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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 run 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
• Extech digital sound level meter
• 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
|
0.95
|
3.35
|
0.93
|
5.04
|
6.03
|
12.04
|
0.50
|
5.01
|
0.20 | -12.02 |
|
225W
|
1.70
|
3.34
|
1.70
|
5.04
|
12.38
|
12.04
|
1.00
|
5.01
|
0.20 | -12.03 |
|
450W
|
3.00
|
3.34
|
3.05
|
5.03
|
32.24
|
12.03
|
1.50
|
5.00
|
0.30 | -12.03 |
| 675W | 4.07 | 3.33 | 4.05 | 5.01 | 49.00 | 12.02 | 2.00 | 5.00 | 0.30 | -12.03 |
|
850W
|
5.00
|
3.34
|
5.23
|
5.03
|
65.59
|
12.01
|
2.50
|
5.00
|
0.50 | -12.03 |
Load regulation is superb with all rails exhibiting very minor fluctuation under load.
| Seasonic PRIME 850W Platinum 850W |
Maximum Load |
| 932W |
We managed to get the power supply to deliver 932W before it would shut down, delivering around 82W more than 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 | |
| 760W | 1.0 | 3.35 | 1.0 | 5.04 | 60.0 | 12.00 | 0.2 | -12.02 | 0.50 | 5.00 |
| 165W | 15.0 | 3.32 | 18.0 | 5.02 | 2.0 | 12.04 | 0.2 | -12.01 | 0.50 | 5.00 |
The power supply dealt with the demanding cross load test very well exhibiting little fluctuation. It was tasked with 60A on the +12V rail and it held at 12.00V. The other rails delivered excellent results also.
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 | 5 | 5 | 5 | 5 |
| 225W | 5 | 5 | 15 | 5 |
| 450W | 5 | 5 | 15 | 5 |
| 675W | 5 | 5 | 20 | 10 |
| 850W | 10 | 5 | 25 | 10 |
Noise suppression results are really impressive, hitting 10mV and 5mV on +3.3V and +5V rails respectively. The +12V rail peaks at 25mV under full load conditions. Great results really overall.
|
Efficiency (%)
|
|
|
100W
|
89.4
|
|
225W
|
91.7
|
|
450W
|
94.1
|
|
675W
|
92.3
|
| 850W | 91.4 |
Efficiency is extremely impressive, peaking at just over 94 percent at 50 percent load. This drops to around 91.5 percent 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)
|
|
|
100W
|
<28.0
|
|
225W
|
<28.0
|
|
450W
|
30.7
|
|
675W
|
33.9
|
| 850W | 35.6 |
The large fan spins relatively slowly under most load conditions, it is only in the last 200 watts of rated power output that it spins up and can be audible. It is a quiet 850 watt power supply and rates highly in regards to low levels of noise emission.
|
Temperature (c)
|
||
|
Intake
|
Exhaust
|
|
|
100W
|
37
|
39
|
|
225W
|
38
|
41
|
|
450W
|
40
|
48
|
|
675W
|
45
|
53
|
|
850W
|
47
|
59
|
The high levels of efficiency of this unit help reduce expelled heat. At full load we measured a +12c variable.
|
Maximum load
|
Efficiency
|
|
932 watts
|
90.8
|
At 932 watts, the efficiency level measures 90.8%. Not a practical situation to be running 24/7, but worth noting.
