Fanless PSUs: Kingwin Stryker STR-500 & Silverstone ST50NF

Power
Viewing page 4 of 6 pages. Previous 1 2 3 4 5 6 Next

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.


Previous 1 2 3 4 5 6 Next

Power - Article Index
Help support this site, buy from one of our affiliate retailers!
Search: