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[nextpage title=”Introduction”]

Originally released with 650 W and 750 W versions, Seasonic expanded their 80 Plus Gold X-Series to include 560 W, 660 W, 760 W and 850 W versions. Let’s take an in-depth look at highest-wattage model.

Seasonic also has a fanless series based on the X-Series models, aptly called X Fanless. We’ve already reviewed the 400 W version from this other series, and also the 560 W and 650 W versions of the standard X-Series, and all proved to be outstanding products.

Seasonic X-Series 850 W power supplyFigure 1: Seasonic X-Series 850 W power supply

Seasonic X-Series 850 W power supplyFigure 2: Seasonic X-Series 850 W power supply

The Seasonic X-Series 850 W is 6.3” (160 mm) deep, with a 120 mm, dual ball bearing, Japanese fan from Sanyo Denki (San Ace 120), just like other members of the X-Series family.

Like all other members of the X-Series family, the new Seasonic X-Series 850 W has a fully 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, 23.2” (59 cm) long
  • One cable with one EPS12V connector, 25.6” (65 cm) long
  • One cable with two ATX12V connectors that together form an EPS12V connector, 25.6” (65 cm) long
  • Four cables with one six/eight-pin connector for video cards each, 25.6” (65 cm) long
  • Two cables with three SATA power connectors each, 21.6” (55 cm) to the first connector, 5.9” (15 cm) between connectors
  • One cable with two SATA power connectors, 21.6” (55 cm) to the first connector, 5.9” (15 cm) between connectors
  • Two cables with three standard peripheral power connectors each, 22” (56 cm) to the first connector, 5.9” (15 cm) between connectors
  • One cable with two standard peripheral power connectors, 22” (56 cm) to the first connector, 5.9” (15 cm) between connectors
  • One adapter to convert one standard peripheral power connector into two floppy disk drive power connectors

The cables with SATA and peripheral power connectors use 18 AWG wires, but the main motherboard cable, the EPS12V/ATX12V cables and the video card cables use thicker 16 AWG wires, which is always nice to see.

We think that Seasonic should have added more SATA power connectors, since we’ve seen several 850 W power supplies with 12 SATA power connectors around. It would also be nice if this unit had six video card power connectors instead of only four, this way you could install three high-end video cards without needing to use adapters.

Seasonic X-Series 850 W power supplyFigure 3: Cables

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

[nextpage title=”A Look Inside The Seasonic X-Series 850 W”]

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.

Seasonic X-Series 850 W power supplyFigure 4: Top view

Seasonic X-Series 850 W power supplyFigure 5: Front quarter view

Seasonic X-Series 850 W power supplyFigure 6: Rear quarter view

Seasonic X-Series 850 W power supplyFigure 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 Seasonic X-Series 850 W has all the required components, as you can see in Figure 9.

Seasonic X-Series 850 W power supplyFigure 8: Transient filtering stage (part 1)

Seasonic X-Series 850 W power supplyFigure 9: Transient filtering stage (part 2)

In the next page we will have a more detailed discussion about the components used in the Seasonic X-Series 850 W.

[nextpage title=”Primary Analysis”]

On this page we will take an in-depth look at the primary stage of the Seasonic X-Series 850 W. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses two GBJ1506 rectifying bridges in parallel, 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% eff
iciency, 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 components used in the X-400 Fanless, X-Series 560 W, and X-Series 650 W.

Seasonic X-Series 850 W power supplyFigure 10: Rectifying bridges

The active PFC circuit uses three SPP24N60C3 MOSFETs, each one capable of delivering up to 24.3 A at 25° C or up to 15.4 A at 100° C (note the difference temperature makes) in continuous mode, or up to 72.9 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.

Seasonic X-Series 850 W power supplyFigure 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 components on the printed circuit board, as capacitors with lower capacitance are physically smaller than capacitors with higher capacitance. The X-Series 850 W uses two 390 µF x 420 V capacitor connected in parallel; this is equivalent of one 780 µF x 420 V capacitor. These capacitors are Japanese, from Chemi-Con, and are labeled at 105° C.

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

Seasonic X-Series 850 W power supplyFigure 12: Active PFC controller

In the switching section, two STP26NM60N MOSFET transistors are used, each one capable of handling up to 20 A at 25° C or up to 12.6 A at 100° C in continuous mode, or up to 80 A at 25° C in pulse mode, with an RDS(on) of 165 mΩ.

Seasonic X-Series 850 W power supplyFigure 13: Switching transistors

The switching transistors are connected using a design called LLC resonant, 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.

Seasonic X-Series 850 W power supplyFigure 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 IPD031N06L 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. These transistors are more powerful than the ones used on other X-Series models below 750 W.

Seasonic X-Series 850 W power supplyFigure 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 X-Series 850 W these converters are installed on the modular cabling printed circuit board.

Seasonic X-Series 850 W power supplyFigure 16: The DC-DC converter

Seasonic X-Series 850 W power supplyFigure 17: 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.

In Figure 18, 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.

Seasonic X-Series 850 W power supplyFigu
re 18:
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). This circuit has four OCP channels (+3.3 V, +5 V and two +12 V), but the manufacturer decided to use only one for the +12 V output, making this power supply a single-rail unit.

Seasonic X-Series 850 W power supplyFigure 19: Monitoring circuit

[nextpage title=”Power Distribution”]

In Figure 20, you can see the power supply label containing all the power specs.

