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PC Power & Cooling Silencer MK III 750W 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
• Extech digital sound level meter
• 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
75W
1.23
3.38
1.19
5.05
4.95
12.25
0.50
5.04
0.20
-12.07
150W
2.17
3.36
2.83
5.03
10.07
12.18
1.00
5.03
0.30
-12.08
375W
6.15
3.36
6.05
5.02
26.15
12.13
1.50
5.02
0.50
-12.10
565W
10.31
3.33
10.86
5.00
38.34
12.07
2.00
5.01
0.60
-12.12
750W
10.72
3.31
13.84
4.97
53.59
12.03
3.00
5.00
0.80
-12.13

Regulation is very good, all rails hold close to reference figures at full load.

PC Power & Cooling Silencer MK III 750W Maximum Load
823W

We managed to reach around 823W before the unit would shut down gracefully, after the protection kicked in.

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
734W 1.0 3.36 1.0 5.03 60.0 11.97 0.2 -12.03 0.50 5.03
154W 15.0 3.34 15.0 4.95 2.0 12.18 0.2 -12.01 0.50 5.02

The unit passes our Cross Load testing with a set of very good results. Even when we hit the +12V output with 60A, the line held at 11.97V.

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
75W 10 15 15 10
150W 10 15 15 15
375W 10 20 25 15
565W 15 20 35 15
750W 15 20 40 20

Ripple results are good, and all well within rated tolerance levels. The +12V output peaked at 40mV at full load which is an excellent result.

Efficiency (%)
75W
86.67
150W
88.72
375W
90.88
565W
89.23
750W
88.34

The PC Power & Cooling Silencer MK III 750W is a very efficient unit, peaking at almost 91% at 50% load. This drops to around 88.34% at full load.

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 Digital Sound Level Noise Decibel Meter Style 2 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 Refrigerator
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)
75W
<28.0
150W
<28.0
375W
29.3
565W
32.3
750W 33.1

We tested the supply with the switch in the ‘normal’ position. The large 140mm fan proved to be very effective and quiet at all times, even when loaded hard.

Temperature (c)
Intake
Exhaust
75W
36
38
150W
38
41
375W
39
45
565W
45
53
750W
47
57

The 140mm fan is well optimised as the load increases. At full load it peaks at a 10c above ambient intake.

Maximum load
Efficiency
823W
87.74

For those interested, we measured efficiency when stressing the unit to breaking point. 87.7 percent efficiency at 823W … hardly practical, but interesting regardless.

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