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Additional technical assistance: Peter McFarland and Jeremy Price.
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 – 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
• SkyTronic DSL 2 Digital Sound Level Meter (6-130dBa)
• 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 | |
|
100W
|
1.55
|
3.35
|
1.78
|
5.04
|
6.66
|
12.18
|
0.50
|
5.02
|
0.20
|
-12.01
|
|
250W
|
3.45
|
3.34
|
4.46
|
5.01
|
17.17
|
12.12
|
1.00
|
5.02
|
0.30
|
-12.01
|
|
500W
|
7.07
|
3.33
|
9.13
|
4.97
|
34.64
|
12.08
|
2.00
|
5.01
|
0.50
|
-12.01
|
| 750W |
11.07
|
3.32
|
13.74
|
4.94
|
52.75
|
12.02
|
2.50
|
5.01
|
0.60
|
-12.02
|
|
1000W
|
16.92
|
3.31
|
18.97
|
4.92
|
72.00
|
11.94
|
3.00
|
5.02
|
0.80
|
-12.02
|
Load regulation is quite good, holding at around 2 percent fluctuation.
| OCZ Fatal1ty 1000W | Maximum Load |
| 1097W |
We managed to get another 97W from the power supply before the protection circuitry kicked in. The protection circuitry worked well and the unit restarted with a lower demand.
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 | |
| 885W | 2.0 | 3.34 | 2.0 | 5.04 | 72.0 | 11.93 | 0.2 | -12.01 | 0.50 | 5.02 |
| 240W | 20.0 | 3.31 | 24.0 | 4.90 | 2.0 | 12.12 | 0.2 | -12.02 | 0.50 | 5.01 |
The power supply handled these tests quite well, although the +5V output dropped down to 4.90 when hit with 24A.
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 | 15 | 5 | 15 | 5 |
| 250W | 15 | 5 | 20 | 5 |
| 500W | 20 | 5 | 25 | 10 |
| 750W | 20 | 10 | 30 | 10 |
| 1000W | 20 | 10 | 40 | 15 |
Ripple suppression is fantastic. The +3.3V output peaks at 20mV, the +5V peaks at 10mV and the +12V peaks at 40mV. All well within rated tolerance levels.
|
Efficiency (%)
|
|
|
100W
|
83.78
|
|
250W
|
88.31
|
|
500W
|
91.45
|
|
750W
|
90.89
|
|
1000W
|
89.02
|
The efficiency results are good. The 1000W power supply peaks at 91.45% efficiency at 50 percent load. At full load this drops to just above 89% efficiency.
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 Refridgerator
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
|
30.3
|
|
750W
|
35.2
|
| 1000W | 38.1 |
If you load the power supply below 500W then it is almost silent. The fan spins up significantly in the last 250W of output, becoming clearly audible at around 750W and becoming loud between 950w-1000W. It isn't practical to be loading this power supply at 1000W on a regular basis, but you will certainly be able to hear it if you do.
|
Temperature (c)
|
||
|
Intake
|
Exhaust
|
|
|
100W
|
35
|
39
|
|
250W
|
36
|
45
|
|
500W
|
39
|
48
|
|
750W
|
43
|
55
|
|
1000W
|
47
|
57
|
The fan becomes very active in the last 200W of total power output and the temperatures are held well inside. We think the designers should have placed bigger heatsinks in the power supply which would have helped lower fan noise levels.
|
Maximum load
|
Efficiency
|
|
1097W
|
88.9
|
Pushing the power supply above its rated limits generates an efficiency level of around 88.9%. This is not a viable ‘real world’ situation, but its interesting nonetheless.
