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Circular Connectors Address High Power and Harsh Environment Applications

Wed, 07/20/2011 - 9:36am
Russell Park, ITT Interconnect Solutions, www.ittcannon.com
Circular connectors can be used in a wide range of high power and harsh environment applications. Whether designing casualty power connectors for shipboard use, high-power connectors for electric submersible pumps in oil wells, high-temperature connectors for use under railway cars, or miniature power connectors for portable electronics applications, circular connectors can be designed to meet harsh environment application requirements. To ensure reliability, durability and high performance, connector manufacturers need to consider several critical component specifications and parameters including amperage, temperature resistance, sealing, as well asshock and vibration resistance when developing connectors for high power and harsh environments.

Amperage
In a variety of high power applications, including telecommunications, power supplies, military equipment, transportation and even lighting systems, customers often require a specific amperage for their applications. Connector manufacturers must be able to match this specification in their connector designs in order to meet application-specific needs. However, as with many components, meeting high power requirements requires a variety of hurdles to be overcome.

One of the most significant challenges comes in meeting high amperage requirements while maintaining a low connector profile. As amperage increases, typically the connector size increases as well, making it increasingly difficult to meet both current and real estate constraints. Manufacturers of hybrid vehicles, for example, are looking for a quick charge connection into the vehicle, while requiring higher amperage in a smaller device. Despite the connector being implemented in a larger application, the device size needs to be minimized because in hybrid vehicles, reduced weight of the overall car is key to improving fuel efficiency. Since the car has multiple areas to connect, hybrid vehicle manufacturers are often requiring connectors to do more in a condensed package.

Not only is the trend shifting to higher amperage requirements, but customers also look for high amperage ratings over several poles, despite the fact that increased amperage is typically consistent with a single position connector. Still, engineers often prefer the design flexibility and freedom to control several high current circuits in one connector.

There are several options to meet this challenge in customer design requirements. When driving high power through several contacts within a single shell, selecting a high conductivity material that will generate little heat is imperative, particularly because the closer the contacts are placed to each other, the more difficult it is to dissipate heat. Materials such as copper alloy 101 or tellurium are the first choices, although tellurium is much more costly. Using such high conductivity materials also allows contacts to be placed much closer together than if using brass or beryllium copper (BeCu). While heat will always be a factor as long as power increases, the size of the contacts, base materials, and finish will work together to handle and dissipate heat as necessary.

While it is much more cost-effective to employ a conventional brass material than a more expensive material such as a copper alloy, brass does not exhibit properties that, when used in a smaller footprint, allow a higher current to pass through, effectively disperse heat, and, as a result, eliminate degradation in terms of current fall-off, as copper alloy does. ITT Interconnect Solutions, for example, is continuing to investigate the use of alloys that are able to carry a higher current in a smaller form factor, while still meeting cost constraints.

Voltage
Additionally, the higher the voltage rating, the more the connector pin will need to be de-rated from its peak, or maximum rating. All components, including connectors, have their limits. The diameter, plating and homogeneity of the connector material will determine how well it will be able to withstand the maximum rated load and therefore contribute to the de-rating calculation of the connector. For example, throughout the testing process, as voltages are applied and currents are induced, there will come a point where the materials that comprise the pin terminal will not be able to withstand the voltage and thus fail testing.

To achieve maximum power in the connector design, insulator material should be of a high dielectric strength and high conductivity contact material should be employed, as noted darlier. Other design considerations include designing the interface so as to eliminate free-standing contacts with no encasement. As a result, the creepage and air gap distance will be short, causing electrical issues. This is solved by isolating the contacts with a plastic wall between them, thereby increasing the air gap and creepage distances.

Temperature
Temperature is a concern, particularly in rail applications where components must be flame-retardant to UL94-V0 flamability requirements. While materials like neoprene are suitable for temperatures ranging from -55°C to +25°C, connectors utilizing silicon are capable of operation from -55°C to +200°C. Further still, some connectors are designed to meet European CEN/TS 45545 standards governing railway fire safety, and thus must be capable of withstanding a high temperature exposure period of at least 15 minutes at the ISO 834-1 heating curve, where maximum temperature is 800°C.

Figure 1. ITT’s CIR Series connectors feature reverse bayonet coupling and are capable of withstanding temperatures to 800°C, making them ideal for use in harsh environments.High-temperature connectors are often constructed with machined copper alloy-plated contacts, a machined stainless steel shell and ceramic inserts. Conventional connector inserts are constructed with plastic or rubber, but these materials melt under extreme temperatures or if exposed to a fire. Ceramic, however, is resistant to fire as well as brittleness caused by moisture evaporation; and the rigidity of the material makes it less susceptible to vibration and breaking. A ceramic insert is kept in place in the shell by the use of a metal retention ring. As a result, the connector is easy to disassemble, allowing for quick, simple field maintenance and service.

Sealing
Sealing requirements depend strictly on the application. For example, sealing for ship, oil or rail applications requires more than meeting IP69or IP69K standards. Because of these applications, connectors must be waterproof to 10 meters for up to 12 hours. Incorporating wire sealing, silicon rubber grommets on the plug and receptacle interface further enhances the robustness of the connector by sealing the wires against humidity, water and fluid penetration.

Additional standards in high power connector include shielding and sealing requirements to IP65, IP67 and Pollution Degree 3 protection standards to combat environmental elements, such as dust, present in portable applications. Some connector manufacturers are also offering sealing options to meet application-specific needs, such as connectors that are fully sealed with a lid covering the connector ports; or standard sealing, where connectors are sealed only when mated. 

Shock and Vibration
Additionally, shock and vibration resistance is often specified to 50G and 20G, respectively. Once again, the use of a metallic retention clip provides a high integrity contact that will not release under extreme shock and vibration conditions. Designing a connector with bayonet coupling further ensures robustness, high vibration resistance, and the ability to withstand moisture ingress.

Figure 2. ITT’s 38999 Series III connectors are DSCC qualified to meet the stringent testing requirements of Mil-DTL-38999 and designed to meet the high reliability needs of military and commercial avMiniaturization
Finally, as in many markets, size is a critical factor in component designs. While many connectors are small in size, especially given the amount of power they are capable of delivering, customers continually seek smaller designs. Energy applications, such as passing electrical energy through pressure barriers, often requires connectors capable of 5000 VAC at up to 200 A (approximately 800 kW – enough energy to power 200 homes).

Because of advancements in materials –- such as the use of thermosetting elastomeric materials and PEEK (polyaryletheretherketone) engineered plastics -–smaller circular connector solutions are available down to 3" in diameter for many harsh environment applications, even for those requiring higher power and where resistance to high temperatures, high pressure, corrosive liquids and gases are imperative.

Conclusion
When selecting connectors for harsh conditions, voltage specifications, size and resistance to environmental elements are just a few of the critical design parameters that must be considered. However, no specification is more important than amperage. Materials selection is critical, and whether the connector is designed for submersibility, high shock and vibration resistance, high pressure or extreme temperature environments, customers need to know the connector they’ve selected is proven for such use. It is imperative to engage with a connector company that is experienced in designing for these harsh environment applications and that is also familiar with testing parameters from a regulatory and standard bodies standpoint. Connectors must be able to meet high power requirements in addition to harsh environment conditions.
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