Features that affect power performance

System power engineers have many choices in today’s power connector market and the list of options is growing as the industry diversifies to offer more specialised products. Here are some commonly asked questions:

“I have a power application that requires a certain amount of current at a certain voltage with a certain amount of available space. What power connector should I use?” or, “I have a power application that requires a significant leap in efficiency. What power connector should I use?”

These questions have always been important with respect to power connectors. However, the frequency of such questions in today’s business and social environment is increasing.

Individuals, businesses, investors, governments and consumers are demanding more efficient systems that cost less to operate (ie, consume less power) without sacrificing performance.

From a power connector standpoint, this means increasing power density (linear current density) and decreasing contact resistance.

Decreased contact resistance results in reduced power loss through the connector, thus contributing to a more efficient power system.

System designers are being asked to increase overall power efficiency while maintaining, or even increasing, system functionality. Increased rack density and higher wattage power supplies require more effective thermal management.

These increased performance demands apply across all market segments - data, telecom, datcom/networking, medical, alternative/renewable energy (solar, wind, etc), battery technology and instrumentation - and are driving component manufacturers toward advances in product technology.

Power connector technology is evolving to meet these trends in a variety of ways.

It’s beneficial to consider the power connector features that have a material effect on system/connector performance (with performance being primarily defined as current carrying capability and contact resistance).

The following list is not exhaustive, but it attempts to capture the most significant features:

• Power contact design for low contact resistance and increased linear current density;
• Vented housing design for enhanced heat dissipation;
• Power contact pitch options for linear current density and voltage flexibility (AC and DC);
• Lower connector profile heights that block less airflow;
• Number of adjacent power contacts energised simultaneously and their relationship to linear current density;
• System airflow availability (airflow helps power connector performance);
• Second source availability and joint qualification testing/documentation for guaranteed performance;
• Temperature rise requirements/system ambient conditions and their relationship to current rating performance.

Power contact design includes material selection and thickness, beam design, and the number of tails that terminate into the PCB.

Optimisation of these characteristics results in reduced overall contact resistance and increased linear current density.

For example, the FCI HCI power connector system features ultra-low contact resistance (<0.5 mΩ after environmental exposure), very high linear current density (\>339 A/linear inch with <30°C temperature rise, zero airflow and 10 adjacent contacts energised simultaneously).

This connector achieves superior performance by using a high conductivity copper alloy, an optimised beam design with multiple points of contact and 18 tails per contact to route current into the PCB.

Contact resistance is an important feature since it directly relates to power loss through the connector.

Reducing contact resistance from 2.0 mΩ to 0.5 mΩ reduces power loss through the connector by a factor of 4. As a result, systems with high-performance power connectors can achieve improved power efficiency, particularly in high-wattage systems.

Vent windows in the connector housing enhance the structure’s heat dissipation capabilities. Strategically located vent windows and coring have been shown to reduce temperature rise by up to 13% at rated current (neglecting airflow effects).

This increases the connector’s ability to carry more current at a given temperature rise by allowing heat to escape the working parts of the power contact/housing system.

Power contact pitch plays an important role in linear current density and voltage rating.

For a given contact design, current rating increases by up to 10 to 20% when the contact pitch increases from 6.35 to 7.62 mm.

Also, voltage rating increases by 50% due to larger creepage and clearance distances. As such, the larger pitch is generally reserved for higher voltage requirements (6.35 mm for DC power and 7.62 mm for AC).

Varying power contact pitches often fall within the capabilities of today’s modularly tooled power connectors.

Connector profile height is also a key design criterion in many 1U and 2U chassis-based systems. Taller profile heights block more airflow in these height-constrained systems.

This blocked airflow could be otherwise used for system cooling. For example, the FCI HPCE straddle-mount configuration features an ultra-low 2.8 mm profile height.

This configuration is popular in 1U and 2U power supplies because of its ultra-low profile height, ultra-low contact resistance (≤0.6 mΩ after environmental exposure) and very high linear current density (>180 A/linear inch with ≤30°C temperature rise, zero airflow, and multiple adjacent contacts energised simultaneously).

The number of power contacts energised simultaneously has an impact on current rating.

While system airflow is external to the connector, it has an impact on power connector performance.

For example, the HCI connector’s temperature rise decreases by 57% when using 400 LFM of airflow, versus still air (90 A per contact with 10 adjacent power contacts energised simultaneously).

Even with only 100 LFM of airflow, the resulting temperature rise decreases by 34% (same test conditions as noted above).

Second source availability and joint qualification testing also have an impact on power connector selection. Most users require power connector solutions to be available from at least two sources.

Dual sourcing ensures continuity of supply, shorter lead times, competitive pricing and good user support.

As important as these items are, second source partners should also be engaged on an additional level. Joint intermateability testing and joint control documentation between licensed products should be maintained to ensure full electrical and mechanical inter-operability over the product life.

This level of control is a safeguard against the malfunction of non-licensed product. Many non-licensed products do not undergo rigorous product qualification testing and do not have safety agency approval (UL, CSA, TUV, etc).

Temperature rise requirements and system ambient conditions also affect power connector performance.

For example, a 30°C temperature rise is an industry benchmark for rating power connectors. However, most power connectors are rated to at least a 105°C maximum operating temperature.

As long as the system ambient temperature plus the associated temperature rise for a given current do not exceed 105°C, the connector can be safely used at something greater than a 30°C temperature rise.

As an example, HCI can accommodate about 100 A per power contact at a 40°C temperature rise (10 adjacent power contacts energised simultaneously).

If the system ambient temperature is 55°C, the resulting 95°C temperature is well within the 105°C maximum operating temperature.

System power engineers have many choices when specifying power products. They can choose from connectors with innovative features, ultra-low contact resistance, vented housing designs, high linear current density, modular tooling and second source agreements with joint qualification testing and design control.

The end result is tighter, more efficient, and more successful systems.

John Dodds, global product marketing manager - Power Products, FCI