Seasonic Goes Green: The Eco Power 300

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.

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.

NOTE: Because of the Eco Power 300's unusual shape and size, it was difficult to position in our PSU thermal load tester. We used various pieces of foam to block off spaces not covered by the PSU.

TEST RESULTS

Ambient conditions during testing were 21°C and 21 dBA. AC input was 120V, 60Hz.

ANALYSIS

1. EFFICIENCY

Efficiency was excellent across the board, though not quite as high as the predecessor sample we tested. It also missed the marks set by some other unusual power supplies, such as Sparkle's SPI220LE and the picoPSU. In any case, it exceeded the minimum 80% efficiency required by 80-Plus at each of the 20%, 50%, and 100% load marks.

Low-end Efficiency Comparison
Power Level	~20W	~40W	~65W	~90W
picoPSU + 120W brick	77.7%	85.6%	87.1%	87.1%
Seasonic SS-300SFD	–	81.5%	83.6%	84.6%
Sparkle SPI220LE	73.0%	80.5%	82.8%	83.8%
Seasonic Eco Power 300	68.0%	75.4%	81.1%	82.4%

In this matchup of the truly high efficiency power supplies, the Eco Power comes off looking somewhat ordinary, but rest assured that it's not. The comparison is designed to exaggerate the differences between the various power supplies. In all cases, the difference between the most efficient picoPSU and the Eco Power is less than 5W — hardly enough to save the world. And, given that most power supplies (especially high capacity units) struggle around 50% efficiency at 20W, the Eco Power's 68% performance isn't too shabby.

Overall, the efficiency curve is fairly flat, and quite high through most of its range. The peak was just shy of 84%, reached at 200W, but most environmentally conscious users will never push it this high; a basic midrange system should float somewhere between 50~100W under most conditions.

2. VOLTAGE REGULATION was excellent, with all voltages dropping slightly as the load increased. Voltages did not sag significantly at full load, indicating that the unit was fully capable of delivering its rated capacity safely. The most significant voltage drop we saw was during the crossload test, when both 12V lines dropped to ~11.6V, but even this is well within the 5% range required.

3. RIPPLE

Ripple was well within specifications, especially on the all-important 12V line. Peak ripple was observed under both full-load and no-load conditions, but typical ripple was generally about half the peak measured.

4. POWER FACTOR was close to perfect across all loads, as is the norm for most power supplies with active correction circuitry. It remained excellent even at the ultra-low 20W load.

5. LOW LOAD PERFORMANCE

The Eco Power had no issues starting with no load or very small loads. Its power consumption in standby was a little higher than we are used to seeing, but at 0.9W it was still barely a trickle.

6. TEMPERATURE & COOLING

Cooling was pretty good for such a small, packed unit, but that's more a testament of the unit's high efficiency and low capacity than anything else. Seasonic's multi-layered heatsinks may also play a role. The internal temperature rise remained safely below 10°C through all but the full load test. We have no worries about the Eco Power's resilience under load.

7. FAN, FAN CONTROLLER and NOISE

The noise characteristics of the Eco Power weren't really on par with what we expect from Seasonic. In part this is due to the smaller fan and the tight confines of the SFX12V form factor. However, the baseline noise level turned out to be 1 dBA@1m higher than the older SS-300SFD that we tested, so we know Seasonic can to better. The increase in noise is most likely caused by the higher minimum fan voltage in the Eco Power, though the switch to a ball-bearing fan may also have made a difference. A fan swap could certainly help things here.

Subjectively, the noise character wasn't especially smooth, but it was broadband without pure tones. We've certainly heard better (in the Seasonic-made, Antec-branded NeoHE for example) from an 80mm fan, but we've also heard much, much worse.

The fan controller was a regression compared to the one found in Seasonic's ATX models. The noise level rose significantly at ~150W, and anything above this load quickly became load. Users who want to avoid hearing the fan ramp up and down would be advised to keep their systems under 150W peak demand.

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