In response to the need for higher voltage and smaller industrial connectors, manufacturers have redesigned housings, contacts, and sealing interfaces.
By Steven Fitzgerald
As the need for higher amperage and smaller size has increased in today’s high-current interconnect industry, a number of trends have emerged, from tool-less assembly to environmental durability to lower cost. How are connector manufacturers meeting the new demands from a diverse and growing range of high-power interconnect applications? Through robust high-power interconnects-a critical factor in both the installation ease and service life of connector products used in a variety of applications from traditional high-power applications such as oil drilling rigs, to new applications including VoIP and PoE switching hardware.
Tool-less assembly
Bolted connections still account for the majority of high-current connections in most applications, despite substantial weaknesses. Bolted connections are prone to failure due to loosening from shock, vibration, corrosion, and thermal cycling, and they require proper torque to ensure a long-lasting connection. This may require costly installation tools to measure torque and rotations of the installed fasteners, and adds to total installed costs when installation and service labor time is considered.
The proper high-current connector system for specific applications slashes assembly times and reduces labor costs for future service. Reliability increases as the bolt torque uncertainty is eliminated and the often-sealed connector systems improve environmental durability. For nearly any process, changing to pluggable connections that eliminate tools and loose hardware will directly contribute to higher quality and faster install times.
High integrity
Power connections are, of course, a critical link in making any electrical device operable. As such, reliability of these connections is important. Integrity of an electrical connector can be compromised by loss of contact between the male and female terminals, or by degradation of the electrical efficiency (resistance) of the contact area.
 FIGURE 1. The Radsok high-durability environmental connector provides high-amperage connection with a smaller footprint and low insertion force. |
To combat integrity loss, both the connector housing and electrical terminal technologies have greatly evolved. The use of high durability environmental connector housings ensures reliable performance in applications from down-hole oil exploration to space exploration vessels (see Fig.1). Advanced materials feature improved sealing capabilities as well as temperature and corrosion resistance and have even made power connectors more recyclable at the end of their life.
 FIGURE 2. Various contact interfaces influence the electrical performance of the interconnect. |
Regarding electrical terminal integrity, designs are available that ensure constant current flow under several excessive circumstances including high vibration, thermal cycling, frequent mating and unmating, and harsh environmental conditions. Advanced contact designs that feature louver or band-type interfaces between the pin and socket tend to offer better integrity than more traditional power connector designs, since these designs increase the amount of contact between the terminals, providing a more conductive interface area and decreased resistance (see Fig. 2).
Less real estate
Regardless of the application, system designers always seem to require interconnect solutions that are smaller or differently configured than anything readily available. This provides opportunities for connector manufacturers to combine existing technologies or create new designs that meet the needs of advancing market trends. Whether it’s a PCB-mountable product or a 2,000-A connector on a rail car, smaller, it seems, is always better.
To create smaller connectors, the terminal system must allow high current flow in a smaller envelope, often achieved by using less-traditional terminal systems that increase the number of interface points between the pin and socket. Test data shows that 50% or more current can be pushed through these connections at the same temperature rise limits, when compared to four- or six-tine sockets. Using this advanced technology, designers can reduce the space required by the connection system, or offer increased electrical rating in the same connector size.
Environmental durability
As mentioned before, power interconnect applications exist 30,000 ft. below the earth’s surface and millions of miles above it. Connectors are used for bulkhead pass-through on nuclear reactor containment shells. Even the average automotive connector may see ten years or more of salt, dirt, water, and temperatures from -50°F to +250°F (-46°C to 121°C). These applications and thousands more require extreme durability as failure of a connector may result in no less than loss of human life.
Connector housings exist for two basic functions: mechanical and environmental. Mechanically, the housing must be relatively easy to mate and unmate between plug and receptacle, and the mated connector must remain that way unless a user wants to disconnect it for any reason. Many connectors are only mated once, when a system is assembled, and the connector is expected to stay mated for the life of the product. Other connectors, such as those used in medical equipment or test and measurement devices will be mated and unmated thousands of times in their product life cycle. Contact design is critical to ensure that functionality and performance meet the needs of the application.
