is that 20% load for a 400W PSU is 80W, while 20% load for a 450W model is 90W. Similarly, the 50% load mark would be 200W or 225W.

• Did 80 Plus find the unit to be 82% efficient at 80W or 90W?
• Was 80 Plus testing done with 115VAC input or 230VAC input?

The 80 Plus report (PDF) on the ST45NF states that the unit is rated for 450W output with 200~240 VAC input. Its test results shows 83% efficiency was reached at 445W output, 83% efficiency at 91W output, and 85.5% efficiency at 226W. The results are consistent with testing the unit as a 450W PSU. However, a line — which looks like it is part of the standard 80 Plus report template — states: “All measurements were taken with input voltage at 115 V nominal and 60 Hz.”
To further complicate the issue, a graph marked “Input AC Current Waveform” shows a AC waveform of 160V swings, not 115V.

To clarify which VAC input was used, I sought out a contact at Electric Power Research Institute (EPRI), the organization responsible for conducting the PSU tests for 80 Plus verification. The answer from Baskar Vairamohan, one of the engineers in charge of the testing: It was tested at 115VAC. We were both too rushed to discuss the details, but this gave rise to another question: How the unit reach 80 Plus Bronze levels of efficiency at 450W output when Silverstone rates the unit for only 400W output at 115VAC?

The answer may lie in the thermal environment for the 80 Plus test: It is conducted at standard room temperature (the range specified is 23°C, ±5°C). It’s quite possible at such a low temperature range, the unit does reach higher efficiency and can put out 450W with just 115VAC.

To be consistent with 80 Plus, the PSU was treated as a 450W rated unit. It would be interesting to see how it fared in the much hotter conditions of the SPCR test.

TEST RESULTS

The ambient temperature was 21~22°, and the ambient noise level was 11
dBA.

1. EFFICIENCY — This is a measure of AC-to-DC
conversion efficiency. The ATX12V Power Supply Design Guide recommends 80% efficiency
or better at all output power loads. 80% efficiency
means that to deliver 80W DC output, a PSU requires 100W AC input, and 20W is lost
as heat within the PSU. Higher efficiency is preferred for reduced energy consumption
and cooler operation. It allows reduced cooling airflow, which translates
to lower noise.

Our testing for <500W PSUs begins at a super low 20W. At this power level, the ST45NF 20W load, efficiency was decent at 61%. The 80% efficiency mark was reached at 80~90W, and crested 82% somewhere between 100W~150W. It was clearly over 82% at 150W, and climbed all the way to 87.8% at 200W, and stayed >87% to over 300W load. At 448W (full rated power), it was still at 83.3%.

This is excellent performance. In comparison to the 80 Plus test results, the findings on our sample show lower efficiency at low power and higher efficiency at the middle load. Surprisingly, despite the much hotter conditions of our test, efficiency at maximum power matched the 80 Plus results. See the cooling section below for more discussion about the measured temperatures and airflow patterns.

2. VOLTAGE REGULATION refers to how stable the output voltages
are under various load conditions. The ATX12V Power Supply Design Guide calls
for the +12, +5V and +3.3V lines to be maintain within ±5%.

The critical 12V line was 0.29V (+2.4%) high at worst, and even at the
highest loads, the voltages never dropped below 12V. The regulation on the less critical 3.3V and 5V lines was equally good. This is very good, far better than required.

3. AC RIPPLE refers to unwanted “noise”
artifacts in the DC output of a switching power supply. It’s usually very high
in frequency (in the order of 100s of kHz). The peak-to-peak value is measured.
The ATX12V Guide allows up to 120mV (peak-to-peak) of AC ripple on the +12V
line and 50mV on the +5V and +3.3V lines. Ripple on all the lines was very good at all power levels. At maximum power, the 12V ripple peaked at just 51mV, and the ripple on the other lines was about half that level.

4. POWER FACTOR is ideal when it measures 1.0. In the most
practical sense, PF is a measure of how “difficult” it is for the
electric utility to deliver the AC power into your power supply. High PF reduces
the AC current draw, which reduces stress on the electric wiring in your home
(and elsewhere up the line). It also means you can do with a smaller, cheaper
UPS backup; they are priced according to their VA (volt-ampere) rating. Power
factor was very good, running no lower than 0.92 at any point
during testing.

5. LOW LOAD TESTING turned up an anomaly. On standby, the power draw was 2W, which is fairly normal. But with no load, while the PSU started, the power demand was a very high 45W, higher even than with a 20W load! The unit also emitted a buzzing that was not evident through real loads during testing. It would appear that a minimum loading circuit automatically kicks in when a no-load start is seen, perhaps to protect against damage. A no-load start is completely abnormal outside of lab testing; while this behavior might be interesting, it has no practical consequence.

6. LOW & 240 VAC PERFORMANCE

The power supply was set to 300W load with 120VAC through the
hefty variac in the lab. The variac was then dialed 10V lower every 5 minutes.
This is to check the stability of the PSU under brownout conditions where the
AC line voltage drops from the 110~120V norm. The ST45NF is rated for
operation 100-264VAC 50/60 Hz Most power supplies achieve higher efficiency
with higher AC input voltage. SPCR’s lab is equipped with a 240VAC line, which
was used to check power supply efficiency for the benefit of those who live
in 240VAC mains regions.

