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bequiet! Pure Power L8 400W Review


Additional technical assistance: Peter McFarland and Jeremy Price.

Correctly testing power supplies is a complex procedure and KitGuru have configured a test bench which can deliver up to a 2,000 watt DC load. Due to public requests we have changed our temperature settings recently – previously we rated with ambient temperatures at 25C, we have increased ambient temperatures by 10c (to 35c) in our environment to greater reflect warmer internal chassis conditions.

We use combinations of the following hardware:
• SunMoon SM-268
• CSI3710A Programmable DC load (+3.3V and +5V outputs)
• CSI3711A Programmable DC load (+12V1, +12V2, +12V3, and +12V4)
• Extech Power Analyzer
• Extech MultiMaster MM570 digital multimeter
• SkyTronic DSL 2 Digital Sound Level Meter (6-130dBa)
• Digital oscilloscope (20M S/s with 12 Bit ADC)• Variable Autotransformer, 1.4 KVA

DC Output Load Regulation

Combined

DC Load

+3.3V
+5V
+12V
+5VSB
-12V
A
V
A
V
A
V
A
V
A V
80W
1.57
3.34
1.81
5.05
4.83
12.11
1.00
5.02
0.20 -12.03
200W
2.85
3.31
3.62
5.03
13.65
12.00
1.00
5.01
0.30 -12.03
300W
4.94
3.31
5.68
5.02
20.50
11.94
1.50
5.01
0.30 -12.04
400W
3.98
3.26
4.66
4.99
29.32
11.88
2.00
5.00
0.50 -12.04
BeQuiet! Pure Power L8 400W Maximum Load
462W

We pulled 462watts from the unit before it shut down. The overcircuit protection system worked fine and it shut off safely. Load regulation seems reasonably good, and nothing troublesome was documented.

Next we want to try Cross Loading. This basically means loads which are not balanced. If a PC for instance needs 500W on the +12V outputs but something like 30W via the combined 3.3V and +5V outputs then the voltage regulation can fluctuate badly.

Cross Load Testing +3.3V +5V +12V -12V +5VSB
A V A V A V A V A V
385W 2.0 3.31 2.0 5.04 30.0 11.87 0.20 -12.04 0.50 4.99
170W 18.0 3.23 12.0 4.95 4.0 12.10 0.20 -12.03 0.50 4.98

We have seen better results in our Crossloading tests, however the results don’t cause concern.

We then used an oscilloscope to measure AC ripple and noise present on the DC outputs. We set the oscilloscope time base to check for AC ripple at both high and low ends of the spectrum. ATX12V V2.2 specification for DC output ripple and noise is defined in the ATX 12V power supply design guide.

ATX12V Ver 2.2 Noise/Ripple Tolerance
Output
Ripple (mV p-p)
+3.3V
50
+5V
50
+12V1
120
+12V2
120
-12V
120
+5VSB
50

Obviously when measuring AC noise and ripple on the DC outputs the cleaner (less recorded) means we have a better end result. We measured this AC signal amplitude to see how closely the unit complied with the ATX standard.

AC Ripple (mV p-p)
DC Load +3.3V +5V +12V 5VSB
80W 5 10 10 5
200W 10 15 15 10
300W 20 15 30 15
400W 25 20 45 15

Ripple results are very good, with all rails falling well within the rated tolerance levels.

Efficiency (%)
80W
84.42
200W
88.46
300W
87.45
400W
86.10

The supply reaches over 88% efficiency at 50 percent load, and this falls to just above 86% efficiency at full load. Good results for a 80 Plus Bronze certified product.

We take the issue of noise very seriously at KitGuru and this is why we have built a special home brew system as a reference point when we test noise levels of various components. Why do this? Well this means we can eliminate secondary noise pollution in the test room and concentrate on components we are testing. It also brings us slightly closer to industry standards, such as DIN 45635.

Today to test the Power Supply we have taken it into our acoustics room environment and have set our SkyTronic DSL 2 Digital Sound Level Meter (6-130dBa) one meter away from the unit. We have no other fans running so we can effectively measure just the noise from the unit itself.

As this can be a little confusing for people, here are various dBa ratings in with real world situations to help describe the various levels.

KitGuru noise guide
10dBA – Normal Breathing/Rustling Leaves
20-25dBA – Whisper
30dBA – High Quality Computer fan
40dBA – A Bubbling Brook, or a Refridgerator
50dBA – Normal Conversation
60dBA – Laughter
70dBA – Vacuum Cleaner or Hairdryer
80dBA – City Traffic or a Garbage Disposal
90dBA – Motorcycle or Lawnmower
100dBA – MP3 Player at maximum output
110dBA – Orchestra
120dBA – Front row rock concert/Jet Engine
130dBA – Threshold of Pain
140dBA – Military Jet takeoff/Gunshot (close range)
160dBA – Instant Perforation of eardrum

Noise (dBA)
80W
<28.0
200W
<28.0
300W
<28.0
400W
30.4

The BeQuiet! Pure Power L8 400W is barely audible at all, even under load. We really do love the SilentWings fans, they are some of the best fans that money can buy. The BQT T12025-MS-16 fan in this unit spins very slowly, even at full load.

Temperature (c)
Intake
Exhaust
80W
35
37
200W
38
44
300W
43
49
400W
47
58

The large SilentWings fan helps to generate high levels of airflow across the components inside the chassis, with 11c above ambient recorded at full load.

Maximum load
Efficiency
462W
84.9

Pushing the PSU above its rated limits generates an efficiency level of around 84.9%. This is not a viable ‘real world’ situation, but its interesting nonetheless.

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