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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.
No acoustic recordings were made of this PSU, as it is essentially identical to the S12-500/600. Please check the sound files in the S12-500/600 review if you're interested.
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 23°C and 20 dBA, with
input of 120 VAC / 60 Hz measured at the AC outlet.
|
SS-400HT Active PFC F3 TEST RESULTS
|
|
DC Output (W)
|
40
|
65
|
90
|
150
|
200
|
250
|
300
|
400
|
|
AC Input (W)
|
54
|
83
|
110
|
180
|
229
|
283
|
337
|
443
|
|
Efficiency
|
74%
|
78%
|
81%
|
83%
|
87%
|
88%
|
89%
|
90%
|
|
Intake Temp (°C)
|
25
|
28
|
30
|
34
|
35
|
39
|
41
|
45
|
|
PSU Exhaust (°C)
|
26
|
30
|
32
|
36
|
38
|
43
|
46
|
50
|
| Fan Voltage |
3.8
|
3.8
|
3.8
|
3.9
|
5.1
|
7.4
|
9.3
|
11.0
|
| SPL (dBA @ 1m) |
22
|
22
|
22
|
22
|
23
|
30
|
36
|
38
|
|
Power Factor
|
0.96
|
0.99
|
0.99
|
0.98
|
0.99
|
0.99
|
0.99
|
0.99
|
|
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.
|
ANALYSIS
1. VOLTAGE REGULATION was truly excellent, within -/+2% on all lines from the lowest to the highest loads. The low and high voltage seen on each of the main lines is shown. Actually, it was only at 400W output that voltage regulation fell outside 1% tolerance.
-
+12V: 12.00 -12.09
-
+5V: 4.89 - 4.98
-
+3.3V: 3.25 - 3.32
2. EFFICIENCY was the best ever measured, reacing 90% at full power. The PSU was generating just 43W of heat within itself while producing 400W DC output. The 80 Plus certification assures that efficiency is 80% or higher at 20%, 50% and 100% loads, which works out to 80W, 200W and 400W, respectively. Our closest test points were 90W, 200W and 400W, where the calculated efficiency was 81%, 87% and 90%. respectively. The 80 Plus test configuration is somewhat different from ours, and their published report for the Seasonic SS-400HT Active PFC F3 shows considerably lower numbers, 81.5%, 85.3% and 83.2%.
The discrepancy between the 80 Plus test results and ours at maximum load is significant, and a bit disconcerting. We're actually in touch with the 80 Plus PSU testing team to try to determine the source of the measured efficiency difference.
3. POWER FACTOR was typical for a unit with active PF correction: Excellent, at or near the theoretical maximum. This, along with the high efficiency, ensures the lowest AC current (amperes) draw for any system of PC components. As previously mentioned, >0.9 PFC and high efficiency are the main requirements of the 80 Plus program. This sample certainly meets and exceeds the requirements.
4. TEMPERATURE AND COOLING
The design of Seasonic's heatsinks combined with the high efficiency worked to keep the temperature
rise through the power supply stayed at just 5°C of better throughout the power range. At lower loads, it barely went to 3°C. This is outstanding performance.
5. 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.
Overall, the noise performance is excellent, bettered only by the current fan-cooled PSU champ, the Seasonic S12-430. By most standards, this would be considered an extremely quiet PSU. It's mostly wind turbulence noise at most levels, along with a touch of the buzziness that's characteristic of a ball-bearing fan. The behavior of this fan and its fan controller is essentially identical to that of the S12-500 / 600. The fan controller circuit is the same, as is the the fan. The heatsinks, too, are the same. The small reduction in heat output does not seem to have been enough to make any significant change in noise. The same slow rise to speed is seen in the fan controller, which keeps fan voltage at the default start level till >34°C intake temp level, which equates in our test setup for the SS-400HT, to a high ~200W output.
As mentioned earlier, no acoustic recordings were made of this PSU, as it is essentially identical to the S12-500/600. Please check the sound files in the S12-500/600 review if you're interested.
6. COMPARED TO S12-500 & S12-430
We couldn't help wondering how this PSU fares against the S12-500, which is the non-80 Plus approved version of the 500W retail model, and the S12-430 (Rev.A2 with ball-bearing fan), which is Seasonic's retail model closest to the SS-400HT in terms of power rating. The S12-430 is based around a slightly lower efficiency circuit and a slightly quieter fan. It is also the quiet champ among fan-cooled PSUs.
