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Seasonic SS-400HT power supply, 80 Plus version

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It is the least powerful of three ATX PSUs by Seasonic that have achieved 80 Plus approval. A plain-jane OEM model that’s not available in a retail package, the 80 Plus version SS-400HT keeps all of its considerable strengths beneath its battleship gray appearance.

August 3, 2005 by Mike
Chin
with Devon Cooke

  • POSTSCRIPT added Oct. 20, 2005
Product
Seasonic SS-400HT Active PFC F3 – 80 Plus
400W ATX12V 2.0 Power Supply
Manufacturer
Seasonic

MSRP

$99.99; to be available mid-Sept, 2005 from Jameco Electronics, Power-on, & Microstandard

Seasonic has managed to maintain an exalted position among SPCR tested power supplies with products that continue improving with every generation, quietly and purposefully doing precisely what they are asked to do. Devoid of flash, with all the strengths hidden beneath subdued exteriors, they have fit the classic definition of “sleepers”. The Seasonic SS-400HT Active PFC F3- 80 Plus continues this tradition.

This particular model was the first ever to be approved by the 80 Plus program as a > 80% efficiency computer PSU. The sample came to us in a plain box, with bubble wrap around the unit. It is not available in a retail package. The sample has an 80 Plus label affixed to the side of its battleship gray housing. It’s the first time we’ve seen the 80 Plus label, whose fine print reads, “more than 80% efficient at 20%, 50% and 100% load”.

Anyone who has seen SPCR’s previous Seasonic PSU reviews will notice something different about the appearance of the sample pictured above. It has an auxiliary screw mounting bracket on the back edge. This type of mounting is not useful for most consumer power supplies because typical desktop and tower style cases do not have the matching mounting holes. They are much more common in server cases, however. It tells us that this product is clearly intended for the server market, which is where the 80 Plus Program actually has economic appeal.

The 80 Plus program provides a rebate of $5 or $10 for each 80 Plus approved PSU that is used in a system by a commercial system integrator. Aside from the >80% efficiency requirement, the program calls for a Power Factor of >0.9. Only active power factor correction can achieve such a high PF. The 80 Plus program, administered by Ecos Consulting on behalf of a consortium of US utility companies, encourages the use of power-efficient power supplies by offsetting their higher initial cost. Why? To quote the 80 Plus web site, “Saving a kilowatt-hour through cost-effective energy-efficiency programs is more economical than building the new generation, transmission and distribution lines that are needed to meet growing energy demands.”

FAMILY MATTERS

The SS-400HT Active PFC F3 is the smallest in a line of three OEM / ODM models. The other two are the SS-500HT Active PFC F3 and the SS-600HT Active PFC F3. They have the same mechanical design and circuit topology, and differ only in maximum power output.

For your information,

  • OEM = Original Equipment Manufacturer – A company that builds components used in systems sold by a value-added reseller
  • ODM = Original Design Manufacturer – A contract manufacturer that uses its own designs and intellectual property.

Note that the latter two model numbers are the same as the Seasonic S12-500 & S12-600 retail package models, reviewed here previously. Alas, the S12 models are not the same as the OEM versions of the SS-500HT or SS-600HT models. They have the same basic design, mechanically and electronically, but the S12 models have longer output cables and the black paint finish, along with the box, manual and other accessories. Seasonic’s OEM / ODM business takes precedence over their retail operation, and the S12-500 and S12-600 are best viewed as variants of the SS-xxxHT OEM line.

The SS-400HT and the other models in this lineup are available with any combination of the following features for OEM / ODM customers.

  • 80 Plus Certified – This requires a number of component substitutions to the same design. Call them tweaks for even higher efficiency.
  • With or without 240VA current limiter on the 12V1 and 12V2 lines – For OEM / ODM applications, this often provides better flexibility and improved performance / cost benefits.
  • With customized wiring harness – Usually shorter, and/or with fewer cables for best performance.

What we are reviewing here is an OEM version of the SS-400HT Active PFC F3 with the tweaks for 80 Plus efficiency conformance. Seasonic has informed me that the 80 Plus versions are typically 2~3% more efficient, especially at the low end of the power scale.

NOTE: MARKET AVAILABILITY

Because of the unpackaged, non-retail friendly status of this model, the SS-400HT APFC F3 w/ 80 Plus approval, will not be sold through normal retail channels. Instead, it will be made available through selected resellers who normally serve commercial clients. This information is in the header box at the top of this page. The suggested retail price of $99.99 compares favorably with the similarly priced S12-430, whose typical selling price is $90~$100. The S12-430, a retail product with longer cables and a full accessories package, is based on a slightly less efficient design and is the quietest fan-cooled PSU we’ve tested thus far.

OUTPUT SPECIFICATIONS



The Rev.A2 designation indicates that this sample has the same Adda ball bearing fan as in the current Seasonic S12-500 and 600.

