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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. 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
|
4.99
|
6.00
|
12.04
|
0.50
|
5.01
|
0.20 | -12.00 |
|
170W
|
1.70
|
3.33
|
1.67
|
4.98
|
12.35
|
12.04
|
1.00
|
5.01
|
0.20 | -12.00 |
|
425W
|
3.00
|
3.33
|
3.05
|
4.98
|
32.20
|
12.03
|
1.50
|
5.01
|
0.30 | -12.00 |
| 640W | 4.05 | 3.29 | 4.05 | 4.98 | 49.00 | 12.01 | 2.00 | 5.01 | 0.30 | -12.00 |
|
850W
|
5.00
|
3.28
|
5.23
|
4.98
|
65.52
|
12.00
|
2.50
|
5.00
|
0.50 | -12.01 |
Load regulation is really good on all the rails but we noticed some dips on the +3.3V rail.
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 | 5.00 | 60.0 | 12.00 | 0.2 | -12.01 | 0.50 | 5.01 |
| 165W | 15.0 | 3.26 | 18.0 | 4.96 | 2.0 | 12.02 | 0.2 | -12.00 | 0.50 | 5.00 |
The power supply coped fairly well, but there is some noticeable droop on the +3.3V rail which could be improved
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 | 7 | 11 | 15 |
| 225W | 6 | 9 | 16 | 18 |
| 450W | 11 | 12 | 21 | 21 |
| 675W | 14 | 14 | 27 | 24 |
| 850W | 16 | 15 | 36 | 29 |
Noise suppression is strong across all the rails. Specifically on the minor rails.
|
Efficiency (%) 240V
|
|
|
100W
|
89.3
|
|
225W
|
91.4
|
|
450W
|
93.2
|
|
675W
|
92.1
|
| 850W | 91.4 |
The efficiency results are really good, peaking at around 93% between 45-55% load, and dropping to around 91.5% at full load. An impressive 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
|
31.3
|
|
675W
|
34.2
|
| 850W | 39.1 |
The fan remains inactive at lower power demands with some action appearing once the power demand exceeds 300 watts. PSU noise rises and becomes audible around 650 watts load. At full load the fan is clearly working quite hard to help maintain temperatures and stability.
|
Temperature (c)
|
||
|
Intake
|
Exhaust
|
|
|
100W
|
37
|
40
|
|
225W
|
38
|
42
|
|
450W
|
40
|
44
|
|
675W
|
45
|
53
|
|
850W
|
46
|
58
|
Temperatures inside the chassis remain relatively cool even at higher load levels. The fan at higher demands really helps ensure the temperatures never become a problem at the cost of noise emissions.
