Testing

Physical Weight

 

One of the basic measures of any ATX power supply is the unit’s overall physical weight.  This may seem rather simplistic but it generally holds true that more components and larger heatsinks equal a better PSU.  

 

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The SP-500W is relatively heavy for its size (including modular cables) and is slightly longer than the typical ATX power supply (160mm).

 

 

DC Output Voltage Load Regulation

 

To simulate real world operation, the Spire SP-500W PSU was connected to my home made load tester, supplied with 115 VAC, and allowed to burn-in for 24 hrs before voltage readings were taken.  In this test we are interested in seeing how well a PSU can maintain the various output voltages while under a moderate load.  The DC output voltages were measured with a FLUKE digital multimeter at the ATX connector. 

 

The ATX tolerance for voltages states how much each output (rail) is allowed to fluctuate. 

 

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The following table lists the DC voltage results for the Spire SP-500W PSU while operating on 115 VAC, 60 Hz.

 

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The Rocketeer V produced very good voltage regulation on the main outputs while operating under a variety of combined loads.  The single +12V rail held up well under a heavy load. 

 

AC Ripple (electrical noise) on DC Outputs

 

The amount of AC ripple present on the outputs was checked using an oscilloscope.  This AC component may be present in the KHz range where most switching power supplies operate or it may be more prevalent at the 60 Hz line frequency.  I adjusted the O-scope time base to look for AC ripple at both low and high frequencies. 

 

The ATX specification for DC output noise/ripple is defined in the ATX12V Power Supply Design Guide.

 

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Ideally we would like to see no AC noise on the DC outputs — the cleaner the better!  But in reality there will always be some present.  I measured the amplitude of the AC signal (in millivolts, peak-to-peak) to see how well the power supply complied with the ATX standard.  The following table lists the ripple/noise results during our 263 w load test for the five main output voltages of interest.

 

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The Spire SP-500W power supply exhibited good AC ripple suppression on all of the measured outputs. 

 

Power Factor (PF)

 

Power factor (PF) is one of those mysterious properties of AC that even most electrical engineers have a hard time explaining.  A thorough technical discussion goes beyond the scope of this review (not to mention this author’s understanding).  For a more detailed discussion about PF, please look here.

 

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Power factor is defined as the ratio of true power (measured in watts) to apparent power (measured in Volt Amps).  It measures how effectively AC power is being used by a device.  The difference between true power and apparent power is expressed as the power factor and results from the way true power and apparent power are measured.  Ideally we would like to have true power and apparent power equal to one another, which would result in a PF of 1.00 or 100% effective power utilization. 

 

I measured the AC Power Factor with a WattsUp? Pro power analyzer.  The US version of the Spire SP-500W power supply does not incorporate active power factor correction circuits, which resulted in PF readings typical for passive correction. 

 

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