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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
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DC Output Load Regulation
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||||||||||
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Combined DC Load |
+3.3V
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+5V
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+12V
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+5VSB
|
-12V | |||||
|
A
|
V
|
A
|
V
|
A
|
V
|
A
|
V
|
A | V | |
|
88W
|
2.11
|
3.32
|
1.98
|
5.11
|
5.93
|
12.19
|
1.28
|
5.05
|
0.20 | -12.04 |
|
200W
|
5.92
|
3.26
|
4.89
|
5.08
|
12.07
|
12.14
|
1.28
|
5.03
|
0.25 | -12.05 |
|
340W
|
9.62
|
3.21
|
8.82
|
5.03
|
23.21
|
12.02
|
1.28
|
5.00
|
0.30 | -12.06 |
|
430W
|
9.61
|
3.19
|
8.85
|
4.93
|
30.12
|
11.87
|
1.28
|
4.97
|
0.40 | -12.08 |
| BeQuiet! Pure Power L8 430W CM | Maximum Load |
| 512W |
We pulled 512W from the unit before it would switch off. The overcircuit protection system worked fine and it shut off safely. Load regulation isn't the best we have seen, with quite a fluctuation on the +12V and +3.3V output. That said, nothing fails outside the rated safety parameters, so no problems here.
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 | 5.09 | 30.0 | 11.92 | 0.20 | -12.06 | 0.50 | 4.97 |
| 170W | 18.0 | 3.19 | 12.0 | 4.90 | 4.0 | 12.18 | 0.20 | -12.04 | 0.50 | 4.98 |
The BeQuiet! Pure Power L8 430W CM handled the Cross loading tests reasonably well, although we have seen better results in recent months.
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.
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ATX12V Ver 2.2 Noise/Ripple Tolerance
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|
|
Output
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Ripple (mV p-p)
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|
+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 |
| 88W | 5 | 10 | 10 | 5 |
| 200W | 10 | 15 | 15 | 10 |
| 340W | 10 | 15 | 25 | 15 |
| 430W | 10 | 20 | 35 | 20 |
Ripple results are excellent, peaking at only 35mV at full load. All output rails are well within rated tolerance levels, which is good to see.
|
Efficiency (%)
|
|
|
88W
|
84.34
|
|
200W
|
88.32
|
|
340W
|
87.23
|
|
430W
|
85.66
|
The supply reaches over 88% efficiency at 50 percent load, and this falls to just under 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
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Noise (dBA)
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|
|
88W
|
<28.0
|
|
200W
|
<28.0
|
|
340W
|
<28.0
|
|
430W
|
30.9
|
The BeQuiet! Pure Power L8 430W CM is a very quiet power supply which is barely audible, even at 400W load. The maximum noise emission we recorded was 30.9 dBa meaning this power supply is almost silent regardless of load.
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Temperature (c)
|
||
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Intake
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Exhaust
|
|
|
88W
|
35
|
38
|
|
200W
|
38
|
43
|
|
340W
|
43
|
48
|
|
430W
|
46
|
54
|
The large SilentWings fan helps to generate high levels of airflow across the components inside the chassis, with 8c above ambient registered at full load.
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Maximum load
|
Efficiency
|
|
512W
|
84.6
|
Pushing the PSU above its rated limits generates an efficiency level of around 84.6%. This is not a viable ‘real world’ situation, but its interesting nonetheless.