From an environmental standpoint, the connector must ensure whatever is outside the connector stays outside the connector. Sealing performance varies greatly with different types of connectors, but solutions are available for most applications. Some common seals include panel-mount connector seals and inline cable connector seals.
Few environmental materials improve performance between two mating electrical terminals. Whether brass, copper, tin, nickel, silver, or gold plated, a dry and non-corrosive contact is the best environment for electrical performance.
Low resistance
Efficient electrical systems require low resistance in all conductors and connectors, or thermal loss can be substantial. Especially with power circuits and the potential for greater losses, high electrical efficiency has to be one of the top concerns of manufacturers today.
In nearly all cases, copper is used to move power from point A to point B, and often lots of it. Whether heavy-gauge cable or busbars are preferred, the inherent bulk resistance of the alloy is a known, but fixed, limitation. High conductivity alloys, usually low-oxygen coppers, keep thermal losses to a theoretical minimum. Wire crimps and busbar connections are other areas where losses occur, and some termination methods have proven better than others. Considering a securely fastened bolted connection or a well-applied crimp, solder, or weld termination, there is little influence on electrical performance.
High-current connectors that maximize conductivity between the male and female terminals directly improve system efficiency. As mentioned before, spring-band or louver-type interfaces can increase the amount of contact between the terminals, offering a more conductive interface area, thereby lowering resistance. Contact designs that feature spring bands under tension deflected by the mating contact may offer the best combination of low mating force, high current rating, and high durability.
Low mating force
Climbing power requirements have increased the awareness of how un-user-friendly some older high-current connectors can be. As all systems continue to become more modular for easy assembly or transport, the power interconnect industry will continue to grow. As mentioned above, the beauty of tool-less assembly is an advantage of using a connectorized solution, so using tools to mate or unmate connections is not an attractive alternative to high mating forces.
The two major contributors to connector mating force are sealing interfaces and terminal insertion force. A variety of sealing methods exist to minimize resistance to mating-from low friction materials to well-placed seal locations that don’t affect the mating force until the last fraction of travel. To reduce terminal insertion force, a variety of options are available from lubricants to low- or zero-insertion-force contacts. As with everything, there is a perceived tradeoff in low insertion force contacts: if the mating force is low, then the normal force must be low and the current rating is negatively affected. Fortunately for power connector users, the aforementioned spring band and louver-type contacts offer both low insertion force and high current rating. Terminals with 1,000-A ratings can have an engagement of less than five pounds of force with these types of terminal systems.
Other features
Of course, there are many other integrated technologies that customers often want to see designed into high-power connectors. These include break-under-load, or hot-break connectors, and they require durable contacts and special designs, such as ceramic tips to quench any arcing that may occur.
Also common is electro-magnetic interference (EMI) shielding on AC power connectors. Metal-shelled connectors are useful for EMI shielding, as are metal inserts or plating on molded plastic connectors. Various EMI shield-terminating devices now exist to attach the cable shield to the connector shell as well, ensuring a fully shielded cable assembly system.
Another recent development is in-connector filtering of high-power circuits. While not as common as signal circuit filtering, the power filter is likely to increase in popularity as system technologies continue to advance.
Low cost
While all of this technology sounds great, it also sounds expensive, right? The trend towards higher volume and lower cost has not escaped the power connector arena, either. Traditionally, power connectors were machined metal shells with resilient inserts and machined copper contacts. Recent trends include initiatives to increase the use of stamped and formed power contacts, and move towards molded plastic connectors. As the type of applications requiring reliable, durable power connectors continue to increase, expect costs to drop as more parts are molded and stamped rather than machined.
Steven Fitzgerald is RADSOK product manager at Amphenol Corporation, 34190 Riviera Drive, Fraser, MI 48026. Tel: (586) 294-7400; Email: sfitzgerald@amphenol-radsok.com.