Seasonic X-Series 850 W power supplyFigure 20: 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 single +12 V rail (the EPS12V connector was installed on the +12VB input of our load tester).

Input Test 1 Test 2 Test 3 Test 4 Test 5
+12VA 6 A (72 W) 13 A (156 W) 18.5 A (222 W) 25 A (300 W) 31 A (372 W)
+12VB 6 A (72 W) 12 A (144 W) 18.5 A (222 W) 25 A (300 W) 31 A (372 W)
+5V 2 A (10 W) 4 A (20 W) 6 A (30 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 350.2 W 512.3 W 685.4 W 848.7 W
% Max Load 20.4% 41.2% 60.3% 80.6% 99.8%
Room Temp. 45.2° C 44.3° C 45.5° C 48.9° C 45.2° C
PSU Temp. 48.6° C 48.7° C 49.7° C 52.2° C 52.7° C
Voltage Regulation Pass Pass Pass Pass Pass
Ripple and Noise Pass Pass Pass Pass Pass
AC Power 196.7 W 386.3 W 572.3 W 779.0 W 981.0 W
Efficiency 88.3% 90.7% 89.5% 88.0% 86.5%
AC Voltage 114.4 V 112.2 V 109.2 V 107.1 V 104.5 V
Power Factor 0.988 0.994 0.993 0.995 0.996
Final Result Pass Pass Pass Pass Pass

The Seasonic X-Series 850 W can really deliver its labeled wattage at high temperatures.

Efficiency was very high, between 86.5% and 90.7%. Unfortunately this unit can’t hold 87% efficiency during full load (850 W) at high temperatures, even though the 80 Plus Gold certification promises 87% minimum at full load. This happened because Ecos Consulting (the company behind the 80 Plus certification) tests power supplies at only 23° C, and we test power supplies between 45° C and 50° C, and efficiency drops with temperature. But 86.5% is far from being a “bad” result.

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 the +12 V and -12 V outputs, and 50 mV for the +5 V, +3.3 V, and +5VSB outputs. All values are peak-to-peak figures.

Seasonic X-Series 850 W power supplyFigure 21: +12VA input from load tester during test five at 848.7 W (17.2 mV)

Seasonic X-Series 850 W power supplyFigure 22: +12VB input from load tester during test five at 848.7 W (20.2 mV)

Seasonic X-Series 850 W power supplyFigure 23: +5V rail during test five at 848.7 W (13.6 mV)

Seasonic X-Series 850 W power supplyFigure 24: +3.3 V rail during test five at 848.7 W (12.6 mV)

Let’s see if we can pull even more from the Seasonic X-Series 850 W.

[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 easily pull 1,000 W from it. In fact, we had to stop our test at 1,000 W only because this is the limit of our load tester, and this power supply
may be able to deliver even more. During this extreme condition, efficiency dropped to 82.4%, but noise and ripple levels were still extremely low and voltages were still within 3% from their nominal values.

Input Overload Test
+12VA 33 A (396 W)
+12VB 33 A (396 W)
+5V 23 A (115 W)
+3.3 V 23 A (75.9 W)
+5VSB 3 A (15 W)
-12 V 0.5 A (6 W)
Total 998.4 W
% Max Load 117.5%
Room Temp. 44.8° C
PSU Temp. 55.4° C
AC Power 1,212 W
Efficiency 82.4%
AC Voltage 102.7 V
Power Factor 0.997

[nextpage title=”Main Specifications”]

The specs of the Seasonic X-Series 850 W include:

  • Standards: NA
  • Nominal labeled power: 850 W
  • Measured maximum power: 998.4 W at 44.8° C ambient
  • Labeled efficiency: 87% at light (20% or 170 W) and full loads, and 90% at typical load (50% or 425 W), 80 Plus Gold certification
  • Measured efficiency: Between 86.5% and 90.7% at 115 V (nominal, see complete results for actual voltage)
  • Active PFC: Yes
  • Modular Cabling System: Yes, full
  • Motherboard Power Connectors: One 20/24-pin connector, one EPS12V connector, and two ATX12V connectors that together form an EPS12V connector
  • Video Card Power Connectors: Four six/eight-pin connectors on separate cables
  • SATA Power Connectors: Eight on three cables
  • Peripheral Power Connectors: Eight on two cables
  • Floppy Disk Drive Power Connectors: Two, if the included adapter is used
  • Protections (as listed by the manufacturer): Over voltage (OVP), under voltage (UVP), over power (OPP), over current (OCP), over temperature (OTP), and short-circuit (SCP) protections
  • Are the above protections really available? Yes
  • Warranty: Five years
  • More Information: https://www.seasonicusa.com
  • Average Price in the US*: USD 200.00

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

[nextpage title=”Conclusions”]

Like all other X-Series units from Seasonic we’ve reviewed so far, the X-Series 850 W power supply is an impressive product, with extremely high efficiency (above 90%), 3% voltage regulation (i.e., voltages closer to their nominal value than necessary), and extremely low noise and ripple levels. On top of that, due to its highly overspec’ed components, we could easily pull 1,000 W from it.

The main “problem” with this power supply is its price. Two hundred dollars is a lot of money for the average user, but this product is definitely targeted to users that demand “the best of the best” and is willing to pay for it.

A minor issue with this product, in our opinion, is the relatively reduced number of SATA power connectors (eight), especially when there are some high-end 850 W units out there offering 12 of them. It would also be nice if the manufacturer had added six video card power connectors instead of “only” four, which would allow us to install three high-end video cards together without the need of adapters.