Corsair AX850W Power Supply Review

[nextpage title=”Introduction”]

The new Corsair AX power supply series have 80 Plus Gold certification, full modular cabling system, and single +12 V rail, being based on Seasonic’s X Series. Seasonic offers 400 W (fanless), 460 W (fanless), 650 W, and 750 W models in their X series, while Corsair offers 750 W, 850 W, and 1,200 W models. We’ve already tested the Fanless 400 W and 650 W models from Seasonic, and they proved to be outstanding products. Let’s see if the Corsair AX850W achieves the same outstanding performance.

Figure 1: Corsair AX850W power supply

Figure 2: Corsair AX850W power supply

The Corsair AX850W is 6.3” (160 mm) deep and comes with a 120 mm dual ball bearing fan from the Japanese manufacturer Sanyo Denki on its bottom. It has a full modular cabling system, meaning that even the main motherboard cable is modular. This system has 10 connectors and the power supply comes with the following cables:

• Main motherboard cable with a 20/24-pin connector, 23.6” (60 cm) long
• Two cables with two ATX12V connectors each that together form an EPS12V connector, 23.6” (60 cm) long
• Four cables with one six/eight-pin connector for video cards each, 23.6” (60 cm) long
• Two cables with four SATA power connectors each, 15.7” (40 cm) to the first connector, 5.9” (15 cm) between connectors
• Two cables with two SATA power connectors each, 15.7” (40 cm) to the first connector, 5.9” (15 cm) between connectors
• Two cables with four standard peripheral power connectors each, 15.7” (40 cm) to the first connector, 5.9” (15 cm) between connectors
• One adapter to convert one standard peripheral power connector into one floppy disk drive power connector

All wires are 18 AWG, which is the minimum recommended gauge.

The cable configuration is very good for an 850 W product, allowing you to have up to two high-end video cards without the need of adapters. It would be even better if the unit came with two extra video card power connectors for allowing the installation of a third high-end video card.

Figure 3: Cables

Let’s now take an in-depth look inside this power supply.

[nextpage title=”A Look Inside The Corsair AX850W”]

We decided to disassemble this power supply to see what it looks like inside, how it is designed, and what components are used. Please read our Anatomy of Switching Power Supplies tutorial to understand how a power supply works and to compare this power supply to others.

This page will be an overview, and then in the following pages we will discuss in detail the quality and ratings of the components used.

Figure 4: Top view

Figure 5: Rear quarter view

Figure 6: Front quarter view

Figure 7: Printed circuit board

[nextpage title=”Transient Filtering Stage”]

As we have mentioned in other articles and reviews, the first place we look when opening a power supply for a hint about its quality, is its filtering stage. The recommended components for this stage are two ferrite coils, two ceramic capacitors (Y capacitors, usually blue), one metalized polyester capacitor (X capacitor), and one MOV (Metal-Oxide Varistor). Very low-end power supplies use fewer components, usually removing the MOV and the first coil. 

The AC receptacle used in this power supply isn’t a simple connector, but a complete filtering circuit. The Corsair AX850W has all the required components, as you can see in Figure 9.

Figure 8: Transient filtering stage (part 1)

Figure 9: Transient filtering stage (part 2)

In the next page we will have a more detailed discussion about the components used in the Corsair AX850W.

[nextpage title=”Primary Analysis”]

On this page we will take an in-depth look at the primary stage of the Corsair AX850W For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses two GBJ1506 rectifying bridges, which are attached to an individual heatsink. Each bridge supports up to 15 A at 100° C so, in theory, you would be able to pull up to 3,450 W from a 115 V power grid. Assuming 80% efficiency, the bridges would allow this unit to deliver up to 2,760 W without burning themselves out. Of course, we are only talking about these components, and the real limit will depend on all the other components in this power supply. These are the same bridges used in the X Fanless 400 W and X Series 650 W models from Seasonic.

