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) 1,000 watts of AC power going in would result in 1,000 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 Seasonic X-1250 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.
As expected, the overall efficiency of the Seasonic X-1250 power supply is very good and meets the criteria for 80Plus Gold certification, even while operating on 115 VAC and at elevated temperatures.
80 Plus Program
Note 1: Power Factor =0.90 (50% to 100% Load)
Note 2: Tests conducted at room temperature (25°C)
Spending a little more money up front to purchase a high efficiency power supply may very well help 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, some of the warm exhaust air from the PSU under test is recirculated back to the intake through a passive air duct, which allows the PSU air inlet 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 ~27 dBA.
Note: Operating in Normal (S2FC silent-cooling mode)
During our tests, even with the fan running in "Normal" mode, the Seasonic X-Series 1250W PSU was virtually silent up to ~600W combined output. Only at full load and elevated temperatures did the fan speed up to the point where it would be considered loud. But seriously, if you are pushing a 1250W PSU to its upper limits you probably aren't worried about a little fan noise. In my opinion, this is an excellent fan control strategy that offers both minimal noise at low to mid power and excellent cooling at the higher loads when you really need it; well done!