So we set up a comparison table of summary data.
|
Comparison: Seasonic SS-400HT, S12-500 & S12-430
|
|
Model
|
Output (W)
|
65
|
90
|
150
|
200
|
250
|
300
|
400
|
|
S12-430
|
Efficiency
|
77%
|
78%
|
79%
|
82%
|
82%
|
80%
|
80%
|
|
400HT-80+
|
78%
|
81%
|
83%
|
87%
|
88%
|
89%
|
90%
|
|
S12-500
|
77%
|
83%
|
85%
|
87%
|
87%
|
87%
|
87%
|
|
S12-430
|
Temp Rise (°C)
|
3
|
4
|
5
|
5
|
7
|
8
|
8
|
|
400HT-80+
|
1
|
2
|
2
|
3
|
4
|
5
|
5
|
|
S12-500
|
2
|
1
|
3
|
3
|
3
|
5
|
5
|
|
S12-430
|
Noise (dBA@1m)
|
20
|
20
|
22
|
25
|
29
|
32
|
37
|
|
400HT-80+
|
22
|
22
|
22
|
23
|
30
|
36
|
38
|
|
S12-500
|
21
|
21
|
22
|
25
|
28
|
34
|
39
|
The measured data between the 400HT and the S12-500 is very close, and a bit inconsistent, ° the 80 Plus model does not edge out the S12-500 in all categories, although it does reach higher efficiency. Most of the other differences can be easily explained away by sample variance. The comparison probably tells us more about the margin of error in our testing setup and procedure than about the differences between these PSU samples.
The measured differences between the SS-400HT and the S12-430 are more interesting, actually. The efficiency difference is very clear. At 300W output and higher, the difference amounts to double the heat generated in the S12-430 -- 20% of incoming energy lost as heat versus 11% in the SS-400HT. This is also reflected in the temperature rise through the PSU, which is only 5°C for the SS-400HT and 8°C for the S12-430. However, this temperature rise difference is not attributable just to the efficiency difference. The SS-400HT also has a slightly more powerful fan. From an acoustic perspective, the lower efficiency S12-430 wins out because of the slower, quieter fan. But remember, the S12-430 is the low noise PSU champ .
It must be noted that all three PSUs in the comparison table are very quiet at <200W load, which is where most systems run most of the time.
CONCLUSIONS
The 80 Plus version of Seasonic's OEM SS-400HT Active PFC F3 power supply is exactly what we expected: Aside from the lower maximum power rating, very similar to the S12-500 / 600 models in terms of noise, with slightly better efficiency at the extremes. From a retail consumer point of view, the S12-430 offers better value because it is quieter, with a more user-friendly package and longer cables for greater flexibility in case and setup options.
Still, it's good that Seasonic is planning to offer the 80 Plus version to the retail consumer. Some users will be interested in obtaining this PSU for its highest efficiency. Swapping out the stock fan for a quieter one -- the one used in the S12-430 would do fine -- would give it true championship performance in every category: Efficiency, cool operation and acoustics. The MSRP is reasonable, given the performance level of this product.
The case for system integrators to use the 80 Plus approved SS-400HT seems quite strong. Not only is the price reduced by the $5 or $10 rebate, the product has great stability and performance, along with the potential for long, reliable service, given its cool operation. The acoustic performance is probably unmatched by any PSU meant for the OEM market, which has traditionally been inattentive to noise. With the 80 Plus approved SS-400HT and reasonable care in other component selection, almost any system integrator could list low operational noise. One imagines that in the large order quantities sought by commercial system integrators, the additional cost of an 80 Plus version would be easily offset by the rebate.
* * *
Much thanks to Seasonic USA for the opportunity to examine this power supply.
|
POSTCRIPT: Efficiency Correction
October 20, 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 level 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 both tests.
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: Seasonic 400HT Active PFC F3 "80 Plus"
|
|
Target Output
|
40W
|
65W
|
90W
|
150W
|
200W
|
250W
|
300W
|
400W
|
|
Actual Output
|
42.1W
|
63.6W
|
90.2W
|
153.5W
|
197.2W
|
251.2W
|
297.9W
|
401.3W
|
|
Efficiency
|
Corrected
|
76.6%
|
81.5%
|
82.8%
|
85.3%
|
85.3%
|
84.3%
|
83.9%
|
82.6%
|
|
Original
|
74%
|
78%
|
81%
|
83%
|
87%
|
88%
|
89%
|
90%
|
In this case, our original efficiency calculations were 2~3% too low through to about 150W output. Above that, the original results were too high, and the error kept increasing with rising output power till it reached over 7 percentage points off at maximum load. The new figures closely match the published results of testing done by the 80 Plus program. The new efficiency figures show that this model would comfortably pass the 80 Plus requirements of 80% minimum efficiency at 20%, 50% and 100% of rated power.
|
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