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Fanless PSUs: Kingwin Stryker STR-500 & Silverstone ST50NF

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We review and compare two fanless 500W ATX12V power supplies from quality brands. One has 80 Plus Platinum efficiency; the other sports Silver. In other ways, they appear similar, with the exo-heatsink design of so many passively cooled devices.

Product
ST50NF 500W ATX Power Supply Stryker Fanless
500W
(STR-500) ATX PSU
Sample Supplier
Silverstone Technology Kingwin
Technology
Market Price
US$199
US$159

Our
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.

SPECS & FEATURES: KINGWIN STRYKER FANLESS
500W

As with most brand name computer components these days. the Kingwin is nicely packaged and presented. The package has a distinct resemblance to that of the LZP-550.


Fairly big full color package for the Kingwin STR-500.


Nice packaging, including a pouch for the cables.


The essence of the product: Power supply, all the cables, and four thumbscrews
to mount the PSU. The attached cables are sleeved, the relatively short
detachable ones are in the flat data-cable style. The flat profile can
make those cables easier to route in some cases.


The PSU itself features
a thick aluminum extrusion with fins for the top plate. This is similar
to umpteen other fanless PSUs that have come before: The case itself acts
as a heatsink. All other sides (except the bottom) are well vented.


There are four output plugs for detachable SATA and IDE power cables.



We had no interest in opening up the Kingwin or the Silverstone
(perhaps spoiling any cured TIM between internal and external heatsinks), but
a side panel proved easily removable. This provides a glimpse of one of
the two heatsinks PCB that extend up and mechanically couple to
the top extrusion cover, which helps dissipate heat outside the PSU. The
same cooling system is used in the Silverstone.

FEATURE & BRIEF Our comment
Compliance with ATX 12V v2.2, EPS 12V v2.91, and SSI EPS 12V v2.92 Specification Good.
Fanless 0 dBA Operation We’ll see.
Crystal Cube Modular Plug w/ Patented Power Connector Cable Management System Just looks like a different connector.
Hybrid Dual Voltage Automatic Switch System (Patent) What does this mean?
EuP (Energy-using Products) instructions: energy consumption during shut off status less than 1W. Great!
More than 2,000 Times ON/OFF Test OK.
80 PLUS® Platinum High Efficiency Power Supply Certified — 50% Load (92% Efficiency), 20% Load (90% Efficiency), 100% Load (89% Efficiency) Should make fanless operation a cinch.
Stable + 12V Current Single 12V rail?
Safety certifications: cTÜVus, TÜV, CB, CE, FCC, CCC, C-Tick, BSMI As expected.
Over Power/Under Power/Over Voltage/Short Circuit Protections OK.
Full Range Design from 115V ~ 250V (Active PFC) Like most high end PSUs.
5 year warranty Excellent.
170(L) x 150(W) x 86(H)mm; 6.61 lbs or 3 kg 20mm longer than normal.
Kingwin STR-500 SPECIFICATIONS
AC Input
115~240VAC, 10A, 50/60 Hz
DC Output
3.3V
5V
12V
-12V
5Vsb
20A
20A
41.5A
0.5A
2.5A
100W
498W
6W
12.5W
550W
0ºC ~ 50ºC operational temperature
Kingwin STR-500 Output Cables
Fixed
ATX (565mm)
1
4+4 pin EPS12V/ATX12V
1
6 pin + 6/8 pin PCIe (730mm)
1
Detachable
6 pin + 6/8 pin PCIe (550mm)
1
4 SATA (880mm)
1
3 4-pin Molex + 1 floppy (880mm)
1
2 SATA + 2 4-pin Molex (+880mm)
1

SPECS & FEATURES: SILVERSTONE ST50NF

Silverstone has always done a good job with packaging and presentation. No surprises here. The silver color box of the Silverstone fanless series remains largely
unchanged from their previous fanless models


Big silver color box.


Nice packaging, with excellent shock protection.


The ST50NF output cables are long, plentiful and permanently attached.
It might be hard to keep the cables tidy in a small or minimalist system.
As with all previous fanless Silverstones, the top panel is a thick aluminum
extrusion with fins and vent holes. All but one other side is well vented.


