Efficiency, Differential Temperature and Noise


The overall efficiency of a power supply is very important. The less waste heat generated the better! 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.

I measured the AC power input to the High Current Pro 1000W Platinum PSU with the Extech power analyzer while the total DC load was found by adding all the individual +3.3V, +5V, +12V, -12V and +5VSB loads together.

During our tests the PSU was able to just meet the 80Plus Platinum requirements while operating on both 115 VAC and 240 VAC, even under real world operating temperatures (up to 40°C); OK, we rounded 88.9 up to 89 so we’ll call it a pass. However, we never saw the 94% efficiency that Antec claims and I’m not buying into their marketing claims that this power supply will save you up to 25% on your electric bill.

Note 1: Power Factor =0.90 (50% to 100% Load)
Note 2: 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 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 inlet 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 PSU in an otherwise quiet room. The ambient noise level was ~28 dBA.

Below ~600W output and 30°C inlet air temperature, the High Current Pro 1000W Platinum PSU is very quiet, pretty impressive for a 1000W PSU. As the load continues to increase all the way up to 1,000W the cooling fan speeds up to where it becomes noticeable but never really loud. Note: I was not able to take SPL readings at the higher loads due to all the programmable DC load cooling fans running.

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