Seasonic S12II-380 Power Supply

Seasonic has been making quiet, efficient, high performance, power supplies for many years. The S12II series is their latest mainstream line. We test drive the 380W model on our torture track. It gets the checkered flag without a single glitch.

August 16, 2007 by Mike Chin

Seasonic has a long history of making quiet, efficient, high performance, power supplies. Whether marketed under their own brand name or under others’ (such as Corsair Memory and Antec), Seasonic power supplies have become the most popular choice of quiet computing enthusiasts around the world. The consistency over the years has been unmatched, as virtually every Seasonic PSU ever tested by SPCR has scored high marks.

As the brand is such a strong presence among quiet PC enthusiasts, a quick review of their current lineup is worthwhile; it appears to be a time of transitions for Seasonic products:

*S12II 330, 380, 430, 500 – The lineup in which the model under review belongs. All are 80 Plus certified for >80% efficiency. This line replaces the lower rated models of the S12 line, which is now discontinued.

*S12 Energy Plus 550, 650 – High power models 80 Plus certified based on the second generation of the S12 line.

*M12 500, 600, 700 – Detachable cables, 80 Plus certified.

There’s talk of a very high power model becoming available in late fall or winter, something around the 900W mark. There may also be modifications and changes to the modular cable M12 line, but details are unavailable as of yet.

The model designation S12 came simply from the size of the fan used in these models: 12 cm. Most readers probably know that until 3~4 years ago, most PSUs sported a single 80mm fan; a few had a second 92mm fan. There were almost no PSUs with 12 cm fans, so the S12 model designation made perfectly good sense.

S12II is obviously a major rework of the original S12, which underwent at least one significant revision during its >two-year life-cycle. (See Seasonic S12-430: Beyond the Super Tornado and Seasonic S12-330 PSU, new sleeved version).
Interestingly, the S12II-380 is not our first look at this new series of power supplies from Seasonic. The Corsair VX450W we reviewed a month ago is basically a member of the same series.

The S12II 380 is one of the most modestly rated ATX12V PSUs, not only for Seasonic, but in the retail market today. Median power ratings appear to fall in the 400~500W range these days. Yet, our research shows that no desktop system with a single CPU and a single graphics card demands anywhere near that level of power. The 380W rating of this model may be just about ideal for the vast majority of desktop systems built by DIYers today.

Modest size full color retail package.

The modesty continues inside: The PSU is inside a bubble-plastic bag. There’s a user’s manual, screws, plastic cable straps, and AC power cable.

FEATURE HIGHLIGHTS AND SPECIFICATIONS

Seasonic SS-380GB ouput specifications on label. As with most recent ATX12V PSUs, most of the output capacity is at the 12V line.

EXTERNAL TOUR

The exterior of the is matte black. The only color is in the small blue tag at the enter of the fan grill.

Nothing out of the ordinary here.

No vents
other than the fan intake and backside exhaust grill.

A single 120mm fan draws air into the power supply from below, blows it across the heatsinks, then out the back grill. A low airflow impedance wire grill protects the fan.

OUTPUT CABLES

All the output cables are sleeved.

The output cables are all sleeved, and not quite as long as those on some other recent PSUs. There are a total of seven connected cable sets:

• 20" cable for main 20+4-pin ATX connector
• 20" cable for 2x12V AUX12V
• 20" cable for 6-pin PCIe connector
• 20" cable with two SATA drive connectors
• 24" cable with two SATA drive connectors
• 22" cable with three 4-pin IDE connectors
• 26" cable with three 4-pin IDE connectors

And for those who need it, a Y-adapter with two floppy drive connectors is also supplied.

INTERIOR

The internal layout of the components on the PCB is neat and tidy, and the black (painted, most likely) heatsinks are quite small. If it looks familar to regular readers, that’s no surprise; it looks virtually identical to the innards of the Corsair VX450W (made by Seasonic) that we reviewed a couple weeks ago.

Clean layout typical of Seasonic.

Rather small heatsinks.

The only obvious difference from the Corsair VX450W is the use of a more standard 85°C main capacitor rather than the Corsair’s 105°C rated one.

