Discussing several issues that are critical to heavy-duty vehicle electrical connections

Problems within the electrical system have long been an issue in automobiles. One of the most common areas for circuit failure is the battery connection. The heavy-duty terminals required for large AWG wires, such as those used for battery connections, are gaining attention from manufacturers that supply terminals to the automotive industry. Electrical terminal manufacturers devote much of their engineering resources to developing new products or improving existing terminals to meet the needs of an industry that is also focused on cost, improving fuel mileage, reducing lead use (RoHS), and vehicle weight.

Many factors must be considered when developing terminals for heavy-duty automotive applications. This report will discuss several issues that are critical to manufacturing rugged, heavy-duty automotive electrical connections that must meet or exceed customer specifications and SAE standards.

01

Terminal material selection

Since the implementation of the RoHS directive, lead terminals are being replaced by terminals made from other lead-free materials. Terminals can be made from steel and exotic alloys with a variety of plating options, including bright and matte finishes. A good material choice for heavy-duty battery terminals is tin-plated brass. It outperforms lead in terms of conductivity, corrosion resistance, tensile strength, hardness, and durability. All of these metal properties provide the best heavy-duty terminals. For those looking to save weight, lead-free stamped battery terminals made with tin-plated brass are an ideal alternative to heavy-duty cast terminals.

02

Terminal Design and Features

A good engineering team will develop the terminal design to be part of the best possible connection and include design features that make it easier for the harness manufacturer to handle the terminal. In addition to metal selection, they will consider the following:

1. The overall size and wiring range of the terminal. Determine the amount of metal required to produce the best terminal. Evaluate the terminal length and material thickness.

2. Terminal crimping area. The pocket/U-shaped area of ​​the terminal that will form the connection with the wire. This part is designed with specific reinforcement ribs and serration features, etc., which will facilitate the crimping connection.

3. Mating area geometry. The part of the terminal that will mate with its counterpart to form a connection. This requires coupling characteristics that ensure circuit integrity. The mating form will provide the maximum surface-to-surface area contact, thereby maintaining a strong bond.

4. Layout considerations for terminal production will include determining the side-by-side, or end-to-end configuration and its delivery length. Pay attention to the direction of terminal stripping, as it needs to be wound on the reel in a manner that meets the needs of the application.

03

Terminal crimping

Crimping is a solderless crimping method used to secure a terminal to a wire. There are several types of crimp terminals. One type consists of a straight cylinder located on the back of the terminal that is inserted into the insulation stripped portion of the wire. The cylinder is then clamped onto the wire. The collapsed portion of the cylinder forms a joint between the terminal and the wire strands. Another type

of crimp preferred by most quality harness manufacturers is the F-type crimp. This type of crimp has a U-shaped portion on the back of the terminal that is used to form an envelope around the exposed wire strands and moves between a properly sized punch and die. The resulting connection of the F-type crimp is a tight joint so tight that each strand is visibly reshaped by the geometry and compression of the crimping tool. A good crimp is essential to keep the wire well retained.

Selecting the proper tool and terminal in the recommended equipment, with the correct settings, will always produce a quality crimp as shown below. A good terminal manufacturer will develop and provide tools that provide the best crimp. A flare with the proper flaring on the wire side to reduce cutting strands and produce a joint with the best wire retention with the lowest resistance.

Cross section of terminal connected to 6 AWG stranded copper wire. Crimp height is .1857" and crimp width is .2885". Strand count is 268. This cross section shows that each wire strand has been compacted by the crimp. The terminal "crimp wings" are rolled evenly with no spaces between the wire strands.

04

Terminal Type

Major manufacturers of heavy-duty terminals for automotive applications will sell battery terminal posts that are specifically designed to fit the different geometries of positive and negative terminals. The terminals feature engineered ribs or crimp marks (serraTIons) to ensure optimal uniformity in the connection. The terminals will have + and – symbols clearly printed on them to identify them as positive or negative terminals.

In addition, a wide variety of heavy-duty ring terminals are available, which are also manufactured to SAE specifications and have different hole size options to meet customer requirements. The terminals are made of high-quality electrical for durability and corrosion resistance and are supplied in a continuous strip with the crimp wings facing up for automatic or manual termination.

05

Crimping equipment

The crimping department of a trusted supplier should provide all the necessary equipment to ensure optimal terminal wire crimping. Engineered dies and crimping dies used in the recommended press will provide the best results. A variety of connection equipment should be available to accommodate the manufacturer's terminal range. Heavy-duty crimping dies for heavy-duty terminals are designed for use in 5-ton electric presses and 10-15-ton heavy-duty air/hydraulic presses. Crimping dies should be able to accommodate terminals with "00" specification wire and provide detailed setup and operating instructions. Crimping dies can be designed for semi-automatic and fully automatic crimping processes. Feed direction and application type should be clearly stated in the accompanying instructions. Look for crimping dies designed to terminate multiple terminals.

Crimp dies made with engineered tooling made from hardened tool steel are machined and polished to specific geometries to produce repeatable, high-quality crimps. Heavy-duty presses for heavy terminals provide an efficient, simple application. Pneumatic/hydraulic presses are easy to maintain, requiring little or no adjustments when changing wire sizes.

A 15-ton air/hydraulic press is used to attach lightweight RoHS-compliant battery terminals to the wires, ready for installation.

Fixing of terminals and wires

The following table provides retention values, expressed in Newtons and pounds per force, for the minimum force required to separate the wire from the wire crimping wings of the terminal. (Measured without the influence of the insulation crimping wings) In some cases, terminal manufacturers will recommend higher extraction forces for increased conductivity and specify crimp heights for the best all-around crimp performance.

Position the battery using a new set of optimally crimped battery cables.