Electric terminal manufacturers utilize a good portion of their engineering resources to develop new products or improve existing terminals for the automotive industry. Sam Francois of ETCO examines the keys to choosing heavy-duty terminals for automotive applications.
Problems within a vehicle’s electrical system have long plagued the automotive industry. One of the most common areas for an electrical circuit failure is battery connections. Manufacturers that provide terminals to the automotive industry now pay increasing attention to the heavy-duty terminals required for large AWG wires. Electric terminal manufacturers utilize a good portion of their engineering resources to develop new products or improve existing terminals for the automotive industry, which itself is focused on costs, improving fuel mileage, reducing the use of lead (RoHS), and vehicle weights.
Many things must be considered when developing a terminal for heavy-duty automotive applications. Let’s look at several concerns vital to manufacturing a robust, heavy-duty automotive electrical connection that meets or exceeds customer specifications and SAE standards.
Material Selection for Terminals
Since the implementation of the RoHS directive, lead terminals have been replaced by a number of materials. Terminals can be manufactured from steel and exotic alloys with various plating options that include bright and matte finishes. A great material choice for a heavy-duty battery terminal is tinned brass. Its properties are superior to lead for electrical conductivity, corrosion resistance, tensile strength, hardness, and durability. All of those metal characteristics provide for an optimal heavy-duty terminal. For those looking to reduce weight, a lead-free stamped battery terminal made of tinned brass is an ideal substitute for a heavy-cast terminal.
Terminal Design and Features
A good engineering team will develop a terminal design that enables the best possible connection with design features that facilitate the terminal’s processing by the wire harness manufacturer. Some things they will consider beyond the metal choice are:
- Overall size and wire range of terminal – Determine how much metal is needed to produce the best terminal and evaluate the length of the terminal and material thickness.
- Crimp area of the terminal – The pocket/U-shaped area of the terminal that will form the bond to the wire is designed with specific coin, rib, and serration features that will aid in this union.
- Mating area geometry – The portion of the terminal that will mate with its opposite to form the connection requires coupling features that will ensure the integrity of the circuit. Matching forms will provide maximum surface-to-surface area contact that will maintain a solid bond.
- Layout considerations for a terminal’s production will include determining a side-by-side or end-to-end configuration and its feed length. Pay attention to the direction of the terminal strip, as it will need to be wound onto reels in a fashion that complements the needs of the application process.
The crimp is a solderless termination method used to fasten the terminal to the wire. There are several styles of crimp terminations. One type incorporates a straight cylinder shape located at the back of a terminal where an insulation-stripped portion of a wire is inserted; the cylinder is then pinched onto the wire. The collapsed portion of the cylinder forms the union between the terminal and the wire strands.
Another type of crimp, preferred by most quality wire harness manufacturers, is the F-type crimp. This type of crimp has a U-shaped portion at the back of the terminal designed to form an envelope around the exposed wire strands and be wedged between a sized punch-and-die, also know in the industry as roll tool and anvil. The resulting connection of the F-type crimp is a union so tight that every wire strand is distinctly reshaped by the geometry of the crimp tooling and the compression force.
A good crimp is imperative for good retention to wire. Proper tooling and terminal selection in the recommended equipment with the correct settings will consistently yield quality crimps like the one shown below. A good terminal manufacturer will develop and provide tooling that will offer the best possible crimp – one that has a properly flared bell mouth on the wire side to reduce cut strands and yields a joint that offers optimal wire retention with the lowest electrical resistance.
Some major manufacturers of heavy-duty terminals for automotive applications market battery post terminals specifically designed to mate with the different geometries of the positive and negative battery posts. Terminals that feature engineered ribs or serrations that work within the connection ensure the best possible unification. These terminals are clearly stamped with the + and – symbols to identify them as positive or negative terminals. When specifying, look for a supplier that offers a large assortment of heavy-duty ring terminals made to SAE specifications in a diverse selection of hole sizes to accommodate specific requirements. The terminals made for superior electrical durability and corrosion resistance are supplied on reels as a continuous strip with the crimp ears up for automatic or manual termination.
A trusted supplier’s applicator department should offer all the equipment needed to ensure an optimal terminal-to-wire crimp. Engineered tooling and applicators used in recommended presses offer best results. A variety of attaching equipment should be available to accommodate the manufacturer’s range of terminals. Heavy-duty applicators used for heavy-duty terminals are designed for five-ton electric presses and 10- to 15-ton heavy-duty air/hydraulic presses. The applicators should accommodate terminals for up to “00” gauge wire and offer detailed set-up and operating instructions. An applicator can be designed for semi-automated and fully automated crimping processes. Direction of feed and type of application should be clearly explained in accompanying collateral. Look for applicators that are designed to terminate more than one terminal.
Terminal Retention to Wire
The chart below offers retention values showing the minimum force required to separate the wire from the terminal’s wire crimp ear in both Newtons and lbs/force (measurements taken without influence of an insulation ear). In some cases the manufacturer will recommend higher pullout forces to increase conductivity and specify crimp height to accomplish best all-around crimp performance.
Author Ed Jacques is director, research & development, at ETCO Incorporated.