This photo of the ST50NF from the Silverstone web site shows how the internal
heatsinks are mechanically and thermally joined with the top external
plate, just like in the STR-500.

FEATURE & BRIEF Our comment
Fan-less thermal solution, 0 dBA acoustics We’ll see.
Efficiency 84%~88% at 20%~100% loading The 80 Plus test report rates it a Silver, but the retail box cites Bronze. Curiously, the product web page makes no mention of 80 Plus whatsoever.
Strict ±3% voltage regulation OK.
PCI-E 8pin & 6pin connector support Pretty standard.
Powerful class-leading single +12V rail Its rated 38A is actually lower than the Kingwin’s 41.5A.
Aluminum construction OK.
Support ATX 12V 2.3 & EPS 12V Par for the course.
Over Current Protection, Over
Power Protection, Over Voltage Protection, Over Temperature Protection,
Short Circuit Protection
OK.
Full Range Design, 99V ~ 264V (Active PFC) Like many high end PSUs.
1 year warranty Short compared to others.
150(W) x 86(H) x 160(D) ; 7.7 lbs or 3.7 kg 10mm longer than standard.
Silverstone ST50NF SPECIFICATIONS
AC Input
199V ~ 264V, 50/60 Hz
DC Output
3.3V
5V
12V
-12V
5Vsb
18A
18A
38A
0.5A
2.5A
120W
456W
6W
12.5W
500W
0 ~ 45°C operational temperature
Silverstone ST50NF Output Cables
1 x 24 / 20-Pin ATX connector (550mm)
1 x 8 / 4-Pin EPS / ATX 12V connector (550mm)
1 x 8/6-Pin PCIE connector (550mm)
1 x 6-Pin PCIE connector (550mm / 150mm)
6 x SATA connector (500mm / 150mm / 150mm)
6 x 4-Pin connector (500mm / 150mm / 150mm)
2 x 4-Pin Floppy (500mm / 150mm / 150mm / 150mm)

INITIAL COMPARISON

On paper, and in one’s hands, there doesn’t seem much to differentiate these
fanless power supplies. But look closer, and the Kingwin edges the Silverstone
in every category.

  • The Kingwin claims slightly higher current capacity on the 12V rail
  • The Kingwin’s maximum efficiency is 92%, compared to 88% for the Silverstone.
    If we assume all other factors to be equal, the Silverstone will run hotter,
    and thermal protection shutdown may occur sooner under high load.
  • The Kingwin’s top operating temperature is 50°C, compared to 45°C
    for the Silverstone.
  • The Silverstone is a touch heavier.
  • The Kingwin has detachable cables for peripherals; all the Silverstone cables
    are permanently attached.
  • The Kingwin has a 5 year warranty, while the Silverstone offers 1 year.
  • At Newegg, the Kingwin is priced at $160 while the Silverstone sells for
    $200.

The comparison is pretty one sided in the end. We’ll see how all this translates
in the lab tests.

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
.

SPCR’s
PSU Test Platform V4.1
. is the basic setup for the testing. It is a close simulation of
a moderate airflow mid-tower PC optimized for low noise.

There is one major change: The primary testing is done with the PSU NOT inside the hotbox but atop it, out of the heat path. This is in recognition of several realities that prevail today:

  • In SPCR’s earlier test platforms, the internal temperature varied proportionately
    with output load. The tested PSU was subject to this heat, and operating ambient temperature rose with increased load, reaching >40°C and often much higher at full power. This was a realistic simulation of a mid-tower PC case where the PSU is mounted conventionally at the top back portion of the case.
  • However, in 2011, the vast majority of "serious" PC cases for the home builder no longer position the PSU at the top back corner. They put the PSU at the bottom/back corner, mostly out of the path of heat from the other components in the case. This design concept took root with the Antec P180 going back over 5 years, and it dominates the DIY case arena. This means the PSU generally has to dissipate only its own heat.

With the current test, we’re reversing our approach: The PSU may be tested briefly in the hotbox only to check on what happens to noise, fan speed and temperatures when it is used in an outmoded case design.

Acoustic measurements are performed in our own 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.

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. It is true that very elaborate systems with the most power hungry dual
video cards today might draw as much as another 150~300W, but the total should
remain under 600W.

