Testing – Cont’d

Testing — Efficiency


The overall efficiency of a power supply is very important, especially when operating in a silent, fan-less mode.  The less waste heat generated the better!  Efficiency is defined by the power output divided by the power input and is usually expressed as a percentage.  If a PSU were a 100% efficient (which none are) 400 watts of AC power going in would result in 400 watts of DC power coming out (with no waste heat to dissipate).  In the real world there are always inefficiencies and power is lost in the form of heat during the conversion process.


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The latest revisions to the ATX12V Power Supply Design Guide V 2.2 have continued to increase the efficiency recommendations for PC switching mode power supplies.  And the latest revision (Ver 2.2) now lists both required and recommended minimum efficiencies.


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I measured the AC power input to the Phantom 500 with the WattsUp? Pro watt meter and calculated the combined DC power output by summing the products of all the DC outputs (volts x amps) for five different DC loads.


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The overall efficiency of the Antec Phantom 500 power supply was very good, and actually exceeded the new ATX design recommendation of 80%.  While it didn’t quite meet Antec’s claim of 86%, the Phantom 500 power supply did exhibit one of the highest efficiencies I have measured to date. 


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The 80 Plus Computer Power Supply Program


There is a growing awareness among users, PC manufacturers and electric utilities regarding the money and natural resources that could be saved by adopting higher efficiency power supplies.  One group that is spearheading this new movement is Ecos Consulting.  You can learn more about their efforts to promote power supplies with better than 80% efficiency by visiting the 80 Plus Program website.


Spending a little more money up front to purchase a high efficiency power supply may very well pay for itself over the lifetime of the PC… 🙂



Testing — Differential Temperature and Noise Levels


The differential temperature across the Phantom 500 power supply was calculated by subtracting the ambient room air temperature (T in) from the temperature of the warm exhaust air flowing out of the power supply (T out) when the fan was running.  In addition, I also recorded the case temperature.


Thermocouples were placed at the air inlet, exhaust outlet, and top-center of the case.  The ambient room air temperature was 24ºC (75ºF) +/- 1ºC during testing.


T in = temperature of air entering power supply

T out = temperature of air exhausting from power supply

ΔT = T out – T in


Sound pressure level readings were taken 3′ in front of the PSU in an otherwise quiet room.  The power supply was placed on a foam rubber mouse pad during testing.  The ambient noise level was ~30 dBA. 


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Here we see some interesting results.  Initially as the power output increases both the power supply case temperature and ΔT increase.  But you will notice temperatures actually fall a little mid-power when the fan kicks in and starts moving some air thru the PSU.


With the fan speed temperature profile switch set on the #1 position, the fan started turning slowly during the 138 watt load test as internal temperatures hit the 40ºC mark.  Fan noise did not become noticeable until the 332 watt load test and when the load was increased to the maximum 471 watts, the fan was running full speed and noticeable.  In reality though, very few systems will place more than a 150~300 watt combined DC load on the PSU.

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