Efficiency, Differential Temperature and Noise
EfficiencyThe 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.
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 SilverStone ST45SF 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.
The overall efficiency of the SilverStone ST45SF is very good. The efficiency curves appear to peak around 250W and remain 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.
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. The SilverStone ST45SF we are looking at today is certified 80 Plus Bronze, which means it should produce up to 82% (or higher) efficiency while operating between 20% and 100% load and up to 85% efficiency when operating at a 50% load, which it did, even while operating at elevated, real-world temperatures.
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.
Differential Temperature and Noise Levels
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 PSU in an otherwise quiet room. The ambient noise level was ~28 dBA.
The SilverStone ST45SF PSU is very quiet while operating under a light to medium load; just what you want for a Media Center or HTPC. Only when the load was increased to the maximum 450W output did the fan noise become really noticeable.
Very good review. There seem
Very good review. There seem to be a few power supplies out now in this form factor that are competing with this unit. After reading this review, I think I would only buy a power supply that was 80 plus certified. It gives me a warm feeling that somebody other than the manufacturer looked at the product and certified that it works the way it’s suppose to.