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Seasonic SS-300SFD 80 Plus: Little Big PSU

November 30, 2005 by Mike
Chin

Product
Seasonic SS-300SFD Active PFC F3 - 80 Plus

300W SFX12V v3.0 Power Supply
Manufacturer
Seasonic
MSRP
US$60

In the midst of all the gleaming silver, blue-glowing, features-bursting power supplies that dance across the SPCR test bench, it can be a relief to come across a product utterly devoid of excess. The Seasonic SS-300SFD - 80 Plus version is such a functional-oriented product that it is not even available in a retail package; it is sold only as an OEM product. This usually means it is hard to find. Seasonic USA says this model can be obtained through industrial supply sources, Jameco Electronics, Power-on and Microstandard. At time of writing, only Power-on had stock, for $55.

SFX power supplies are considerably smaller than ATX power supplies, and are usually rated for much lower power output. Typical SFX ratings in the past have been 180W, 200W, 220W, and more recently, 250W. This Seasonic is the first and only 300W SFX model that has been available in the marketplace, as far as we know. That it has the high efficiency certification of the 80 Plus program makes it doubly unusual. The product has been available in the US for a few months.



The most powerful SFX power supply to date.

Why is this power supply interesting?

  • Interest and development in smaller PC systems continues to grow. Aside from the obvious breadbox-size small form factor system from the likes of Shuttle and AOpen, there are also many more highly featured microATX boards being released. These need both suitable cases and power supplies, especially for media PCs, which is the source of much of the interest in small computers.
  • A 300W PSU is probably about right for a media PC. This Seasonic is the first to offer 300W.
  • Seasonic has a long reputation for making very quiet, highly efficient power supplies. This 80 Plus model promises the best of all worlds.
  • A Seasonic SFX12V power supply was used in an early mini-ITX DIY system created by yours truly a few years ago. I called it PC in a Breadbox. It was virtually silent.

WHAT IS SFX?

Some of you may be wondering about the "SFX12V v3.0" designation. This power supply form factor was created by Intel in 1997 as an alternative to the ATX power supply in small systems. The details can be found at Form Factors. In their document called microATX System Design Suggestion, Intel suggests that SFX power supplies be used for mATX systems. SFX PSUs, or variants thereof, have been used in systems by some big brands, including HP and eMachines.

The most recent SFX12V revisions are v3.1 (dated March 2005 but only released very recently) and v3.01 (dated June 2004). Version 3.0, which the PSU under review conforms to, dates back to February 2004.

You might ask fairly why this Seasonic PSU conforms to a standard that is over 18 months old. The answer is that there is always a lag between the release of a standard and the first release of products that conform to that standard. Product development takes time. Then there is the simple issue of demand. SFX power supplies are sold in small quantities compared to ATX. Demand dictates quantity, revenue potential, profitability. Naturally products in lower demand are updated less frequently, never mind how often Intel changes the spec.

In truth, the difference between the three versions mentioned are small. Version 3.01 introduced two changes:

? Updated 3.3 V remote sense pin # on the main power connector

? Updated 12V2 DC Output Noise/Ripple

Version 3.1 introduced three more changes:

? Updated typical power distribution tables for 180W, 220W, 240W, 270W and 300W.

? Updated required efficiency and recommended efficiency targets.

? Added High Current Series contacts for SFX12V Main Power Connector

The most interesting of these changes are in V3.1.

1) The recommended power distribution for a 300W model in v3.1 are as follows:

SFX12V v3.1: Recommended Power Distribution for a 300W model
DC Output
+3.3V
+5V
+12V1
+12V2
-12V
+5VSB
Maximum Output Current
20A
12A
8A
16A
0.4A
2.0A

How does the Seasonic fare against this recommendation? Well, here are the specs:

SEASONIC SS-300SFD Active PFC F3 - 80 PLUS
AC Input
100 ~ 240 VAC ~5A, 50-60 Hz
DC Output
+3.3V
+5V
+12V1
+12V2
-12V
+5VSB
Maximum Output Current
20A
20A
8A
14.5A
0.8A
2.0A
Maximum Combined
125W (28A)

270W

9.6W

10W
300W

So the Seasonic, predictably, offers a bit too much 5V current, and 1.5A too little +12V2 current. The latter is more important, but 1.5A does not seem like much of a variance. It looks pretty close.

