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) 850 watts of AC power going in would result in 850 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.
We measured the AC power input to the HCP-850 Platinum PSU with an Extech power analyzer while the total DC load was found by adding all the individual +3.3V, +5V, +12V, -12V and +5VSB loads together.
During our tests the PSU easily met the 80Plus Platinum requirements while operating on 240 VAC but struggled to obtain 92% efficiency at the 50% load mark while operating on 115 VAC. This is likely due to the real world, elevated operating temperatures where we perform our tests, which are higher than the 25°C the 80Plus organization uses (lower operating temperatures typically result in higher efficiency). However, these results are well within the range of experimental error and rounding up gives us 92% so we’ll call it a pass.
80 Plus Program
Note 1: Power Factor ≥0.90 (50% to 100% Load)
Note 2: Tests conducted at room temperature (25°C)
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 ~28 dBA. I was not able to take SPL readings at the higher loads due to the background noise generated by all the DC Load cooling fans cycling on and off.
Below ~600W output and 30°C inlet air temperature, the HCP-850 Platinum PSU is very quiet. As the load continues to increase, the cooling fan speeds up to where it becomes noticeable but never really loud. Note: I was not able to take SPL readings at the higher loads due to all the programmable DC load cooling fans cycling on and off.