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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
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DC Output Load Regulation
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||||||||||
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Combined DC Load |
+3.3V
|
+5V
|
+12V
|
+5VSB
|
-12V | |||||
|
A
|
V
|
A
|
V
|
A
|
V
|
A
|
V
|
A | V | |
|
174W
|
3.27
|
3.35
|
3.25
|
5.00
|
11.55
|
12.00
|
0.76
|
5.02
|
0.12 | -12.00 |
|
352W
|
7.55
|
3.33
|
7.55
|
4.99
|
23.08
|
12.00
|
1.52
|
5.02
|
0.25 | -12.00 |
|
525W
|
11.27
|
3.31
|
11.29
|
4.97
|
34.53
|
11.97
|
2.26
|
5.01
|
0.37 | -12.01 |
|
700W
|
15.05
|
3.31
|
15.05
|
4.94
|
46.64
|
11.92
|
3.02
|
5.00
|
0.50 | -12.01 |
The Silverstone Strider Plus 700W delivers decent regulation with minor droop on all rails.
| Silverstone Strider Plus 700W | Maximum Load |
| 731W |
We managed to squeeze 731W 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 | 3.35 | 1.0 | 5.00 | 48.0 | 11.90 | 0.2 | -12.01 | 0.5 | 5.01 |
| 190W | 18.2 | 3.30 | 20.1 | 4.92 | 2.0 | 12.00 | 0.2 | -12.01 | 0.5 | 5.01 |
Cross load results rate as decent, with the +12V rail dropping from 12.00V to 11.90V when hit with 48A.
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 | 25 | 10 |
| 352W | 15 | 10 | 35 | 10 |
| 525W | 15 | 15 | 55 | 15 |
| 700W | 25 | 15 | 75 | 15 |
The unit scores reasonably well in this test with +3.3V and +5V rails peaking at 25mV and 15mV respectively. The +12V rail crept up a little higher than we would like to see, hitting 75mV at full load. This is still within rated industry tolerance levels.
|
Efficiency (%)
|
|
|
174W
|
82.24
|
|
352W
|
85.59
|
|
525W
|
84.23
|
|
700W
|
82.32
|
Efficiency is excellent, peaking over 92 percent at 50 percent load. At full load this drops to just over 82 percent 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 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)
|
|
|
174W
|
<28.0
|
|
352W
|
32.7
|
|
525W
|
34.3
|
|
700W
|
36.8
|
Under modest load the fan spins very slowly, barely heard at a reasonable distance. At 50% load the fan spins up a little, although it is still relatively quiet. Under higher loads, the fan gets faster, hitting a peak noise level of 36.7dBa. This is clearly audible and not something you will want to deal with all the time. That said if you need to deliver a constant 650-700 watts, you need a more substantial unit anyway.
|
Temperature (c)
|
||
|
Intake
|
Exhaust
|
|
|
174W
|
36
|
41
|
|
352W
|
38
|
47
|
|
525W
|
42
|
54
|
|
700W
|
47
|
60
|
The internal temperatures are maintained well, rising to a maximum 13c above ambient at full load in our test environment.
|
Maximum load
|
Efficiency
|
|
731W
|
81.8
|
We measured the efficiency beyond the rated limits of the supply and recorded 81.8% at 731W. Its not a real world everyday rating, but interesting regardless.