Seasonic SS-400HT Active PFC F3 SPECIFICATIONS

AC Input

100-240V~ 8A @ 50/60 Hz

DC Output Line

+3.3V

+5V

+12V1

+12V2

-12V

+5VSB

Maximum Output Current

30A

30A

14A

15A

0.8A

2.0A

Maximum Combined

150W

348W

9.6W

10W

400W

Please note the difference between the total combined output and the combined lines output. The maximum total rated output power is 400W. This means that if your system is actually drawing 150W, 9.6W and 10W from the +3.3V & +5V, -12V, and +5VSB lines, only 230.4W will be available on the 12V line, not 348W. Conversely, if the system is demanding 348W on the 12V lines, then the remaining lines will only be able to provide 52W.

TECH TIP: ABOUT “INDEPENDENT” 12V LINES

Intel’s ATX12V V2.2 PSU Design Guide, the industry bible for PSU makers, states:

“In cases where expected current requirements is greater than 18A a second 12 V rail should be made available.

“The 12V rail on the 2 x 2 power connector should be a separate current limited output to meet the requirements of UL and EN 60950.

“12V1DC and 12V2DC should have separate current limit circuits to meet 240VA safety requirements.”

It’s important to remember that when there are two 12V lines, they still draw from the same main source. It’s not like there are two 120VAC:12VDC power conversion devices in a PSU, this would be way too costly and inefficient. There is only one, and the two rails draw from the same transformer. Each rail is coming from the same 12V source, but through its own “controlled gateway”.

An analogy that may help: Think of 12V1 and 12V2 as two identical water taps fed off short pipes joined in a Y-junction to a single larger pipe. The total amount of water flow available through the two pipes is always the same, it’s dictated by the pressure behind the big pipe. Each of the two taps have a maximum potential water flow potential that is lower than the maximum available through both taps together. How much water flows through each pipe depends on how much each is open. The “position of the tap” in the PSU is dictated by the power demand of the components connected to it.

PSU makers’ specs are misleading in that they rate the current capacity of each 12V rail independently. What really matters is the total 12V current: Generally, up to 20A is available on any one 12V line, assuming the total 12V current capacity or the total current capacity on all the output lines is not exceeded.

What the above means is that you don’t need to worry about imbalances in power draw on the 12V lines — as long as no single rail is asked to deliver more than 20A. PSU makers seem to mark each line for max current on a purely arbitrary basis. A PSU like the Seasonic SS-400HT, rated for 29A max total on the 12V lines, can be labeled many different ways:

12V1: 11A, 12V2: 18A
12V1: 12A, 12V2: 17A
12V1: 13A, 12V2: 16A
12V1: 14A, 12V2: 15A
12V1: 15A, 12V2: 14A
12V1: 16A, 12V2: 13A

12V1: 17A, 12V2: 12A

12V1: 18A, 12V2: 11A

It could also be marked 19A + 10A or 20A + 9A, but being a cautious bunch, engineers will probably not specify more than 18A on any one line. This allows a 2A margin of error for the current limiting circuit.

PHYSICAL DETAILS

The Seasonic SS-400HT Active PFC F3 has a utilitarian appearance. The casing is the traditional gray, as befits an OEM product.


A flush wire grill is fitted over the 120mm fan.

The hexagonal hole pattern found on other Seasonic 120mm fan PSU exhaust grills is used here. There are some vents other than the exhaust grill, including the four small slots in the photo above, and the row of slots on the inside panel shown below.

One can only assume these exhaust slots are near hot components to ensure there is some airflow across them. Because of the right angle juxtaposition of the fan and the main exhaust vent, there is considerable back pressure and turbulence that might cause this back corner edge to get poor airflow. These slot help overcome any potential cooling issues.

The interior is identical to the Seasonic S12-500 and 600, as far as we can see. The fins from each heatsink are staggered in two double rows for what is arguably the highest cooling surface area of any fan-cooled power supply we’ve tested.


Inventive heatsink fins for arguably the highest cooling surface area of any fan-cooled power supply.


Familiar tidy inductors and layout.


Same fan as in the S12-500 / 600.

The fan is the same one used in the S12-500 / 600, which means it’s slightly noisier than the one used in the S12-330, 380 and 430. We cannot expect this model to break new quiet records, but it should be at least as quiet as the S12-500 / 600.

CABLES AND CONNECTORS

There are a total of six cable sets plus a fan RPM cable to provide fan speed
information to the motherboard:

  • 11″ cable for main 24-pin ATX connector
  • 12″ cable w/AUX12V connector
  • 12″ cable w/8-pin EPS12V connector
  • 2 x 26″ cable with three 4-pin IDE drive connectors and one floppy
    drive power connector
  • 22″ cable with two SATA drive connectors
  • 24″ cable fan monitor with 3-pin connector for motherboard fan header


The main cables are short, which is typical for OEM PSUs.

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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