Corsair AX850 Power Supply Review

1. Introduction2. Corsair AX850 Power Supply3. Corsair AX850 (Internal)4. Testing Methodology and Results5. Closing Thoughts6. View All Pages

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 23c 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
100W	1.58	3.35	1.77	5.02	6.64	12.18	0.50	5.00	0.20	-12.15
225W	3.70	3.34	3.83	5.02	15.55	12.17	1.00	5.01	0.20	-12.17
450W	7.50	3.34	8.37	5.01	30.68	12.16	1.50	5.01	0.30	-12.18
675W	11.30	3.34	12.39	5.01	47.46	12.12	2.00	5.00	0.50	-12.18
850W	1.29	3.33	1.10	5.00	71.03	12.11	0.50	5.00	0.20	-12.20

The AX850 deliverd excellent load regulation on all output channels across a wide range of loads. These are exceptional results and the +3.3V and 5V rails remained firmly within +/-2% of the nominal voltage instead of the recommended +/-5% and the +12V rail held within +/- 1%, even when it was forced to deliver over 70 Amps. Massively impressive results indeed.

Corsair AX850	Maximum Load
	1045W

We managed to force the PSU to 1045W before it turned off which is almost 200W more than the rating. It was able to run at 1045W for quite some time before shutting down safely. We are again very happy to report that the overcircuit protection system is working perfectly as the unit didn't fizzle and die it just shut down and waited until we acted more sensibly with our testing equipment.

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
760W	1.0	3.32	1.0	5.06	65.0	12.01	0.2	-12.18	0.50	5.02
165W	15.0	3.29	18.0	5.03	2.0	12.02	0.2	-12.15	0.50	5.01

Once again the Corsair AX850 does not fail to deliver the goods with very little fluctuation when cross loaded.

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
100W	5	10	10	5
225W	10	10	10	10
450W	10	10	15	10
675W	15	20	20	15
850W	15	20	20	15

The AX850 ripple results are just as impressive as the AX1200 model, in fact we noticed slightly lower (5mV) on the +12V and 5VSB readout. Once again Corsair seem to have nailed this perfectly as we know from previous experience that the older TX850 was registering around 90 mv on the 12V reading.

Efficiency (%)
100W	90.12
225W	90.33
450W	92.28
675W	91.74
850W	90.26

While efficiency is not quite as high as the AX1200, it is still reading over 90% throughout the entire range of readings which easily puts this into the upper echelons of efficiency performance on the market. Remember Gold Certification requires a 87% efficiency rating at 100% load. 3.26% higher based on our testing which is exceptional.

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)
100W	0
225W	17.3
450W	23.2
675W	28.7
850W	34.8

Another strong set of results with the unit only becoming audible over 80-85% load. Standard case fans are likely to even drown this out. The San Ace 120 really is an exceptional fan.

Exhaust Temperature (c)
100W	23.9
225W	27.3
450W	29.8
675W	32.3
850W	35.9

Exhaust temperatures were what we expected after using the PSU for several days before testing, very cool indeed. The high efficency rating helps this unit to run really cool internally and this is reflected by the air being expelled. Once again, excellent results.

Maximum load	Efficiency
1045W	86.1%

For those interested, we measured efficiency when stressing the unit to breaking point. Over 86% at 1045W, higher than some units rated to over 1000W.

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