Seasonic S12 Energy Plus: Efficient Power for Connoisseurs

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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 22°C and 17 dBA, 121V/60Hz.

The two models performed almost identically, so the data for the two units was amalgamated into a single set. The majority of the data presented below comes from our test of the 550W model. Data from the 650W test can be identified by the green background in the data table. Variations between the two tests are noted in the text where it is pertinent.

OUTPUT & EFFICIENCY: Seasonic S12 Energy Plus 550 / 650
DC Output Voltage (V) + Current (A)
Total DC Output
AC Input
Calculated Efficiency
+12V1
+12V2
+5V
+3.3V
-12V
+5VSB
12.23
0.98
12.21
1.75
5.03
0.00
3.41
0.99
0.1
0.2
38.8
56
68.8%
12.21
1.92
12.21
1.75
5.04
1.95
3.41
0.96
0.1
0.4
61.0
82
74.7%
12.20
1.91
12.18
3.33
5.02
2.88
3.40
2.78
0.1
0.5
91.4
116
78.6%
12.18
3.84
12.16
5.00
5.02
4.67
3.39
3.73
0.2
0.8
150.0
183
81.9%
12.19
6.64
12.17
4.98
5.04
6.38
3.42
4.56
0.3
1.1
198.4
234
84.8%
12.13
7.80
12.09
6.49
4.98
8.03
3.37
7.56
0.4
1.4
250.2
297
84.3%
12.10
7.80
12.06
9.65
4.97
9.75
3.35
7.59
0.5
1.6
298.6
355
84.1%
12.06
12.38
12.02
11.29
4.94
12.15
3.33
10.97
0.6
2.2
399.8
482
82.9%
12.02
16.01
11.98
14.34
4.92
14.23
3.31
13.28
0.7
2.7
500.2
616
81.2%
12.00
15.95
11.95
17.26
4.87
16.54
3.30
14.86
0.8
3.0
551.8
692
79.7%
11.98
20.93
11.98
18.90
4.91
18.90
3.30
16.11
1.0
3.0
650.1
820
79.3%
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.

OTHER DATA SUMMARY: Seasonic Energy Plus 550 / 650
DC Output (W)
38.8
61.0
91.4
150.0
198.4
250.2
298.6
399.8
500.2
551.8
Intake Temp (°C)
24
25
26
32
38
39
42
42
43
49
Exhaust Temp (°C)
26
27
29
37
46
51
52
54
56
63
Temp Rise (°C)
2
2
3
5
8
12
10
12
13
14
Fan Voltage (V)
3.8
3.8
3.8
3.8
3.8
3.9
5.6
9.9
11.3
11.3
SPL (dBA@1m)
20
20
20
20
20
20~21
25
38
40
40
Fan Voltage (V)
3.8
3.8
3.8
3.8
3.8
4.1
5.3
9.1
10.9
10.9
SPL (dBA@1m)
20
20
20
20
20
21
25
36
43
43
Power Factor
0.98
1.00
1.00
1.00
0.99
1.00
1.00
1.00
1.00
1.00
AC Power in Standby: 0.6W / 0.16 PF
AC Power with No Load, PSU power On: 11.3W / 0.43 PF
NOTE: The ambient room temperature during testing can vary a few degrees from review to review. Please take this into account when comparing PSU test data.

ANALYSIS

1. LOW LOAD PERFORMANCE

The half watt that the Energy Plus consumed in standby is small enough to be considered irrelevant. Taking power factor into consideration, the apparent power draw was just under 4VA — not enough to worry about.

No-load performance was also quite good. The power supply had no problem starting with no load, and the 11.3W it consumed is as good as any other we've seen. The PicoPSU is the only power supply we've seen that consumes less power with no load, and that has the advantage of using an external power brick as its power source.

For some reason, both Energy Plus samples generated a sharp electronic clicking when no load was applied. The noise seemed to be perfectly normal — the power supply remained fully functional both during and after the clicking, and both models exhibited it. The clicking went away as soon as more than 5W were applied to any combination of voltage lines, so it's more of a curiosity than anything to worry about. It is not possible to build a system that consumes that little power.

2. VOLTAGE REGULATION was very good. Both the +12V and +5V lines stayed within ±2% of nominal throughout testing. The +3.3V line was slightly less well regulated, showing a variance of ~4%. It should be noted that this greater variance may well be a mathematical artifact. In absolute terms, the line fluctuated by ~0.11V — slightly less than the ~0.12V variance displayed by the +5V line. However, because voltage regulation is measured as a percentage difference, the +3.3V line appears less well regulated.

All three of the main voltages hit the nominal voltage on the dot either at or just before full load. The largest variance was typically at the lowest loads, when all of the voltages were slightly higher than nominal.

