Testing — Efficiency
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) 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 the latest revision (Ver 2.2) now lists both required and recommended minimum efficiencies.
I measured the AC power input to the Zeus 750W PSU with the WattsUp? Pro watt meter and calculated the combined DC power output by summing the products of all the DC outputs (volts x amps) for five different DC loads.
The overall efficiency of the ST75ZF power supply was very good and actually exceeded the new design recommendations of 80% efficiency for a typical load.
The 80 Plus Computer Power Supply 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 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 PCâ€¦ 🙂
Testing — Differential Temperature and Noise Levels
The differential temperature across the Zeus 750W power supply was calculated by subtracting the ambient room air temperature (T in) from the temperature of the warm exhaust air flowing out of the power supply (T out) when the fan was running.
Thermocouples were placed at the air inlet and exhaust outlet. The ambient room air temperature was 24ÂºC (75ÂºF) +/- 1ÂºC during testing.
T in = temperature of air entering power supply
T out = temperature of air exhausting from power supply
Î”T = T out – T in
Sound pressure level readings were taken 3′ in front of the PSU in an otherwise quiet room. The power supply was placed on a foam rubber mouse pad during testing. The ambient noise level was ~30 dBA.
Moving the single 80mm fan to the front side of the Zeus power supply made a big difference in the overall noise output. The new Zeus 750W PSU is significantly quieter than previous Zeus models!