OCC ATX Power Supply Testing Methodology
paulktreg - June 11, 2008Testing (Continued):
Efficiency & Power Factor
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ATX12V V2.2 Minimum Efficiency vs. Load
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Loading
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Full
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Typical
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Light
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Required Minimum Efficiency
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70%
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72%
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65%
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Recommended Minimum Efficiency
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77%
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80%
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75%
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During the Voltage Regulation tests, a note of the relevant figures required to calculate the efficiency of the power supply will be made and the results given in tabular form as shown below:
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Output And Efficiency
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DC Load (W)
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AC Load (VA)
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AC Load (W)
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PF
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Efficiency (%)
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Pass/Fail
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173.43
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232
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216
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0.93
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80.3
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Pass
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462.11
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615
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598
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0.97
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77.3
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Pass
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569.24
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797
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779
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0.98
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73.1
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Pass
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I do appreciate any concerns some people may have that are familiar with AC theory. If the Power Factor and VA values are taken into account, the efficiency value would be slightly higher, but I am for now going to stick with this rather simplistic way of presenting the results.
AC Ripple On DC Outputs
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ATX12V Version 2.2 AC Ripple/Noise Tolerance Maximums
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DC Output
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+3V3
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+5V0
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+12V0(1)
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+12V0(2)
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-12V0
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+5VSB
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Ripple (mV p-p)
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50
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50
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120
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120
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120
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50
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The maximum ripple/noise will occur at the mains frequency before and after rectification (50Hz – 100Hz) and to a greater extent at the switching frequency of the power supply. The switching frequency will be different for all power supplies and will usually be set above audible range at >20kHz and for this reason, I will scan up to and beyond 100kHz to find the maximum level.
The noise/ripple on the DC lines will be measured with an oscilloscope at the maximum loading of the power supply and the results presented in tabular form, as shown below:
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OCZ Stealth X Stream AC Ripple/Noise Measurements
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DC Output
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+3V3
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+5V0
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+12V0(1)
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+12V0(2)
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-12V0
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+5VSB
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Ripple (mV p-p)
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40
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50
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120
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120
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100
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40
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Pass/Fail
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Pass
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Pass
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Pass
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Pass
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Pass
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Pass
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Temperature, Noise Level & Fan Speed
The testing of the power supply temperatures involves too many variables to draw any valid conclusions. The temperature of the air leaving the unit will depend to a large extent on the ambient air temperature, the enclosure, the cooling of the CPU, case cooling fans fitted, etc., etc. Do not place too much importance on any results given here and regard them as for information only. I will raise any concerns regarding temperature if I feel there may be a problem.
The temperature of the air entering and leaving the power supply will be monitored and the results given in tabular form, as shown below:
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DC Loading
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Temp In (°C)
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Temp Out (°C)
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Δ Temp (°C)
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Fan Speed (RPM)
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173.43W
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20.2
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26.0
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5.8
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1245
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462.11W
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19.2
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28.8
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9.6
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1995
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569.24W
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19.6
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32.0
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12.4
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2005
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This test will be performed with a digital thermometer and a type K thermistor in the air path. I appreciate this is a rather crude method, but as long as the thermistor sensor is in a consistent position for all power supply reviews it may prove informative.
The fan speed will be monitored at the various load levels using an optical tachometer. This will involve the attachment of a piece of reflective tape to one of the fan blades and a direct, very accurate, speed measurement in rotations per minute given.
I do not have access to a sound level meter at this time and all noise levels will be my own personal opinion, which I appreciate may differ from your own.
