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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
|
3.32
|
0.90
|
5.08
|
7.35
|
12.00
|
0.50
|
5.01
|
0.20
|
-12.01
|
|
200W
|
1.60
|
3.32
|
1.64
|
5.08
|
15.13
|
12.00
|
1.00
|
5.02
|
0.20
|
-12.00
|
|
500W
|
3.21
|
3.32
|
3.24
|
5.08
|
38.60
|
12.00
|
1.50
|
5.01
|
0.20
|
-12.01
|
| 750W |
4.03
|
3.32
|
4.17
|
5.08
|
58.53
|
12.00
|
2.00
|
5.01
|
0.30
|
-12.00
|
|
1000W
|
5.45
|
3.32
|
5.51
|
5.08
|
78.13
|
11.99
|
2.50
|
5.02
|
0.30
|
-12.01
|
The load regulation of this power supply is pretty good across the board.
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 | 3.32 | 2.0 | 5.08 | 72.0 | 11.98 | 0.2 | -12.01 | 0.50 | 5.00 |
| 240W | 20.0 | 3.31 | 23.0 | 5.06 | 2.0 | 12.00 | 0.2 | -12.01 | 0.50 | 5.00 |
The supply handled our cross load test very well, holding stable results across the range.
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/lower) 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 | 8 | 9 | 8 | 6 |
| 250W | 11 | 10 | 10 | 6 |
| 500W | 12 | 11 | 13 | 9 |
| 750W | 14 | 12 | 15 | 11 |
| 1000W | 16 | 14 | 22 | 12 |
The unit passes the ripple test without any issues, falling well within industry rated tolerance across the board. Both secondary rails peak at around 15mV at full load, with the primary +12V rail peaking at around 22mV.
|
Efficiency (%)
|
|
|
100W
|
90.4
|
|
250W
|
92.8
|
|
500W
|
94.5
|
|
750W
|
92.5
|
|
1000W
|
90.7
|
The efficiency results are excellent, peaking at 94.5% at around 50% load. This drops to around 91.4% 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 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
|
<28.0
|
|
750W
|
29.3
|
| 1000W | 32.4 |
In general use the power supply is extremely quiet, and it is only when 750 watts is tasked from it that the fan starts to actively ramp up to deal with rising temperatures inside the chassis.
At full load, the fan is audible, but still very quiet, at just over 32dBa. Some great results from this fan they are using. I did notice a little bearing noise at lower RPM's (often inherent with dual ball bearing fan designs) but it was not anything that would stop me using the power supply in my own system.
|
Temperature (c)
|
||
|
Intake
|
Exhaust
|
|
|
100W
|
37
|
40
|
|
250W
|
38
|
43
|
|
500W
|
40
|
48
|
|
750W
|
45
|
54
|
|
1000W
|
47
|
60
|
Temperatures inside the chassis are excellent thanks to the efficiency levels, and at higher loads the fan is actively pushing warm air outside the chassis, ensuring the temperatures are never too much of an issue.
