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Corsair AX1200 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. Over the coming months this configuration is likely to be adjusted further and fine tuned. Ambient room temperatures are kept to a ‘real world’ realistic condition of 25c with air conditioning.

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
330W
5.50
3.37
5.50
5.02
21.25
12.20
0.87
5.03
0.20 -12.20
620W
11.00
3.35
11.00
5.02
42.50
12.18
1.75
4.99
0.40 -12.21
918W
16.50
3.31
16.50
5.01
63.75
12.06
2.62
4.97
0.60 -12.24
1204W
22.00
3.25
22.00
4.95
85.00
12.02
3.5
4.94
0.80 -12.30
Corsair AX1200 Maximum Load
1545W

Incredibly we managed to wrangle 1545W from the unit – and what is even more stunning is that it was happy to run at this for some time. If we loaded it higher than this it would shut off after a short while. We are pleased to report that the Overcircuit protection system works wonders as the unit didn’t POP and just shut off safely until we restarted with lower load. The results in the table above speak for themselves, no unusual lowering or raising of figures as we increased the load.

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
1190W 1.0 3.33 1.0 5.01 62.0 12.05 0.05 -12.25 0.05 5.03
195W 22.0 3.30 22.0 4.98 1.0 11.98 0.05 -12.20 0.05 5.03

A stellar sets of results for the AX1200, it deals well with the crossloading tests, very little fluctuation throughout.

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 Corsair unit complied with the ATX standard.

AC Ripple (mV p-p)
DC Load +3.3V +5V +12V 5VSB
330W 5 5 10 5
620W 10 10 15 10
918W 10 10 20 15
1204W 20 20 25 20

These are outstanding results and without a doubt, class leading. We recorded only 25mV of noise on the 12V line fully loaded – remember this is with 1200W of energy being drawn!

Efficiency (%)
330W
92.21
620W
93.78
918W
93.54
1204W
90.67

Once again, we have never seen efficiency figures anywhere near this level and even under full load it still managed to achieve a 90%+ efficiency rating which is mind blowing. These efficiency figures are basically off the chart.

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 Corsair 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 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)
330W
26.4
620W
28.9
918W
29.8
1204W
32.3

These are a great set of results, and while Corsair rate the AX1200 maximum noise output at 30dBa we measured slightly higher at 32.3dBa, which is still not that noticeable under real world conditions, more than likely drown out by several case fans (if you could load it over 1kW). Very good set of results, yet again.

Exhaust Temperature (c)
330W
26
620W
28
918W
40
1204W
44

The power supply delivers a great combination of very low noise with reasonable levels of heat being removed. The 140mm preset fan settings throughout the range seem to be well adjusted by Corsair.

Maximum load
Efficiency
1545W
87.12%

For those interested, we measured the efficiency when stressing the unit to breaking point.over 87% at 1545W, are you impressed yet?

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