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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 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 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
12V output is combined for our testing.
|
DC Output Load Regulation
|
||||||||||
|
Combined DC Load |
+3.3V
|
+5V
|
+12V
|
+5VSB
|
-12V | |||||
|
A
|
V
|
A
|
V
|
A
|
V
|
A
|
V
|
A | V | |
|
500W
|
7.60
|
3.38
|
8.80
|
5.17
|
36.02
|
12.25
|
1.5
|
5.15
|
0.30 | -12.01 |
|
750W
|
12.61
|
3.35
|
14.12
|
5.12
|
52.03
|
12.16
|
2.0
|
5.12
|
0.30 | -12.08 |
|
1000W
|
17.72
|
3.29
|
20.02
|
5.08
|
72.23
|
12.09
|
2.5
|
5.05
|
0.50 | -12.12 |
| 1250W | 18.82 | 3.27 | 24.05 | 5.02 | 90.12 | 12.00 | 3.0 | 5.02 | 0.60 | -12.14 |
|
1500W
|
18.85
|
3.22
|
24.62
|
5.00
|
115.90
|
11.92
|
3.5
|
4.98
|
0.80 | -12.19 |
Load regulation is good, although the +3.3V output suffers from a little dip to 3.22 at full load.
| ThermalTake Toughpower 1500W Modular | Maximum Load |
| 1667W |
We managed to get the PSU to achieve 1667W before it would shut down, delivering around 167W more than the rated specifications.
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 | |
| 1150W | 3.0 | 3.36 | 2.0 | 5.12 | 92.0 | 11.91 | 0.2 | -12.21 | 0.50 | 5.01 |
| 250W | 20.0 | 3.27 | 24.0 | 5.00 | 5.0 | 12.21 | 0.2 | -12.15 | 0.50 | 5.00 |
The power supply passed the cross load tests, falling well within safe parameters, even when hit with 92A on the +12V output.
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 |
| 500W | 10 | 5 | 5 | 10 |
| 750W | 15 | 10 | 10 | 10 |
| 1000W | 20 | 10 | 15 | 15 |
| 1250W | 25 | 15 | 15 | 15 |
| 1500W | 30 | 15 | 25 | 20 |
These ripple results are extremely impressive, especially from the +12V output, which peaks at 25mV at full load, well within the rated guidelines of 120mV. All the other results are great too. 3.3V is a little higher, but still within the tolerance guidelines of 50mV.
|
Efficiency (%)
|
|
|
500W
|
89.11
|
|
750W
|
90.13
|
|
1000W
|
89.32
|
|
1250W
|
88.65
|
| 1500W | 87.76 |
The efficiency ratings are excellent, peaking at over 90 percent when at 50 percent load. It drops to just under 88% 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)
|
|
|
500W
|
29.7
|
|
750W
|
32.4
|
|
1000W
|
33.6
|
|
1250W
|
34.4
|
| 1500W | 35.8 |
The power supply is relatively quiet until around 900W when the fan works a little harder to remove excessive heat. The fan cranks up a little at 1100W, emitting around 34dBa of noise, which holds steady until around 1350W when it steps up another gear, emitting just under 36 dBa. Overall, it is surprisingly quiet throughout the range, and will likely be drown out by other case fans, even when loaded to over 1,000W.
|
Temperature (c)
|
||
|
Intake
|
Exhaust
|
|
|
500W
|
36
|
40
|
|
750W
|
38
|
44
|
|
1000W
|
41
|
50
|
|
1250W
|
45
|
55
|
|
1500W
|
48
|
58
|
The fan handles the internal temperatures well, maintaining good ambient temperatures. It rises to around 10c above ambient at full load.
|
Maximum load
|
Efficiency
|
|
1667W
|
86.3%
|
At 1667W, the efficiency level is still good, measuring 86.3%. Not a practical situation to be running 24/7, but worth noting.