3. EFFICIENCY

Efficiency is the raison d'être for the Energy Plus, and it didn't disappoint. Efficiency for both models peaked just shy of 85% at around 200W output. This is similar to the efficiency of the SS-400HT — the most efficient power supply we've tested — and marginally higher than the S12-500 and S12-600 samples we've tested in the past. Both models were above 80% efficiency at 20% and 50% load, but dipped a hair below 80% at full load. Most likely, the extremely tough thermal conditions of our test bench caused efficiency to drop more than it would in a properly cooled system. The margin is also within the error range of our test rig.

The 550W model was slightly more efficient (a percentage point at most) at low loads than the 650W version, while the 650W version maintained its efficiency closer to full load. Interestingly, at the low power levels that most systems idle at, the Energy Plus samples were not quite as efficient as certain other models that we've tested — including some of the original S12 models. The table below shows the efficiency of several Seasonic Power supplies at 65W output — a reasonable estimate of average power consumption.

Seasonic Power Supplies at 65W Output
Model
S12-330
S12-430
S12-500
SS-400HT 80+
SS-300SFD 80+
S12 Energy+ 550
Efficiency at 65W
75.5%
78.3%
75.1%
81.5%
83.6%
74.7%
Peak Efficiency
82.0%
81.8%
82.0%
85.3%
85.2%
84.8%

Of all the Seasonic power supplies that we've tested on our current test bench, the Energy Plus is the least efficient at 65W, which is not an unusual idle power level for minimalist systems today. The difference is not huge, especially discounting the two other 80 Plus power supplies which weren't widely available. The peak efficiency of the Energy Plus is higher than the regular S12 models, so it is at high loads in the high power systems in which a 550W PSU would be employed that the advantage of the Energy Plus models would become apparent.

4. POWER FACTOR was excellent as usual for Seasonic. For much of the test, our power meter measured a perfect 1.00 power factor.

5. TEMPERATURE & COOLING

Thermal performance was good at lower levels, and good enough at higher levels. The temperature rise across the power supply jumped up significantly at around 200W output — just before the fan ramped up. Beyond this point, the thermal rise stayed around 10~15°C, which is higher than Seasonic's past models. The thermal rise in the S12-600 was just 7°C at full load — half that of the Energy Plus.

The two models did not differ much in their cooling; the faster fan in the 650W model did keep it slightly cooler at higher fan speeds, but the difference was never more than two or three degrees, and the temperature rise barely changed at all.

6. FAN, FAN CONTROLLER and NOISE

One of Seasonic's biggest strengths has always been their fan controller, which ramps up more slowly and at higher loads than the competition. It's hard to imagine how this could be improved on, but somehow Seasonic has managed to go ahead and do it anyway. In the past, we have been impressed if the noise level stayed under 30 dBA@1m at 250W output — we've never encountered a power supply that stayed quiet above this level.

The Energy Plus shook loose our expectations and set a new standard for quiet: At 250W, the fan was just beginning to rise above its minimum level, and it did not exceed 30 dBA@1m until past the 300W mark. The medium and high speed fans in the different models sounded more or less identical until they speed up. Both were very quiet at minimum speed. As long as they weren't spinning too fast (most of the time), the fan noise was quite smooth and pleasant.

What this means is that the Energy Plus should be close to inaudible in almost every system. It is child's play to build a system into the 250W envelope that would never cause the Energy Plus to ramp up. The only systems that require more power than this either have multiple video cards or are heavily overclocked, usually both. Even then, it is difficult to push power consumption much above 300W — and systems that consume more than that inevitably have other fans that are not quiet.

Power Supply Fan Noise Vs. Power Output
Model
65W
90W
150W
200W
250W
300W
400W
Seasonic S12-330
21
21
22
30
35
37
Seasonic S12-430
20
20
22
25
29
32
37
Seasonic S12-500/600
21
21
22
25
28
34
39
Seasonic SS-300SFD-80+
22
22
25
30
34
38
Seasonic SS-400HT-80+
22
22
22
23
30
36
38
Seasonic S12 Energy Plus 550/650
20
20
20
20
21
25
38
Zalman ZM460-APS
22
23
26
29
31
34
37
Enermax Liberty
EL500AWT/EL620AWT
21
21
24
30
35
38
41

The table above does a good job of illustrating how the fan behavior of the Energy Plus differs from other Seasonic power supplies. All of the power supplies are similar at lower loads, but that is not where the Energy Plus finds its advantage. The real difference can be seen at the 250W and 300W marks. In both cases, the Energy Plus is 7 dBA@1m quieter than the next quietest model — a substantial and audible difference.

What this means is that, unless you're building a very powerful system, the acoustic advantage of the Energy Plus will be limited to differences at minimum speed — which are not huge. Yes, the Energy Plus is close to inaudible at minimum speed, but so are numerous other power supplies. It's not difficult to build a mid-range system into the 150W envelope where most of our past recommendations have remained quiet. Given the expense of the Energy Plus, it only really makes sense to use it in systems where its acoustic advantage will be noted: In very high powered systems.



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