Archive: SPCR's PSU Test Platform V.3

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NEW MEASURED DATA REPORTS

We've been able to present all the measured data in our PSU reviews in a single table thus far. This is no longer practical, given the additional data we wish to include. So changes have been made. The new test data for the Seasonic SS-400HT PSU which we've been referring to all through this article will be used to guide you through the new presentations. For many readers, it will be self-explanatory.

1) Output & Efficiency

This table lays out the AC input required to achieve a given target DC Output, and the Voltage and Current measured for each output line on the PSU.

OUTPUT & EFFICIENCY: Seasonic SS-400HT Active PFC F3
DC Output Voltage (V) + Current (A)
Total DC Output
AC Input
Calculated Efficiency
+12V1
+12V2
+5V
+3.3V
-12V
+5VSB
12.10
0.99
12.10
1.67
5.00
1.01
3.31
0.99
0.1A
0.1A
42.1W
55W
76.6%
12.10
1.92
12.10
1.67
5.00
2.10
3.31
2.11
0.1A
0.3A
63.6W
78W
81.5%
12.10
1.92
12.10
3.22
5.00
2.85
3.31
2.84
0.2A
0.4A
90.2W
109W
82.8%
12.10
3.88
12.10
4.96
4.96
4.78
3.25
4.69
0.3A
0.8A
153.5W
180W
85.3%
12.10
5.81
12.10
4.96
5.00
7.21
3.21
7.40
0.3A
0.8A
197.2W
231W
85.3%
12.05
7.81
12.05
6.69
4.92
7.21
3.19
8.78
0.5A
1.4A
251.2W
298W
84.3%
12.05
8.68
12.05
8.00
4.92
9.80
3.19
10.50
0.6A
1.6A
297.9W
355W
83.9%
12.00
11.60
12.00
11.10
4.90
13.70
3.19
14.40
0.6A
1.7A
401.3W
486W
82.6%

NOTE: The current and voltage for -12V and +5VSB lines is not measured but based on switch settings of the DBS-2100 PS Loader. It is a tiny portion of the total, and potential errors arising from inaccuracies on these lines is <1W.

Voltage at specific Current loads are reported for each line. Note that the required tolerance for voltage is °5% on the 12V1, 12V2, 5V and 3.3V lines. The -12V and 5VSB lines are much less critical and only need °10%.

DC Output is obtained by multiplying the measured voltage and current to obtain the power for each line, then adding them all up. Our standard power output targets are 40W, 65W, 90W, 150W, 200W, 250W, 300W. Above that range, the targets will go up by increments of 100W or 150W, depending on the rating of the PSU. The actual DC output will usually not be right on target because of the effect of voltage variances and the limited steppings in our PSU loading system. This is unavoidable, but we will strive to get within 5~10W of the target output.

AC Input is taken directly from the Seasonic Power Angel or Kill-a-Watt AC power meter that goes between the wall AC outlet and the PSU AC plug. These AC power meters are probably made by the same manufacturer, judging by the features and overall look and feel. The accuracy is typically 0.5%.

Efficiency is DC Output as a proportion of AC Input: DC Output ° AC Input x 100%. The difference between input and output power is the heat generated within the PSU during the AC:DC conversion process. It's useful to think about efficiency inversely. The difference between a 70% efficient PSU and one that's 80% doesn't seem big, but 30% of AC input being converted to heat compared to 20% is very substantial. For a system that draws 200W, a 70% efficient PSU will generate 85W of heat. An 80% efficent PSU will only generate 50W of heat. That 35W of heat is nothing to scoff at. Assuming efficiency is the only difference, the 80% PSU will run cooler with the same airflow. Alternately, less airflow will be required to keep it at the same temperature as the first, which means lower noise ° and this acoustic result is the primary reason for our interest in high efficiency. For fanless PSUs, high efficiency is mandatory.

2) Other Data Summary

This table summarizes all the other data measured at each power level. The procedure for collection of this data remains unchanged from before.

OTHER DATA SUMMARY: Seasonic SS-400HT Active PFC F3
DC Output (W)
42.1
63.6
90.2
153.5
197.2
251.2
297.9
401.3
Intake Temp (°C)
25
28
30
34
35
39
41
46
Exhaust Temp (°C)
26
30
32
36
38
43
46
51
Temp Rise (°C)
1
2
2
2
3
4
5
5
Fan Voltage
3.8
3.8
3.8
3.9
5.1
7.4
9.3
11.0
SPL (dBA@1m)
22
22
22
22
23
30
36
38
Power Factor
0.96
0.99
0.99
0.98
0.99
0.99
0.99
0.99

NOTE: The ambient room temperature during testing varies a few degrees from review to review. Please take this into account when comparing PSU test data.