(NOTE: Motherboard and VGA card makers tend to exaggerate power supply requirements in order to protect against misrepresentation by unscrupulous PSU sellers of their products’ output capabilities. There were cases in the past where some suppliers would offer the same el-cheapo no-name PSU with different power labels (400W, 500W or even 600W) at the retailer’s discretion, all at the same $11/unit (or similarly low) bulk pricing. Such PSUs certainly did not deliver their "rated" power safely into any real load, sometimes causing damage to the computer components when stressed or as the PSU failed. Component manufacturers would then get embroiled in warranty claims, etc. Our advice is to stay with well-reviewed products from reputable brands to avoids such potential mishaps. Truly bad PSUs appear to have disappeared from the market, at least in the US and Canada, but they probably still exist in some markets. Hence, the cautious tendency of motherboard and VGA card makers [who distribute worldwide] to overstate PSU power needs remains.)

TEST RESULTS

The ambient temperature was 21~22°, and the ambient noise
level was ~10.5 dBA.

Test Results: Kingwin STR-500

DC Out (W)

AC In
(W)
Heat
(W)

Eff %
PF
Temp.
21.7
30
8.3
72.3
0.88
24°C
41.2
48
8.8
85.9
0.94
27°C
64.2
73
8.8
88.0
0.98
29°C
90.5
101
10.5
89.6
0.99
30°C
149.9
163
13.1
92.0
0.99
31°C
200.7
215
14.3
93.3
0.99
35°C
250.7
268
17.3
93.6
1.00
40°C
300.4
320
19.6
93.9
1.00
42°C
400.2
436
35.8
91.9
1.00
47°C
500.2
550
49.8
91.0
1.00
60°C
Crossload Test
(1A on 5V and 3.3V lines; the rest on 12V line)
418
443
25
94.6%
1.00
48°C
12V Ripple: <29mV @ <250W~38mV@500W
5V Ripple: <25mV @ <200W~32mV @ 500W

3.3V Ripple: <25mV@<200W~ 0mV@500W
AC Power in Standby: 0.5W
AC Power with No Load, PSU power On: 6.5W / 0.56 PF
Test Results: Silverstone ST50NF

DC Out (W)

AC In
(W)
Heat
(W)

Eff %
PF
Temp.
21.4
38
16.4
56.3
0.93
25°C
40.2
60
19.8
67.0
0.94
27°C
65.3
84
18.7
77.7
0.98
32°C
90.2
110
19.8
82.0
0.99
36°C
150.4
176
25.6
85.4
1.00
39°C
199.1
230
30.9
86.6
1.00
41°C
250.2
283
32.8
88.4
1.00
47°C
299.7
340
40.3
88.1
1.00
50°C
400.4
467
66.6
85.7
1.00
55°C
499.1
585
85.9
85.3
1.00
67°C
Crossload Test
(1A on 5V and 3.3V lines; the rest on 12V line)
412.0
467
55.0
88.2%
1.00
48°C
12V Ripple: <49mV@<300W~98mV@500W
5V Ripple: <28mV@<200W~50mV@ 500W

3.3V Ripple: <25mV@<200W~45mV@500W
AC Power in Standby: 0.3W
AC Power with No Load, PSU power On: 15.8W / 0.62 PF

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 draws 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. The 80 Plus Platinum standard requires 90% efficiency at 20% load, 92% efficiency at 50% of rated load, and 89% at full rated load.

STR-500: The efficiency of the sample was very similar to that of the Kingwin LZP-550 sample tested last May, which is no surprise as the two models likely share the same basic components and electronic design. At the super low 20W load, efficiency was excellent at over 72%. Efficiency
rose quickly as the load was increased. 90% efficiency was reached around the
90W mark, broke 93% at 200W, and stayed above 93% to 300W load. With higher load, efficiency dropped just a bit. At full power, the efficiency dopped down to 91.0%, well above the mark demanded by Platinum, and slightly higher than its brethren, despite the higher temperature the internal components were surely subject to, compared with the fan-cooled LZP-550.

Along with the LZP-550, the STR-500 is the most energy efficient PSU we’ve tested. It is a step above the Gold tested models, although the difference is quite small at typical PC idle levels and does not become really significant until around a couple hundred watts load is reached. An example: The Gold 80 Plus rated Enermax Modu87+ 500W drew 76W AC to output 65W DC , compared to 73W for the Kingwin Platinum — a modest 3W difference. But at 250W output, the Gold rated Enermax drew 278W vs 267W for the Kingwin — a more significant 11W difference.

