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Corsair RM850x ATX V3.1 (3rd Gen 2024) Review

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. We run at 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
85W
0.95
3.33
0.92
5.01
6.00
12.01
0.50
5.00
0.20 -12.00
170W
1.70
3.33
1.67
5.01
12.35
12.01
1.00
5.01
0.20 -12.01
425W
3.00
3.33
3.05
5.01
32.20
12.00
1.50
5.00
0.30 -12.01
640W 4.05 3.33 4.05 5.01 49.00 11.99 2.00 5.00 0.30 -12.00
850W
5.00
3.33
5.23
5.01
65.52
11.98
2.50
5.00
0.50 -12.01

Load regulation is really good on all the rails.

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 5.01 60.0 11.99 0.2 -12.02 0.50 5.01
165W 15.0 3.32 18.0 5.01 2.0 12.01 0.2 -12.01 0.50 5.01

The power supply dealt with the demanding cross load test without any major concerns.

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 8 10 10 10
225W 11 12 12 11
450W 12 13 15 13
675W 13 14 18 14
850W 17 16 23 15

Noise suppression is exceptional across +3.3V, +5V rails. The +12V rail results are superb as well.

Efficiency (%) 240V
100W
89.5
225W
91.5
450W
92.0
675W
91.3
850W 89.4

The efficiency results are really good, peaking at around 92% between 45-55% load, and dropping to around 89.4% at full load. A good set of 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)
100W
<28
225W
<28
450W
32.1
675W
34.7
850W 37.8

The fan is quiet at slower speeds before spinning up at 600 Watts to compensate for rising temperatures inside the chassis. At full load it's clearly audible.

Temperature (c)
Intake
Exhaust
100W
37
41
225W
38
44
450W
40
52
675W
45
57
850W
46
60

Temperatures inside the chassis remain solid even at higher load levels.

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