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) 500 watts of AC power going in would result in 500 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 Kingwin LZG-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. 

*Overclocked to 650W

The overall efficiency of the Kingwin LZP-550 power supply is excellent – the best we have seen to date and does in fact meet the new 80PLUS Platinum certification criteria (see table below) even when it was overclocked to 650W!

Ecos 80PLUS 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 80PLUS 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 Ecos 80 PLUS Program website.

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

What this really shows is the LZP-550 is actually a 650W PSU that has been conservatively de-rated to insure compliance with the 80PLUS Platinum criteria. However, during our tests, the LZP-550 was able to maintain 80PLUS Platinum status even while being overclocked to 650W; well done Kingwin!

Differential Temperature and Noise Levels

To simulate real world operation the Kingwin LZP-550 power supply was mounted in a modified mid tower case (Lian Li PC60) 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. 

*Overclocked to 650W

Below 400W output with a relatively cool ambient air temperature of 28°C, the LZP-550 PSU is dead silent.  The cooling fan didn’t even turn on until we increased the load to 413W (75% load). Even under full load at 550W the PSU was still very quiet.

Note 1: The PSU cooling fan was not running during the first three load tests.
Note 2: I was not able to take SPL readings at the 650W load due to all the programmable DC load cooling fans running.

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