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) 800 watts of AC power going in would result in 800 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.

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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.

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I measured the AC power input to the Antec CP-1000 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. 

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The overall efficiency of the Antec CP-1000 power supply is good.  The efficiency appears to peak around 400W and remains consistently above 80% throughout most of the curve. 

80 Plus Program

There is a growing awareness among users, PC manufacturers and electric utilities regarding the money and natural resources that could be saved by adopting higher efficiency PC power supplies.  One group that is spearheading this movement is the 80 Plus Program, which is supported by the electric utilities industry.  You can learn more about their efforts to promote power supplies with better than 80% efficiency by visiting the 80 Plus Program website.

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    Note 1: Power Factor =0.90 (50% to 100% Load)
    Note 2: Tests conducted at room temperature (25°C)

Earlier last year 80 Plus added three new certifications (Bronze, Silver, and Gold) to help differentiate and acknowledge PSUs that meet even higher efficiency specifications. However, the Antec CP-1000 is still only certified 80 Plus, which means it should produce up to 80% (or higher) efficiency while delivering between 20% and 100% load.  During our tests the PSU was able to easily meet these requirements while operating on 240VAC but struggled a little under max load while operating on 115VAC.  The probable reason for the apparent lower efficiency while operating on 115VAC is that our tests are conducted at real world operating temperatures (up to 40°C) while the 80 Plus Organization tests are conducted at room temperature.  And higher operating temperatures typically result in lower efficiency.

Spending a little more money up front to purchase a high efficiency power supply may very well pay for itself over the lifetime of the PC, especially when you are using this much power… 🙂

Differential Temperature and Noise Levels

To simulate real world operation the Antec CP-1000 power supply was mounted in a modified mid tower case during testing.  Some of the warm exhaust air from the PSU under test is recirculated back into the case, which allows the internal case air 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. 

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Below 500W output and 30°C inlet air temperature, the CP-1000 is virtually silent; pretty impressive for a 1,000W PSU!  Temperatures continue to build as the load increases and the cooling fan finally speeds up to where it becomes noticeable at the higher loads.  Antec certainly has succeeded in delivering excellent cooling with minimal noise.

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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