Note that the stiff, clear plastic airflow control baffle found in the VX450W is absent here. It was used to ensure that none of the fan’s airflow would slip out the back vent without first travelling across the heatsinks. Seasonic informed us that in the S12II line, this baffle is used only on the 500W model. The lower power models apparently do not get hot enough to require the baffle.

Remember the clear plastic baffle to prevent any airflow "short circuit" in the Corsair VX450W?

The medium speed ball bearing fan is made by Adda, similar to others used in previous Seasonic-built PSUs.

Familiar Adda fan.

TESTING

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.4. 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.

The 120mm fan responsible for "case airflow" is deliberately run
at a steady low level (~6-7V) when the system is run at "low" loads.
When the test loads become greater, the 120mm fan is turned up to a higher speed,
but one that doesn’t affect the noise level of the overall system. Anyone who
is running a system that draws 400W or more would definitely want more than
20CFM of airflow through their case, and at this point, the noise level of the
exhaust fan is typically not the greatest concern.

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.

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 power-hungry 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 the most power hungry video card today could draw as much as another
60~100W, but the total still remains well under 400W in extrapolations of our
real world measurements. As for high end dual video card gaming rigs… well,
to be realistic, they have no place in silent computing today.

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.

TEST RESULTS

Ambient conditions during testing were 22°C and 18 dBA. AC input was 120V,
60Hz.

ANALYSIS

1. EFFICIENCY was excellent. At the super low load of just 21.6W, it was already 65.4%. This compares favorably with the Corsair VX450W’s 61% efficiency at the same power load. Most PSUs we’ve tested barely reach such efficiency at double the power output, but with the S12II-380, by ~40W, efficiency had reached 76.3%. The benchmark 80% efficiency was seen at about 70W. The peak of 84% was centered at about 200W, and >80% efficiency was maintained to full rated 380W output, as expected of a model certified 80 Plus.

2. VOLTAGE REGULATION was excellent. At virtually all loads, all the voltages were just about dead on, within a minuscule -0.1V and +0.3V range. The worst voltage drop of 0.29V on the 12V line occurred during the extreme crossloading test. This represents a drop of 2.4%, which excellent for the very worst single variance, as up to 5% (0.6V) is allowed.

3. RIPPLE (measured peak-to-peak) was well within the requirements of the ATX12V specification.
The highest ripple occurred at full load, where it reached 26mv on 12V.
To put that in perspective, the ATX12V requires +12V ripple to be below 120
mV, and below 50mV on the +5V and +3.3V.

4. POWER FACTOR was excellent thanks to the active power factor correction
circuit, staying at or very close to the theoretical maximum of 1.0.

5. LOW LOAD PERFORMANCE

Power draw on Standby was just 0.5W. When turned on with no load, it was just 7.2W. The sample started fine without any load. This PSU should have no trouble starting with very low load.

6. LOW AC VOLTAGE PERFORMANCE

The power supply was set to 300W load with 120VAC through the hefty variac in the lab. The variac was then dialed 10V lower every 10 minutes. The S12II-380 is rated for operation at 100~240VAC input. We pushed it down to 80VAC. We also checked the efficiency at 245VAC input for the sake of readers in the 200~250VAC world.

The S12II-380 worked fine with very low AC voltage. Neither voltage regulation
nor ripple changed measurably during the test, and efficiency dropped only marginally. At 245VAC, efficiency improved at the 300W load to 85.3% (from 82.2% for 120VAC). That’s a 3.1% advantage compared to the 120VAC input.

7. TEMPERATURE & COOLING

The cooling worked well. Temperature rise remained very modest and did not reach double digits until about 250W output. From 200W to 380W, the temperature rise stayed at about 9~13°C. This suggests a very well cooled PSU despite the low fan speeds.

8. FAN, FAN CONTROLLER and NOISE

Upon turn on, the PSU fan started at just below 4V, then stabilized at 4.12 within a couple of minutes. The Sound Pressure Level (SPL) reading was 20 [email protected], which was audible at 1m, but quiet and smooth.
There was no audible buzzing from a meter away at any load. When the fan was stopped with a plastic wire tie jammed into the blades, a bit of buzz could be heard from about a foot away, but this was about at the same level as fanless PSUs we’ve tested; audible buzzing or humming was not an issue with this sample.

The fan noise and voltage remained unchanged in our thermal test rig to 250W output load. This is extremely quiet performance.

