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A short while ago we reviewed Corsair's top of the line AX1200 PSU and it walked away with a score of 9.5/10 and our top award. It earned this by delivering record breaking efficiency (93%) with an incredibly potent and ultimately stable power delivery.
The only downside with this unit was the £235 price tag which it carried, ensuring that only the richest and most demanding of enthusiast users could ever afford it.
A few weeks ago we received the AX850 power supply and we have put it through its paces since then, ensuring that it can deliver in the same manner as its bigger brother. This model will be more appealing as it is much more affordable. When you see that Corsair are offering an industry leading 7 year warranty then it seems they have every faith in this unit to be a long term investment.
The packaging follows the same design ethic as the AX1200 we reviewed a few weeks ago – very artistic and ‘corporate' in appearance.
Internally it is sandwiched by a very substantial foam encasing with a felt bag wrapped around the PSU itself for protection against markings during shipping.
Above is a picture of all the cabling which is supplied in a handy little carrying bag.
Corsair also supply mounting screws and cable ties to help keep your system build neat and tidy.
| Corsair AX850W PSU – connectivity | |
| ATX 24 pin & 20 pin | x1 |
| EPS/ATX12V 8-4 Pin | x2 |
| 6+2 pin PCI-E | x4 |
| Sata | x12 |
| 4-Pin Peripheral/Molex | x8 |
| FDD | x2 |
We have to mention the fact that Corsair appearing to be listening to public feedback and have removed the floppy drive connectors from the end of cabling chains. They give a little converter cable for people still using one. You could always get a USB floppy drive which saves a considerable amount of hassle if you ever need one.
The quality of sleeving is high throughout and the whole bundle falls in line with what we would expect from a Professional Series Corsair bundle.
The AX850 is designed in a similar fashion to the AX1200 unit. With a very muted appearance tying in with the ‘professional' naming convention well. There is a large 120mm fan taking centerstage and an AX850 sticker on one side of the PSU. The finish is deep and looks beautiful.
The weight is 2.85kg and it measures 15cmx16cmx8.6cm. The unit is completely modular with an array of connectivity on one side for the system build.
| Model | CMPSU-850AX | |
| AC Input Rating | ||
| AC input | 90-264V | |
| Input Current | 12A | |
| Frequency | 50/60hz | |
|
DC Output Rating
|
||
| Max Load | Max Output | |
| +3.3V | 25a | 125w |
| +5V | 25a | |
| +12V | 70a | 840w |
| -12V | 0.5A | 6w |
| +5VSB | 3.0A | 15w |
| Total Power | 850W @ 50c Ambient Temperature | |
We noticed that Corsair had not marked the connectors on the PSU body in the same manner as they did on the AX1200 unit – it shouldn't cause any confusion for a system builder mind you as its pretty obvious how they connect. The 24 pin power feed is directed into two feeds which are shown furthest left, top row and bottom row. The PCIe feeds take up the remaining three slots at the bottom. Sata and Molex power is fed from the five 6-pin power connectors top right.
The fan inside the unit is a San Ace 120 – Model 9S1212F404. This is a 120mm unit (140mm fan in the AX1200) and it is a 7 blade design rated at 12v/0.19A. This fan normally spins in the 1200rpm zone, but has a maximum rating of 2,400 rpm creating 40dBa – we will look at this later. If you are interested in the full range of Sanyo Denki fans then check out this page.
Corsair are keen to extoll the virtues of their Hybrid Silent fan control system – it offers 3 modes of cooling which is dependant on the current status of power load. up to 20% load for instance the fan is disabled which generates no noise and then between 20% and 50% load it spins into low fan mode. Above this it then turns into performance mode for demanding load requirements.
Sanyo Denki are well known to make some of the best fans in the business, but they are noticeably more expensive than many others. It is good to see Corsair not cutting a corner here with a cheap fan.
Internally, the design is neat, and while there is obviously less physical space when directly compared with the AX1200, there are no glaring build issues. Wiring is noticeably tight, ensuring the best possible connection quality. Soldering quality is high as we would expect.
The Corsair AC850 is using a design which means that the 3.3V and 5V DC outputs are situated on an independent DC output connector board.
The connector board features an integrated voltage regulation module (VRM) which produces the 3.3V and 5V output directly from a low current 12V DC input. This is a similar principle to the AX1200 we reviewed and it results in a much higher efficiency rating compared to traditional designs that place all the DC output connectors on the same board.
The capacitors used for the PFC stage are 390uF rated to 105C. This Corsair unit boosts efficiency by minimising the loss in the PFC stage by switching the primary power on and off when the cycle is at 0 voltage and 0 current.
The Corsair AX850 uses a high quality double sided PCB design which offers advantages when compared against standard PCB layouts. The primary point to note is that this specific design doubles the amount of copper used for traces and return planes and it also increases the efficiency as a result of lower resistive losses which helps to improve cooling characteristics. The AX850 also incorporates ‘through-hole' soldering which means higher levels of reliability.
As we would expect there is over current and under voltage protection and the PSU conforms to all required international safety standards. Over current protection (OCP) for example is present on all rails, including the single +12V rail (which can deliver 70 Amps – 840w). Over Temperature Protection (OTP) and Short Circuit Protection (SCP) are also included.
All of this is covered by a full 7 year warranty for added peace of mind.
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.
We always expect Corsair Professional Series Gold power supplies to perform well and the AX850 has not failed to meet the grade, yet again. The top of the range AX1200 is the best power supply on the market right now, but it comes with a price tag high enough to cause palpatations.
The AX850, while identical in finish to the AX1200 is physically much smaller and has a different connector layout and design. They both are quite stunning to look at, we love the understated design and simple aesthetic appeal.
Inside, the design is as good as you will find at this price point, with independent DC output boards, double sided PCB and zero voltage switching helping to raise efficiency and improve thermal performance. Our test results show just how good the thermal performance and efficiency are. Over 90% efficiency throughout the whole range is a result that Corsair should be immensely pleased with.
Acoustically, the unit is the top of its class, with a hybrid fan system which means that at low loads, it turns itself off to create no noise. We can actually see a media based enthusiast audience buying this unit for a low powered media system just to utilise the silence. If they ever need to upgrade, then this will assuredly handle whatever is required, for years to come.
We tested the system in a real world environment with a 980X clocked to 4.5ghz on water with two Powercolor HD 5870 PCS+ cards in Crossfire X and it performed without a problem, often able to keep the fan spinning low, at around 22 dBa.
Pricing in the UK is going to be around the £150 price point which we feel is great value for money, with a 7 year warranty this is surely going to last a potential customer a very long time indeed, so we consider it a worthwhile long term investment. This would be our first choice PSU under £200 and I can't give it a higher recommendation than that.
KitGuru says: It seems Corsair can do no wrong lately, and if they keep producing quality power supplies like the AX850 and AX1200 then they will quickly earn a massive following.
