Testing (Cont’d)



The efficiency of a power supply 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.  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 power supply with a 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 Thermaltake 750W power supply was very good, and actually exceeded the new ATX design recommendation of 80% under a typical load.  Better efficiency translates to lower operating costs. 



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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… 🙂



Differential Temperature and Noise Levels


The differential temperature across the Thermaltake 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).  Thermocouples were placed at the air inlet and exhaust outlet of the power supply.  The ambient room air temperature was 24ºC (75ºF) +/- 0.5ºC during testing.


T in = temperature of air entering power supply

T out = temperature of air exhausting from power supply

ΔT = T out – T in


The Toughpower 750W power supply uses a single temperature-controlled fan that speeds up as the load (internal heat generation) increases.


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.  The sound level meter used for these tests is only calibrated down to 35 dBA.  All readings below this were recorded as <35 dBA.  In my opinion this is very quiet and would not be noticed over normal case fan and hard disk drive noise.


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The Toughpower 750W power supply was very quiet, even while operating continuously under a moderately heavy load.  The fan did become noticeable as the output power approached 500 watts but this is to be expected. 


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