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TEST METHODOLOGY
| Parameters |
Tools |
| DC load on PSU |
DBS-2100 PSU load tester |
|
Ambient temperature
|
Any number of thermometers |
|
Fan voltages / Voltage regulation
|
Heath / Zenith SM-2320 multimeter |
|
AC power
|
Kill-A-Watt Power Meter |
|
Noise
|
Heath AD-1308 Real Time Spectrum Analyzer |
The core PSU test tool on SilentPCReview's test bench is the DBS-2100 load tester, made (in Taiwan by D-RAM Computer Company) specifically for testing computer power supplies. The machine consists of a large bank of high power precision resistors along with an extensive selection of switches on the front panel calibrated in Amps (current) and grouped into the 5 voltage lines: +5, +12, -12V, +3.3, -5, +5SR. Leads from the PSU connect into the front panel. It is shown above with leads from a PSU plugged in.
To ensure safe current delivery, the DC output connector closest to the PSU on each set of leads is hooked up to the load tester. This ensures that the current delivered is distributed to as many short leads as possible. When pushing a PSU to its rated output, the heat generated in the wires can be an issue.
The PSU is tested at 4 DC output power levels:
- 22.5W: The total of the minimum load that can be applied on each voltage line.
- 90W: Established previously as a typical max power draw of a mid-range desktop PC.
- 150W: For higher power machines.
- Maximum: The rated maximum power of the PSU.
Care is taken to ensure that the load on each of the voltage lines exceed the ratings for the tested unit. The PSU is left running at least 10 minutes at each power level before VR measurements are made several times.
The DBS-2100 is equipped with 2 individually fused AC outlets and 4 exhaust fans on the back panel. A switch allows the the fans to be turned off for noise measurements. The resistors get very hot under high loads.
Kill-A-Watt AC Power Meter is plugged into the AC outlet on the side of the DBS-2100 in the above picture. The AC power draw of the PSU is measured at each of the 4 power loads. The efficiency of the PSU at each power level is calculated thus: divide DC power output by AC power consumption. It always varies with load, and also temperature. PSUs seem to run more efficiently when warmer, up to a point.
The Heath / Zenith SM-2320 multimeter, a fairly standard unit, is used to measure fan output voltages and the line voltages of the PSU output. The latter is done via terminal pins on the front panel of the PSU tester. It somewhat simulates voltage readings off the wiring on the motherboard.
Note: The most "pure" voltage output reading is obtained on PSU output connectors that are not connected; this bypasses the resistance of the wires and the connectors and tells you exactly what the output DC voltages are as it leaves the PSU. However, it is a somewhat artificial measurement as the cables and connectors are part of the PSU as well.
The Test Lab is a spare kitchen measuring 12 by 10 feet, with an 8 foot ceiling and vinyl tile floors. The acoustics are quite lively. The PSU under test is placed on a piece of soft thick foam to prevent transfer of vibrations to the table top. Temperature in the lab is usually ~20C.
In-case Thermal Simulation
Sited next to the CPU, the PSU is always subject to external heat. The low ambient temperature of the test lab explains why the fan in the Nexus NX3000, for example, never reached 12V during testing, even at full power output for over 20 minutes. I have applied a solution first suggested by contributor John Coyle after the publication of his article, Fanless (or Not) with TKPower 300 & VIA C3. Thanks, John!
The solution is a 100W AC bulb in an empty case with the PSU mounted normally. The distance between the bottom of the PSU and the top of the bulb is about 7-8 inches. All the case back panel holes are blocked with duct tape. The only significant exit for the hot air in the closed case is the PSU, which is then subject to a fair amount of heat, probably a bit more than would be seen by a PSU in a real case because there are usually other air exits. The bottom front panel case intake hole is very large. In testing, the front of the case is moved so it hangs over the edge of desk, over free air, to ensure good fresh convection airflow. There are no case fans.
A thermistor taped to the bottom of the PSU close to its right front is used to monitor temperature. It's the little blue nub hanging down off the black wire in the photo above. Its temperature is somewhat affected by the airflow of the PSU fans but not directly in the airflow path.
The simulation means the PSU must cope with the 100W of heat generated by the light bulb plus whatever heat it generates within itself. It is a good simulation when the PSU is actually putting out ~100W of DC voltage, although in real-life systems, there would be other air exhausts paths, resulting in a bit lower case temperature.
No PSU Temperature Measurements were made. Discussions in the SPCR forums have convinced me that there are far too many variables at play to make internal PSU temperature a reliable gauge of... anything. There are way too many ways to interpret the numbers. Check this thread for the full discussion. The most critical parameter for thermal performance is efficiency. If efficiency is high, the size of the heatsinks and vent openings large, and the fan can blow a lot of air at full power, then excellent cooling is ensured.