Figure 10: Rectifying bridges

The active PFC circuit uses three IPP60R160C6 MOSFETs, each one capable of delivering up to 23.8 A at 25° C or up to 15 A at 100° C (note the difference temperature makes) in continuous mode, or up to 70 A in pulse mode at 25° C. These transistors present a 160 mΩ resistance when turned on, a characteristic called RDS(on). The lower this number the better, meaning that the transistors will waste less power and the power supply will achieve a higher efficiency. These transistors are a little bit more powerful than the ones used in the Seasonic X-Series 650 W.

Figure 11: Active PFC diode and transistors

This power supply uses two electrolytic capacitors to filter the output from the active PFC circuit. The use of more than one capacitor here has absolute nothing to do with the “quality” of the power supply, as laypersons may assume (including people without the proper background in electronics doing power supply reviews around the web). Instead of using one big capacitor manufacturers may choose to use two or more smaller components that will give the same total capacitance, in order to better accommodate space on the printed circuit board, as two capacitors with the same total capacitance are physically smaller than a single capacitor with equivalent capacitance. The Corsair AX850W uses two 390 µF x 420 V capacitors connected in parallel, the equivalent of one 780 µF x 420 V capacitor. They are manufactured by Chemi-Con, a Japanese brand, and labeled at 105° C.

The active PFC circuit is controlled by an NCP1654 integrated circuit.

Figure 12: Active PFC controller

In the switching section, another two IPP60R160C6 MOSFETs are used, and their technical specs were already published above. These transistors are more powerful than the ones used in the Seasonic X-Series 650 W.

Figure 13: Switching transistors

The switching transistors are connected using a design called “LLC resonant,” also known as series parallel resonant converter, being controlled by a CM6901 integrated circuit, which operates under PWM (Pulse Width Modulation) mode when the power supply is operating under light load but under FM (Frequency Modulation) mode under other loads.

Figure 14: LLC resonant controller

Now let’s take a look at the secondary of this power supply.

[nextpage title=”Secondary Analysis”]

This power supply uses a synchronous design in its secondary, meaning that the Schottky rectifiers were replaced by MOSFET transistors in order to increase efficiency. On top of that, this unit uses a DC-DC design, meaning that this unit is basically a +12 V power supply, with the +5 V and +3.3 V outputs being generated by two small power supplies attached to the +12 V output.

The +12 V output is generated by four IPD031N06L3 MOSFETs, each one capable of handling up to 100 A at 100° C in continuous mode or up to 400 A at 25° C in pulse mode, with an RDS(on) of only 3.1 mΩ. These transistors are soldered directly on the solder side of the printed circuit board, and the power supply housing is used as a heatsink for them. The +5 V and +3.3 V are produced from the +12 V output, but just as an exercise if all power from this unit was pulled exclusively from the +12 V rail, this unit would have a maximum theoretical current of 286 A or 3,429 W. These transistors are more powerful than the ones used in the Seasonic X-Series 650 W.

Figure 15: +12 V transistors

Usually power supplies that use DC-DC converters in the secondary to generate the +5 V and +3.3 V outputs have two separate printed circuit boards installed in the secondary, one for each output. Like other “X-Series” power supplies from Seasonic, in the Corsair AX850W these converters are installed on the modular cabling printed circuit board.

Figure 16: The DC-DC converter

Both outputs are managed by an APW7159 PWM controller, and each output is generated by four IPD060N03L MOSFETs, each one capable of handling up to 50 A at 100° C in continuous mode, or 350 A at 25° in pulse mode, with an RDS(on) of only 6 mΩ. These transistors are the same used in the Seasonic X-400 Fanless, but more powerful than the ones used in the Seasonic X-Series 650 W.

In Figure 17, you can see how there are several solid capacitors in the secondary (and the capacitors that aren’t solid are made in Japan, by Chemi-Con), and how Seasonic added some interesting heatsinks connected straight to the printed circuit board.

Figure 17: Heatsinks and solid capacitors

The secondary is monitored by a PS223 integrated circuit. This chip supports OCP (over current protection), over voltage protection (OVP), under voltage protection (UVP) and over temperature protection (OTP).

