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TEST RESULTS
For a fuller understanding of ATX power supplies, please read our article Power
Supply Fundamentals & Recommended Units. Those who seek source materials
can find Intel's various PSU design guides, closely followed by PSU manufacturers,
at Form Factors.
For a complete rundown of testing equipment and procedures, please refer to
the article SPCR's Revised
PSU Testing System. It 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 far too many variables in
PCs and far 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 reasonable overall representation of that person, 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
recently conducted system tests to measure the maximum power draw that an actual
system can draw under worst-case conditions. Our most powerful P4-3.2
Gaming rig drew ~180W 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 150W, 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 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 25°C and 20 dBA, with an
input of 120 VAC / 60 Hz measured at the AC outlet. It was a couple of degrees
warmer than usual in the lab, and the Intake Temp readings in the measured data
table below reflects this.
|
ANTEC SMARTPOWER 2.0 SP-450 TEST RESULTS
|
|
DC Output (W)
|
40
|
65
|
90
|
150
|
200
|
250
|
300
|
400
|
442*
|
|
AC Input (W)
|
62
|
91
|
120
|
193
|
249
|
321
|
391
|
520
|
572
|
|
Efficiency
|
65%
|
71%
|
75%
|
78%
|
80%
|
78%
|
77%
|
77%
|
77%
|
|
Intake Temp (°C)
|
27
|
29
|
31
|
33
|
36
|
39
|
41
|
45
|
46
|
|
PSU Exhaust (°C)
|
31
|
34
|
37
|
39
|
42
|
44
|
46
|
51
|
53
|
| Temp Rise (°C) |
4
|
5
|
6
|
6
|
6
|
5
|
5
|
6
|
7
|
| Fan Voltage (intake)** |
5.3
|
5.3
|
5.3
|
5.3
|
6.7
|
10.0
|
12.5
|
12.6
|
12.6
|
| SPL (dBA @ 1m) |
21
|
21
|
21
|
27
|
32
|
37
|
40
|
40
|
40
|
|
Power Factor
|
0.60
|
0.61
|
0.62
|
0.64
|
0.65
|
0.66
|
0.66
|
0.66
|
0.66
|
|
NOTE: The ambient room temperature during testing
varies a few degrees from review to review. Please take this into account
when comparing PSU test data.
* See Section 3 on stability below
** See Section 6 for more information about the fan controller.
|
ANALYSIS
1. VOLTAGE REGULATION was within the 5% specified by ATX12V throughout
the test, and the +3.3V and +5V lines were typically within 2-3%. The +12V line
was consistently high throughout the test, but the total variance from high
to low was small. The biggest voltage drop on the +12V line was seen at 400W
and above, but it still stayed above 12V.
-
+12V: 12.24 to 12.54
-
+5V: 4.86 to 5.04
-
+3.3V: 3.27 to 3.32
2. EFFICIENCY was good for a model that does not claim to be
top-of-the-line. While we've regularly seen efficiency curves that peak in the mid
eighties, these are typically high-end models that cost significantly more. The best efficiency was not achieved in the SmartPower 2.0 until the 150W - 200W
range, which some PCs may demand under heavy loads. However, most systems
do not see sustained use at this level. Efficiency at the lower loads (<150W) where
most systems operate was about average.
3. STABILITY
For the most part, the SmartPower 2.0 had no trouble powering the loads we placed
on it. However, one of
the protection circuits kicked in when we tried to go from 400W up to 444W.
This happened repeatedly, every time we tried to reach full load.
The power supply could be reset within ten seconds by cycling the
AC power switch, which suggests that the problem was an overly sensitive protection
circuit, not a failure.
The shutdown occurred with the +5V and +3.3V lines fully loaded and delivering
their combined maximum of 150W. Small loads (<5W) were also placed on the
-12V and +5VSB lines. A combined load of 21A (252W) on the two +12V rails could
be handled without problems. However, adding a single ampere (12W) to the +12V
line triggered an immediate shutdown. The same 12W increase could be achieved
by adding power to the +5V or +3.3V line without causing the power supply to
shut down, even though this exceeded the published specification for these lines.
