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Seasonic Prime 850W Titanium Power Supply Review

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

We test in a single +12V configuration.

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
3.34
1.76
5.03
6.66
12.04
0.50
5.02
0.20 -12.02
225W
3.75
3.34
3.86
5.02
15.59
12.03
1.00
5.02
0.20 -12.02
450W
7.54
3.34
8.35
5.02
30.78
12.03
1.50
5.01
0.30 -12.02
675W 11.33 3.33 12.35 5.02 47.46 12.02 2.00 5.01 0.50 -12.01
850W
1.52
3.33
1.17
5.01
63.53
12.02
0.50
5.01
0.20 -12.01

Load regulation is superb with all rails exhibiting very minor fluctuation under load.

Seasonic Prime 850W Titanium Maximum Load
1098W

We managed to get the power supply to deliver 1098W before it would shut down, delivering around 152W more than rated specifications.

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 3.34 1.0 5.03 60.0 12.02 0.2 -12.03 0.50 5.02
165W 15.0 3.32 18.0 5.00 2.0 12.05 0.2 -12.03 0.50 5.02

The power supply exhibited no problems when dealing with our intensive Cross Loading test. It was tasked with 60A on the +12V rail and it held at 12.02V. The other rails delivered excellent results also.

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 5 5
225W 5 5 10 5
450W 5 5 10 5
675W 5 10 15 5
850W 5 10 15 5

Noise suppression results are truly sublime, peaking at 5-10mV on both +3.3V and +5V rails. The +12V rail peaked at 15mV under full load – well within the rated parameters.

Efficiency (%)
100W
91.67
225W
92.75
450W
95.89
675W
94.37
850W 93.44

Efficiency is extremely impressive, peaking at almost 96 percent at 50 percent load. This drops to around 93.5 percent at full load.

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
29.4
675W
33.1
850W 34.2

The large fan spins relatively slowly under most load conditions, it is only in the last 200 watts of rated power output that it spins up and can be audible. That said, with a few standard high grade case fans in the mix, the power supply fan will likely not even be heard.

Temperature (c)
Intake
Exhaust
100W
37
38
225W
38
41
450W
40
45
675W
45
50
850W
47
56

The high levels of efficiency of this unit help reduce expelled heat. At full load we measured a +9c variable.

Maximum load
Efficiency
1098 watts
92.5

At 1098 watts, the efficiency level measures 92.5%. Not a practical situation to be running 24/7, but worth noting.

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