Intake Temp is the air temperature measured at a point 1" below and 1" behind the PSU in its mounted position in the thermal simulation box. If the ambient temperature is kept the same, this temperature should be affected primarily by the output power of the PSU. The heat is rising up from the PSU resistive banks that are being loaded. If 200W is the load, the same amount of heat is in the thermal simulation box regardless of PSU. The intake temp reading will be slightly affected by the airflow of the test PSU fan, and by the airflow created by the exhaust fan on the "back panel" of the thermal simulation box. If the airflow generated by the PSU is higher or lower than usual, this will show up as a correspondingly lower or higher intake temp.

Here's is an interesting observation: Looking back at the PSU review data over the past 2 years, if the temp data is "normalized" to the typical ambient temp of 21°C, the intake temp is 30~31°C at 150W load for nearly all fan-cooled PSUs we considered to be quiet. Naturally these had lower airflow. The noisier PSUs have lower intake temps at this load, as low as 26°C. The noise level varies from a low of 20 dBA@1m to a high of over 32 dBA@1m.

Exhaust Temp is the air temperature measured directly at the hottest point of the back exhaust panel of the PSU. This temp is affected by all the factors that affect Intake Temp, plus the amount of heat produced within the PSU (the inverse of efficiency) and the efficacy of the PSU's cooling system. The latter includes the size, shape and design of the heatsinsk as well as the fan and fan controller.

Temp Rise (°C) is the difference between Intake and Exhaust temps. It tells us in a single number the aggregate effects of efficiency and the PSU cooling system. Lower is better, especially in combination with low SPL.

Fan Voltage is the voltage measured across the PSU fan(s) teminals. It usually varies with temperature and load. It is a very good indicator of noise at a given power output load, and tells us how important forced airflow is for cooling in a given PSU design.

SPL is the sound pressure level measured in decibels (A-weighted) from a distance of 1 meter, at a slight angle behind the back panel of the PSU. This number is never complete by itself. It should be considered together with the text about the quality of the noise and the noise recordings made at specific levels.

Power Factor is taken directly from the Seasonic Power Angel or Kill-a-Watt AC power meter the test PSU is plugged into. Note that power factor has nothing to do with efficiency. For details on PF, please read page 5 of the article, Power Supply Fundamentals & Recommendations.

The ambient noise and temperature during testing are always noted separately in the accompanying text, along with AC voltage. We are lucky that the AC electricity supply here in Vancouver is extremely stable. I have never seen it go higher than 121V or lower than 118V.

UPDATING EXISTING PSU REVIEWS

Some of the questions that will be on readers minds... and answers to those questions.

1) What is the real efficiency of the PSUs you have already tested?
In general, most of the efficiency figures for power levels up to about 250W are only very slightly too high. It's the reported efficiency for 300W and higher that are more seriously affected.

2) Can reported efficiency for future PSU reviews be fairly compared to that from existing reviews?
Not for power levels above ~250W, as noted above. We are tackling this issue by running new efficiency tests on all the PSUs we have on hand that are still in production and on the recommended PSU lists. The revised data will be reported in a separate article, and links to this new article will be posted in all the older PSU reviews.

3) Are any of the other results affected, in particular the analysis and data regarding noise? How about their relative rankings for noise or efficiency?
No and No. The noise profile for each tested PSU remains unchanged. The rankings in the Recommended PSU lists are unchanged, not for efficiency nor for noise. The main issue is that the power load was slightly lower than what we reported it to be at the various test points, which is why the reported efficiency numbers were affected. As we've mentioned many times in the PSU reviews, noise levels are more directly tied to PSU intake temperature than to power output; the relationship between intake temperature and noise remains unaffected by our new findings.

It's pertinent to note that the biggest errors in efficiency measurements occurred at very high output power levels that will rarely be reached by the vast majority of desktop systems.

CONCLUSION

Testing equipment and procedures require routine maintenance and calibration, especially when errors are noted. They also require updating when the primary target specifications of the tested products change significantly. This article described major changes made to the equipment and procedures used in the SPCR power supply testing system. The work was done in the spirit of continuous self-improvement in order to provide accurate and realistic assessment of PC products for noise-conscious consumers. I expect it to be but one of many steps in our ongoing quest.

* * *

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