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[nextpage title=”Introduction”]

Corsair HX850W is a power supply with modular cabling system and high-end components promising up to 90% efficiency, launched to compete with Antec Signature series and Seasonic M12D series. Let’s see if it survives our tests.

It is very important to notice that Corsair HX750W, HX850W and HX1000W have nothing to do with other models from this same series. They use a complete different (and better, by the way) design using a DC-DC converter to generate their +5 V and +3.3 V outputs, like Antec Signature series and Seasonic M12D series. These HX models are manufactured by CWT, while other models from HX series are manufactured by Seasonic. Why Corsair kept the same name is a mystery. In our opinion they should have used a different name so consumers would know they are facing a different product class, targeted to users looking a power supply with high-end parts and very high efficiency.

Corsair HX1000W uses two transformers inside, while HX850W and HX750W use only one.

Corsair HX850W power supplyFigure 1: Corsair HX850W power supply.

Corsair HX850W power supplyFigure 2: Corsair HX850W power supply.

HX850W is somewhat long, being 7 3/32” (180 mm) deep, using a 140 mm fan on its bottom and featuring active PFC, of course. It also features a single-rail design.

It comes with a modular cabling system, but the main motherboard cable (20/24-pin), the ATX12V/EPS12V cable (two ATX12V connectors that together form an EPS12V one) and two six/eight-pin auxiliary power cable for video cards come from inside the unit. These cables are protected with nylon sleevings that come from inside the power supply housing.

The modular cabling system has ten connectors and HX850W comes with ten cables plus two adapters to convert standard peripheral power plugs into floppy disk drive power plugs. The cables included are:

  • Four auxiliary power cables for video cards, with one six/eight-pin connector on each one of them.
  • Three SATA power cables with four plugs each.
  • Three peripheral power cables with four plugs each.

The number of cables and connectors available is really impressive. With six auxiliary power connectors for video cards you can easily install up to three very high-end video cards under SLI mode without using any kind of adapter (each video card from this class requires two auxiliary power connectors).

The main motherboard cable, the ATX12V/EPS12V cable and the video card cables are long, measuring 23 5/8” (60 cm), so you probably won’t have any trouble using this power supply on a big full tower case. Peripheral and SATA power cables have a distance of 15 ¾” (40 cm) between the end that goes on the power supply and the very first connector on the cable. The distance between each connector on these cables is of 5 1/8” (13 cm).

The main motherboard cable use 16 AWG wires, which are thicker, while all other wires are 18 AWG, which is the correct gauge to be used.

Corsair HX850W power supplyFigure 3: Cables.

Now let’s take an in-depth look inside this power supply.

[nextpage title=”A Look Inside The HX850W”]

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. The first thing that caught our attention was that all capacitors used are Japanese from Chemi-Con and the secondary filtering stage uses some solid capacitors.

Corsair HX850W power supplyFigure 4: Overall look.

Corsair HX850W power supplyFigure 5: Overall look.

Corsair HX850W power supplyFigure 6: Overall look.

[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.

This power supply has all required components plus one extra X capacitor and two extra Y capacitors. The MOV is behind the fuse in Figure 8 and thus not shown.

Corsair HX850W power supplyFigure 7: Transient filtering stage (part 1).

Corsair HX850W power supplyFigure 8: Transient filtering stage (part 2).

In the next page we will have a more detailed discussion about the components used in the Corsair HX850W.

[nextpage title=”Primary Analysis”]

On this page we will take an in-depth look at the primary stage of Corsair HX850W. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses one GBU1506 rectifying bridge in its primary, supporting up to 15 A at 100° C
if a heatsink is used (which is the case), so in theory, you would be able to pull up to 1,725 W from the power grid; assuming 80% efficiency, the bridge would allow this unit to deliver up to 1,380 W without burning itself out. Of course we are only talking about this component and the real limit will depend on all other components from the power supply.

Two SPW35N60C3 power MOSFETs are used on the active PFC circuit, each one capable of delivering up to 34.6 A at 25° C or 21.9 A at 100° C in continuous mode (note the difference temperature makes) or up to 103.8 A at 25° C in pulse mode.

Corsair HX850W power supplyFigure 9: Rectifying bridge and active PFC 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 or more capacitors with small capacitance are physically smaller than one capacitor with the same total capacitance. Corsair HX850W uses two 390 µF x 400 V connected in parallel; this is equivalent of one 780 µF x 400 V capacitor.

