bequiet! Dark Power Pro 10 550W Power Supply

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TESTING

For a fuller understanding of ATX power supplies, please read the reference article Power Supply Fundamentals. Those who seek source materials can find Intel's various PSU design guides at Form Factors.

SPCR's PSU Test Platform V4.1. is the basic setup for the testing. It is a close simulation of a moderate airflow mid-tower PC optimized for low noise. There is one major change: The primary testing is done with the PSU NOT inside the hotbox but atop it, out of the heat path. This is in recognition of several realities that prevail today:

  • In SPCR's earlier test platforms, the internal temperature varied proportionately with output load. The tested PSU was subject to this heat, and operating ambient temperature rose with increased load, reaching >40°C and often much higher at full power. This was a realistic simulation of a mid-tower PC case where the PSU is mounted conventionally at the top back portion of the case.
  • The vast majority of "serious" PC cases for the home builder place no longer position the PSU at the top back corner. They put the PSU at the bottom/back corner, mostly out of the path of heat from the other components in the case. This design concept took root with the Antec P180 going back over 5 years, and dominates the DIY case arena. This means the PSU generally has to dissipate only its own heat.

Now, we've reversed our approach: The PSU is tested briefly in the hotbox only to check what happens to noise, fan speed and temperatures when it is used in an outmoded case design.

Acoustic measurements are performed in our own anechoic chamber with ambient level of 11 dBA or lower, with a PC-based spectrum analyzer comprised of SpectraPLUS software with ACO Pacific microphone and M-Audio digital audio interfaces.

REAL SYSTEM POWER NEEDS: While we test the PSU to full output 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 40W and 300W, because it is the power range where most systems will be working most of the time. It is true that very elaborate systems with the most power hungry dual video cards today might draw as much as another 150~300W, but the total usually remains under 600W.

TEST RESULTS

The ambient temperature was ~22°, and the ambient noise level was ~10 dBA. The DPP 10 550W was tested with all of its 12V lines combined into a single line.

Test Results: bequiet! Dark Power Pro 10 550W
DC Output (W)
AC Input
(W)
Heat loss
(W)
Efficiency %
Power Factor
Exhaust
SPL* (dBA@1m)
21.4
33
11.6
65.0
0.96
24°C
<11
39.3
52
12.7
75.6
0.98
24°C
<11
63.7
79
15.3
80.6
0.99
25°C
<11
92.2
109
16.8
84.6
1.00
26°C
<11
151.7
174
22.3
87.2
1.00
28°C
<11
200.0
223
23.0
89.7
1.00
29°C
<11
250.8
280
29.2
89.6
1.00
31°C
<11
299.7
334
34.3
89.7
1.00
34°C
<11
400.5
439
38.5
91.2
1.00
38°C
12
499.6
558
58.4
89.5
1.00
41°C
13
550.0
618
68.0
89.0
1.00
41°C
15
Crossload Test
(1A on 5V and 3.3V lines; the rest on 12V line)
459.0
515
56.0
89.1%
1.00
33°C
21
+12V Ripple (peak-to-peak): <10mV @ <350W ~ 25mV @ 550W
+5V Ripple (peak-to-peak): <6mV @ <350W ~ <13mV @ 550W
+3.3V Ripple (peak-to-peak): <7mV @ <3500W ~ <16mV @ 550W
AC Power in Standby: 0.4W
AC Power with No Load, PSU power On: 10.5W / 0.68PF
* See text discussion about noise.


1. EFFICIENCY This is a measure of AC-to-DC conversion efficiency. The ATX12V Power Supply Design Guide recommends 80% efficiency or better at all output power loads. 80% efficiency means that to deliver 80W DC output, a PSU draws 100W AC input, and 20W is lost as heat within the PSU. Higher efficiency is preferred for reduced energy consumption and cooler operation. It allows reduced cooling airflow, which translates to lower noise. The 80 PLUS Gold standard requires 87% efficiency at 20% load, 90% efficiency at 50% of rated load, and 87% efficiency at full rated load.

At the super low 20W load, efficiency was low at 65% but rose fairly quickly as the load was increased. 80% efficiency was reached around 65W. This sample probably did not quite reach 87% at 20% of rated load (130W); it was 87.2% at 150W. At 50% load, it fell just about 0.3% short of 90%, but easily exceeded the required 87% efficiency at full load. I did not test at higher loads, but the curve had the look of a PSU which might actually produce significantly higher than rated power, as peak efficiency of >91.2% was reached at a fairly high 400W, or 73% of rated power. It's more common to see the peak efficiency a little bit lower, perhaps at 60%. I would call it a borderline pass on 80 PLUS Gold — if I was more confident that my Frankensteinish PSU tester was accurate to that kind of tolerance.

There was no issue with crossloading. With over 90% of a 428W load on 12V, naturally, efficiency improved over the standard loading.

2. VOLTAGE REGULATION refers to how stable the output voltages are under various load conditions. The ATX12V Power Supply Design Guide calls for the +12, +5V and +3.3V lines to be maintained within ±5%.

The critical 12V line was very tightly regulated. It started a touch high at very low load, +0.06V (+0.5%). It dropped gradually as load was increased, reaching a low of 11.96V (-0.4%) at full power. The 5V line was similarly tight, starting at 5.04V (+0.8%) and dropping down to 4.95V (-1%) at full load. 3.3V ranged from 3.36V to 3.28V (+1.8% to -0.6%). This is as good as the best voltage regulation I've encountered.

3. AC RIPPLE refers to unwanted "noise" artifacts in the DC output of a switching power supply. It's usually very high in frequency (in the order of 100s of kHz). The peak-to-peak value is measured. The ATX12V Guide allows up to 120mV (peak-to-peak) of AC ripple on the +12V line and 50mV on the +5V and +3.3V lines. Ripple on all the lines was excellent at all power levels, staying under 10mV on 12V at all power levels up to around 350W, and only reaching 25mV momentarily at full load only. The lower voltage lines ran about half that amount of ripple. This is excellent.

4. POWER FACTOR is ideal when it measures 1.0. In the most practical sense, PF is a measure of how "difficult" it is for the electric utility to deliver the AC power into your power supply. High PF reduces the AC current draw, which reduces stress on the electric wiring in your home (and elsewhere up the line). It also means you can do with a smaller, cheaper UPS backup; they are priced according to their VA (volt-ampere) rating. Power factor was very good for this model, running 1.0 through most of the loads.

5. LOW LOAD TESTING revealed no problems starting at very low loads. Our sample had no issue starting up with no load, either, but the power draw of 13.3W was a little higher than most recently tested PSUs. The 0.4W power draw in standby (power switch on but computer off) is very commendably low.

6. LOW & 240 VAC PERFORMANCE

The power supply was set to 428W load at various AC input voltages. Most full-range input power supplies achieve 2~3% higher efficiency with 220~240 VAC, compared to 110~120 VAC. SPCR's lab is equipped with a 240 VAC line, which is used to check power supply efficiency for the benefit of those who live in higher mains voltage regions. We also used a hefty variac to check the stability of the PSU under brownout conditions where the AC line voltage drops from the 120V norm.

Various VAC Inputs:
bequiet! Dark Power Pro 10 550W
VAC
AC Power
DC Output
Efficiency
243V
457W
428W
93.7%
120V
473W
90.5%
100V
478W
89.5%

Efficiency improved to nearly 94% at 240VAC. The sample passed the 100VAC minimum input load without any issues, with a 1% drop in efficiency. Neither voltage regulation nor ripple changed appreciably during these tests.



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