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Cooler Master GX 450 Power Supply 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
A
V
A
V
A
V
A
V
75W
1.05
3.34
1.47
5.07
4.84
12.13
0.50
5.05
150W
2.41
3.32
3.17
5.05
9.70
12.19
1.00
5.05
250W
3.69
3.31
5.18
5.02
16.50
12.05
1.50
5.02
350W
4.97
3.27
7.06
4.98
23.52
12.02
2.00
5.00
450W
6.73
3.23
9.15
4.96
31.24
11.93
2.50
4.95

Load regulation seems fine, and falls within specifications.

Cooler Master GX 450 Maximum Load
473.4

We managed to push the supply to 473.4 watts before it would shut down safely.

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
385.4W 2.0 3.28 2.0 5.03 30.0 11.98 0.2 -11.98 0.50 5.02
170.5W 18.0 3.21 12.0 4.88 4.0 12.08 0.2 -11.75 0.50 4.95

Our first test placed a heavy load (30a) on the +12 V output with a light load on the remaining voltages. The GX 450 held fairly well, remaining well within specification. It also passed the second test within recommended specifications.

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 Cooler Master unit complied with the ATX standard.

AC Ripple (mV p-p)
DC Load +3.3V +5V +12V 5VSB
75W 25 15 30 10
150W 30 20 30 15
250W 35 25 35 20
350W 40 25 45 25
450W 45 30 50 25

Ripple results were all within ATX12V specification, although the +3.3V showed 45 mV under full load, still within specification, but close to the edge.

Efficiency (%)
75W
83.45
150W
84.23
250W
84.78
350W
83.13
450W
81.44

For an 80 Plus unit, the efficiency figures are pretty good across the full range of our testing.

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)
75W
27.8
150W
28.6
250W
29.4
350W
32.7
450W 36.8

The 120mm fan is reasonably quiet until the unit is pushed to 80%+ of the rated output level, then it can be heard, at full load it is clearly audible generating almost 37 dBa of noise.

Temperature (c)
Intake
Exhaust
75W
35
38
150W
36
39
250W
38
47
350W
40
50
450W
43
55

The 120mm fan helps to maintain reasonable ambient temperatures inside the chassis, rising to a maximum of 55c under full load.

Maximum load
Efficiency
473.4W
79.3

Pushing the PSU above its rated limits generates an efficiency level of around 79.3%. This is not a viable ‘real world’ situation, but its interesting nonetheless.

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