ST50NF: The Silverstone has fine efficiency when considered on its own, showing the 88% peak efficiency which gave it the 80 Plus Silver rating. In comparison with the Kingwin STR-500, it trails a couple steps behind, however. The difference in efficiency between them is more or less constant across the entire output range. The column in the tables marked "Heat" refers to the power that is lost as heat within; the ST50NF loses roughly twice the power of the STR-500, across the board.

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 maintained within ±5%.

STR-500: The critical 12V line was a touch high (+0.23V or 2.66%)
at low load, and gradually dropped to a low of 11.96V at full load. This is excellent regulation. The 5V line started a touch high, too, at 5.16V, and went down to 5.04V at full load (+3.2% to +0.9%). 3.3V ranged from 3.38V to 3.29V (+2.4% to -1.2%). These are all excellent voltage regulation results, better than they actually need to be for any PC.

ST50NF: All three of the main output lines started dead accurate at low load, and gradually dropped as load was increased. At 200W to 400W output, the 12V line was down 0.1~0.15V. At full load, it was -0.25V, nearly 5% down. The droop on the 5V line was just 0.09V at full load, and the 3.3V line was down 0.1V. These results are not quite as good as but only near or at full output load did the voltage variation get close to recommended limits. Overall, the voltage regulation is stable and good enough.

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 Power Supply Design Guide allows up to 120mV of AC ripple on the +12V
line and 50mV on the +5V and +3.3V lines.

STR-500: Ripple on all the lines was excellent
at all power levels, staying well under 30mV through the lower half of
the power range. At maximum power, the 12V ripple measured 38mV.
This is not quite as good as the earlier LZP-550 sample, but still very good.

ST50NF: The ripple on all the lines was slightly lower than in the STR-500, at low loads, but as the load was increased, it climbed considerably higher. Up to around 300W, the ripple on the 12V line stayed under 50mV, but at full load, the peaks went up to 100mV. The maximum ripple on the 5V line, at full power, was around 50mV. These are mediocre results, close to the maximum recommended by the ATX12V Guide.

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. PF was very good for both reviewed model, running at or close to 1.0 through most
of the loads and no lower than 0.88 even at very low load.

5. LOW LOAD

STR-500 had no problems starting at very
low loads. Our sample had no issue starting up with no load, either, and the
power draw was low. The 0.5W power draw in standby (power
switch on but computer off) is excellent.

ST50NF had no problems starting at very
low or no loads. The 0.3W power draw in standby (power
switch on but computer off) is excellent. The fairly high 16W power draw when powered up without any load suggests that there is an internal minimal load which automatically kicks in to ensure reliable startup under very low load conditions. This is indicative of an older circuit design.

6. LOW & 240 VAC PERFORMANCE

The power supply was set to 300W load at various AC input
voltages. Most full-range input 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 higher
mains voltage regions. We also used a hefty variac to check the stability of the PSU
under brownout conditions where the AC line voltage drops from the 120V norm.

Various VAC Inputs
VAC
AC Power
DC Output
Efficiency
Kingwin STR-500
244V
312W
300W
96.1%
120V
320W
300W
93.9%
100V
326W
300W
92.0%
Silverstone ST50NF
244V
329W
300W
91.2%
120V
340W
300W
88.2%
100V
346W
300W
86.6%
There were no surprises with either of these power supplies. Both improved efficiency by at least 3% points at the higher VAC, and dropped 1.5~2% at 100VAC. They passed the 100VAC minimum input at 300W load without any issues.
Neither voltage regulation nor ripple changed appreciably during these tests.

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.

NOISE COMPARISONS

The new comparison table below shows the SPL versus Power Load data on
PSUs tested in ambient room temperature, typically 20~24°C. It is most relevant when PSUs are used in cases that provide wide open access to cooler outside air for the PSU cooling fan.

