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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 2,500 Watt DC load. This has recently been upgraded to accommodate a higher power output.
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 test at 230V.
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
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DC Output Load Regulation
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||||||||||
|
Combined DC Load |
+3.3V
|
+5V
|
+12V
|
+5VSB
|
-12V | |||||
|
A
|
V
|
A
|
V
|
A
|
V
|
A
|
V
|
A | V | |
|
75W
|
0.95
|
3.30
|
0.93
|
5.01
|
5.13
|
12.10
|
0.50
|
5.07
|
0.20
|
-12.05
|
|
150W
|
1.65 |
3.30
|
1.66
|
5.01
|
10.61
|
12.08
|
1.00
|
5.07
|
0.20
|
-12.05
|
|
375W
|
3.00
|
3.30
|
3.02
|
5.01
|
28.11
|
12.07
|
1.50
|
5.06
|
0.30
|
-12.04
|
| 565W |
4.05
|
3.30
|
4.07
|
5.00
|
42.94
|
12.05
|
2.00
|
5.05 |
0.30
|
-12.02
|
|
750W
|
4.90
|
3.30
|
5.24
|
5.00
|
57.48
|
12.02
|
2.50
|
5.03
|
0.50
|
-12.04
|
Load regulation is not bad across all rails. Not the best results we have seen, but nothing ugly reared its head during the testing.
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 | 3.30 | 1.0 | 5.01 | 60.0 | 12.02 | 0.2 | -12.02 | 0.50 | 5.06 |
| 154W | 15.0 | 3.27 | 15.0 | 4.97 | 2.0 | 12.11 | 0.2 | -12.01 | 0.50 | 5.06 |
The unit passes the cross load tests – not the greatest results, but it performed within spec. When hit with 60A the +12V rail held at 12.14.
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 | 8 | 16 | 15 | 7 |
| 150W | 11 | 18 | 18 | 12 |
| 375W | 13 | 20 | 22 | 15 |
| 565W | 15 | 22 | 27 | 17 |
| 750W | 18 | 24 | 35 | 19 |
Ripple suppression is pretty good, falling well within industry rated tolerances, peaking at 18mV and 24mV respectively on the +3.3V and +5V lines and 35mV on the +12V line.
|
Efficiency (%) 230V
|
|
|
75W
|
83.8
|
|
150W
|
88.2
|
|
375W
|
89.5
|
|
565W
|
88.6
|
|
750W
|
86.5
|
As this is basically an 80 Plus Bronze rated unit, efficiency levels are fine – peaking at 89.5% efficiency and dropping to 86.5% efficiency 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)
|
|
|
75W
|
<28.0
|
|
150W
|
<28.0
|
|
375W
|
33.4
|
|
565W
|
37.4
|
| 750W | 41.3 |
At lower load demands, the fan spins very slowly and is not audible to our meter (over ambient noise) or the human ear. When load reaches around 500W the fan starts to spin up rapidly to help deal with rising heat levels. At full load the fan was spinning at around 1,800 rpm.
|
Temperature (c)
|
||
|
Intake
|
Exhaust
|
|
|
75W
|
36
|
41
|
|
150W
|
38
|
45
|
|
375W
|
39
|
53
|
|
565W
|
45
|
59
|
|
750W
|
47
|
64
|
Temperatures are well maintained through the range.
