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) 450 watts of AC power going in would result in 450 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 SilverStone NJ450-SXL 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 SilverStone NJ450-SXL power supply is excellent and easily meets the 80 Plus Platinum guidelines, even when operating on 120VAC and at elevated temperatures.

80 Plus Program

    Note: Tests conducted at room temperature (25°C)

Differential Temperature and Noise Levels

The Nightjar fan-less power supply was tested on an open bench with a relatively cool (23°C) room air temperature. A thermocouple was attached to the center of the top plate to measure the power supply’s surface temperature.

T out = temperature of top plate
T in = temperature of ambient air
Delta T = T out – T in

The SilverStone NJ450-SXL power supply was dead silent throughout our testing. The surface temperature of the outer side panels increased with load as expected over time. Performance will vary depending on what type of enclosure the NJ450-SXL is mounted in and how much airflow is available to the power supply for cooling.

Word of Caution: Just because a power supply is fan-less does not mean it doesn’t still need airflow for cooling. The last thing you want to do with a fan-less power supply is stuff it in an enclosure with no airflow. Waste heat has to go somewhere or the power supply will overheat. The power supply needs at least some airflow to keep it cool. Like other passively cooled PSUs, the NJ450-SXL relies on internal case airflow to keep it cool whether it is an open case with good natural convection cooling or utilizes one or more case fans to generate airflow.

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