The ePower Tiger 550: Hot & Quiet

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. 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 22°C and 20 dBA, 122V/60Hz.

ANALYSIS

1. VOLTAGE REGULATION was so-so. With the exception of the full load test, all voltages remained within the ±5% specified by ATX12V, although the +3.3V line was very close to being more than 5% high in the lower output range. The +5V line was also quite high. At full load, the Tiger overheated and was unable to regulate its voltages properly. The test was halted when the +12V line reached 11.3V — more than 6% from nominal. The voltage was visibly falling at a rate of roughly 0.02 volts per second at the time when we stopped the test.

Even prior to the meltdown at full load, the fluctuation between the highest and lowest measured voltages was quite high, changing by 3% for the +12V lines and as much as 5% for the lower voltage lines.

2. EFFICIENCY was average through the lower output range; it managed to peak above 80% when the output hit 250W. In general, though, efficiency was nothing special, remaining in the 70~80% range through most of the tests. Efficiency dropped sharply after it hit its peak, perhaps because it began to overheat. In a better cooled system, efficiency might have remained higher for longer.

3. POWER FACTOR

The Tiger comes with passive power factor correction, so the power factor was generally slightly higher than it would have been without it. However, many high-end power supplies now use active power factor correction, which is usually capable of achieving a power factor of at least 0.95.

4. TEMPERATURE & COOLING

Cooling proved to be quite good at lower output levels but inadequate under heavy load. The thermal rise across the power supply stayed below 5°C through most of the lower test points. Some kind of threshold was reached at 200W, as the temperature rose sharply and the fan quickly increased in speed to keep up. But, even with this additional cooling, the temperature continued to rise, culminating in a thermal overload as noted above.

It should be mentioned that, while our test bed is quite realistic at normal power levels, it is unrealistic to expect any power supply to be the primary source of cooling in a (hypothetical) system that draws 500 watts. At higher levels, the test bed provides a punishing thermal environment that is tougher than any real system.

5. FAN, FAN CONTROLLER and NOISE

The residual noise level of the Tiger was not very good. At 23 dBA@1m, it was far from loud, but certainly not as quiet as the best units we've seen. Subjectively, it was very easy to notice it, as it had a distinct whine and a low drone underneath. The resulting two-pitch harmony was far more irritating than the noise measurement suggests.

On the other hand, it took a lot of effort to force the noise level to increase. The fan did not increase in speed until the output reached 250W (!) and the internal temperature had reached a toasty 37°C. Even then, it remained reasonably quiet until the internal temperature had climbed another 5°C — well above 300W output.

The practical result of all this is that, at high loads, the Tiger may well be the quietest fanned power supply we've tested, but it is also not cooled well enough to give it much more than a half-hearted recommendation.

CONCLUSIONS

The ePower was a very mixed bag, with some things that we liked a lot (quiet even above 250W output) and some things that we didn't like (thermal meltdown).

Let's start with the goods: It's flashy, so it will look good in a showpiece. It has a shiny, reflective finish, and nicely sleeved cables, some of which can cut down on EMI. It also has intelligently designed detachable cables that are unlikely to lead to user error.

Although it is comparatively quiet at higher loads, the low noise comes at the cost of good cooling and reliability. In addition, its good performance under high loads needs to be put into perspective to understand how the Tiger will perform in an actual system:

1. Very few systems can sustain an output of even 200W. Only fancy gaming systems with dual VGA cards and possibly dual processors require this much power.
2. Unless the system is water-cooled, there will likely be other sources of noise that are louder than the power supplies. In particular, hot graphics cards are very challenging to cool quietly, and may well be a more significant source of noise than any power supply

On the bad side of things, the electronics are quite pedestrian. Efficiency and power factor are average, and voltage regulation is only so-so. But, the real kicker is the cooling: The internal heatsinks just aren't good enough. While it may be quiet under heavy load, it isn't well cooled enough to trust it for anything mission critical. In addition, the sleeve bearing fan is unlikely to last long in such a harsh environment.

Despite its acoustic performance, we can't really recommend the Tiger except in very limited circumstances. It's best suited for use in a high-end showpiece, where it needs to look good and sound quiet, but long-term reliability is not an issue, either because it is frequently upgraded or because it is used solely for gaming.

In the end, our feelings about the Tiger are much the same as those for its semi-fanless cousin, the Lion: Quiet it may be, but even low noise can't save it from the rest of its shortcomings, especially since the low noise comes at the cost of proper cooling.

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Much thanks to ePower Technology 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
ePower Lion EP-450P5-L1: Semi-Fanless PSU from ePower
Seasonic S12-430: Our current low-noise champ
Seasonic S12-500/600 Rev. A2

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