Seasonic S12-330 PSU, new sleeved version

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.

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 20 dBA, 122V/60Hz.

ANALYSIS

1. VOLTAGE REGULATION was good, within ±3% of the nominal values throughout the test. Both the +12V and +3.3V lines were slightly lower than nominal throughout the test, which is fairly unusual; most power supplies are slightly high.

2. EFFICIENCY was almost identical to the Rev. A1 S12-430 that we tested, which is to say that it is among the select (but growing) number of power supplies that reaches above 80%. It didn't do quite as well at the very low end of its output range, but even then the difference was rarely more than a watt or two. At 150W and above, any differences were typically less than half a percentage point and could easily be put down to sample variance.

3. POWER FACTOR was excellent thanks to the active power factor correction circuit. A couple of times, it was so close to the ideal value of 1.0 that no difference could be measured. And, unlike some other active PFC circuits, the power factor remained above 0.99 even at the very low end.

4. TEMPERATURE & COOLING

Temperature was not an issue, and the temperature rise remained below 10°C even at full load, so there is no reason to believe that the smaller heatsinks are inadequate for the 330 watt capacity. The only indication that they are not quite as effective as the ones in the S12-430 is the fact that the fan reached full speed even before full load was reached.

5. FAN, FAN CONTROLLER and NOISE

As mentioned, the fan did not change with the new revision, so the noise character tended to be very similar to the previous S12's, especially the 430 watt version (higher capacity models use a faster fan). Our latest sample produced a more pronounced buzz than the models we've heard previously, although the difference was quite subtle and the volume was not loud.

Of more concern was the fact that the fan ramped up much more quickly than in the previous tests. The fan remained very quiet until just above 150W load, but it jumped up very quickly after that. This was probably caused by the smaller heatsinks that could not cope as well with heavy loads. The end result is that the S12-430 is a better choice for a quiet mainstream or high powered system, since these often peak between 150W and 200W under load. Systems with lower power consumption are less likely to see a difference between the two models.

CONCLUSIONS

The newest version of the S12 brings some much requested features to the table, mostly to do with cable selection and management. Those who were requesting the features will no doubt be thrilled, but we can't help but notice that none of the improvements really cater to the low-noise crowd. Longer cables and more connectors are all very well if they are needed, but the extra wiring does need to be hidden if it's not used. Considering the minimalist preferences of the silencing crowd, the changes in cabling seem like much ado about very little. We also miss the 5V fan headers that used to be included.

Overall, our favorite change has very little to do with the technical details at all but with the way the power supplies are manufactured: We are pleased so see that the S12 is now RoHS compliant and lead-free. No doubt many users in the EU will agree, since it means that S12's will continue to be available in Europe.

The different revision aside, our inspection of the low capacity S12 was a bit of a let-down from an acoustic viewpoint. The S12-430, 500 and 600 models' biggest strength has been their ability to remain quiet even in the 150~250W output range, but the smaller heatsinks mean that the S12-330 ramps up comparatively early. The end result is a power supply that is not the best in its class but is one of several quiet power supplies that become noisier when they are heavily stressed in a medium-to-high powered system.

The S12-330 is still very efficient, stable and well cooled. However, our ultimate concern is noise, and the higher capacity S12s beat the S12-330 at >150W loads. The S12-330 is a good choice for a lower-powered system, and it does have a price advantage over the other models.

It has to be said that the >150W fan rampup is probably a much smaller issue than it might have been even a few months ago. Most silent PC builders tend to choose lower power components, and today, with Athlon 64 and 64X2 processors running as cool as they are already, the Intel Core Solo and Duo components starting to come into the market, keeping even a highly capable computer under 150W DC maximum load is not at all difficult to do.

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

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SPCR Articles of Related Interest:
Power Supply Fundamentals & Recommended Units
Power Distribution within Six PCs
Seasonic S12-430
Seasonic S12-500/600 Rev. A2

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