Keeping Systems Running Cooler

Michael Bean, Global Product Manager, High Current Power, Molex Incorporated, Lisle, Illinois


Developing highly efficient power supplies

Taming the heat is one of the biggest design challenges facing system architects and power supply manufactures today. Free air flow through the power supply is critical for improving performance in both system and supply. Data centers are on the front line when it comes to targeting energy consumption. With the explosive growth in size and number of large data centers, server manufacturers are in hot pursuit of efficient system designs that include space-saving power supply strategies. Striving to achieve as much system efficiency as possible, the microprocessors, chassis fans and power supply losses combine to account for 50-80% of the total energy used in the average high-capacity server. On average, every 100 watts generated to power the system demands an additional 50 watts just to cool the system. Power supplies must not only exhaust self generated heat but also be capable of exhausting some of the heat produced by the system which is why free airflow through the power supplies is vital. Better cooling strategies can reduce energy usage, lower carbon dioxide (CO2) emissions, improve efficiencies and lower the chance you will suffocate your power supply. Connector size, height profile, length, and design determine current densities and can have a significant impact on airflow within a power supply enclosure. Essentially, air flow must not be interrupted by the connector. The stronger the airflow, the more cooling that will take place. If air flow is inhibited or prevented from entering or exiting the enclosure, recirculation increases, static air mounts, draft is limited, and the temperature of internal components rises. Choosing the right power connector is critical to the achieving the ideal thermal design equation. A new approach to low profile connectors enables greater airflow and lower temperatures through the power supply. Traditional SSI connectors v. EXTreme LPH™ connectors Consider, for example, a typical 1800 watt, 12.0V power supply with an 87% efficiency rating running two parallel 40mm fans. And let's say the enclosure size is 295.0mm long x 106.0mm wide x 40.0mm high. Comparing two connectors, both with 10 power blades and 32 signal pins integrated into a single housing, one connector is a standard SSI type, the Molex EXTreme PowerPlus™, which is 100.3mm long x 14.5mm high. The other connector is a newer design, a low profile version by Molex called EXTreme LPHPower™ that is only 92.3mm long x 7.5mm high. The LPH connector is half the height profile of the standard connector. That height difference proves to be a measurable advantage in airflow. If, at 1800 watts and 87% efficiency, there are 200 watts of heat to exhaust from the power supply enclosure. Assuming a target of 20°C temperature rise for safety rating purposes with 60% free air flow at the non EMC boundary grate, one can calculate the basic airflow required to meet the intended design specifications by calculating CFM using heat to be dissipated and desired temperature rise. In this example, Q = 1.76 W / Tc (Q=CFM airflow required; W = watts heat to be dissipated; Tc = temperature rise above ambient; and, slope=1.76). So, the required airflow should be 23.67 CFM to meet the desired design goal. LPH connectors yield 14%-25% improved cooling The EXTreme PowerPlus indicates 22.70 CFM at the measurement point, midway through the power supply, requiring fans running at full RPM to cool the supply, yielding excess energy usage. The taller connector tends to keep the movement of air to the upper half of the enclosure, producing stagnant and recirculated air flow to the bottom of the supply.

Recirculation may be desirable for large computer cabinets, but in small power supply enclosures most airflow is lost due to recirculation. A cross-sectional view demonstrates airflow blockage with the traditional SSI connector, based on velocity contours. Red indicates areas of high velocity, which is most desirable.

Conversely, the lower profile Molex EXTreme LPHPower™ connector in the same environment indicates airflow of 25.90 CFM - an increase of 14% over the taller connector. Although that may seem relatively insignificant, the difference equates to an increase power supply to 2000 watts, while maintaining safe 20°C temperature rise without altering thermal specifications. The extra airflow headroom also allows an extra boost of system cooling to accommodate ambient or other component conditions.

The contour plot of velocity for LPHPower shows that draft is also vastly improved and promotes greater air flow to reach the lower extremes of the enclosure - meaning more internal components are cooled more efficiently.

On smaller sized 850 - 1200 watt power supplies that may have only a single 40.0mm fan squeezed next to the standard AC input IEC connector, the effects of the lower profile LPH style connector are even more pronounced. Compared with traditional SSI connectors, in identical test situations, the Molex EXTreme LPHPower™ connector can gain 25% more airflow with improved draft through the enclosure.

Industry demand for reduced energy and costs will continue to fuel demand for smaller enclosures, and better utilization of data center real estate—and will also accelerate the need for proven thermal reduction strategies. Smaller, higher speed fans can be a double-edged sword, boosting energy consumption and noise, while reducing MTBF (Mean Time Before Failure) of the fans and other internal components. Connector selection is a critical aspect of fan performance and overall power system design. Molex EXTreme LPHPower connectors offer space-saving high-current configurations for improving power supply performance that help solve thermal design challenges associated highly efficient systems.