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TEST RESULTS
Ambient conditions during testing were 21°C and 20 dBA, with input of 120 VAC
/ 60 Hz measured at the AC outlet.
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Clever Power SPS-400 TEST RESULTS
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DC Output (W)
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65
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90
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150
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250
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400
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AC Input (W)
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90
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118
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192
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312
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525
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Efficiency
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72%
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76%
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78%
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80%
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76%
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Intake Temp (°C)
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26
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27
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32
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35
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39
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PSU Exhaust (°C)
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32
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33
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38
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42
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50
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Fan Voltage
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6.4
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7.2
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9.1
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11.0
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11.8
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Noise (dBA/1m)
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31
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33
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37
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41
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42
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Power Factor
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0.65
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0.67
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0.68
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0.70
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0.73
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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.
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ANALYSIS
Any new or unusual way of doing things always has some element of risk. The
test bench will determine whether the fancy airflow and blower fan actually
have any practical benefit for quiet computing.
1. VOLTAGE REGULATION was excellent, within ±2% on all lines
at every load. The 12V was consistently low, but only by 0.1~0.2 V.
-
+12V: 11.8 to 11.9
-
+5V: 4.9 to 5.0
-
+3.3V: 3.3
2. EFFICIENCY was fairly average by today's standards, staying in the 78-80% range for the
crucial 150-250W range. When this PSU was released a year ago these numbers
would have been excellent, but the competition in this area has stiffened a
lot in the past year.
3. POWER FACTOR was quite good, ranging between 0.65 and 0.73. While
it's obviously not an active PFC unit, we've seen much worse numbers from
more expensive power supplies.
4. FAN, FAN CONTROLLER and NOISE: The Clever Power starts up with a
quick 12V burst to make sure the fan starts and immediately drops to the lowest
voltage required to keep it spinning, around 4.3V. At this voltage, the fan
is practically inaudible from 1 meter. The noise it produced
was close to our ambient noise level of ~20 dBA. Could it be that Clever Power's
claim of 18-25 dB be accurate?
Of course, if you've been reading carefully, you will have noticed that our
voltage table starts at 6.4V. Why not 4.3V? The 4.3V reading that we measured
was obtained in open air while the PSU was cold. Installing the Clever Power
in our test setup had the immediate effect of boosting the fan voltage (and
noise). The noise level of 31 dBA/1m at 65W would not be acceptable in a quiet computer;
if the PSU is mounted in an actual case, the bass hum of the fan will never totally
disappear.
Moving to a higher load has an immediate and audible effect on the Clever Power.
The transitions between voltages are not very smooth, and changes in fan speed
are clearly audible. The thermal sensor is sensitive enough that it responds
audibly when the exhaust path is blocked.
The fan controller appears to be very conservatively tuned, and responds linearly to increases in load / heat. Almost all of the
adjustment range is used below 150W, which means that in a high powered system, the PSU fan may never run below ~9V. This is too high a voltage to produce acceptable
noise levels. The designers of this PSU would do well to examine the more "stepped" or exponential fan speed-to-heat response curves of the best quiet PSU fan controllers.
CONCLUSIONS
There was a considerable amount of thought put into designing the
Clever Power SPS-400. A negative pressure airflow system and a built-in power
strip are not common features for a power supplies. Unfortunately, it seems that not enough time was spent on the test bench; tampering with the internal airflow does not seem to have produced any tangible benefits. It is true that the AC outlets are indirectly made possible by the use of a blower-style fan that does not require the whole back to be used as an exhaust vent. However, the fan controller that the blower is paired with makes it difficult to consider this power supply for use in even a moderately quiet system. A system
with a fresh air intake duct for the PSU might prevent the blower fan
from ramping up in speed.
The extra AC outlets could be quite useful depending on
how your system is set up. For people who want to centralize their cable management
(and don't mind adding even more cables to the tangle behind their case), this
could be quite a welcome addition. The 2A maximum current may be too low for
some applications though. In North America, larger CRT monitors and laser printers
routinely draw more than 2A. For countries that have 240V power systems this
will be less of an issue because the higher line voltage effectively halves
the current draw of all electrical appliances.
For $45, the Clever Power is cheap enough that it might be worth integrating
it into a system that is specially designed for it. We had no issues about
either its stability or its efficiency. However, anyone looking for a cheap
quiet power supply to drop into their existing system would be best advised to look
elsewhere. Just about any PSU in our Recommended table will be quieter. This power supply will be a significant source of noise in any situation
in which it is expected to exhaust warmed air from a case.
* * *
Much thanks to Clever
Power for the opportunity to examine this power supply.
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