Seasonic X-Series 650W KM3 Power Supply Review

Review Score:
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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
• SkyTronic DSL 2 Digital Sound Level Meter (6-130dBa)
• 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
152W
2.03
3.33
2.04
5.04
10.12
12.06
0.50
5.03
0.20
-12.03
270W
3.02
3.33
3.05
5.04
19.14
12.05
0.50
5.03
0.30
-12.03
400W
4.05
3.32
5.00
5.03
29.17
12.04
1.00
5.03
0.30
-12.03
523W
6.08
3.32
7.04
5.03
38.19
12.02
1.50
5.02
0.30
-12.04
650W
8.00
3.32
9.00
5.02
48.00
12.01
2.50
5.01
0.30
-12.04

Voltage regulation is class leading, with hardly any fluctuation at all, even when loaded to maximum. As good as we have seen in the last 14 months.

Seasonic X-Series 650W KM3 Maximum Load
812W

The power supply would shut down at 812W, gracefully. The protection circuitry worked well.

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
590W 1.0 3.33 1.0 5.04 48.0 12.01 0.2 -12.02 0.50 5.00
145W 12.0 3.31 15.0 5.02 2.0 12.05 0.2 -12.03 0.50 5.01

Cross load results are class leading. All rails held close to nominal values, 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
152W 10 5 15 10
270W 10 10 20 15
400W 15 10 25 15
523W 15 15 25 15
650W 15 20 30 15

Ripple suppression is great, with the +3.3V output peaking at 15mW. The +5V output peaks at 20mV. +12V output peaks at 30 mV. All of these are well within tolerance guideline specifications. Excellent results.

Efficiency (%)
152W
85.31
270W
88.45
400W
92.03
523W
91.37
650W
89.21

Efficiency is exceptionally strong, peaking around 92 percent at 50 percent load. At full load this drops to just over 89 percent efficiency.

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 SkyTronic DSL 2 Digital Sound Level Meter (6-130dBa) 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 Refridgerator
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)
152W
<28.0
270W
<28.0
400W
29.1
523W
30.4
650W 32.8

This power supply is extremely quiet, even quieter than the 850W in the last 20 percent of load. When delivering 650W of power it is barely audible and registers just under 33 dBa on our sound meter.

Temperature (c)
Intake
Exhaust
152W
36
39
270W
39
44
400W
42
48
523W
45
52
650W
47
57

The internal temperatures are very impressive, rising to an 10c above ambient threshold when placed under full load.

Maximum load
Efficiency
812W
86.3

Pushing the PSU above its rated limits generates an ultimate efficiency level of around 86.3%. This is not a viable ‘real world’ situation, but its interesting nonetheless.

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Rating: 5.0/5 (1 vote cast)
Seasonic X-Series 650W KM3 Power Supply Review, 5.0 out of 5 based on 1 rating
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  • Black Mamba

    Excellent, as we would expect by now !

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  • harris

    My only problem with Seasonic is the pricing, they may be great, but I can’t afford the products of theirs I want to buy, I have to get cheaper.

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  • Alex

    I have their last 650W PSU and I am happy with it. I always thought ribbon cabling was worse than the fat sleeved cabling, but I was clearly wrong.

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  • Stevie

    Great company, always buy their products, and they last many many years, never had a seasonic fail. wise to see corsair and other companies using their designs.

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  • Ivan

    Just ordered one as I needed a new 650w, my thermaltake 750w died and it was noisy too.

    THanks for review

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  • Darth Digglers

    Bah! Newegg dont list these as KM2 or KM3, what a mess. they needed to change the name to R2 or something so retailers would list them properly. they are all falling under the X series name, which is a mess.

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  • djoCC22

    i 1 it!!! great product but not great price for me.. i need titanium cert…..

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    Rating: 0 (from 0 votes)
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