Efficiency, Differential Temperature and Noise
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) 750 watts of AC power going in would result in 750 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 Hydro PTM 750W 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.
The overall efficiency of the FSP Hydro PTM 750W power supply is excellent and meets the criteria for 80 Plus Platinum certification even when operating at elevated temperatures and with 120 VAC input.
80 Plus Program
Note: Tests conducted at room temperature (25°C)
Differential Temperature and Noise Levels
To simulate a demanding environment, 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.
The FSP Hydro PTM 750W PSU cooling fan started out spinning slowly and stayed that way through the 50% load test. At the 75% load mark the fan noise was still relatively quiet and even at the 100% load mark the fan noise never became really loud. I was not able to take a SPL reading at the 100% load because all the programmable DC load cooling fans were running almost constantly by that time. Having good efficiency helps keep the waste heat and fan noise to a minimum.
(Courtesy of FSP)