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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 | |
|
174W
|
3.26
|
3.38
|
3.23
|
5.05
|
11.52
|
12.19
|
0.76
|
5.17
|
0.12 | -12.09 |
|
352W
|
7.52
|
3.35
|
7.52
|
5.02
|
23.03
|
12.18
|
1.52
|
5.08
|
0.25 | -12.12 |
|
525W
|
11.23
|
3.28
|
11.27
|
4.97
|
34.47
|
12.08
|
2.26
|
5.02
|
0.37 | -12.16 |
|
700W
|
15.02
|
3.25
|
15.03
|
4.92
|
46.52
|
12.02
|
3.0
|
4.98
|
0.50 | -12.18 |
The LEPA G700 is able to deliver solid load regulation on all of the outputs throughout our varied load tests – even when fully loaded, a situation not often experienced in the real world.
| LEPA G700W | Maximum Load |
| 787W |
We managed to squeeze 787W from the PSU before it would shut down safely.
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.
| Combined DC Load | +3.3V | +5V | +12V | -12V | +5VSB | |||||
| A | V | A | V | A | V | A | V | A | V | |
| 590W | 1.0 | 3.32 | 1.0 | 5.02 | 48.0 | 11.88 | 0.2 | -11.93 | 0.5 | 5.01 |
| 190W | 18.2 | 3.27 | 20.1 | 4.95 | 2.0 | 12.03 | 0.2 | -11.97 | 0.5 | 5.00 |
The LEPA unit deals very well with the crossloading tests with very little fluctuation throughout.
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 |
| 174W | 15 | 10 | 35 | 10 |
| 352W | 20 | 10 | 40 | 15 |
| 525W | 25 | 15 | 45 | 15 |
| 700W | 30 | 25 | 55 | 20 |
Ripple results were very good, with the +12V output peaked at 55 mV, well within the tolerance guidelines. The +5V output peaked at 25mV, also well within the rated tolerance figures. The +3.3V output hit 30mV when fully loaded, well within specifications.
|
Efficiency (%)
|
|
|
174W
|
89.12
|
|
352W
|
92.56
|
|
525W
|
91.23
|
|
700W
|
88.87
|
The efficiency figures are impressive, achieving 92.56% efficiency at 50% load. This drops to just under 89% 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 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)
|
|
|
174W
|
28.8
|
|
352W
|
29.5
|
|
525W
|
33.8
|
|
700W
|
35.8
|
The power supply is quiet, emitting some noise once it starts delivering around 500W of power. The noise emissions rise to just under 36 dBa at full load.
|
Temperature (c)
|
||
|
Intake
|
Exhaust
|
|
|
174W
|
36
|
38
|
|
352W
|
38
|
44
|
|
525W
|
40
|
47
|
|
700W
|
43
|
51
|
The large Twister fan, as we hoped, keeps temperatures well in check, rising to a 8c above ambient figure at full load.
|
Maximum load
|
Efficiency
|
|
787w
|
87.3%
|
We measured the efficiency beyond the rated limits of the supply and recorded 87.3% at 787W. Its not a real world rating, because if you need this power output 24/7 you would need to aim higher up the product range.
