Antec EarthWatts 430: Green Computing Hits Mainstream

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.

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 21°C and 19 dBA. AC input was 117V, 60Hz.

ANALYSIS

1. EFFICIENCY was excellent, as we expected of an 80 Plus certified unit. However, we were a little surprised that it missed the 80% mark at both 20% and 100% load. To be sure, it didn't miss by much, but it was a surprise nonetheless. A second sample that we tested proved to have similar efficiency.

2. VOLTAGE REGULATION was excellent; by our usual tests, none of the lines fluctuated by more than 2%, and the +12V and +3.3V lines were within 1% of nominal throughout the test.

Things got more interesting when we tried our Crossload Test: Full load on the +12V lines (30A) and a token 2A on each of the +5V and +3.3V lines. This is a new test, and is designed to push the voltage regulation to its limits and better simulate the kind of unbalanced load that a real system might to have. The Earth Watts had no problem staying within spec though — the +12V line regulation sagged to -4% of nominal, and the +5V line jumped up to its highest level during the test. The +3.3V line did not appear to be affected by the cross loading, and stayed unchanged at 3.32V.

3. RIPPLE

Ripple was also tested, and remained uniformly excellent under every condition that was tested. The worst ripple occurred during the cross loading when the +12V ripple peaked at 4.6 mV. To put that in perspective, the ATX12V requires +12V ripple to be below 120 mV. The Earth Watts has more than a little headroom in this respect. Ripple on the other lines was similarly low, and fluctuated very little no matter how the power supply was loaded.

+12V ripple (left) was ~3.0 mV, and +5V (right) ripple was ~3.0mV, both measured at 150W.

+3.3V ripple at 150W output was ~2.5 mV.

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

5. LOW LOAD PERFORMANCE

Standby and no-load performance were both reasonably efficient, with standby coming in well under one watt, and no-load at a little under ten. The Earth Watts had no issues starting or staying on with no load applied.

6. LOW AC VOLTAGE PERFORMANCE

The power supply was set to about 75% load with 120VAC through the hefty variac in the lab. The dial on the variac was then set 10V lower every 10 minutes. Since most power supplies are only rated for operation at 100~240VAC, our test calls for a minimum input voltage of 90VAC. However, in this case, we pushed it down to 80VAC.

The Earth Watts stood up to the drops in AC voltage admirably, even when operating well below its rated input voltage of 100V. Neither voltage regulation nor ripple changed measurably during the test, and efficiency dropped only marginally under the most severe conditions.

I must admit that the adolescent boy in me was a little disappointed when the Earth Watts showed no visible stress in this test. The last time we played with low AC voltages we had some fireworks: One unit shut down as soon at the voltage dropped to 100V; another sparked and failed entirely!

To be fair, these earlier tests were done at 100% load, but we were pleased to find that the Earth Watts was quite happy to keep running indefinitely even with the voltage dropped to 80V!

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