Seasonic X-Series 850W KM3 Power Supply Review

1. Introduction2. Seasonic X-Series 850W KM3 (Bundle & Cables)3. Seasonic X-Series 850W KM3 (External)4. Seasonic X-Series 850W KM3 (Internal)5. Seasonic X-Series 850W KM3 (Super High Res Gallery)6. Testing Methodology7. Closing Thoughts8. View All Pages

Seasonic have been consistently releasing some of the finest power supplies for the enthusiast audience this year. This is the reason why their designs are often used by respected companies such as Corsair and BeQuiet! Part of the Seasonic strategy is always to keep an active refresh schedule in place. With this in mind we are analysing their latest KM3 850W model today, the replacement for the award winning KM2 which we reviewed back in September.

The X-Series 850W KM3 is not just a simple refresh however, the internal design is completely different and we will take a look at this shortly. The KM2 was already a very impressive power supply so we are interested to see how far the company can push the new design.

They have three models already in the KM3 range, a 650W, 750W and 850W model all with a single +12V rail, fan controller and new modular cabling.

Special Features –

• 80PLUS® Gold Certified Super High Efficiency
• Full Modular Cabling Design
• Patented DC Connector Module with Integrated VRM [Voltage Regulator Module]
• DC to DC Converter Design
• Seasonic Hybrid Silent Fan Control
• Sanyo Denki San Ace Silent Fan
• Conductive Polymer Aluminum Solid Capacitors
• Highly Reliable 105℃ Japanese Brand Capacitors
• Tight Voltage Regulation [±1%]
• Active Power Factor Correction [99% PF Typical]
• High +12V Output
• High Current Gold Plated Terminals
• Dual Sided PCB Layout
• Ultra Ventilation [Honeycomb Structure]
• Multi-GPU Technologies Supported
• All-in-One DC Cabling Design
• Easy Swap Connector
• Universal AC Input [Full Range]
• 7 Years Warranty

The box artwork has been changed since the KM2, although the overall concept keeps the same colour scheme and understated ethic.

The supply is shipped protected between foam panels and is wrapped in a felt bag. We see very little possibility it could get damaged in transit.

Seasonic include a user manual, plastic and felt cable ties, alongside mounting screws. The cables are stored inside a two pouch bag, which can be reused. A regional specific power plug is also included.

Seasonic have changed the cabling to the popular ‘flat' ribbon style which can ease the routing phase and improve system airflow. They are still using high grade 18AWG cables, which is good to see.

The configuration of cables has changed. The older KM2 model had 4x PCI-E 8/6 Pin connectors, the new model ships with x6 of these headers. This is more than adequate, even for the most demanding SLI and Crossfire system builds.

The unit is nicely finished, with thick paint which proves resistant against rough handling. We ran our screwdriver down the side with a little force and it didn't mark at all.

The large fan is hidden behind a strong honeycomb grill, we will check this out later when we open the unit for analysis.

One side of the power supply is vented to help improve air flow. At the side is a power switch and connector. The company branding is seen underneath this.

The KM3 modular panel has changed completely over the last revision. There is now a ‘hybrid' fan switch which you can toggle on or off – the blue sticker alerts you to this initially and should be removed before using the supply. Seasonic have said this is the industries first ‘advanced three phased thermal control'.

The Hybrid Silent Fan Control provides three operational stages:  Fanless, Silent, and Cooling Mode. In addition, there is a switch provided to allow for manual selection between the Seasonic S2FC (fan control without Fanless Mode) and the S3FC (fan control including Fanless Mode).

The power supply looks great from all angles and only measures 160mm x 150 mm x 86 mm (LxWxH), meaning it will fit into any mainstream ATX compliant chassis.

Seasonic X-Series 850W Power Supply (KM3)
DC Output	+3.3V	+5V	+12V	-12V	+5Vsb
Max Output	25A	25A	70A	0.5A	3A
Total Power	125W		840W	6W	15W
	850W

70A can be delivered to the +12V rail, plenty of power on tap for demanding gaming systems.

Seasonic are using a very high grade 120mm Sanyo Denki San Ace fan (9S1212F404). This fan uses dual ball bearings to enhance life span and reliability. It is constructed around 7 blades which are sculpted to reduce noise while maintaining a high level of airflow. This same model was also incorporated into the KM2 supply. We have no complaints as this is genuinely one of the best fans that money can buy.

Seasonic are using a new fully modular design and the overall build quality is exceptional. This is a full bridge design compared to the half bridge design on the KM2. This should help improve reliability and efficiency even further. We noticed MOSFET on the daughter card, instead of the main PCB which helps to improve the space utilisation to improve cooling efficiency. There are several little rows of heatsinks to ensure adequate cooling reaches the critical components.

The outputs of the unit are monitored by an integrated circuit which supports over voltage, under voltage and over current protection. There are four OCP channels, two for +12V, one for +5V and another for +3.3V.

