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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.
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The Test rig is physically set up for ATX power supplies. For this
small SFX power supply, special arrangements had to be made so that it
could be placed for correct thermal simulation. Duct tape and foam came
in handy.
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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 21°C and 19 dBA. AC input was 121V
and 60 Hz, measured at the outlet.
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OUTPUT & EFFICIENCY: Seasonic SS-300SFD APFC F3
"80 Plus"
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DC Output Voltage (V) + Current (A)
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Total DC Output
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AC Input
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Calculated Efficiency
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+12V1
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+12V2
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+5V
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+3.3V
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-12V
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+5VSB
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11.95
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0.94
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11.95
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1.7
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5.12
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0.99
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3.33
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0.95
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0.1A
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0.1A
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41.5W
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51W
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81.5%
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12.03
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1.90
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12.03
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1.72
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4.92
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1.97
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3.28
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1.88
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0.2A
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0.4A
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64.4W
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77W
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83.6%
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11.98
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1.84
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11.98
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3.19
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4.91
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2.77
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3.28
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3.62
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0.2A
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0.5A
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89.7W
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106W
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84.6%
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11.99
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3.75
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11.99
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3.42
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4.90
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4.50
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3.27
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5.67
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0.3A
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0.9A
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152.0W
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180W
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84.5%
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11.95
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3.76
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11.95
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4.90
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4.89
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6.15
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3.27
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8.24
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0.4A
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1.2A
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203.7W
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240W
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85.2%
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11.95
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3.76
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11.95
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6.63
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4.88
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6.21
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3.26
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9.93
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0.5A
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1.6A
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253.4W
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313W
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81.0%
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11.95
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6.54
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11.95
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9.57
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4.87
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6.86
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3.25
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10.62
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0.6A
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1.7A
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303.5W
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380W
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79.9%
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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.
The loading formula is the same one used by Efficient
Power Supplies, which can be downloaded as a PDF file from
the linked page. This is the testing arm of the 80
Plus program, which encourages the use of high efficiency power
supplies in computers in the US and Canada.
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OTHER DATA SUMMARY: Seasonic SS-300SFD APFC F3 "80
Plus"
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DC Output (W)
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41.7
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64.2
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90.7
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152.0
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203.7
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253.0
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303.5
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Intake Temp (°C)
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25
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27
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30
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34
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36
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37
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40
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Exhaust Temp (°C)
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30
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32
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36
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40
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42
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44
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49
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Temp Rise (°C)
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5
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5
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6
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6
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6
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7
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9
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| Fan Voltage |
3.8
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3.8
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3.9
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5.0
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6.6
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8.2
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10.4
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| SPL (dBA@1m) |
22
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22
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22
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25
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30
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34
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38
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Power Factor
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0.98
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0.98
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0.98
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0.98
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0.99
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0.99
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0.99
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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.
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ANALYSIS
1. VOLTAGE REGULATION was excellent, well with the ±5% tolerance allowed. The ranges were:
- 12V: 11.95~12.03 (-0.4%, +0.25%)
- 5V: 4.87~5.12 (-2.6%, +2.4%)
- 3.3V: 3.25~3.33 (-1.5%. +1.0%)
2. EFFICIENCY was close to the best measured on our V.3 test setup. It exceeded the minimum 80% rating on all test loads, even at the very low, demanding 41.5W output. The efficiency curve was very flat, with the high of 85.2% centered at ~65% of maximum output. Only at maximum power was there even the slightest question of not meeting the 80% spec. Our calculated 79.9% efficiency at 303.5W is close enough to consider it a pass, as the accuracy of our test methods can be no better than about ±1%.
3. POWER FACTOR was stable, and about as high as it can be.
4. TEMPERATURE AND COOLING
The cooling efficiency was very good. The temperature rise through the unit was 5°C at the start and rose only to 7°C at 250W. At 300W, the temperature rise was still just 9°C. It is surprisingly good cooling, especially given the small size of the unit.
5. FAN, FAN CONTROLLER and NOISE
Overall, the noise of the SS-300SFD can be described as fairly quiet and smooth in its response to output load and heat. It does ramp up a little quicker as load is increased than the ATX Seasonic models we've tested recently, but it is still very well behaved. The changes in fan speed are smooth and gradual, and don't call undue attention.
The noise of the fan from minimum load to about 100W output was a low 22 dBA@1m. The voltage at the fan started at a low 3.8V. The sound was characterized by a slight hum and lower frequency buzzing when listened to close up. It is not a particularly smooth sound, but it's not terribly harsh, either, and it's at a very low level. Overall, it's quite acceptable, as you'll hear in the MP3 recordings on the next page.
As load was increased, the fan ramped up slowly. The drive voltage reached 5V at 152W, at which point the noise level hit 25 dBA@1m. The overall noise signature did not change much, except for a bit more of a clicking aspect. It was still pretty quiet.
Between 152W and 203.7W, the fan voltage increased from 5V to 6.6V, and it resulted in a 5 dBA increase, the single biggest jump in noise between any two test points. At 30 dBA, it is borderline quiet in our view. But most of the noise was the whoosh of wind turbulence, a relatively benign sound. Beyond 200W, the fan speed increased steadily to a high of 38 dBA@1m at full power output. It became progressively higher pitched, but never became a whine. The wind turbulence continued to dominate the sound.
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