80 Plus hits Retail: Silverstone's Element ST50EF-Plus

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 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.

Note that the low speed 80mm fan responsible for "case airflow" in the thermal simulation rig is deliberately kept at a steady low level (~6V) even when the PSU is operating at very high power and the PSU fan is spinning fast enough to drown out any noise contribution of the "case fan". This is to keep a level playing (thermal) field for all the PSUs tested, but it is admittedly somewhat unrealistic. Most users will want to increase airflow in the case if their system is drawing that much power from the PSU frequently or on a long term steady-state basis. Keep in mind that some PSUs will actually perform more quietly in a real system with higher case airflow than in our low airflow thermal test box.

Great effort has been made to devise as realistic a quiet 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 20°C and 18 dBA, with 121VAC/60Hz input.

ANALYSIS

1. LOW LOAD PERFORMANCE

Despite the warning about minimum loads, the Element Plus had no problems running with no load — and it drew a very respectably low 5.5W while doing so. Lower quality power supplies can draw as much as 15~20W just by being turned on, so the low no-load performance is impressive (just don't try to calculate efficiency).

Although it would run with no load, we were able to trigger a shutdown condition by loading either the +5V or the +3.3V line without putting a load on the +12V line. The reverse was not true — the power supply remained stable when the only load was on the +12V line. Every system draws some power from +12V, so it is unlikely that this will lead to any misbehavior powering a real system.

2. VOLTAGE REGULATION was excellent — within 2% across the board, and within 1% for all but the two highest power test points. The +5V and +3.3V line varied by just 0.04V each. This is well within spec for both the 5% tolerance required by ATX12V and the 3% tolerance required by EPS12V.

3. EFFICIENCY was topnotch — not that we really expected anything different from an 80 Plus power supply. Efficiency peaked surprisingly early in the test at just above 85%. Most systems will not consume the 200W required to reach this peak, but efficiency was excellent even at lower outputs. 74% efficiency at 40W output may not hit the magic 80% number, but its still very impressive — the more so because it is representative of the power consumption in a typical system.

4. POWER FACTOR stayed close to the ideal value of 1.00 thanks to active power factor correction.

5. TEMPERATURE & COOLING were good throughout the most commonly used output range. The thermal rise through the power supply stayed below 5°C until the fan ramped up at ~250W output, and it never exceeded 10°C. The high efficiency and excellent voltage regulation at full load both suggest that the power supply never came close to overheating, and the 45°C intake temperature was within the 50°C thermal specifications.

6. FAN, FAN CONTROLLER and NOISE

The residual noise level was a little higher than it could have been, mainly because the starting voltage for the fan was a little too high. 23 dBA@1m is very quiet, but it was still clearly audible in our test lab — unlike the best power supplies, which are just barely audible at one meter. Even so, the fan noise was smooth and inoffensive, characterized mostly by a low growl that blended easily into the background.

Of more concern was the wheezing electronic squeal that the power supply gave off when there was not enough load on the +5VSB line. The squeal was high pitched and very irritating, and it was present whenever the power supply was running unless at least 0.3A were applied to the +5VSB line. Smaller loads would affect the pitch and rhythm of the squeal, but would not eliminate it entirely. It's not clear how serious this issue is. 0.3A represents just 1.5W, and all motherboards require a little power in standby mode. Exactly how much is an open question — as far as we know, nobody has looked at it in detail.

The fan slope was excellent. The fan speed didn't even start to increase until the intake temperature approached 40°C, during the 250W test point. The vast majority of systems fit into this power envelope, which means that the fan noise should stay low and constant no matter what load is placed on the system. Only very powerful gaming systems with dual graphics cards are likely to require more power — and even then the noise may still go unnoticed, as cooling of the components demanding over 250W total will probably require other fans (like the CPU fan, the case fan and the VGA fan) to be spinning at considerable speed and concomittant noise.

MP3 RECORDINGS

Each of these recording have 10 seconds of silence to let you hear the ambient sound of the room, followed by 10 seconds of the product's noise.

• Silverstone Element Plus ST50EF-Plus at 0~200W, 23 dBA@1m: One meter, One foot (30cm)
• Silverstone Element Plus ST50EF-Plus at 250W, 25 dBA@1m: One meter, One foot (30cm)
• Silverstone Element Plus ST50EF-Plus Squealing: +5VSB @ <0.3A: One meter, One foot (30cm)

• Seasonic S12-430 at 0~90W, 20 dBA@1m: One meter, One foot (30cm)
• Seasonic S12-500 at 0~90W, 21 dBA@1m: One meter, One foot (30cm)
• Antec NeoHE 430 at 0~90W, 20 dBA@1m: One meter, One foot (30cm)

CONCLUSIONS

Despite a few quibbles the Element Plus has proved itself a worthy product, with very strong fundamentals. It's well regulated, highly efficient, and didn't start to get noisy until 300W output. What's not to like?

We did mention a few quibbles... Yes, it is fairly quiet, but we know other power supplies that are quieter — we know that Adda's fans start reliably at voltages below 4.5V, so we would have liked to see that taken advantage of. Also, the odd squealing when the +5VSB line was underloaded may prove to be a problem... or it may just be a meaningless artifact of testing — we won't know until people start using the unit in real systems.

The high minimum load requirements — and the fact that we could readily ignore them — make us question just how meaningful the load specifications are. We are very thankful that these specifications did not seem to be hard-and-fast requirements, as a large number of systems would violate them.

All in all, the Element Plus is a big improvement over the last Silverstone power supply we looked at, especially in the acoustics department. The 80 Plus certification was suggestive, but our test confirms it: The Element Plus can stand with the best.

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SPCR Articles of Related Interest:
Power Supply Fundamentals & Recommended Units
Power Distribution within Six PCs
Desktop CPU Power Survey, April 2006
Silverstone Strider ST56F Power Supply
FSP Zen Fanless 300W Power Supply (80 Plus)
Enhance ENP-5136GH 360W PSU: A New 80 Plus Brand
Seasonic SS-400HT Power Supply, 80 Plus Version

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Much thanks to Silverstone for the opportunity to examine this power supply.

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