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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
|
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
|
3.35
|
0.92
|
5.02
|
5.12
|
12.02
|
0.50
|
5.01
|
0.20
|
-12.04
|
|
150W
|
1.67
|
3.35
|
1.65
|
5.01
|
10.67
|
12.01
|
1.00
|
5.00
|
0.20
|
-12.04
|
|
375W
|
3.00
|
3.34
|
3.04
|
5.00
|
28.14
|
11.98
|
1.50
|
5.00
|
0.30
|
-12.03
|
| 565W |
4.00
|
3.34
|
4.05
|
4.98
|
42.95
|
11.95
|
2.00
|
4.99 |
0.30
|
-12.04
|
|
750W
|
4.90
|
3.34
|
5.20
|
4.96
|
57.50
|
11.94
|
2.50
|
4.99
|
0.50
|
-12.03
|
Load regulation rates as very strong with no discernable problems.
| FSP Hydro PTM 750W |
Maximum Load |
| 837W |
We managed to reach around 837W before the unit would shut down gracefully. Or another 87 watts over the rated maximum.
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 | 5.02 | 60.0 | 11.90 | 0.2 | -12.02 | 0.50 | 5.00 |
| 154W | 15.0 | 3.33 | 15.0 | 4.94 | 2.0 | 12.03 | 0.2 | -12.03 | 0.50 | 5.01 |
The unit passes our Cross Load testing. The +3.3V rail holds rock steady around 3.34/3 while there is some fluctuation on the +5V rail, dropping from around 5.02 to 4.94 when hit with 15A. The +12V rail drops from 12.03 to 11.90 when hit with 60A. Decent results.
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 | 10 | 15 | 5 |
| 375W | 10 | 10 | 15 | 10 |
| 565W | 10 | 15 | 20 | 15 |
| 750W | 10 | 15 | 25 | 15 |
Ripple suppression is very good, and well within the industry tolerance levels. +3.3V and +5V rails peak at 10mV and 15mV respectively. The +12V rail peaks at 25mV.
|
Efficiency (%)
|
|
|
75W
|
88.6
|
|
150W
|
92.4
|
|
375W
|
94.3
|
|
565W
|
92.4
|
|
750W
|
91.8
|
The power supply delivers great efficiency results, peaking at 94.3% at 50% load. This drops to around 92% 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
|
30.7
|
|
565W
|
33.5
|
| 750W | 36.7 |
At 370 watts demand the large fan starts to spin up a little, hitting a noise rating at just under 31dBa. As the last 200 watts are demanded the fan spins up with a maximum measurement of just under 37dBa in our tests. The fan is audible at a full 750watt load but its not really that intrusive due to the pitch. Generally its a fairly quiet unit especially under 500 watts load.
|
Temperature (c)
|
||
|
Intake
|
Exhaust
|
|
|
75W
|
36
|
38
|
|
150W
|
38
|
43
|
|
375W
|
39
|
46
|
|
565W
|
45
|
53
|
|
750W
|
47
|
57
|
The large 135mm fan cools very well, holding temperatures well inside the ‘safe’ zone.
|
Maximum load
|
Efficiency
|
|
837W
|
91.43
|
For those interested, we measured efficiency when stressing the unit to breaking point. 91.43 percent efficiency at 837W … hardly practical, but interesting regardless.
