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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
|
0.95
|
3.34
|
0.93
|
5.04
|
5.13
|
12.00
|
0.50
|
5.05
|
0.20
|
-12.08
|
|
150W
|
1.65 |
3.34
|
1.66
|
5.04
|
10.61
|
11.98
|
1.00
|
5.05
|
0.20
|
-12.07
|
|
375W
|
3.00
|
3.34
|
3.02
|
5.03
|
28.11
|
11.95
|
1.50
|
5.04
|
0.30
|
-12.07
|
| 565W |
4.05
|
3.33
|
4.07
|
5.02
|
42.94
|
11.92
|
2.00
|
4.99 |
0.30
|
-12.07
|
|
750W
|
4.90
|
3.31
|
5.24
|
5.01
|
57.48
|
11.90
|
2.50
|
4.98
|
0.50
|
-12.06
|
Load regulation proves to be very good, holding within 2% of the recommended guidelines.
| Corsair SF750 SFX | Maximum Load |
| 788W |
We managed to reach around 788W before the unit would shut down gracefully, after the protection kicked in. This is around 40 watts more than the rated output.
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 | 3.34 | 1.0 | 5.03 | 60.0 | 11.88 | 0.2 | -12.07 | 0.50 | 5.03 |
| 154W | 15.0 | 3.29 | 15.0 | 4.97 | 2.0 | 12.03 | 0.2 | -12.06 | 0.50 | 5.06 |
The unit passes our Cross Load testing without any problems. When hit with 60 AMPS the +12V rail held at 11.88. Not a very realistic situation in real life, but a good sign that the design works well.
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 | 5 | 10 | 5 |
| 150W | 5 | 5 | 10 | 10 |
| 375W | 5 | 5 | 15 | 10 |
| 565W | 5 | 10 | 20 | 10 |
| 750W | 5 | 10 | 20 | 10 |
Noise suppression results are superb, hitting 5mV and 10mV on +3.3V and +5V rails respectively. The +12V rail peaks at 20mV under full load conditions. Great results really overall.
|
Efficiency (%) 240V
|
|
|
75W
|
90.4
|
|
150W
|
92.4
|
|
375W
|
94.2
|
|
565W
|
93.6
|
|
750W
|
92.7
|
Efficiency is excellent, peaking at just over 94% around 50% load. At full load the power supply maintains a 92.7% efficiency level, which is impressive.
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
|
29.3
|
|
565W
|
35.7
|
| 750W | 38.9 |
The 90mm fan is not active when the power supply is running at lower power demands. We didn't hear any coil whine either, which is excellent. At higher loads, the fan does spin up a little more, becoming more audible when the load hits around 600 watts. At full load the fan is clearly audible, but it is only 90mm and we would expect this.
This is not the kind of power supply you would want to be running at 750 watt all the time anyway. I personally found that the fan wasn't too annoying at all until the system was loaded to more than 600 watts.
|
Temperature (c)
|
||
|
Intake
|
Exhaust
|
|
|
75W
|
36
|
40
|
|
150W
|
38
|
42
|
|
375W
|
39
|
47
|
|
565W
|
45
|
54
|
|
750W
|
47
|
57
|
The large fan works well to expel heat out the rear of the chassis. The overall results are very good indeed.
|
Maximum load
|
Efficiency
|
|
788W
|
91.6
|
At 788 watts, the efficiency level measures 91.6%. Not a practical situation to be running 24/7, but worth noting.
