Single bolt fuse assembly with an electrically isolated bolt

A single bolt fuse assembly and method to connect a single bolt fuse to a circuit or device are disclosed. The single bolt fuse assembly enables the single bolt fuse to be used on any electrical device having a hole suitable for receiving a threaded shaft and connectable to a circuit or device that electrically connects to a female battery or power cable. The apparatus includes a separate high-conductive metal terminal that mates with the stud that mechanically attaches the fuse between the electrical devices. The stud is insulated to avoid becoming part of the electrical circuit and to ensure proper operation of the fuse. By mechanically attaching the stud to the metal terminal, the stud is unlikely to get separated from the fuse.

FIELD OF THE DISCLOSURE

Embodiments of the present disclosure relate to single bolt fuses and, more particularly, to a novel way to attach the single bolt fuse to a female battery or power cable.

BACKGROUND

Fuses are current-sensitive devices designed to serve as the intentional weak link in an electronic circuit. Fuses provide protection of discrete components or of complete circuits by reliably melting under current overload conditions. Fuses come in a variety of packages and ratings to suit to their intended application.

Single bolt fuses, also known as battery terminal fuses, are a particular type of fuse package in which the fuse is attached to a device or circuitry by a threaded connection, such as a bolt or stud. The fuse includes a hole through which a single bolt may be inserted to mechanically connect the fuse to the device or circuit. The bolts are specially adapted, such as by being insulated or otherwise materially treated, so that they do not disrupt or become part of a current path through the fuses, ensuring that the single bolt fuses operate as designed.

To use the single bolt fuses, the specially treated bolt is separated from the fuse, the fuse is attached to the circuit or device to be protected, the bolt is inserted through the hole in the fuse. Sometimes, the bolt has an integrated nut, or bolt may be secured by a separate nut. Because of the assembly needed with single bolt fuses, the bolt (and nut, if present) may become separated from the fuse and lost. Customers may be tempted to replace the lost bolt with a standard bolt that is not specially adapted for the single bolt fuse. Unfortunately, this results in the single bolt fuse not functioning as designed. Further, the single bolt fuse is designed to be connected between a power terminal and either a battery terminal or a bus bar, which somewhat limits the applications in which the fuse may be used.

It is with respect to these and other considerations that the present improvements may be useful.

SUMMARY

An exemplary embodiment of a fuse assembly in accordance with the present disclosure may include an insulated steel bolt and a metal terminal. The insulated steel bolt includes a shaft that is part threaded and part insulated. Connected to the shaft, the insulated steel bolt also includes a base, which is a rectangular cube having a first dimension. The shaft is positioned vertically atop one side of the base. The metal terminal features a bolt base receptacle, also shaped like a rectangular cube, and having a hollow interior with a second dimension that is greater than that of the base. The base of the steel bolt fits into the hollow interior of the bolt base receptacle. The metal terminal also has a threaded shaft on one side of the bolt base receptacle. The shaft of the insulated steel bolt is to be fed through a cylindrical opening of a fuse.

Another exemplary embodiment of a fuse assembly in accordance with the present disclosure may include an electrically conductive landing pad which has a threaded shaft and a hollow receptacle. The threaded shaft fits into a receiving aperture of an electrical device. The fuse assembly also features a stud that has an insulated base portion, an insulated washer, and a shaft. The shaft has a threaded portion, an unthreaded portion, and an insulated portion. The base portion of the stud fits into the hollow receptacle of the landing pad and the shaft portion fits through a cylindrical opening of a single bolt fuse. In the fuse assembly, current passes from the electrical device, through the single bolt fuse, and to a second electrical device without passing through the stud.

