Nexus NX-9003 350W Hybrid PSU

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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.

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 20°C and 20 dBA, 122V/60Hz.

OUTPUT & EFFICIENCY: Nexus NX-9003 SFB
DC Output Voltage (V) + Current (A)
Total DC Output
AC Input
Calculated Efficiency
+12V1
+12V2
+5V
+3.3V
-12V
+5VSB
12.04
0.95
12.03
1.72
5.15
1.00
3.37
0.96
0.0
0.2
41.5
59
70.4%
12.07
1.90
12.06
1.72
5.17
1.99
3.37
1.89
0.1
0.4
63.5
87
73.0%
12.08
1.89
12.07
3.30
5.13
2.96
3.36
2.78
0.1
0.5
90.9
120
75.9%
12.07
3.82
12.05
4.98
5.12
4.79
3.35
4.64
0.1
0.8
151.4
195
77.7%
12.08
4.77
12.05
6.70
5.09
5.77
3.32
7.58
0.2
1.1
200.8
252
79.7%
12.09
5.69
12.05
8.16
5.09
8.34
3.31
9.20
0.2
1.4
249.4
320
77.9%
12.10
6.65
12.05
9.70
5.05
10.11
3.27
11.66
0.3
1.7
298.6
394
75.8%
12.11
7.81
12.06
11.36
5.02
12.64
3.26
12.41
0.3
2.0
349.1
475
73.5%

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: Nexus NX-9003 SFB
DC Output (W)
41.5
63.5
90.9
151.4
200.8
249.4
298.6
349.1
Intake Temp (°C)
24
27
32
33
35
36
40
40
Exhaust Temp (°C)
29
30
39
43
49
54
60
64
Temp Rise (°C)
5
3
7
10
14
18
20
24
Fan Voltage (V)
1.9
1.9/5.2*
1.9/5.2*
5.2
5.2
5.2/7.4*
7.4
7.4/10.6*
External Fan (V)
1.9
1.9
1.9
1.9
1.9
1.9
1.9
1.9
SPL (dBA@1m)
–
–/26
–/26
26
26
26/33
33
33/40
Power Factor
0.59
0.61
0.63
0.66
0.67
0.67
0.69
0.69

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.
*For data points where two values are given, the power supply cycled between the two value every couple of minutes.

ANALYSIS

1. VOLTAGE REGULATION was excellent, within ±1% for the +12V line and ±3% for the others.

2. EFFICIENCY was a huge improvement over the older NX-3500 (which never reached 70%), but not exceptional by today's standards. The peak efficiency was reached at 200W output, where it was just shy of 80%. Efficiency was otherwise mostly in the mid-70s.

3. POWER FACTOR

The power factor correction in the NX-9003 is of the passive variety and is in the 0.60~0.70 range. We would have preferred to see a unit with active power factor correction, which can approach the maximum theoretical value of 1.0.

4. TEMPERATURE & COOLING

At lower output levels, thermal performance was adequate but far from spectacular. However, as the output rose, the thermal rise inside the power supply approached and then exceeded 20°C. Considering the maximum capacity of 350W, this is poor performance. In spite of the ever increasing fan speed, cooling did not appear to improve.

5. FAN, FAN CONTROLLER and NOISE

At the minimum test point of 40W output, the hybrid fan controller showed its strength: The fan never turned on so the power supply was effectively silent. Near-field listening revealed a very slight electronic hiss, but it was inaudible from the normal user distance.

In the 65-90W range where the majority of systems idle, that strength turned into a weakness. The fan would cycle on and off every couple of minutes. Whenever the fan turned on, it would burst up to full speed (to ensure it started) before it settled down to its lower speed. The erratic changes in fan speed made it impossible to ignore the fan noise.

Even without the changes in fan speed, the default noise level was still too high. The fan spins too quickly to be quiet, even at 5 volts. To put this in perspective, the fan in the NX-9003 is louder at 5V than the Nexus "Real Silent" 120mm fan is at full speed. About the only good thing that can be said for the noise is that it is fairly smooth in character and mostly broadband.

Things improved once the power output rose high enough for the fan to stop cycling. Then, the fan speed stayed constant until the output reached above 200W — above the maximum power draw in most systems. The 100-200W output range is where most systems find themselves when they are put under load, so most users should never see the fan increase beyond the first voltage step.

Two further fan steps were discovered at even higher output levels, both of which were much too loud to be considered quiet. As with the steps at the lower level, the fan speed often cycled repeatedly between two steps for some time before settling into the higher step.

6. EXTERNAL FAN HEADERS

Although the exhaust temperature next to the thermal sensor reached over 60°C — double what Nexus claims is the trigger temperature — the external fan controller never received more than 1.9V, not enough to start any fan that we know of. It is unclear why this occurred. Perhaps the fan controller will not increase the voltage unless it detects that a fan is connected. However, given the performance of the main fan controller, we have no interest in investigating any further. Two fans cycling on and off at once is too much for our poor ears to handle.



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