2) The recommended efficiency in v3.1 is as follows:

SFX12V v3.1: Efficiency Vs Load
Loading
100%
50%
20%
Required Min. Efficiency

70%

72%

65%
Recommended Min Efficiency
77%
80%
75%

This 80 Plus model can be expected sail past these efficiency standards. It is certified, after all, to provide 80% or better efficiency at all three of the loads specified by Intel.

3) "Added High Current Series contacts for SFX12V Main Power Connector"... actually refers to a call for 18 AWG for all output wires. The Seasonic has 18 AWG on the AUX 12V and 4-pin Molex cables, and 20 AWG cables for all the main 24-pin ATX cable.

FEATURE HIGHLIGHTS

The input/output specifications were already presented above. The following table was compiled after scanning the product datasheet from Seasonic.

Feature Highlights of the Seasonic SS-300SFD Active PFC F3 - 80 PLUS
FEATURE & BRIEF COMMENT
High Efficiency >80%; 80 Plus certified
An increasingly
common claim, but rarely backed with the 80 Plus tag.
Forward converter circuit This feature first showed up on Seasonic's Super series; it's part of what makes them efficient.
Super low noise fan control It's been true of other Seasonic models. The same fan controller circuit is used.
Protection against short circuit on all outputs, over-voltage, and over-power. Sounds good.
Ripple & noise Meets the requirements of SFX12V v3.0.
Active PFC for 99% PF As per all recent Seasonic models; very "green"
Certifications for safety and EMI from UL, CSA, CE, TUV, CB, FCC, etc. The more the merrier.

Curiously, the operating temperature is not mentioned.

PHYSICAL BASICS

The design is similar to the bottom mounted 120mm fan ATX power supplies that are commonplace today. The difference is that the SFX model is much smaller and uses an 80mm fan. The exact dimension are 130L x 125W x 76.5H in mm (5.1" x 4.9" x 2.5").



ATX vs. SFX.

The casing is standard battleship gray. Aside from the fan intake on the bottom and the open grill main output on the back, there is also a 1" square grid of holes next to a large inductor on one side. This probably provides some cooling airflow for that inductor and critical components nearby.



A small vent on one side.



The label.

INSIDE THE SS-300SFD

The unit opens up into two C-sections, roughly speaking. It's pretty tightly packed, and the staggered fin aluminum heatsinks seen in other Seasonic PSUs are also used here. Getting it open without causing any damage was a challenge.



A full house inside.

The fan is the same model used in some previous Seasonic power supplies. It is made by ADDA, a good brand. It is a sleeve bearing model rated at 0.25A at 12V. I could not find the sleeve bearing version at ADDA's web site, but the ball bearing version is rated for 38 CFM and 34 dBA (presumably at 1 meter). The sleeve bearing may be a bit quieter; it is usually smoother.



Innocuous 80mm sleeve bearing fan.

Because the space in this PSU is quite constricted, it's probably good or cooling that a relatively high speed fan is being used. Hopefully, at typical power loads, the fan controller will keep the speed and noise of the fan in check.

CABLES AND CONNECTORS

There are a total of five cable sets. They are all quite short, but as the PSU is meant to go into a small system, the lengths are probably about right.

  • 11" cable for main 24-pin ATX connector
  • 11" cable for 4-pin AUX12V connector
  • 15" cable with two SATA drive connectors
  • 2 x 18" cables with two 4-pin IDE drive connectors and one floppy connector



Short, plain cables: The ruler is just 18" long.

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.


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.

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.

OUTPUT & EFFICIENCY: Seasonic SS-300SFD APFC F3
"80 Plus"











DC Output Voltage (V) + Current (A)

Total DC Output

AC Input

Calculated Efficiency
+12V1
+12V2
+5V
+3.3V
-12V
+5VSB

11.95

0.94

11.95

1.7

5.12

0.99

3.33

0.95

0.1A

0.1A

41.5W

51W

81.5%

12.03

1.90

12.03

1.72

4.92

1.97

3.28

1.88

0.2A

0.4A

64.4W

77W

83.6%

11.98

1.84

11.98

3.19

4.91

2.77

3.28

3.62

0.2A

0.5A

89.7W

106W

84.6%

11.99

3.75

11.99

3.42

4.90

4.50

3.27

5.67

0.3A

0.9A

152.0W

180W

84.5%

11.95

3.76

11.95

4.90

4.89

6.15

3.27

8.24

0.4A

1.2A

203.7W

240W

85.2%

11.95

3.76

11.95

6.63

4.88

6.21

3.26

9.93

0.5A

1.6A

253.4W

313W

81.0%

11.95

6.54

11.95

9.57

4.87

6.86

3.25

10.62

0.6A

1.7A

303.5W

380W

79.9%
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


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.

