Efficiency, Differential Temperature and Noise
Efficiency
The overall efficiency of a power supply is very important, especially when operating at higher power levels. 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) 400 watts of AC power going in would result in 400 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.
The latest 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 Enermax Liberty DXX 500W 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.
Two years ago the overall efficiency of the
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 power supplies. One group that is spearheading this new movement is Ecos Consulting. You can learn more about their efforts to promote power supplies with better than 80% efficiency by visiting the 80 Plus Program website.
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 Enermax Liberty DXX 500W power supply was mounted in a modified mid tower case (Lian Li PC60) for 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 internal case air temperature is allowed to increase up to 40ºC and then held constant from then on at 40ºC.
The differential temperature across the Liberty 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 radiator
T in = temperature of air entering power supply radiator
ΔT = T out – T in
Sound pressure level readings were taken 3’ away from the rear of the power supply in an otherwise quiet room. The ambient noise level was 28 dBA.
The Enermax Liberty DXX 500W power supply was very quiet at low to medium power levels and never became what I would consider noisy even at maximum output when supplied with relatively cool room air. Not surprisingly, as the load increased along with the synthetic case air temperature, the fan ramped up at max load when sucking in nearly 40°C air. Overall, I was impressed by just how quiet the
Note: I was not able to take SPL readings at the max load due to all the programmable DC load cooling fans running.
