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Seasonic X-Series 1250W Power Supply (SS-1250XM2)

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 – 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

We test the Seasonic Platinum 1200W power supply with the fan in the ‘normal’ state.

DC Output Load Regulation

Combined

DC Load

+3.3V
+5V
+12V
+5VSB
-12V
A
V
A
V
A
V
A
V
A V
100W
1.55
3.38
1.75
5.03
6.65
12.17
0.50
5.01
0.20
-12.11
200W
3.13
3.37
3.50
5.02
13.50
12.17
1.00
5.01
0.20
-12.11
400W
6.40
3.36
7.05
5.02
27.50
12.16
1.50
5.01
0.30
-12.12
600W
9.80
3.35
10.77
5.01
41.70
12.15
2.00
4.99
0.30
-12.12
800W
13.25
3.35
14.55
5.01
56.40
12.12
2.50
4.98
0.50
-12.13
1000W 16.55 3.33 15.75 5.00 71.40 12.07 3.00 4.98 0.60 -12.13
1250W 9.02 3.32 9.41 5.00 96.00 12.07 3.45 4.97 0.80 -12.14

Load regulation is excellent with all the rails holding tight, within 2%.

Seasonic X-Series 1250W Maximum Load
1355W

We managed to squeeze 1355W out of the unit before it would shut down gracefully.

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
1190W 4.0 3.35 3.0 5.02 88.0 12.04 0.2 -12.11 0.50 5.00
240W 19.0 3.32 22.0 4.97 2.5 12.14 0.2 -12.09 0.50 5.01

The Seasonic X-Series 1250W power supply delivered a good set of results in the demanding Cross load test, as shown above.

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 10 15 15 10
200W 10 15 15 10
400W 10 15 25 15
600W 10 15 30 15
800W 15 15 35 15
1000W 15 20 40 20
1250W 15 20 40 20

Noise suppression is very good. All of the rails exhibit very low ripple and the +12v rail for instance peaks at 40mV, well within the rated specifications.

Efficiency (%)
100W
85.4
200W
88.6
400W
89.8
600W
92.0
800W
91.4
1000W 90.7
1250W 89.8

The overall efficiency results are excellent, peaking at 92% at 50% load. This drops to 90% efficiency at full load … a very impressive result.

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 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
200W
28.0
400W
28.0
600W
28.5
800W 31.2
1000W 33.2
1250W 34.1

The Seasonic X-Series 1250W power supply is basically silent until around 650-700W load is demanded and the fan starts spinning up at a faster cycle. At full load, the fan is clearly audible, although not that intrusive.

Temperature (c)
Intake
Exhaust
100W
37
40
200W
37
44
400W
39
47
650W
41
49
800W
42
51
1000W 44 53
1250W 47 57

Temperatures are well controlled as the fan spins actively once load hits 1000W load and beyond.

Maximum load
Efficiency
1355W
88.0

Pushing the power supply above its rated limits generates an efficiency level of around 88.0%. This is not a viable ‘real world’ situation, but its interesting nonetheless.

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