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Corsair AX1500i Digital ATX 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
• Extech digital sound level meter
• Digital oscilloscope (20M S/s with 12 Bit ADC)
• Variable Autotransformer, 1.4 KVA

12V output is combined for our testing.

DC Output Load Regulation

Combined

DC Load

+3.3V
+5V
+12V
+5VSB
-12V
A
V
A
V
A
V
A
V
A V
500W
7.60
3.33
8.80
5.03
36.02
12.01
1.5
5.00
0.30 -12.01
750W
12.61
3.32
14.12
5.02
52.03
12.00
2.0
4.98
0.30 -12.02
1000W
17.72
3.31
20.02
5.01
72.23
12.00
2.5
4.97
0.50 -12.03
1250W 18.82 3.30 24.05 5.00 90.12 11.98 3.0 4.94 0.60 -12.03
1500W
18.85
3.29
22.62
4.98
115.90
11.98
3.5
4.92
0.80 -12.04

Load regulation is absolutely stellar, all rails hold tight across the board.

Corsair AX1500i Digital ATX Power Supply
Maximum Load
1622W

We managed to get the PSU to achieve 1622W before it would shut down, delivering around 122W more than the rated specifications.

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
1150W 3.0 3.33 2.0 5.02 92.0 11.98 0.2 -12.01 0.50 5.00
250W 20.0 3.29 24.0 4.97 5.0 12.02 0.2 -12.02 0.50 4.98

The power supply stormed through the the cross loading tests, falling well within safe parameters, even when hit with 92A on the +12V output.

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
500W 5 5 5 5
750W 5 5 5 5
1000W 5 5 15 5
1250W 10 5 15 5
1500W 10 10 20 10

These ripple results are some of the best we have seen to date, showing that Flextronics really do know how to make a high end power supply. Corsair claimed slightly worse figures than these in their own literature — very impressive.

Efficiency (%)
500W
94.35
750W
95.93
1000W
95.92
1250W
95.87
1500W 93.98

The efficiency ratings are superb, peaking at close to 96% between 50% and 60% 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)
500W
<28.0
750W
29.4
1000W
31.8
1250W
33.6
1500W 34.8

Below 500watts the fan wasn’t spinning during our tests, and the noise rated as ‘silent’ (less than 28dBa which is the realistic limit of our meter). The fan spins up slowly and even at 750 watts, it is barely audible at all, completely drown out by a single CPU cooler fan. At 1000W the fan spins up a little more, and becomes audible around 1250 watts. At full 1,500 watt demand, the fan spins around 1,700 rpm, and measures 34.8dBa. This is still quiet and a remarkable result when considering it is delivering 1,500 watts!

Temperature (c)
Intake
Exhaust
500W
36
40
750W
38
43
1000W
41
48
1250W
45
53
1500W
48
57

The large fan copes with the heat inside the chassis, undoubtedly aided by the superb efficiency of the design.

Maximum load
Efficiency
1622W
93.1

At 1667W, the efficiency level is still good, measuring 91.5%. Not a practical situation to be running 24/7, but worth noting.

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