It is possible (not likely, but possible) that the overcurrent protection was
legitimately shutting down the power supply, if the specifications on
the web site, not the box, are correct (see page 2 of this review). Adding 12W to the +12V
line would have put the output power on the +3.3V, +5V, and +12V rails at 414W
? a pithy four watts over the "maximum" of 410W. However, as
mentioned above, adding a similar load to either the +3.3V or +5V line did not
have the same effect. The other factor to consider is that because the 12V line was actually at 12.25V at full load, the real load was about 6W higher than intended. But this seems a very small "overload" to cause instant shutdown.
We contacted Antec about this problem, and they sent us a
second sample to see if it would behave the same way. Fortunately, it did
not. The second sample reached the maximum of 444W load without any problem,
and stayed running at that output level for some time.
Because the inability to reach full power was probably the result of an overly sensitive protection
circuit, not a failure, the problem that we saw with the first sample is largely
trivial. No ordinary system is likely to draw more than half of the
load at which the first sample shut down. A dual processor, SLI system might peak around
400W, but such a system cannot be connected to this power supply without multiple
adapters.
4. POWER FACTOR was typical for a unit without power factor correction,
ranging from 0.60~0.66, increasing with power draw.
5. TEMPERATURE AND COOLING
The flow-through design of the SmartPower 2.0 works very well. The temperature
rise through the power supply stayed at just 5~6°C through
almost all of its output range. At lower loads, this is fairly normal, but as
the load increases, it is more impressive. Many power supplies
we've tested had a thermal rise of well over 10°C at 400W load, whereas the SmartPower
2.0 managed to keep it to just 6°C.
6. FAN, FAN CONTROLLER and NOISE
The test environment is live, so readings are higher than would be obtained
in an anechoic chamber readings, due to reflections and reinforcement of sound
waves off the walls, ceiling and floor.
As with every power supply we test, the positive wire of each fan was tapped
so we could measure the input voltage. The neutral line was tapped at one of
the common ground wires via an IDE drive connector. However, this method initially
gave us a reading of -12V ? obviously wrong. This implied that the fan
control circuit is completely separate from the rest of the power supply.
So, we also tapped the common wire of each fan. No matter what load was placed
on the PSU, both fans were always fed the same voltage, which should have meant
that they were always at roughly the same speed. However this was not the case:
The input voltage remained at 5.3V at low loads, but sometimes the exhaust fan
was spinning, and sometimes it wasn't. Since the voltage did not change, there
was no apparent reason for the rear fan to have suddenly started spinning.
For this reason, we were unable to determine experimentally how the rear (exhaust) fan is
controlled. One possibility is that the fan itself is thermally
controlled independently of the fan control circuit, but Antec could not verify
this yet. So, the voltages reported in the data table above reflect the input voltage
to the intake fan.
The fan control circuit seemed to have an odd side effect that dismayed many
users in our forums: When the fan monitor cable is plugged into a motherboard,
the rear fan runs at full speed ? making it useless for a quiet computer.
However, unplugging the cable solves the problem and the fans behave as they
should. Antec informed us that this problem had been noted and corrected after the first shipment that went out to retail.
Without the fan monitor cable plugged in, the rear fan does not spin at
all when the temperature is low. This is excellent for silencers.
It means that the only source of noise is the intake fan in the middle of the
case, away from any direct paths to the user's ears. It also spins slowly enough
that it is probably close to or below the ambient noise level in most rooms, effectively making
it silent in a low power system. The low-profile
intake fan is quite well-behaved, even at the relatively high starting voltage
of 5.3V.
The exhaust fan begins to spin when the intake temperature reaches the mid-thirties ? at about 150W load in our test environment. The ambient temperature
during this test was a bit higher than usual, which caused the fan to start earlier
than it would have otherwise. The exhaust fan has a noticeable effect on the
noise. It is louder, and there is a small amount of whine from the motor. Fortunately,
the transition as the fan turns on is not very audible. There is enough hysteresis
in whatever is controlling the exhaust fan that it ramps up slowly and smoothly.
