 Figure 1. In this circular connector application, an insert band provides multiple contacts that surround the inside circumference of a socket. |
Connector insert bands increase the number of contact points between a pin and socket.
By Glenn Steinhauer
Faced with the need for connectors that can carry higher current loads, design engineers have few options. They can pick a larger connector, but that may adversely affect the overall device design and raise costs. They can increase the mating force on the connector contacts to lower resistance levels, but that leads to higher insertion and withdrawal forces, depending on the number of connector positions.
Multiplying Contact Points
A third, less conventional, option employs specialized connector insert bands designed to increase the number of contact points between a pin and socket. In addition to socket insert bands, variants of this technology can wrap around pins or sit between busbar contacts.
The insert bands for sockets employ a ring of louver-like contact springs arranged along the length of the socket. The louvers provide multiple contacts that surround the inside circumference of the socket (see Figure 1). As the connector pin enters the socket, the louvers act like multiple springs, contacting the pin at many points around its surface rather than at just one or two points. The insert bands are designed to allow each louver on the band to make equal contact with the mating pin, or in the case of a male band, the socket cavity.
By distributing the current flow more uniformly, higher current ratings are achieved. The contacts offer very low resistance, which greatly reduces voltage drops compared to conventional contacts. As a result, a given current causes a lower temperature rise in the connector.
Heat is created as a byproduct of increased current. This heat has to be dissipated through the contact interface. In conventional contact interface systems, which usually consist of only one or two areas of contact, this heat is filtered through fewer points. Therefore, the temperature rise is much sharper than if insert bands are used. Simply stated, more contact points mean less heat per point of contact.
 Figure 3. The louvers in female torsional bands rotate about their own axis. |
The insert bands also help to eliminate "hot spots." A hot spot is usually created when a contact interface system dissipates most of its heat through one point. With insert bands, the contact points are not only increased, but they are fairly uniform in contact pressure, thereby decreasing the danger of a point of contact that is "hotter" than the rest.
 Figure 4. The louvers in female bridge bands have their arc depressed upon mating. |
Despite the multiple contact points, the spring-loaded louvers require relatively low forces for insertion and withdrawal of the pins. Conventional systems of power transfer have relatively few electrical contact points. High contact forces must be designed to achieve a lower contact resistance. This results in high mating forces.
In addition, connectors fitted with these insert bands require less space for the same amount of current-carrying capability. For example, adding the bands to a four-circuit connector virtually doubles its current-carrying capacity (see Figure 2). A fully loaded, four-circuit connector can carry up to 31.0 A per contact with a 30°C temperature rise. The standard contacts for this connector are rated at 14.9 A. This means design engineers can specify a smaller connector for higher current loads with no sacrifice to connector reliability or safety.
Torsional and Bridge Louvers
Insert bands come in two basic types: torsional bands and bridge bands. In the torsional type, the louvers rotate about their own axis in applying the spring contacting force (see Figure 3). In the bridge type, the louver arc simply depresses (see Figure 4). Because the louvers on the torsional bands are much larger than those on the bridge bands, the torsional bands accept a wider range of pin, or socket, tolerance. The louvers on the bridge bands are smaller, and therefore require a tighter range of tolerance on the pin, or socket, diameter. Torsional bands cannot be used in pin diameters of less than 0.312". Bridge bands can be used with pin diameters as low as 0.020".
For larger connectors, both types of insert bands are available as strips that can be sized with scissors to retrofit an installation on-site. These can be applied to flat busbar and circular contact applications.
A male band can wrap around the outside diameter of a large pin. The female band fits within the inside diameter of a socket. Various retainer mechanisms can be employed to hold the female bands in place, such as counterbore/dovetail designs on smaller torsional bands, retaining rings (steel or plastic) on larger torsional bands, and counterbore and retaining dimple designs on bridge bands.
Torsional bands can serve in several types of connector configurations, including:
- Standard plug-in connectors with circular contacts
- Flat, fork-like connectors for connections to busbars
- Rotating joints, full 360° in both directions
- Sliding contacts
- Butt-type contacts
- Expansion contacts
Bridge bands can be used with standard plug-in connectors having contacts of circular cross-section, as well as in flat busbar applications.
Insert Band Variables
These variables should be considered when specifying insert bands to increase a connector's current capacity:
- Thickness of the band — it may affect dimensional aspects of the designer's application.
- Surface of the band and mating contacts, plated or unplated — bare band surfaces such as beryllium copper and tin plating corrode with exposure to moisture and temperature, whereas gold plating, which is a noble metal, does not; however, gold is much more expensive.
- Surface finish of the mating contacts — rough surface finishes can decrease a contact's durability, while increasing the mating force.
- Materials of the mating contacts — materials vary in properties, such as electrical conductivity, which may decrease the effectiveness of the bands.
These variables affect durability, mating force, voltage drop and resistance. For example, a 0.006" bridge band allows a minimum of 10,000 operation cycles. A thinner band can produce a cycle life of several hundred thousand. Bands have an operating temperature range of 200°C, excluding platings that have low melting points, such as tin or tin/lead. They also operate when fully immersed in oil (the oil helps to carry away heat) and can be used with most lubricants and greases. Connector insert bands allow a designer to increase an application's current flow, without increasing the physical size of the application.
GLENN STEINHAUER is Product Engineer III, AMP, a part of Tyco Electronics Corp., P.O. Box 3608, Harrisburg, PA 17105-3608; (717) 592-2409; Fax: (717) 592-6146; Web site: www.tycoelectronics.com.
SPEC SHEET
End Applications:
High-current applications
Related Products:
Power connectors, pin-and-socket connectors
Main Point:
Connector insert bands allow an application's current flow to increase, without increasing the physical size of the application. Insert bands use a ring of louver-like contact springs that provide multiple contact points bysurrounding the inside circumference of the socket. Certain variables should be considered when specifying insert bands to increase a connector's current capacity. These variables affect durability, mating force, voltage drop and resistance.
