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Seasonic Snow Silent 750W PSU 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

DC Output Load Regulation

Combined

DC Load

+3.3V
+5V
+12V
+5VSB
-12V
A
V
A
V
A
V
A
V
A V
75W
1.23
3.34
1.19
5.06
4.95
12.13
0.50
5.01
0.20
-12.04
150W
2.17
3.34
2.83
5.06
10.07
12.12
1.00
5.01
0.30
-12.04
375W
6.15
3.33
6.05
5.05
26.15
12.11
1.50
5.01
0.50
-12.05
565W
10.31
3.33
10.86
5.03
38.34
12.08
2.00
5.00
0.60
-12.06
750W
10.72
3.33
13.84
5.03
53.59
12.07
3.00
4.99
0.80
-12.06

Load regulation is fantastic, holding tight within 1.5%

Seasonic Snow Silent 750W PSU Maximum Load
875W

We managed to reach around 875W before the unit would shut down gracefully, after the protection kicked in.

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
734W 1.0 3.32 1.0 5.05 60.0 11.97 0.2 -12.03 0.50 5.01
154W 15.0 3.32 15.0 5.00 2.0 12.10 0.2 -12.02 0.50 5.00

The unit passes our Cross Load testing with a set of excellent results. Even when we hit the +12V output with 60A, the line held at 11.97V.

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
75W 5 10 15 5
150W 10 15 15 5
375W 10 15 25 5
565W 10 15 25 10
750W 20 20 40 15

The +12V output peaked at 40mV at full load which is a good result. +3.3V peaked at 20mW and the +5V output hit 20mV at full load. No issues with the power supplies noise suppression.

Efficiency (%)
75W
88.56
150W
90.67
375W
94.21
565W
93.45
750W
92.12

The power supply delivers great efficiency results, peaking at over 94% at 50% load. This drops to around 92% at full load. Impressive results.

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)
75W
<28.0
150W
<28.0
375W
30.3
565W
32.8
750W 33.9

The fan in the Snow Silent 750W is an exceptional performer, holding at under 34dBa at full load. We would class this power supply as very quiet most of the time – almost inaudible with a general load under 300 watts. The fan can be heard at loads over 500 watt – however the move to a quality fluid dynamic bearing fan has certainly helped.

Temperature (c)
Intake
Exhaust
75W
36
39
150W
38
40
375W
39
43
565W
45
51
750W
47
59

The high levels of efficiency of this unit help reduce expelled heat. At full load we measured a +12c variable.

Maximum load
Efficiency
875W
91.5

For those interested, we measured efficiency when stressing the unit to breaking point.91.5 percent efficiency at 875W … hardly practical, but interesting regardless.

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