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

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.

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