DETAILED DESCRIPTION

A single bolt fuse assembly and method to connect a single bolt fuse to a circuit or device are disclosed. The single bolt fuse assembly enables the single bolt fuse to be used on any electrical device having a hole suitable for receiving a threaded shaft and connectable to a circuit or device that electrically connects to a female battery or power cable. The apparatus includes a separate high-conductive metal terminal that mates with the stud that mechanically attaches the fuse between the electrical devices. The stud is insulated, thus isolating the bolt from becoming part of the electrical circuit and ensuring proper operation of the fuse. By mechanically attaching the stud to the metal terminal, the stud is unlikely to get separated from the fuse. The metal terminal and stud may be part of a kit available to customers who purchase the single bolt fuse.

FIG. 1is a representative drawing of a 250 A single bolt fuse100for providing circuit protection, according to the prior art. The single bolt fuse100features a receptacle102, such as a cylindrical hole, for receiving a like-sized threaded bolt, known as a stud. The fuse simply slips over the bolt or stud. Two studs110A and110B (collectively, “studs110”) are also shown, the stud110A featuring a threaded shaft104and the stud110B featuring a threaded shaft106and further including a flange nut108. The studs110are designed to be electrically isolated when inserted through the fuse hole102of the single bolt fuse100. Accordingly, the studs110may be insulated or otherwise materially treated so that the studs do not become part of the electrical path through which current flows when the single bolt fuse100is connected to a circuit or device to be protected.

FIGS. 2A and 2Billustrate another single bolt fuse200, according to the prior art. Two fuses200are depicted inFIG. 2A, each including a hole202for receiving a threaded stud210. The stud210includes an insulated, threaded portion208and an integrated nut206. As illustrated in the single bolt fuse assembly218(FIG. 2B), the fuse200is to be connected to a battery204, which has a receiving aperture214sized to support the threaded portion208of the stud210. A sealed power cable212to connect the battery204to other circuitry/device (not shown) also includes a receiving aperture216. The single bolt fuse200is placed between the battery204and the sealed power cable212, with the insulated bolt210threading through respective holes214and216, sealing the components together.

FIGS. 3A-3Cillustrate an assembly302featuring single bolt fuses300, according to the prior art, with the assembly shown in three parts (302A,302B, and302C). In the assembly302, three threaded studs310are inserted through a busbar306, from the bottom. A battery terminal304is then placed over the center stud. Three single bolt fuses300are then placed on the studs310. Output power cables312are then placed on top of the fuses300, also over the studs310, as the cables include ring terminals for this purpose. The components are then secured with nuts308.

Thus, the fuses100,200, and300are designed to be used with their respective studs110,210, and310. The studs are insulated to isolate current so that the current passes through the fuse (and not the stud), enabling the fuse to protect the circuit (e.g., the circuit or device connected to the output cable212(FIG. 2B) or output cable312(FIG. 3C)) as intended.

One problem with single bolt fuses, including the above illustrated single bolt fuses, is that the studs that are specially made to be used with the fuses may become separated from the fuses. Customers may then be tempted to replace the missing studs with standard bolts that are uninsulated. When this occurs, the fuse will not operate as designed.

For example, in the assembly ofFIG. 2B, current from the battery204passes through the fuse200, then through the sealed power cable212to other circuitry (not shown); in the other direction, current passes through the sealed power cable212, through the fuse200, and to the battery204. If an overcurrent condition from the battery204occurs, the fuse200includes a breakaway portion therein that will break, protecting any circuitry connected to the sealed cable212. The assembly218thus operates as designed.

If, in the alternative, the insulated stud210is replaced with an uninsulated stud not designed to be used with the fuse200, current will flow from the battery204, through the uninsulated stud, and through the sealed cable212, completely bypassing the fuse200. The same will happen in the other direction: current will flow from the circuitry to be protected (not shown) through the sealed cable212, through the uninsulated stud, and to the battery204, completely bypassing the fuse200. Put another way, the uninsulated stud will electrically connect the top and the bottom of the fuse, removing the fuse from the circuit. Thus, the use of a stud not designed to be used with the fuse200will prevent the fuse from operating as designed to protect the circuitry. Similar problems will exist for the fuses100and300if they are used with uninsulated studs.

