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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 test ambient temperatures 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
• SkyTronic DSL 2 Digital Sound Level Meter (6-130dBa)
• 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 | |
|
100W
|
0.90
|
3.33
|
0.90
|
5.04
|
7.35
|
12.16
|
0.50
|
5.00
|
0.20
|
-12.01
|
|
200W
|
1.60
|
3.33
|
1.64
|
5.04
|
15.13
|
12.15
|
1.00
|
5.00
|
0.20
|
-12.02
|
|
500W
|
3.21
|
3.33
|
3.24
|
5.03
|
38.60
|
12.08
|
1.50
|
5.00
|
0.20
|
-12.01
|
| 750W |
4.03
|
3.32
|
4.17
|
5.01
|
58.53
|
12.03
|
2.00
|
5.00
|
0.30
|
-12.01
|
|
1000W
|
5.45
|
3.32
|
5.51
|
5.01
|
78.13
|
12.00
|
2.50
|
5.01
|
0.30
|
-12.01
|
The load regulation of this power supply is average with a fair bit of fluctuation on +12V.
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.
The power supply had no problems sustaining at constant 1000W load.
| Cross Load Testing | +3.3V | +5V | +12V | -12V | +5VSB | |||||
| A | V | A | V | A | V | A | V | A | V | |
| 885W | 2.0 | 3.33 | 2.0 | 5.03 | 72.0 | 12.00 | 0.2 | -12.02 | 0.50 | 5.01 |
| 240W | 20.0 | 3.31 | 21.0 | 4.98 | 2.0 | 12.15 | 0.2 | -12.01 | 0.50 | 5.01 |
The supply handled our cross load test without any major problems but it is far from the best results we have seen in recent years.
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 | 12 | 12 | 13 | 7 |
| 250W | 13 | 14 | 17 | 11 |
| 500W | 13 | 18 | 22 | 14 |
| 750W | 15 | 20 | 28 | 17 |
| 1000W | 17 | 22 | 32 | 20 |
Ripple noise suppression is pretty decent, with the minor rails falling around the 20mV mark under full load. The +12V rail peaks at around 32mV which is well within industry rated parameters. Not the best we have seen, but not the worst either.
|
Efficiency (%)
|
|
|
100W
|
89.7
|
|
250W
|
90.4 |
|
500W
|
92.6
|
|
750W
|
91.9
|
|
1000W
|
89.8
|
The efficiency results are fine for a gold rated unit, peaking at just over 92% in the sweet spot between 40-60% load. At full load the efficiency drops to just under 90%.
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 SkyTronic DSL 2 Digital Sound Level Meter (6-130dBa) 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
|
<28.0
|
|
250W
|
<28.0
|
|
500W
|
31.1
|
|
750W
|
33.2
|
| 1000W | 36.3 |
At modest loads, the FDB fan is unobtrusive, and while there is no semi-active mode, it's a reasonably quiet power supply under most load situations. In the last 250 watts of load, the fan does ramp up to deal with rising heat inside the chassis. At full load it is clearly audible, but this is not a realistic situation you should be in. If you need 1000 watts all the time, you should be considering a 1500 watt power supply.
|
Temperature (c)
|
||
|
Intake
|
Exhaust
|
|
|
100W
|
37
|
43
|
|
250W
|
38
|
46
|
|
500W
|
40
|
52
|
|
750W
|
45
|
59
|
|
1000W
|
46
|
65
|
Temperatures are pretty good overall.