These capacitors are Japanese, from Chemi-Con and are labeled at 105° C. This is good for two reasons, first, Japanese capacitors do not leak; and second, usually manufacturers use 85° C capacitors here, so it is good to see a manufacturer using a capacitor with a higher temperature rating.

In the switching section, two SPW20N60C3 power MOSFET transistors are used on the traditional two-transistor forward configuration. Each transistor supports up to 20.7 A at 25° C or 13.1 A at 100° C (note the difference temperature makes) or 62.1 A in pulse mode at 25° C.

Corsair HX850W power supplyFigure 10: Active PFC diode and switching transistors.

This power supply uses a CM6802 active PFC/PWM combo controller.

Corsair HX850W power supplyFigure 11: Active PFC/PWM combo 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, where the rectifiers are replaced with transistors. Also this power supply basically produces only the +12 V output. +5 V and +3.3 V outputs are generated from the +12 V output by two little power supplies located on a small printed circuit board inside the unit. This design is called DC-DC converter and is also used by Corsair HX1000W, Antec Signature 650 W and Seasonic M12D 750 W.

Five STP160N75F3 are used, each one capable of delivering up to 120 A at 100° C in continuous mode, or up to 480 A at 25° C in pulse mode. Three of them are in charge of the direct rectification, while the remaining two are in charge of the “freewheeling” part of the rectification process (i.e., discharging the coil).

The maximum theoretical current each line can deliver is given by the formula I / (1 – D), where D is the duty cycle used and I is the maximum current supported by the rectifying diode. Just as an exercise, we can assume a typical duty cycle of 30%.

For our math we need to assume the path that has the lower limit, which is the “freewheeling” path. This would give us a maximum theoretical current of 343 A (120 A x 2 / 0.70). This maximum theoretical current limit is for the whole secondary, since +5 V and +3.3 V are also produced from the +12 V output. The practical limit will depend on other factors, but mainly on the coils used and on the design from the small DC-DC converters used to generate the +5 V and +3.3 V outputs. If this 343 A was solely pulled from the +12 V outputs, this would give us 4,114 W.

Corsair HX850W power supplyFigure 12: Transistors used on the +12 V rectification.

This power supply has two separated DC-DC converters, one for +5 V and another for +3.3 V. Each one uses one APW7073 controller and three APM2556N MOSFETs, and they use solid capacitors.

Corsair HX850W power supplyFigure 13: DC-DC converters in charge of generating +5 V and +3.3 V outputs from the +12 V output.

Corsair HX850W power supplyFigure 14: One of the DC-DC converters.

This power supply uses a PS229 monitoring integrated circuit, which is in charge of the power supply protections. Unfortunately there is no information about this circuit on the manufacturer’s website.

Corsair HX850W power supplyFigure 15: Monitoring circuit.

Electrolytic capacitors from the secondary are also Japanese, from Chemi-Con and labeled at 105° C. We could find some capacitors installed on the modular cabling system, which is great (and unusual).

[nextpage title=”Power Distribution”]

In Figure 16, you can see the power supply label containing all the power specs.

Corsair HX850W power supplyFigure 16: Power supply label.

This power supply uses a single-rail design, so there is nothing to talk about here.

Now let’s 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 how the reviewed unit behaved 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 power listed for each test, you may find a different value than what is posted under “Total” below. Since each output can vary slightly (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. On the “Total” row we are using the real amount of power being delivered, as measured by our load tester.

The +12V1 and +12V2 inputs listed below are the two +12 V independent inputs from our load tester and during all test both were connected to the single +12 V rail present on the power supply.

