Efficiency, Differential Temperature and Noise

Efficiency

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) 650 watts of AC power going in would result in 650 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 SuperNOVA 650 GM 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 650 GM power supply is very good and easily meets the criteria for 80 Plus Gold certification, even while operating on 120VAC and at elevated temperatures.  Notice how flat the efficiency curve is, indicating the power supply is operating at a relatively high efficiency over a broad range of loads.

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 ~27 dBA.  

* Fan not spinning

The SuperNOVA 650 GM power supply was silent through the first two tests in fan-less ECO mode. Once the cooling fan started to spin under a 50% load, the noise was still relatively quiet. At full load however, with an elevated ambient temperature, the cooling fan noise became very noticeable.

(Courtesy of EVGA)

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