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) 1,000 watts of AC power going in would result in 1,000 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 AX1500i 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 AX1500i Digital power supply is excellent and easily meets the new criteria for 80Plus Titanium certification, even while operating on 115 VAC and at elevated, real-world temperatures. Very impressive!  

80 Plus Program

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

(Corsair Efficiency Graph – Courtesy of Corsair)

Differential Temperature and Noise Levels

To simulate real world operation, 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, just like it would in a real PC.  

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: Fan not spinning

The Corsair AX1500i Digital PSU is virtually silent at low power levels (below ~30% load) with the fan not spinning. At 50% load the fan was spinning but it was still relatively quiet. At the 75% load mark with the AX1500i delivering 1,125 watts, the fan noise was noticeable but subjectively not loud. I was not able to take SPL measurements at full load due to all of the DC programmable load fans running constantly at this point.

(Corsair AX1500i Fan Noise Graph – Courtesy of Corsair)

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