Input Test 1 Test 2 Test 3 Test 4 Test 5
+12V1 6 A (72 W) 13 A (156 W) 20 A (240 W) 25 A (300 W) 29 A (348 W)
+12V2 6 A (72 W) 12 A (144 W) 17 A (204 W) 25 A (300 W) 29 A (348 W)
+5V 2 A (10 W) 4 A (20 W) 6 A (30 W) 8 A (40 W) 16 A (80 W)
+3.3 V 2 A (6.6 W) 4 A (13.2 W) 6 A (19.8 W) 8 A (26.4 W) 16 A (52.8 W)
+5VSB 1 A (5 W) 1.5 A (7.5 W) 2 A (10 W0 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 173.9 W 350.9 W 515.2 W 689.7 W 852.3 W
% Max Load 20.5% 41.3% 60.6% 81.1% 100.3%
Room Temp. 45.9° C 46.3° C 47.2° C 48.9° C 49.7° C
PSU Temp. 47.0° C 48.9° C 50.7° C 55.1° C 57.0° C
Voltage Stability Pass Pass Pass Pass Pass
Ripple and Noise Failed on +5VSB Failed on +5VSB Failed on +5VSB Failed on +5VSB Pass
AC Power (1) 185 W 372 W 554 W 767 W 985 W
Efficiency (1) 94.0% 94.3% 93.0% 89.9% 86.5%
AC Power (2) 191 W 388 W 578 W 787 W 1,009 W
Efficiency (2) 91.0% 90.4% 89.1% 87.6% 84.5%
AC Power (3) 194.5 W 389.8 W 577 W 789 W 1,009 W
Efficiency (3) 89.4% 90.0% 89.3% 87.4% 84.8%
AC Voltage 111.8 V 110.3 V 108.5 V 105.7 V 103.5 V
Power Factor 0.988 0.992 0.995 0.997 0.998
Final Result Pass Pass Pass Pass Pass

We saw really high efficiency numbers with Corsair HX850W, and we were afraid that our load tester would be defective again. We tested all internal components from our load tester, and they were just fine. We also measured AC power using a second wattmeter (a Kill-a-Watt P4400, marked as “2” on the table above), which gave us different readings from our Brand Electronics 4-1850 (marked as “1” on the table above). With both instruments Corsair HX850W presented an impressive efficiency.

Updated 06/24/2009: We re-tested this power supply using our new GWInstek GPM-8212 power meter, which is a precision instrument and provides accuracy of 0.2% and thus presenting the correct readings for AC power and efficiency (results marked as "3" on the table above). Efficiency was very high all the times, peaking 90% when pulling 40% from the labeled power (340 W). With 20% load (170 W) and 60% load (510 W) efficiency was still very high, at 89%. With 80% load (680 W) efficiency was at 87% and at 850 W efficiency dropped to 84.8%, which is still a very good number. We also added the numbers for AC voltage during our tests, an important number as efficiency is directly proportional to AC voltage (the higher AC voltage is, the higher efficiency is). Also, manufacturers usually announce efficiency at 230 V, which usually inflates efficiency numbers. We added power factor (PF) numbers as well. These numbers measure the efficiency of the power supply active PFC circuit. This number should be as close to 1 as possible. This power supply has a practically perfect PF number under full load and very good numbers in all tests, except under light load (20%), where PF was at 0.988, still a good number but not so good as the ones achieved under other load patterns.

Voltage stability was another highlight from HX850W, with all voltages inside 3% of their nominal values(i.e., voltages were closer to their nominal value than needed, as ATX spec allows voltages to be up to 5% from their nominal values, 10% for -12 V). This includes the -12 V output (except during test one, where it was only 0.01 V short of the 3% mark, i.e., -11.63 V instead of -11.64 V).

Even though noise and ripple levels for the main voltages were very low as we will show below, the standby (+5VSB) output had an enormous ripple level during all load patterns but test five. During test one ripple was at 75.6 mV, during test two ripple was at 117.4 mV, during test three ripple was at 106.8 mV and during test four ripple was at 77.8 mV. During test five it decreased to 39.2 mV, which is acceptable. The maximum allowed for this output is 50 mV.

After this review was posted, Corsair tested this power supply using the same load patterns presented on the table above and, with a different equipment, the noise levels for +5VSB were completely different (very low). The only explanation we have is that our equipment was somehow interfering with the results. This way the comments above about the +5VSB output should not be taken at face value.

Corsair HX850W power supplyFigure 17: Ripple at +5VSB output during test two (117.4 mV).

Below you can see the results for test number five. As we always point out, the limits are 120 mV for +12 V and 50 mV for +5 V and +3.3 V and all numbers are peak-to-peak figures.

Corsair HX850W power supplyFigure 18: +12V1 input from load tester at 852.3 W (36.2 mV).

< a href="https://www.hardwaresecrets.com/wp-content/uploads/hx850_191.gif">Corsair HX850W power supplyFigure 19: +12V2 input from load tester at 852.3 W (36.8 mV).

Corsair HX850W power supplyFigure 20: +5V rail with power supply delivering 852.3 W (10.2 mV).

Corsair HX850W power supplyFigure 21: +3.3 V rail with power supply delivering 852.3 W (12 mV).

Now let’s see if we could pull more than 850 W from this unit.

