Power Supply Testing Methodology
at EXTREME Overclocking
Date Published: June 2, 2005
Author: Jason Rabel |
How We Measure & Compare:
The amount of information recorded for just a single power supply test could easily be several pages of numbers. However for most people it would be information overload and end up as more confusing than useful. The compiled numbers being reported are (in our opinion) the most important out of the set, and give a good general overview of how the PSU will perform under typical real-world situations.
Measurements are taken at four different load levels, light, typical, heavy, and rated maximum. The first three load levels are as close as we could get to the amounts specified in the ATX12V 2.x specifications for a 400W power supply, and will be the same for every power supply that we test. The maximum rated load level will vary based on the PSU specs, however load will be emphasized on the 12V rail(s) since that is the primary power for the processor & video card these days.
The following information will be listed for each load level tested:
- Load Level (Expressed in Watts, also color-coded)
- Voltages (Each main rail is listed, excluding 5Vsb & -12V)
- Efficiency (Expressed as a percentage, rounded to a whole number)
- Power Factor (Expressed as a number between zero and one)
- Case Temperature (Expressed in degrees Celsius)*
*Note: The case temperature isn't meant to be a comparison of how well a PSU can help cool the system. We give the temperature so that you know exactly how hot it is, demonstrating the durability of the power supply to operate within specified operating conditions.
The chart below shows the ATX12V v2.2 cross regulation graph for a typical 450W power supply. The three primary load levels being tested are more or less evenly distributed with a nice linear increase, and fall within the graphed area. The graph is just a sample "generic" power distribution, manufacturers are free to design their power requirements however they feel is appropriate.
The table below gives slightly more accurate figures for load levels being tested than the graph above. These numbers pretty much fall between 400W & 450W load levels in the ATX12V spec when determining PSU efficiency.
| |
Light |
Typical |
Heavy |
| +3.3V |
3A |
6A |
15A |
| +5V |
1A |
6A |
10A |
| +12V1 |
3A |
5A |
12A |
| +12V2 |
3A |
9A |
12A |
| +5Vsb |
0.5A |
0.5A |
0.5A |
| -12V |
0.2A |
0.2A |
0.2A |
| Watts |
~92W |
~223W |
~392W |
DC Voltage Regulation:
ATX12V specifications call for 5% (or better) voltage regulation on the primary rails, and 10% (or better) on the -12V rail. Obviously the closer the voltages are to nominal (or even slightly above), the better off you will be. Usually the 12V rail will fluctuate the most, and should be the one that you keep your eye on. A low 12V rail often is the culprit behind system instability for overclocked or even stock high-end systems.
| -5% |
-4% |
-3% |
-2% |
-1% |
Nominal |
1% |
2% |
3% |
4% |
5% |
| 3.14 |
3.17 |
3.20 |
3.23 |
3.27 |
3.30V |
3.33 |
3.37 |
3.40 |
3.43 |
3.47 |
| 4.75 |
4.80 |
4.85 |
4.90 |
4.95 |
5.00V |
5.05 |
5.10 |
5.15 |
5.20 |
5.25 |
| 11.40 |
11.52 |
11.64 |
11.76 |
11.88 |
12.00V |
12.12 |
12.24 |
12.36 |
12.48 |
12.60 |
PSU Efficiency:
Minimum efficiency under typical load has increased from 60% in the v1.3 spec, to 70% in the v2.01 spec, to 72% in the v2.2 spec. The more efficient the power supply, the better off you will be in the long-run when it comes to paying your electric bill. The percent of energy not converted is lost as heat, and unless you live in a very cold area then the additional heat is not very helpful.
Safety Considerations:
When something goes wrong, you don't want your power supply blowing up. In fact, any ATX12V power supply *should* pass at bare minimum several regulatory specification requirements and/or standards (depending on country). In addition to these regulatory requirements, there is a section in the ATX12V specs titled, "Catastrophic Failure Protection", which is stated below.
- Should a component failure occur, the power supply should not exhibit any of the following:
- Flame
- Excessive smoke
- Charred PCB
- Fused PCB conductor
- Startling noise
- Emission of molten material
In order to prevent "Catastrophic Failure", a number of protection mechanisms should be in place, which include the following:
- Over-voltage Protection
- Short-circuit Protection
- No-load Operation
- Over-current Protection
- Over-temperature Protection (Optional)
A common problem people have is their system mysteriously shutting down, especially when playing games. This is often caused by the power supply being overloaded, and thanks to these safety measures just mentioned, it automatically shuts-down instead of something bad happening.
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