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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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