[nextpage title=”Overload Tests”]

Before overloading power supplies we always test first if the over current protection (OCP) circuit is active and at what level it is configured.

Here we were limited by our load tester, which can pull “only” up to 33 A from each one of its +12 V inputs, giving us a total of 66 A, while Corsair HX850W officially has a 70 A limit. However, when we configured both inputs at 33 A the power supply wouldn’t turn on, indicating that one of its protections was active.

The idea behind of overload tests is to see if the power supply will burn/explode and see if the protections from the power supply are working correctly. This power supply didn’t burn or explode and it shut down when we tried to overload it.

Below you can see the maximum we could pull from this power supply with it still working within specs. Even under this overloading efficiency was above 80%.

Input Maximum
+12V1 32.5 A (390 W)
+12V2 32.5 A (390 W)
+5V 27 A (135 W)
+3.3 V 20 A (66 W)
+5VSB 3 A (15 W)
-12 V 0.5 A (6 W)
Total 1,000 W
% Max Load 117.6%
Room Temp. 54.9° C
PSU Temp. 57.0° C
AC Power (1) 1,204 W
Efficiency (1) 83.1%
AC Power (2) 1,334 W
Efficiency (2) 75.0%
AC Power (3) 1,231 W
Efficiency (3) 81.2 %
AC Voltage 100.4 V
Power Factor 0.998

We could easily pull up to 1,000 W from Corsair HX850W. Under this extreme condition, efficiency was still above 80% (the results marked with "(3)" were measured with our precision equipment and thus are the correct ones). See how the AC voltage drops a lot as we pull more watts! Power factor was excellent, showing that the active PFC circuit from this unit is excellent.

[nextpage title=”Main Specifications”]

Corsair HX850W power supply specs include:

  • ATX12V 2.3
  • EPS12V 2.91
  • Nominal labeled power: 850 W at 50° C.
  • Measured maximum power: 1,000 W at 54.9° C.
  • Labeled efficiency: Up to 90%, 80 Plus Gold Certified.
  • Measured efficiency: Between 84.8% and 90.0% 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 two ATX12V connectors that together form an EPS12V connector.
  • Video Card Power Connectors: Six six/eight-pin connectors (two permanently attached to the power supply, four using the modular cabling system).
  • Peripheral Power Connectors: Twelve in three cables (using the modular cabling system).
  • Floppy Disk Drive Power Connectors: Two converted from two peripheral power plugs.
  • SATA Power Connectors: Twelve in four cables (using the modular cabling system).
  • Protections: Over current (OCP), over voltage (OVP, not tested), over power (OPP), under voltage (UVP) and short-circuit (SCP, tested and working) protections.
  • Warranty: Seven years.
  • More Information: https://www.corsair.com
  • Average price in the US*: USD 190.00.

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

[nextpage title=”Conclusions”]

Corsair HX850W is an impressive power supply, being to this date the power supply with the highest efficiency that we’ve ever tested, beating Seasonic M12D 750 W and Antec Signature 650 W.

The reason why these three models achieved 90% efficiency lies on the chosen design. Instead of having separated rectifiers for each output, these three power supplies produce mainly only one output: +12 V. From this +12 V output two smaller power supplies produce the +5 V and +3.3 V outputs. This is what the manufacturer calls “DC-DC design,” although technically the use of this name itself doesn’t make any sense, as all switching power supplies are DC-DC converters (as they increase and convert the wall voltage into DC before sending to the switching transistors).

Not only this design proved to be superior, but Corsair/CWT decided to use only high-end components inside this unit, which features only Japanese capacitors and solid caps on the DC-DC converters in charge of the + 5 V and +3.3 V outputs.

Voltage stability was another highlight, with all voltages within 3% from their nominal values, i.e., we saw voltages closer to their nominal values than what allowed by the ATX standard, which specifies a 5% tolerance (10% for -12 V).

We could also pull up to 1,000 W at 57° C from this unit, which is really impressive.

The number of cables available is impressive (12 SATA power connectors, 12 peripheral power connectors and six six/eight-pin video card power connectors), allowing you to build a very high-end system with three very high-end video cards without the need of using adapters.

Pricing for this power supply (USD 190) isn’t bad for a superior product, costing less than Seasonic M12D 750 W (USD 210).

The seven-year warranty – probably the highest in the industry – is also another reason to pick this product over competitors.

Corsair HX850W is a very good choice for the very high-end user that wants a power supply with the best internal components and very high efficiency.