PSU Noise (dBA@1m) vs. Power in Ambient Room Temperature
Model
90W
150W
200W
250W
300W
400W
500W
6-700W
850W


Kingwin STR-500 Fanless

<10*
<10
<10
<10
<10
<10
<13
n/a
n/a


Seasonic X-460 Fanless

<10*
<10
<10
<10
<10
<11
<13
n/a
n/a


Kingwin Lazer Platinum LZP-550

<10*
<10
<10
<10
<10
<10
16
n/a
n/a


Seasonic X-400 Fanless

<10*
<10
<10
<10
<10
<11
n/a
n/a
n/a


Silverstone ST50NF Fanless

11
11
11
11
15
15
16
n/a
n/a


Enermax Modu/Pro87+ 500

11
11
11
11
11
11
18
n/a
n/a


Corsair AX850

<10
<10
<10
11~13
12
13
17
24
35


Seasonic X-650

<10
<10
<10
<10
<10
16
27
32
n/a


Nexus NX-5000

11
11
12
12
12.5
14
19
n/a
n/a
Antec CP-850
12
12
12
12
12
14
20
24
40


Enermax Eco80+ 500W

<11
12
12
16
20
23
28
n/a
n/a


Antec TP-750

12
12
12
14
15
27
31
40
n/a
Cougar GX-700
15
15
15
17
21
25
35
35
n/a
The green boxes are >30 dBA@1m SPL.
*<10= below the ambient of our anechoic chamber; immeasurably low
@1m in any environment

Caution: Please keep in mind that
the data in the above table is specific to the conditions of our test setup.
Change the cooling configuration, the ambient temperature and any number of
other factors, and you could change the point at which the fans start speeding
up, as well as the rate of the rise in speed. The baseline SPL is accurate,
however, probably to within 1 dBA.

CONCLUSIONS

We began this comparison review knowing that the Silverstone was outmatched by the Kingwin, and the tests went overwhelmingly to the favorite. Part of the reason for the one-sided outcome is that in a fanless power supply, the effect of efficiency on cooling is enormous. With the STR-500 producing just half the heat of the ST50NF, the heat-related stresses on the components are far less, as is the ease of cooling. With both PSUs using the same external heatsink approach to cooling, the result is inevitable. The Kingwin also has the advantage of the most recent advances in electronic power technology, while the Silverstone uses technology that is at least a few years old.

The Kingwin STR-500 power supply is unique in the marketplace today: Along with the fan-cooled LZP-550, it is the most energy efficient computer power supply, and also the very quietest. It is silent in operation, up to its output limits. Its primary competitors are the Seasonic X series 80 Plus Gold models, the X460 and X400. Its other electrical performance and build quality also appear very good, and the detachable, modular cables are a nice benefit, but the biggest selling factors are silent operation and superior efficiency: At 500W, its AC power consumption is about 15W lower than any 80 Plus Gold model at the same load. The efficiency improvement starts much lower, with a couple watts saved even down at the 50W level. Those who live in 220~240 VAC service areas get the benefit of even higher efficiency, 96% at the peak.

The Silverstone ST50NF is a fine PSU in its own right, but our sample exhibited higher-than-ideal ripple, and it could not escape the limitations of its lower efficiency against the Kingwin. It also exhibited more audible electronic noise under load than either the Kingwin or earlier-tested Seasonic X fanless PSUs. If the latter did not exist, the ST50NF would be the natural choice for a quality fanless ATX PSU. But those superior competitors do exist, and they are being sold at prices significantly lower than the ST50NF’s $200. These factors make the ST50NF a tough sell.

The good news for who seek a fanless ATX PSU is that, as of early September 2011, Newegg is selling the Kingwin STR-500 for $160. That is still a pretty steep price for a 500W PSU, but pretty good for the quietest, most energy efficient 500W ATX PSU in the world. Incidentally, Newegg is currently offering the Seasonic X400 and X460 at even lower bargain prices, $90 and $110, respectively. This is a good time to be a silent PC builder.

Much thanks to Kingwin Technology and Silverstone Technology for the review samples.



Kingwin Stryker Fanless STR-500 receives the SPCR Editor’s Choice Award

* * *

SPCR Articles of Related Interest:

Fanless PSU Torture Test Shootout
Kingwin LZP-550 80 Plus Platinum
Seasonic X-400 Fanless
Power Supply Fundamentals

Recommended Power Supplies
SPCR PSU Test Rig V.4

* * *

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