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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. Over the coming months this configuration is likely to be adjusted further and fine tuned. 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
We are combining 12V output into a single result.
|
DC Output Load Regulation
|
||||||||||
|
Combined DC Load |
+3.3V
|
+5V
|
+12V
|
+5VSB
|
-12V | |||||
|
A
|
V
|
A
|
V
|
A
|
V
|
A
|
V
|
A | V | |
|
75W
|
1.22
|
3.35
|
1.19
|
5.12
|
4.90
|
12.06
|
0.50
|
5.03
|
0.20
|
-12.05
|
|
150W
|
2.18
|
3.34
|
2.80
|
5.09
|
10.00
|
12.04
|
1.00
|
5.02
|
0.30
|
-12.04
|
|
375W
|
6.15
|
3.32
|
6.00
|
5.06
|
26.10
|
12.03
|
1.50
|
5.01
|
0.50
|
-12.04
|
| 565W |
10.30
|
3.30
|
10.87
|
5.03
|
38.34
|
12.00
|
2.00
|
4.99 |
0.60
|
-12.04
|
|
750W
|
10.74
|
3.28
|
13.86
|
5.01
|
53.51
|
11.98
|
3.00
|
4.98
|
0.80
|
-12.03
|
The EarthWatts shows to have good load regulation. These are great results and the +3.3V and 5V rails remained firmly within +/-2% of the nominal voltage instead of the recommended +/-5% and the +12V rail held within +/- 1%, even when it was forced to deliver over 53 Amps.
| EarthWatts 750W Green | Maximum Load |
| 803W |
We managed to reach around 803W before the unit would shut down gracefully, after the protection kicked in.
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 | |
| 734W | 1.0 | 3.32 | 1.0 | 5.04 | 60.0 | 11.95 | 0.2 | -12.03 | 0.50 | 5.01 |
| 154W | 15.0 | 3.29 | 15.0 | 4.98 | 2.0 | 12.01 | 0.2 | -12.04 | 0.50 | 5.00 |
Much like the 650W model, the fluctuation is held safely within the rated parameters, even when we load the 12V line with 60A.
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 Antec unit complied with the ATX standard.
| AC Ripple (mV p-p) | ||||
| DC Load | +3.3V | +5V | +12V | 5VSB |
| 75W | 5 | 5 | 15 | 5 |
| 150W | 10 | 10 | 25 | 10 |
| 375W | 15 | 10 | 30 | 15 |
| 565W | 20 | 15 | 40 | 15 |
| 750W | 25 | 15 | 50 | 20 |
Ripple results are very impressive, across the board. The 12V rail registered around 50 mV at full load with our equipment, which is well within the Tolerance guidelines.
|
Efficiency (%)
|
|
|
75W
|
83.87
|
|
150W
|
87.65
|
|
375W
|
88.19
|
|
565W
|
87.21
|
|
750W
|
83.65
|
For a 80 Plus Bronze specified unit, these results are very strong, peaking at just over 88 percent at 50 percent load. At full load the efficiency drops to just under 84 percent.
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)
|
|
|
75W
|
27.9
|
|
150W
|
28.3
|
|
375W
|
29.8
|
|
565W
|
33.4
|
| 750W | 34.2 |
Noise levels are quite low, with the system only becoming audible in the final 25% of output. Under 400W load it would be hard to know the unit was actually on.
|
Temperature (c)
|
||
|
Intake
|
Exhaust
|
|
|
75W
|
36
|
38
|
|
150W
|
36
|
40
|
|
375W
|
39
|
46
|
|
565W
|
42
|
51
|
|
750W
|
44
|
54
|
Exhaust temperatures are good, rising to a 10c above ambient result at full load. The 135mm manages to combine a reasonably low level of noise with high airflow.
|
Maximum load
|
Efficiency
|
|
803W
|
82.3
|
For those interested, we measured efficiency when stressing the unit to breaking point. 82.3 percent efficiency at 803W … hardly practical, but interesting regardless.