This was true of both fans: Changes in noise level were only audible when specifically
listened for.
Once the exhaust fan turns on, the noise signature rapidly deteriorates. The
intake fan also increases in speed with temperature, and by the time the intake temperature
has climbed above 34~35°C, it is no longer acceptable for use in a quiet system.
The twin 80mm fans sound worse than a single 120mm fan at the same measured
noise level because there are two separate bands of motor noise, both of which
are higher in pitch than a typical 120mm fan, making the noise harder to tune
out.
CONCLUSIONS
The SmartPower 2.0 is a good choice for use in a quiet system as long as
power requirements are not too heavy. Its noise floor is close to that of our
low noise reference, the Seasonic S12, and it is considerably cheaper. That
said, it cannot compare to the noise level of the S12 at high loads in a typical high-end system. Although they start out at the same noise level
and even stay close to level, beyond around 150W output, the SmartPower gets noisier
more quickly and at a lower temperature than the Seasonic. The low noise of the SmartPower 2.0 at low levels can be attributed
to the intelligent flow-through airflow design that cools it very effectively.
Given the straight-through airflow design of this PSU, it is probably a good candidate for use in an Antec P180 case, where the thermal isolation of the PSU would ensure lower temperature at the intake, and thus keep the PSU running at idle-quiet levels even at high load. No other fan would be needed in the bottom chamber of the P180. However, extension cables would be needed for the 2x12V and main ATX connectors to use this PSU in a P180.
The inability of our first sample to deliver its full rated load is a fairly
minor issue, related more to the artificial conditions of our test setup and
luck of the draw than a serious design flaw. It would be more a cause for concern
if the shutdown occurred at a lower load or if it was not related to a protection
circuit. More serious is the short length of the cables, which restricts the cases in
which the SmartPower 2.0 can be used and can make it difficult to route cables.
All in all, the SmartPower 2.0 is a solid choice for a
low-noise system. Those who want a top-of-the-line "designer"
power supply are advised to look elsewhere, but if functionality and price are
your primary requirements, the SmartPower 2.0 should fulfill your needs.
* * *
Much thanks to Antec
for the opportunity to examine this power supply.
|
POSTCRIPT: Efficiency Correction
October 22, 2005
Recently, we discovered that our power supply testing equipment and methodology were providing erroneously high efficiency results. In general, the biggest errors occurred at higher
output load points above 300W. At lower output levels, the efficiency error
was often no more than one or two percentage points. No other tested parameters were significantly affected.
Through a fairly arduous process of discovery, analysis and old fashioned problem solving, we modified our testing equipment and methodology to improve the accuracy of the efficiency results and described it all in the article SPCR's PSU Test Platform V.3. As part of this revision, we re-tested most of the power supplies on our Recommended PSU List. In most cases, the same sample was used in the second test.
The corrected and original efficiency results for all the re-tested PSUs are shown in in the article, Corrected Efficiency Results for Recommended Power Supplies. The relative efficiency of the tested power supplies has not changed.
If the tested PSUs are ranked by efficiency, the rankings remain the same whether we use the original results or the new results.
This
data is also being added to relevant reviews as postscripts like this one.
|
CORRECTED EFFICIENCY: Antec Smartpower 2.0 - 450
|
|
Target Output
|
40W
|
65W
|
90W
|
150W
|
200W
|
250W
|
300W
|
450W
|
|
Actual Output
|
42.1W
|
63.6W
|
86.7W
|
149.3W
|
198.5W
|
254.5W
|
299.4W
|
447.7W
|
|
Efficiency
|
Corrected
|
64.8%
|
73.1%
|
74.7%
|
78.1%
|
79.7%
|
79.1%
|
78.4%
|
75.1%
|
|
Original
|
65%
|
71%
|
75%
|
78%
|
80%
|
78%
|
77%
|
77%
|
In this case, our original efficiency calculations were either dead on or slightly too low except at maximum output, at which point it was a bit too high.
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