Efficiency improved to nearly 89% with 245VAC input at this load. The sample passed the 100VAC minimum input without any issues. (90VAC input also worked fine, but the data was accidentally not recorded.) Neither voltage regulation nor ripple changed appreciably
during the test.

7. TEMPERATURE & COOLING

Please see the discussion on the previous page on interpreting the temperature data.

What the temperature data shows can be summarized as follows:

• For any given load level, the temperature in the test box was higher than with most fan-cooled PSUs. This is natural; there was only one fan, the 120mm case fan, blowing out the heat.
• The temperature of the back of the PSU got quite hot, especially at over 300W. Again, this is not surprising. However, there was no misbehavior of any kind during the load tests, and this includes any misbehavior that could be attributed to overheating.

As there were no other sensors, it’s not known how hot the internal components got. But even if such data was collected, it would not be useful without some points of comparison; the internal temperatures of PSUs under test have never been monitored before. Suffice it to say that despite the high temperature in the test box, and on the external casing of the unit, the ST45NF performed well.

8. NOISE

This part of the review can be really short: There are no sound recordings, frequency spectrum captures or SPL measurements. Why not? Because there was no appreciable noise from the ST45NF at any point during load testing. Oh, if you get close enough in a quiet room, you can hear the trace of buzzing and whine common to all power electronic circuits. But in any normal application, you can call this power supply silent.

It’s possible that a particular combination of loads with specific components might increase electronic noise to a point where it becomes audible, or that not all samples exhibit as low a level of buzzing as this one. However, having used several samples of the ST30NF in a number of different systems and witnessing no audible buzzing from any of them, it’s probably safe to suggest that the silence of the test sample is not unusual.

COMPARISONS

We could spend a couple hundred words here comparing the ST45NF to other power supplies, both fan cooled and fanless. But there’s really no point. It’s quieter than any fan cooled PSU, and quieter than most of the fanless ones, too, in its low level of electronic buzz.

The more relevant discussion concerns how quietly you could cool the rest of your system. The ST45NF cannot really cool itself much beyond 100~150W load without a bit of help. The single 120mm fan exhaust in our simulated PC case was left at minimal speed (around 500rpm) to over 200W load, then adjusted up incrementally to ~11V at full load. The temperature figures reflect this increase in fan speed.

The real question is which would be quieter:

• A system with the ST45NF with minimal noise components, or…
• A similar system with a super-quiet fan-cooled PSU (like the Enermax Modu82+)?

It is probably possible for a careful, experienced builder to assemble an adequately cooled 200~300W peak demand PC with the ST45NF that is a touch quieter than it would be with a fan-cooled PSU. Just how much quieter would depend on the exact component details. Other components in the system still require some cooling, so a fanless systems is usually impractical. Would the residual noise of those other components (hard drives and fans) be enough to mask the difference between a fanless PSU versus a fan-cooled PSU that stays very quiet to a fairly high load? Is the ambient noise level of the room low enough to allow you to appreciate this difference?

These are questions that silent PC fanatics will have to consider along with the hefty price of the ST45NF.

CONCLUSIONS

At any given point in time, there are usually very few fanless computer power supplies on the market. At some point in the past few years, the number of brands might have reached five: Antec, FSP, Silverstone, Silentmaxx and Coolmax. Currently the number is down to two: Silentmaxx (which uses rebranded FSP models) and Silverstone (which as you know from this review, offer units made by Etasis). They are more expensive, probably fail more often due at least partly to user misunderstanding about cooling requirements, and harder to sell. Yet, they persist.

Of all the fanless PSUs we’ve examined over the years, the Silverstone “Nightjar” series have stood the test of time. It’s simply unheard of for a component in the PC retail business to last five years essentially unchanged, which is a testament to the solid design of the original ST30NF.

The Silverstone ST45NF is a natural improvement over the lower power ST30NF. It is substantially more efficient and well deserving of its Bronze 80 Plus tag. It is one of the most efficient PSUs we’ve tested, in fact. For a unit rated at just 400W output (with 115VAC input), our sample’s performance was outstanding, suggesting both robust longevity and good thermal design. The conservatism of Silverstone’s power rating pays off here. About the only lack you might point out is modular cables; at the asking price, this feature would not be unreasonable to expect.

Acoustically, there’s no way to make a PSU any quieter. The noise exhibited by our test sample was essentially nil. It made no appreciable noise in normal testing or use.

These facts have to be balanced by its price, which is much higher than any normally cooled 450W model, and by the awareness that residual noise from other components in the system may erase the noise advantage. For some readers, the balance may tilt too far for the ST45NF to be a viable purchase. For others, it’s a step closer to the holy grail of a noiseless system without any moving parts, especially if a solid state drive is also in use. In some ways, the ST45NF is like a specialized, high performance, soft-top roadster: Use it well and it can give you an experience unmatched by other cars.

Much thanks to Silverstone for this review sample.

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SPCR Articles of Related Interest:
Power Supply Fundamentals

Recommended Power Supplies
SPCR PSU Test Rig V.4
Antec Signature 650
Enermax Modu82+ 625W
Silverstone ST30NF
Silentmaxx Fanless 400W MX460-PFL01
Antec

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