Figure 18: Monitoring circuit

[nextpage title=”Power Distribution”]

In Figure 19, you can see the power supply label containing all the power specs.

Figure 19: Power supply label

This power supply has a single +12 V rail, so there is not much to talk about here.

Let’s now see if this power supply can really deliver 850 W.

[nextpage title=”Load Tests”]

We conducted several tests with this power supply, as described in the article Hardware Secrets Power Supply Test Methodology.  

First we tested this power supply with five different load patterns, trying to pull around 20%, 40%, 60%, 80%, and 100% of its labeled maximum capacity (actual percentage used listed under “% Max Load”), watching the behavior of the reviewed unit under each load. In the table below, we list the load patterns we used and the results for each load.

If you add all the powers listed for each test, you may find a different value than what is posted under “Total” below. Since each output can have a slight variation (e.g., the +5 V output working at +5.10 V), the actual total amount of power being delivered is slightly different than the calculated value. In the “Total” row, we are using the real amount of power being delivered, as measured by our load tester.

The +12VA and +12VB inputs listed below are the two +12 V independent inputs from our load tester. During our tests, both were connected to the power supply’s single +12 V rail.

Input	Test 1	Test 2	Test 3	Test 4	Test 5
+12VA	6 A (72 W)	13 A (156 W)	20 A (240 W)	25 A (300 W)	31 A (372 W)
+12VB	6 A (72 W)	12 A (144 W)	17 A (204 W)	25 A (300 W)	31 A (372 W)
+5V	2 A (10 W)	4 A (20 W)	6 A (6 W)	8 A (40 W)	10 A (50 W)
+3.3 V	2 A (6.6 W)	4 A (13.2 W)	6 A (19.8 W)	8 A (26.4 W)	10 A (33 W)
+5VSB	1 A (5 W)	1.5 A (7.5 W)	2 A (10 W)	2.5 A (12.5 W)	3 A (15 W)
-12 V	0.5 A (6 W)	0.5 A (6 W)	0.5 A (6 W)	0.5 A (6 W)	0.5 A (6 W)
Total	173.7 W	349.8 W	512.3 W	685.3 W	845.2 W
% Max Load	20.4%	41.2%	60.3%	80.6%	99.4%
Room Temp.	46.6° C	45.9° C	48.5° C	46.8° C	49.4° C
PSU Temp.	48.0° C	49.3° C	50.5° C	51.3° C	52.2° C
Voltage Regulation	Pass	Pass	Pass	Pass	Pass
Ripple and Noise	Pass	Pass	Pass	Pass	Pass
AC Power	196.7 W	387.4 W	574.2 W	784.0 W	991.0 W
Efficiency	88.3%	90.3%	89.2%	87.4%	85.3%
AC Voltage	111.1 V	108.5 V	106.7 V	102.8 V	101.3 V
Power Factor	0.984	0.993	0.990	0.993	0.994
Final Result	Pass	Pass	Pass	Pass	Pass

The Corsair AX850W can really deliver its labeled wattage at high temperatures.

Efficiency was extremely high, above 88% at light load (20% load, 170 W) and above 85% at full load, peaking 90.3% at 40% load (340 W). These are good results but since it is an 80 Plus Gold unit, it should present efficiency above 87% at full load. Time and time again we see this happening, because the 80 Plus certification tests are done at a room temperature of only 23° C, while we tested this particular unit at 50° C, and efficiency drops with temperature. The interesting thing is that this unit isn’t listed at the 80 Plus website yet… Hum…

Voltage regulation was another highlight of this product, with all voltages within 3% of their nominal values – including the -12 V output. The ATX12V specification allows voltages to be up to 5% from their nominal values (10% for the -12 V output). Therefore this power supply presents voltages closer to their nominal values than necessary.

