Efficiency, Differential Temperature and Noise


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) 750 watts of AC power going in would result in 750 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. Newer 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 now lists both required and recommended minimum efficiencies.

We measured the AC power input to the 750 GQ PSU with an Extech power analyzer while the total DC load was found by adding all the individual +3.3V, +5V, +12V, -12V and +5VSB loads together.  

The overall efficiency of the EVGA 750W GQ power supply is very good and easily meets the criteria for 80 Plus Gold certification while operating on 120VAC and even at elevated temperatures.  

80 Plus Program

    Note: Tests conducted at room temperature (25°C)

Differential Temperature and Noise Levels

To simulate a demanding environment, some of the warm exhaust air from the PSU under test is recirculated back to the intake through a passive air duct, which allows the PSU air inlet temperature to increase with load, up to 40°C.  

The differential temperature across the power supply was calculated by subtracting the internal case air temperature (T in) from the temperature of the warm exhaust air flowing out the back of the power supply (T out).  

Thermocouples were placed at the air inlet and exhaust outlet. The ambient room air temperature was 23ºC (74ºF) +/- 0.5ºC during testing.

T out = temperature of air exhausting from power supply
T in = temperature of air entering power supply
Delta T = T out – T in

Sound pressure level readings were taken 3’ away from the rear of the case in an otherwise quiet room.  The ambient noise level was ~28 dBA.  

Note: The EVGA 750 GQ power supply was tested with the ECO Intelligent Thermal Control System switched Off (disabling fan-less operation) so we could take SPL measurements during load testing with the fan running.

With the ECO Intelligent Thermal Control System disengaged (silent mode and cooling mode only) the PSU was virtually silent at low to mid power levels. Once the cooling fan started to speed up at the 75% load test, the noise was still barely noticeable. At full load with an elevated ambient temperature, the GQ PSU cooling fan did speed up and the noise became noticeable but I was not able to take a SPL reading because all the DC load cooling fans were running constantly by that point.

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