If the TruePower 550watt is the quality unit, it should supply a steady output (within the designed voltage regulation limits), and under any load condition, within its rated power range. Bench testing a power supply requires a special setup, because all PC power supplies require a load to operate. The following is a list of equipment we used to test the unit:
Digital Multimeter (DMM) - Able to read voltage or current to an accuracy of 0.001 (ie. 1 millivolt). When checking the output voltage across the load, we can consider the output DC voltage to be acceptably steady if the 1/100th (0.01) digit only fluctuates. If the 1/10th (0.1) digit fluctuates we know the power supply is not stable enough. Two DMMs would be good for reading voltage on one and current on the other simultaneously.
Note: Current is measured with the DMM in series with the load resistance. Voltage is measured with the DMM in parallel across the load resistance.
Storage Oscilloscope - For checking AC voltage fluctuations and noise on the DC output voltages. Good filtering should reduce unwanted AC ripple and noise to negligible levels.
Nickel-chromium resistance wires for specially made low value resistors that are oil cooled for handling large currents to prevent the load resistance from getting too hot.
Assorted load resistor networks
Assorted high wattage ceramic encased resistors, etc.
Listen: To the fan noise, to see if it is a quiet power supply. A thermal controlled dual fan will be quieter than one without it. Also, listen for a high-pitched humming noise. If it increases as the load increases, it usually suggests the power supply is over rated for its design, or its components are of poor quality.
Smell: Any burning or overheated odour is a bad sign that the supply might blow out at higher loads.
Feel: Use your hand to feel the air blowing from the supply exhaust fan. If the air is warm or getting hot, it indicates that the components are working very hard or over rated. The cooler the exhaust air, the cooler the supply is running, which also suggests a longer life and a longer Mean Time Between Failure (MTBF).
- Testing Procedure
The power supply was tested with load steps of 10%, 25%, 50%, 75%, 100% of maximum output current. After that, the load was increased to 110% of the maximum output power, to see how well it performed at 110% and above overload (No warranty).
Since the maximum output current of the -5v, -12v and +5v SB are relatively small (0.5A, 1A and 2A respectively), we tested those outputs at maximum current (24 Amps in Total) throughout the whole test. We also used 3 combinations of load that add up to 100% of the power supply's rating of 550 watts. The reason for this is to test the power supply under various load conditions. During each load test, the power supply was run for at least 5 minutes before recording the displayed value. The power supply was run for up to 30 minutes during 100% load testing, to check how the supply performed at maximum output for a reasonable period of time.
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