Beyond 250W, the fan speed and noise climbed quickly, as expected. The overall noise at high loads were audibly lower than measured on the Corsair VX450W, which employs the same model of fan. The measured SPL of some other tested PSUs are in the comparison table below; the >30 [email protected] readings are highlighted in light green.

The above comparison table should not be taken as an absolute. It shows sound pressure levels recorded on SPCR’s test platform. The ambient temperature varies a bit, in a range of 20~23°C, and some of the PSUs may have the small advantage of lower ambient temperature during testing. This can help lower the overall noise curve, and more importantly, increase the power level at which the noise starts getting seriously louder. Still, at higher power levels, the temperature in the test box is determined mostly by the load.

In any case, in the above test data, several models are about equally quiet up to ~200W load. It is satisfying to note that the S12II-380 betters the now discontinued S12-430, staying significantly quieter in the range 200W~300W. (However, it must be noted that the S12-430 was tested in an earlier version of the PSU test system which featured an 80mm fan for cooling rather than the 120mm fan now employed; this difference could shift the power load at which thermally controlled fans begin to speed up.) Its close cousin Corsair VX450W does a bit better at 250W and 300W, but while the S12II-380 peaks out at 39 [email protected], the Corsair keeps getting louder, reaching 44 dBA at the same power level, and 50 dBA at 450W. The difference is directly related to the plastic airflow baffle in the Corsair, which increases wind turbulence noise at higher fan speed. The same factor may be responsible for the lower fan speed (and noise) of the Corsair in the 200-300W range; the baffle may help keep it cooler, hence keeping the fan from speeding faster until >300W.

If you want the best noise performance from the S12II-380, use it in a system that draws no more than 250W (DC), and/or ensure that its immediate environmental temperature does not climb much above 30°C. A system with such parameters is not difficult to build today, especially for energy-savvy PC enthusiasts.

MP3 SOUND RECORDINGS

Each of these recording start with 6~10 seconds of silence to let you hear the ambient
sound of the room, followed by 10 seconds of the product’s noise.

• Seasonic S12II-380 at up to ~200W output, 21 [email protected]: One
  meter, One
  foot (30cm)
• Seasonic S12II-380 at 250W output, 25 [email protected]: One
  meter, One
  foot (30cm)
• Seasonic S12II-380 at 250W output, 31 [email protected]: One
  meter

Sound Recordings of PSU Comparatives

• Corsair VX450W at up to ~250W output, 22 [email protected]: One
  meter, One
  foot (30cm)
• Corsair VX450W at 300W, 26 [email protected]: One
  meter, One
  foot (30cm)
• Corsair VX450W at 350W, 35 [email protected]: One
  meter, One
  foot (30cm)
• Mushkin XP-650 at 150W, [email protected]: One
  meter, One
  foot (30cm)
• Silverstone Element Plus ST50EF-Plus at 250W, 25 [email protected]:
  One meter,
  One foot (30cm)

CONCLUSIONS

The new Seasonic S12II-380 delivers clean, stable power suitable for many PC systems today. It’s among the quietest fan-cooled PSUs we’ve tested. It is very energy efficient, as expected of its 80 Plus certified status. The
sleeved cables are long enough for large cases, and there aren’t too many of them so cable management is less of a headache. Judging by this sample, the S12II should be a fine replacement of the S12 series.

This PSU shows its close family resemblance to the Corsair VX450 in almost every way, from the look, to component layout to details of performance. Even more than the VX450W, the Seasonic S12II-380 answers our call for "lower power models for those of us who seek to make a high efficiency, quiet, yet highly capable computer. 300W would be plenty for such a PC in these days of improving CPU efficiency." The very high efficiency at even <40W load makes the S12II-380 suitable even for energy misers. (As an aside, the EcoPC Reviewer in me asks how much more efficient the S12II-330 might be at super low loads. It’s a question we’ll try to answer in the near future.)

Final words: The Seasonic S12II-380 is extremely quiet, highly efficient, and performs very well. We like it very much.

* * *

SPCR Articles of Related Interest:
Power Supply Fundamentals
Recommended
Power Supplies

Power Distribution within Six PCs
SPCR PSU Test Rig V.4
Silverstone Element Plus ST50EF-Plus
Corsair VX450W
Seasonic S12-430

* * *

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