Noise Measurements
The Heath AD-1308 is a portable half-octave Real Time Spectrum Analyzer with sound level meter (SLM) functions. Below 40 dBA, its accuracy is poor, limited to 3 dB increments, down to ~30 dBA. Some 15 years old, this LED-based unit has long since been displaced by digital devices with better interfaces to PCs. The "A" weighting was used; it most closely approximates the frequency response characteristics of human hearing.
The microphone on the sound meter is positioned about a centimeter to the side of the PSU fan exhaust to avoid fan turbulence in the microphone itself. The dBA obtained here cannot be compared to any other measurements due to the lack of adherence to a repeatable standard and the uncontrolled reflective environment.
The noise measurements are always accompanied by descriptions of subjective perceptions. Without these, the measurements, which are not that reliable, provide only part of the picture.
TEST RESULTS
Measurements were made at 4 power levels: 22.5W, 90W, 150W, and 300W. The unit was allowed to run for at least 10 minutes at each power level before measurements were taken. The room temperature was 20C.
| LOAD |
22.5W
|
VR
|
90W
|
VR
|
150W
|
VR
|
300W
|
VR
|
| +5V |
5
|
+5%
|
20
|
+4%
|
40
|
+3%
|
80
|
+2%
|
| +12V |
12
|
+1%
|
36
|
+4%
|
60
|
+2%
|
144
|
+2%
|
| -12V |
1.2
|
NA
|
3.6
|
NA
|
4.8
|
NA
|
4.8
|
NA
|
| +3.3V |
3.3
|
+2%
|
26.4
|
+2%
|
39
|
+1%
|
65
|
-1%
|
| -5V |
0.5
|
NA
|
2
|
NA
|
2
|
NA
|
2
|
NA
|
| +5VSR |
0.5
|
NA
|
2
|
NA
|
4
|
NA
|
4
|
NA
|
| AC Power |
42W
|
138W
|
227W
|
463W
|
| Efficiency |
53.4%
|
65.2%
|
66.1%
|
64.8%
|
| V Fan |
7.4
|
9.4V
|
10.7V
|
12.1V
|
| Noise (~1 cm) |
43 dBA
|
47 dBA
|
48 dBA
|
48 dBA
|
| Case Temp |
30C
|
31C
|
32C
|
34C
|
VR Under all normal loads (above the 22.5W minimum), the voltage regulation remained within +4%, -1%, which is within the recommended ATX spec. It was consistently a touch high. This may be deliberate to offset the effects of contact wear or increased resistance outside the PSU.
Efficiency never reached above 66% in any of the tests. It is somewhat lower than other models tested here. Most reach at least 70% at some power level during the tests.
V Fan: The voltage to the fan started at ~7V and climbed quickly to 7.4V while idling. At the 90W, the long term power level above which the mid-range PCs in the test lab do not normally reach, the fan voltage rose to 9.4V. This is considerably higher than most noise-reduced PSU models tested thus far. The measured fan noise difference between the 90W output level and full power output was only 1~2 dBA.
Noise was measured ~1 cm from the edge of the PSU fan exhaust, not in the airflow path. In idle operation the High Power HPC-300-102 measured some 3-4 dBA higher than the 1-fan Zalman and Seasonic models, and 3 dBA quieter than the 2-fan Antec TruePower models. At the 90W level, its noise level remained 3-4 dBA louder than the quieter 1-fan models, and actually a bit louder than the 2-fan Antecs.
The dBA measurement cannot differentiate between different types of noises: aside from the whooshing noise of the fan air turbulence, there was also a significant amount of coil hum and whine which could be heard as components of the overall sound, at idle and at the 90W power output level. Stopping the fan made these noises plainly audible.
Case Temp rose by 4C between 90W and 300W, suggesting adequate cooling. The temperature rise would be higher if the light bulb wattage was changed to match the output power at all times.
CONCLUSIONS
The High Power HPC-300-102 provides fine power performance on the test bench, with voltage regulation well within specifications even at sustained maximum output. Its efficiency is a bit lower than usual, which may not bode well for longevity, as more input energy is wasted as heat.
It is the noise performance, however, that leaves most to be desired. Both fan noise, and internal electronic whining and humming noises are significantly higher than with any of our Recommended PSUs. Its noise performance does not make it a good choice for a quiet computing enthusiast. Given the increasing number of quiet PSUs, there are better options for powering a quiet computer.
High Power has many other models in its lineup and it may be that the two samples obtained are not representative of their best. Perhaps we will have a chance to see better efforts from them in the future.
Much thanks to High Power for the review samples.
* * * * *
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