Silentmaxx Fanless 400W MX460-PFL01 power supply

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TEST RESULTS

For a fuller understanding of ATX power supplies, please read the reference article Power Supply Fundamentals & Recommended Units. 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 V.3. The testing system is a close simulation of a moderate airflow mid-tower PC optimized for low noise.

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 open design of the Silentmaxx required a little modification of the test rig to keep the thermal simulation as accurate as possible. Because the power supply is designed to be installed in a case, only the rear panel is designed to be exposed to the open air. However, our test bench left one whole side of the power supply open that would not be open in an ordinary system. To correct this, a piece of cardboard was taped over the offending side to prevent any air from flowing through it.


The side vent was blocked off with cardboard to keep the thermal simulation accurate.

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 our testing loads the PSU to full output (even >600W!) 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 65W and 250W, 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 maximum power draw that an actual system can draw under worst-case conditions. Our most powerful Intel 670 (P4-3.8) processor rig with nVidia 6800GT video card drew ~214W DC 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 SLI could draw as much as another 100W, perhaps more, but the total still remains well under 400W in extrapolations of our real world measurements.

SPCR's high fidelity sound recording system was used to create MP3 sound files of this PSU. As with the setup for recording fans, the position of the mic was 3" from the exhaust vent at a 45° angle, outside the airflow turbulence area. The photo below shows the setup (a different PSU is being recorded). All other noise sources in the room were turned off while making the sound recordings.

INTERPRETING TEMPERATURE DATA

It important to keep in mind that fan speed varies with temperature, not output load. A power supply generates more heat as output increases, but is not the only the only factor that affects fan speed. Ambient temperature and case airflow have almost as much effect. Our test rig represents a challenging thermal situation for a power supply: A large portion of the heat generated inside the case must be exhausted through the power supply, which causes a corresponding increase in fan speed.

When examining thermal data, the most important indicator of cooling efficiency is the difference between intake and exhaust. Because the heat generated in the PSU loader by the output of the PSU is always the same for a given power level, the intake temperature should be roughly the same between different tests. The only external variable is the ambient room temperature. The temperature of the exhaust air from the PSU is affected by several factors:

  • Intake temperature (determined by ambient temperature and power output level)
  • Efficiency of the PSU (how much heat it generates while producing the required output)
  • The effectiveness of the PSU's cooling system, which is comprised of:
    • Overall mechanical and airflow design
    • Size, shape and overall surface area of heatsinks
    • Fan(s) and fan speed control circuit

The thermal rise in the power supply is really the only indicator we have about all of the above. This is why the intake temperature is important: It represents the ambient temperature around the power supply itself. Subtracting the intake temperature from the exhaust temperature gives a reasonable gauge of the effectiveness of the power supply's cooling system. This is the only temperature number that is comparable between different reviews, as it is unaffected by the ambient temperature.

On to the test results...

Ambient conditions during testing were 22°C and 20 dBA, 123V/60Hz.

OUTPUT & EFFICIENCY: Silentmaxx Fanless 400 Watt MX460-PFL01
DC Output Voltage (V) + Current (A)
Total DC Output
AC Input
Calculated Efficiency
+12V1
+12V2
+5V
+3.3V
-12V
+5VSB
12.00
0.95
11.98
1.71
5.06
0.97
3.38
0.00
0.1
0.2
39.0
55
70.6%
11.99
1.87
11.98
1.71
5.06
1.94
3.37
2.59
0.1
0.3
64.2
84
76.6%
11.99
1.87
11.96
3.27
5.05
2.87
3.36
2.58
0.2
0.5
89.6
113
79.6%
11.97
3.71
11.93
4.92
5.04
4.56
3.36
5.09
0.3
0.8
150.8
184
81.9%
11.95
6.41
11.92
4.93
5.02
6.27
3.35
7.05
0.4
1.0
200.3
238
84.1%
11.93
7.51
11.91
6.33
5.01
8.75
3.34
8.44
0.5
1.3
249.5
298
83.7%
11.91
8.45
11.86
8.00
4.99
10.35
3.31
11.46
0.6
1.5
299.8
359
83.5%
11.86
11.89
11.78
11.00
4.95
12.62
3.25
14.20
0.8
2.0
400.1
492
81.3%

NOTE: The current and voltage for -12V and +5VSB lines is not measured but based on switch settings of the DBS-2100 PS Loader. It is a tiny portion of the total, and potential errors arising from inaccuracies on these lines is <1W.


OTHER DATA SUMMARY: Silentmaxx Fanless 400 Watt MX460-PFL01
DC Output (W)
39.0
64.2
89.6
150.8
200.3
249.5
299.8
400.1
Intake Temp (°C)
24
27
31
35
39
40
45
50
Exhaust Temp (°C)
29
32
38
44
50
56
63
70
Temp Rise (°C)
5
5
7
9
11
16
18
20
Power Factor
0.95
0.95
0.96
0.99
0.99
0.99
0.98
0.98

NOTE: The ambient room temperature during testing can vary a few degrees from review to review. Please take this into account when comparing PSU test data.

ANALYSIS

1. VOLTAGE REGULATION was very good, within ±3% throughout the test and often within ±1%. As a general rule, voltages fluctuated very little. Only when we pressed it to the very maximum load did the voltages drop in any significant way.

2. EFFICIENCY was excellent, although it did fall a little short of the 89% efficiency that was claimed. Regardless, the Silentmaxx deserves a high recommendation. We've only tested three power supplies that are more efficient, one of which is the FSP Zen. The other two are 80 Plus certified Seasonic models that are not easy to find on the retail market. Of these only one managed to beat the Silentmaxx across all of the data points tested. The differences between these four top-runners were close enough that they are all at more or less equally efficient.

Compared to the FSP Zen, the Silentmaxx appears to be biased towards efficiency at close to full capacity. Thus, the FSP Zen is more efficient below 250W — where the vast majority of systems spend their time — and the Silentmaxx is more efficient at 250W and above. The Zen earned 80 PLUS certification with >80% efficiency at 20, 50 and 100 percent of rated power (and >0.9 PF). With efficiency measured at 79.6% at 89.6W in our test, this Silentmaxx will probably reach 80% at 100W (20% load), so it too, can probably earn 80 PLUS certification.

3. POWER FACTOR was excellent thanks to the active power factor correction circuit. Power factor stayed close to the theoretical maximum of 1.0 throughout testing.

4. TEMPERATURE & COOLING

The temperature rise across the Silentmaxx was fairly high in ordinary terms, but that is no surprise for a fanless unit. In comparison to other fanless power supplies we've tested, the 20°C rise that we measured at full load is fairly typical: High, but still within the bounds of safety. In comparison with the FSP Zen, the temperatures were better by a few degrees across the board — enough to make us think that the Silentmaxx is a slightly better performer, but not enough to rule out slight variations in the test procedure as a possible cause of the difference. Thermal performance was also roughly on par with the fanless Antec Phantom 350.

5. NOISE

The nice thing about fanless power supplies is they generally don't make any noise. A very slight hum or buzz could be heard within a few centimeters, but no noise was audible from a normal operating position.



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