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) 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 two Seasonic PSUs 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.  

Seasonic P-1050


Seasonic P-1200


The overall efficiency of the two Seasonic Platinum Series power supplies is excellent and meets the criteria for 80Plus Platinum certification, even while operating on 115 VAC and at elevated temperatures.

80 Plus Program

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

Differential Temperature and Noise Levels

To simulate real world operation, some of the warm exhaust air from the PSUs 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 each 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.

Seasonic Platinum 1050

Seasonic Platinum 1200

*Fan not spinning (in Hybrid S3FC mode)

Tests were conducted with the Fan Control switch in the “Hybrid” position (S3FC), which enables fanless mode; starting out with no fan spinning and then speeding up gradually as the heat/load increase. The fan noise is just noticeable around 50% load and certainly not loud. With the Fan Control switch in the “Hybrid” position (S3FC) the fan does not start spinning until the load increases to ~ 35%. I was not able to take SPL measurements at the two higher loads due to all the programmable DC load cooling fans cycling on and off in the background.

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