Noise and ripple levels were always extremely low. Below you can see the results for the power supply outputs during test number five. The maximum allowed is 120 mV for +12 V and -12 V outputs, and 50 mV for +5 V and +3.3 V outputs. All values are peak-to-peak figures.

Figure 20: +12VA input from load tester during test five at 845.2 W (18.4 mV)

Figure 21: +12VB input from load tester during test five at 845.2 W (25.6 mV)

Figure 22: +5V rail during test five at 845.2 W (14.6 mV)

Figure 23: +3.3 V rail during test five at 845.2 W (14.8 mV)

Let’s see if we can pull even more from the Corsair AX850W.

[nextpage title=”Overload Tests”]

Below you can see the maximum we could pull from this power supply. Because of its incredibly overspec’ed components, we could pull 1,000 W from it, but efficiency dropped to 80%. Here we were limited by our equipment, which can only pull up to 1,000 W from power supplies. So, this unit may be able to deliver even more power.

Input	Overload Test
+12VA	33 A (396 W)
+12VB	33 A (396 W)
+5V	25 A (125 W)
+3.3 V	24 A (79.2 W)
+5VSB	3 A (15 W)
-12 V	0.5 A (6 W)
Total	996.3 W
% Max Load	117.2%
Room Temp.	45.4° C
PSU Temp.	51.1° C
AC Power	1,238 W
Efficiency	80.5%
AC Voltage	96.4 V
Power Factor	0.995

[nextpage title=”Main Specifications”]

The specs of the Corsair AX850W include:

• Standards: ATX12V 2.31 and EPS12V 2.92
• Nominal labeled power: 850 W
• Measured maximum power: 1,000 W at 45.4° C ambient
• Labeled efficiency: 87% at light (20% or 80 W) and full loads, and 90% at typical load (50% or 200 W), 80 Plus Gold certification
• Measured efficiency: Between 85.3% and 90.3% at 115 V (nominal, see complete results for actual voltage)
• Active PFC: Yes
• Modular Cabling System: Yes
• Motherboard Power Connectors: One 20/24-pin connector and tw
  o cables with two ATX12V connectors each that together form an EPS12V connector
• Video Card Power Connectors: Four six/eight-pin connectors
• SATA Power Connectors: 12 on four cables
• Peripheral Power Connectors: Eight on two cables
• Floppy Disk Drive Power Connectors: One, if the included adapter is used
• Protections: Over voltage (OVP), under voltage (UVP), over power (OPP), over current (OCP), over temperature (OTP), and short-circuit (SCP) protections
• Warranty: Seven years
• Real Manufacturer: Seasonic
• More Information: https://www.corsair.com
• Average price in the US*: USD 200.00

* Researched at Newegg.com on the day we published this review.

[nextpage title=”Conclusions”]

The new Corsair AX850W is an outstanding power supply. During our tests it achieved very high efficiency, peaking above 90%, voltages very close to their nominal values (3% regulation instead of the traditional 5% regulation), extremely low noise and ripple levels, and a more than adequate number of connectors for an 850 W product. On top of that, due to its highly overspec’ed components, we could easily pull 1,000 W from it (even though efficiency dropped a lot under this scenario).

The two other 850 W power supplies with 80 Plus Gold certification that we’ve tested so far, the NZXT HALE90-850-M and OCZ Z Series 850 W, cost less: USD 180 and USD 185, respectively, while the AX850W costs USD 200. But from the three, the AX850W is the only one to offer a full modular cabling system, it presented a tighter voltage regulation, lower noise and ripple levels, and efficiency that was a tiny bit higher. The number of connectors is comparable, but the model from NZXT comes with six connectors for video cards, which may be an advantage.

So, if you are the kind of user that only wants “the best in class,” then the Corsair AX850W is the 850 W power supply that you should buy. Otherwise you can save a bit and buy a competing product, including Corsair HX850W (USD 170), that achieved  similar efficiency in our tests. Also, if you don’t demand 90% efficiency, you can save a lot and buy a power supply like the XFX 850 W Black Edition, which can achieve 87% efficiency at only USD 130.