OTHER DATA SUMMARY: Seasonic SS-300SFD APFC F3 "80
Plus"
DC Output (W)
41.7
64.2
90.7
152.0
203.7
253.0
303.5
Intake Temp (°C)
25
27
30
34
36
37
40
Exhaust Temp (°C)
30
32
36
40
42
44
49
Temp Rise (°C)
5
5
6
6
6
7
9
Fan Voltage
3.8
3.8
3.9
5.0
6.6
8.2
10.4
SPL ([email protected])
22
22
22
25
30
34
38
Power Factor
0.98
0.98
0.98
0.98
0.99
0.99
0.99
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.

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 [email protected] 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 [email protected] 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 [email protected] at full power output. It became progressively higher pitched, but never became a whine. The wind turbulence continued to dominate the sound.

MP3 Sound Recordings of Seasonic SS-300SFD 80 Plus

Seasonic SS-300SFD 80PLUS @ 90W (22 [email protected])

Seasonic SS-300SFD 80PLUS @ 150W (25 [email protected])

Seasonic SS-300SFD 80PLUS @ 200W (30 [email protected])

Seasonic SS-300SFD 80PLUS @ 250W (34 [email protected])

There was no need to make recordings at higher power levels; it's simply too loud.

Sound Recordings of PSU Comparatives

Seasonic
S12-430 @ 150W (19 dBA/1m)

Antec
Neo HE 430 @ 150W (21 [email protected])

Antec
Neo HE 430 @ 200W (26 [email protected])

Nexus
92mm case fan @ 5V (17 dBA/1m) Reference

HOW TO LISTEN & COMPARE

These recordings were made with a high
resolution studio quality digital recording system. The microphone was 3" from
the edge of the fan frame at a 45° angle, facing the intake side of the fan to
avoid direct wind noise. The ambient noise during all recordings was 18 dBA or
lower.

To set the volume to a realistic level (similar to the original), try playing the Nexus 92 fan reference recording and setting the volume so that it is barely audible. Then don't reset the volume and play the other sound files. Of course, tone controls or other effects should all be turned off or set to neutral. For full details on how to calibrate your sound system to get the most
valid listening comparison, please see the yellow text box entitled Listen to
the Fans
on page four of the article
SPCR's Test / Sound Lab: A Short Tour.

APPLICATION NOTES

It's easy to see a commercial system integrator using this PSU for a quiet custom media PC. The only real question for DIY builders who want to use this power supply is, "Which case?" A lot of microATX cases appear to be set up for ATX power supplies. Some do take SFX12V power supplies, although they usually come equipped with one. The very small ones tend to be barebones types with proprietary power supply types.

Finding a microATX case with the kind of free-flow characteristics ideal for silent computing may be a challenge. We have to admit we have not looked hard for one before.

This model would be a good quiet replacement for a case that already uses an SFX12V PSU; as mentioned, there have been lots of big-brand computers that have used this form factor. Another option is to seek out the metal adapter templates Seasonic used to include with their Super Versatile 200W SFX12V PSU; this allowed the microATX PSU to be used in any ATX case.

CONCLUSIONS

We don't really have any other SFX12V power supplies to compare directly with this model, but the few I've seen in the past have all been loud and much lower powered. The only exception has been another Seasonic, the SS-200SFD I used in my Breadbox PC a few years ago.

This latest iteration, despite its generic looks, is something of a find for custom quiet PC builders. It's small yet quite powerful, highly efficient in converting AC to DC, and pretty quiet all around. The maximum power output of 300W is plenty for something like an Athlon 64-based media center, or even a midrange single video card gaming rig; there is plenty of juice on the 12V line.

The power delivery was excellent throughout testing. Voltage rails
were very tightly regulated, and it delivered the full rated power without complaint. Cooling was excellent even at high loads. Operating environments that are hotter than the 40°C seen by the PSU at full power in the test box might cause faster fan speed ramp-up, but most system builders will not subject this PSU to such high steady steady power load, anyway.

The stock fan is not bad, though it could definitely be improved. The ADDA fan used in the Antec Neo HE series would really make the SS-300SFD shine acoustically. Aside from the slightly mediocre fan, what's not to like in the Seasonic SS-300SFD 80 Plus?

Much thanks to Seasonic USA for the opportunity to examine this power supply.

* * *

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