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Copyrighted Material - Taylor & Francis 6 Low-Power Commercial, Automotive, and Appliance Connections AnthonyCopyrighted Lee and George Drew Material - Taylor & Francis They weighed me, dust by dust— They balanced film by film Emily Dickinson COntents 6.1 Introduction ........................................................................................................................ 376 6.2 Connectors ..........................................................................................................................377 6.2.1 Functional Requirements .....................................................................................377 6.2.2 Types of Connectors .............................................................................................. 378 6.2.3 Mechanical Considerations .................................................................................. 381 6.3 Contact Terminals ..............................................................................................................384 6.3.1 Contact Physics ......................................................................................................384 6.3.2 Terminal Types ......................................................................................................384 6.3.3 Other Electrical Contact Parameters ................................................................... 392 6.4 Degradation of Connector Contact ................................................................................. 393 6.4.1 Surface Films .......................................................................................................... 393 6.4.2 Fretting Corrosion of Tin-plated Contacts ......................................................... 396 6.4.3 Examples of Contact Failures ...............................................................................402 6.4.3.1 Automotive Position Sensor Connector ...............................................402 6.4.3.2 Fuel Injector Connector ..........................................................................403 6.4.3.3 Glowing Contacts ...................................................................................403 6.4.3.4 Electrolytic Corrosion .............................................................................404 6.4.3.5 Incompatible Plating and Low Contact Force .....................................404 6.5 Automotive Connector Contacts .....................................................................................405 6.5.1 Vehicle Conditions .................................................................................................405 6.5.2 High Power Connectors for Electric and Hybrid Vehicles ..............................405 6.5.3 Aluminum Wiring Connections .........................................................................406 6.5.4 Connections for High-Vibration Environment .................................................408 6.6 Summay ..............................................................................................................................408 References ....................................................................................................................................409 375 376 Lee and Drew 6.1 Introduction Perhaps the most useful function of electrical connection systems is to serve as a conve- nience for assembly, installation, and servicing of an electrical device or system. For exam- ple, the internal connections in a timer control module of a dishwasher enable the assembly of such a module. In addition, the electrical connections of the harness to the motor, valves, and power sources complete the entire dishwasher assembly. Likewise, the physical instal- lation of a component such as a motor into a clothes washer drive assembly or a radio into the dashboardCopyrighted of an automobile Material is done first, and- Taylorthen the electrical & Francis circuits are completed by mating the connectors or installing other required electrical connections. As each subassembly is linked, each harness is connected with other circuits and to the power source. Depending on the complexity of the entire electrical system, a variety of connec- tors such as in-lines, junction splices, device connectors, and headers are used. The overall system architecture of the entire “wiring harness” determines the number of points and the location where the circuits will be connected. Also, depending on the type of compo- nents in the circuits, connection systems may serve to connect low-current or low-voltage, high- frequency electronics circuits, high-current power circuits, timer and control circuits, sensor circuits, and communication signal circuits. In this chapter, we deal mainly with electrical contacts of the separable type such as the male and female terminals in connection systems. We will also briefly examine the semi-permanent type of crimp and insulation displacement connections because they are intimately related to connectors and are subject to similar physical principles. As with all electrical connection systems, the basic design of an electrical contact depends on a set of application parameters. Table 6.1 summarizes the range of circuit parameters within the scope of this chapter. The basic design and application of the connections require the consideration of (a) The electrical devices to be connected, which define the voltage and current level, and (b) The functional, physical, electrical, mechanical, and environmental requirements of the system to determine the correct connection system to be used. For example, a con- nection made directly to the motor must have sufficient retention force to withstand the vibration from the motor, whereas a ribbon cable will require a different connector from a power feed line with large-gauge round cables. TABLE 6.1 Application Parameters of Connection Systems in the Area of Low-Power Commercial, Residential, Automotive, and Appliance Circuits Type Circuit Voltage (V) Current (A) Power Appliance/commercial/residential 120–240 ac 10–100 Lighting Appliance/commercial/residential 120–240 ac < 10 Control Appliance/commercial/residential 24–36 ac < 2 Power Automotive 12–36 dc > 1 Power Automotive, Electric Drives ~ 300 ac, dc ~ 300 Control Automotive 5–12 dc < 1 Low Power Electronics 5–12 dc < 1 Signal All < 1 < 0.1 Low-Power Commercial, Automotive, and Appliance Connections 377 The environment has a major impact on the design and material chosen for each type of connector housing and electrical contacts. For example, outdoor versus indoor applications can have a major implication on the design of the terminals and the mate- rial used (see Chapters 2, 3, 7, and 8). Other important parameters include the range of operating temperature, duty cycle, number of insertions, thermal cycling or shock, seal and protection, and the corrosion level of the environment. Section 6.5 will give exam- ples of automotive connectors as applied to the challenging automotive environment. Also, the initial cost of a connection system, including the cost of assembly, may deter- mine the type of connector used. On the other hand, the cost associated with service and maintenanceCopyrighted of such a system Material could be much - higherTaylor than an& alternative, Francis which has a higher initial cost. If such equipment is for an application at a remote location, the total cost of the system may dictate the connection system selected. Various industry standards and specifications have been developed, forming some common ground for both suppliers and users of connectors or connection within a given industry. For example, the American Society of Testing and Measurement (ASTM) has an extensive list of contact-related standards especially related to alloy materials, test- ing methodology, and recommended measurement practices. The Electronics Industries Association (EIA) also has a list of contact-related standards. Many of those standards from both EIA and ASTM have been approved as American National Standards. For appli- ance and consumer-related products, the connection systems are tested and listed together with the product as Underwriter’s Laboratory (UL)-approved. For household and related components, the National Electrical Code (NEC) may also apply. For automotive connec- tors, there are a number of applicable SAE and ISO specifications. Also, the military speci- fications (Mil Specs) have comprehensive connector standards for devices associated with military applications in the United States. In this chapter, Section 6.2 addresses connectors, their function, design, subcomponents, and assembly. In Section 6.3, we will focus on the electrical contact terminals of the electri- cal connections. The connector contact degradation mechanisms are discussed in Section 6.4. Since automotive applications have dominated the recent drastic growth in electrical and electronics systems, we shall devote a new Section 6.5 on this topic in this Second Edition. 6.2 Connectors 6.2.1 Functional Requirements Although the basic function of connectors is to provide electrical interconnections to complete the circuit, a large number of non-electrical factors determine the type of con- nector or connection system used. To begin with, mechanical requirements such as size, shape, mounting, and mating and unmating force and frequency need to be consid- ered. In addition, environmental requirements such as temperature, temperature cycle, humidity, contaminants (solid, liquid, and gaseous), shock and vibration, and sealing fur- ther complicate the design
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