We will start at the wall socket. The test equipment runs on a dedicated 30 amp feed with isolated ground to ensure that power is sufficient for both the testing equipment and the power supply. Here in the U.S. most household circuits are 15 amps, which, at 120V, would provide about 1800 Watts. Obviously this is not enough for our testing needs, so we have doubled this capacity for good measure.
- TrippLite LC2400 Power Conditioner
Since the power provided by the power grid is susceptible to fluctuations and noise, a 2400 Watt line conditioner is employed to ensure that the test equipment is as isolated as possible. By maintaining a constant 120V along with EMI/RFI noise filtering, all of the power supplies reviewed can be directly compared since the electrical source is at a constant.
- FAST ATE 828 and 4200 Active Load Testers
We employ two FAST ATE load testers that have been modified from their original setup to provide loads for up to four independent 12 V rails. This is the heart of our updated testing methodology. The systems can be programmed with six different amperage loads to provide a reliable, repeatable test for the power supply on all voltage levels; 3.3V, 5.0V, 12V, -12V, 5VSB and -5.0V. The latter one will no longer be used as it has been dropped from the current ATX standard. You can read more about that here.
- Velleman PCSU1000 Digital Oscilloscope
The oscilloscope is connected to the selectable waveform output of the load testers. This allows us to measure ripple to help determine how well the power supply can regulate DC output. The digital oscilloscope is then attached via a USB cable to a laptop to gather waveform data with the included software.
- Kill-A-Watt Power Meter
This handy little item will help us measure the amount of power used at the socket to calculate efficiency. This measurement is simply the amount of power supplied by the PSU divided by the amount of power used. It will also allow us to determine the Power Factor of the PSU which is the ratio of Wattage versus apparent power in VA. A good power supply will use less electricity to deliver the same power as a cheaper power supply.
- The Hotbox Torture Chamber
Our custom built hotbox is used to bring the ambient temperature to about 45 degrees Celsius, validated by a dual output temperature probe. The first probe measures intake temperature of the power supply and the second, the exhaust temperature. This torture test is an effective way to determine simply good from great. While it is not an ATX requirement, many premium power supply manufacturers rate their products at a temperature of 50C, while others opt to measure output at much a more modest 25C.
While the current ATX standard only defines 25C for testing, this value is far too low to be considered realistic for a case operating temperature. Considering a power supply can lose up to 10% of the output for every 10 degrees over 30C, you begin to understand the impact of this hotbox test. Premium power supplies will push their full rating at 50C while lesser units may fail to deliver more than 80% of the rated capacity. This test will uncover the strength or the weakness of the tested power supply.
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