Seasonic are using high grade Japanese capacitors throughout the design. The primary stage capacitors are Nippon Chemi Con, rated 420V 330uF @ 105C. Secondary stage capacitors are also high grade 105c rated. This is a power supply focused on quality and subsequently no corners have been cut.

On this page we present some super high resolution images of the product taken with the 24.5MP Nikon D3X camera and 24-70mm ED lens. These will take much longer to open due to the dimensions, especially on slower connections. If you use these pictures on another site or publication, please credit Kitguru.net as the owner/source.

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. Due to public requests we have changed our temperature settings recently – previously we rated with ambient temperatures at 25C, we have increased ambient temperatures by 10c (to 35c) in our environment to greater reflect warmer internal chassis conditions.

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	1.57	3.33	1.76	5.04	6.65	12.06	0.50	5.03	0.20	-12.02
225W	3.74	3.33	3.88	5.03	15.55	12.05	1.00	5.03	0.20	-12.03
450W	7.51	3.32	8.35	5.03	30.76	12.04	1.50	5.02	0.30	-12.04
675W	11.33	3.32	12.32	5.02	47.49	12.03	2.00	5.02	0.50	-12.04
850W	1.52	3.32	1.17	5.01	63.55	12.02	0.50	5.01	0.20	-12.05

Load regulation is most certainly class leading, with barely any fluctuation at all between the load tests. This is as good as we have seen this year.

Seasonic X-Series 850W	Maximum Load
	1,037W

We managed to get the PSU to achieve 1,037W before it would shut down, delivering around 187W more than rated specifications. These are incredible results.

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	3.33	1.0	5.04	60.0	12.03	0.2	-12.03	0.50	5.01
165W	15.0	3.32	18.0	5.00	2.0	12.06	0.2	-12.04	0.50	5.01

Again, these are class leading results and as good as we have seen to date. All rails held close to nominal value, regardless of the demand.

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 unit complied with the ATX standard.

AC Ripple (mV p-p)
DC Load	+3.3V	+5V	+12V	5VSB
100W	5	5	10	5
225W	5	10	15	10
450W	10	10	20	10
675W	10	10	20	10
850W	10	10	25	15

Can it get any better than this? These are again, right at the top of our findings to date. Both +3.3V and +5V peak at 10 mV and +12V peaks at 25mV.

Efficiency (%)
100W	85.20
225W	88.14
450W	92.11
675W	91.33
850W	89.11

Efficiency is superb and above 80 Plus Gold rated rated levels. It is a little more efficient than the KM2.

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 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 Refrigerator
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	<28.0
225W	<28.0
450W	29.1
675W	30.8
850W	33.2

The fan activity is temperature controlled, disabling if a certain threshold is maintained. The unit hardly emits any noise at all, regardless of the switch position and even at full load noise emissions are low. Ideal for the enthusiast user who doesn't want to deal with excessive fan noise.

Temperature (c)
	Intake	Exhaust
100W	37	40
225W	38	44
450W	42	50
675W	45	53
850W	47	58

As we mentioned earlier there are only a couple of heatsinks inside the Seasonic power supply, so the efficiency and fan performance is important. The temperatures are controlled well however, rising to a maximum 11c above ambient threshold at full load.

Maximum load	Efficiency
1,037 watts	85.45

At 1037 watts, the efficiency level measures 85.45%. Not a practical situation to be running 24/7, but worth noting.

The Seasonic X-Series 850W KM3 is right up there in the top 3% of high power units available on the market today. It really is as close to perfect as you are likely to see and will appeal to the high end audience who don't mind paying a little extra for a top of the line supply.

Load regulation is class leading and we have yet to test a more capable unit in this regard. The intensive cross loading test barely phased the unit, with it holding onto nominal readings. Noise suppression is also close to perfect and reinforces the 850W KM3 standing as justifiably the finest power supply on the market today.

The addition of a new fan S2FC/S3FC selector switch and flat ribbon style modular cabling just enhances the overall appeal to the extremely demanding enthusiast audience.

The power supply is basically silent until just over 400W of output when the fan starts to spin up a little. Even at a 700W power demand the unit is whisper quiet. This is particularly appealing to gamers who have spent some time watercooling their system to reduce noise levels as much as possible.

The new KM3 is available in the United Kingdom for around the £150 inc vat mark. It is rather expensive, but when you consider the power characteristics and market leading design, we feel it is well worth the money.

Pros:

• load regulation.
• noise suppression.
• very quiet.
• 80 Plus Gold+ efficiency levels.
• can deliver over 1,000W output without falling over.
• pure modular design.
• fan switch.

Cons:

• Price premium.

Kitguru says: If you want the best, then the Seasonic X-Series 850W KM3 unit is exceptional value. It is simply flawless.

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