Another problem with single bolt fuses is the limited environment in which they can operate. As currently designed, the fuses are connected, at one end, to the battery or power cable and, at the other end, to either a battery terminal or to a bus bar. In the example ofFIG. 2B, the fuse200is positioned between the power cable212and the battery204. In the example ofFIG. 3C, the fuse300is positioned between the power cables312and the busbar306(which is connected to the battery terminal304). Thus, the configurations available for using legacy single bolt fuses is somewhat limited.

An alternative is provided in the apparatus ofFIGS. 4A-4C, a single bolt fuse assembly with an electrically isolated bolt400, according to exemplary embodiments.FIGS. 4A and 4Bare exploded perspective views whileFIG. 4Cis a perspective cutaway view of the single bolt fuse assembly400. The single bolt fuse assembly400features a metal terminal402, an insulated steel bolt408(also known herein as a stud408), a single bolt fuse426, and a female battery or power cable430, which are joined together as described herein. As will be shown, the single bolt fuse assembly400maintains a connection between the insulated steel bolt408and the single bolt fuse426, thus ensuring proper functioning of the fuse as a protector of connected circuits or devices.

The metal terminal402, also known as the “landing pad” of the fuse assembly400, includes a bolt base receptacle404and a threaded shaft406. The threaded shaft406enables connection of the single bolt fuse assembly400with any electrical device having a threaded receiving aperture. The metal terminal402further includes an adjacent side opening424, revealing a hollow interior, as well as an inset portion414. In exemplary embodiments, the threaded shaft406and the bolt base receptacle404of the metal terminal402, including the opening424and the inset portion414, are machined from a unitary metal piece made of electrically conductive material, such as copper or a copper alloy.

The steel bolt or stud408of the single bolt fuse assembly400features a shaft410that has a threaded portion412, an unthreaded portion416, an insulated portion418, an optional integrated washer420, and a base422. In addition to the insulated portion418of the shaft408being insulated, the integrated washer420and the base422are also insulated so as to isolate them from current transmitted through the assembly. In addition to providing insulation so as to prevent current flow through the stud408, the integrated washer420also helps to withstand pressure after the assembly400is secured by the nut440. In an alternative embodiment, the insulation of the base422is sufficient to prevent current flow through the stud and to withstand high mechanical pressures during torque of the nut440. Thus, the stud408may be configured without the integrated washer420. In an exemplary embodiment, the insulated components of the assembly400are insulated using electrically insulating material, such as overmolded plastic, though other insulation materials may also be used.

In the illustrations, the bolt base receptacle404is a rectangular cube shape of a first dimension. The hollow interior of the bolt base receptacle404, which is a second dimension smaller than the first dimension, is disposed on one side adjacent the side with the threaded shaft406. As illustrated inFIG. 4B, the base422of the stud408, which is a third dimension, fits snugly into the bolt base receptacle404of the metal terminal402. Thus, the second dimension is slightly greater than the third dimension, allowing the base422to fit into the hollow interior via the opening424of the base receptacle404. The inset portion404of the bolt base receptacle404is disposed opposite the threaded shaft406, and the shaft410of the stud408fits into the inset portion404as the base422is laterally presented into the base receptacle404. Once fully inserted, the threaded shaft406of the metal terminal402appears to be along the same axis as the shaft410of the stud408, in an exemplary embodiment.

Alternatively, the two shafts406and410may be in different axes. For example, where the bolt base receptacle404is now substantially cubic in shape, a more elongated rectangular cube-shaped receptacle may result in the shaft406of the metal terminal402being in one axis and the shaft410of the stud408being in a different axis, with the two axes being parallel to one another. Or the inset portion414may be machined into a different side of the bolt base receptacle404(a side not opposite the threaded shaft406). This would result in the shaft410of the stud being in an axis orthogonal to the threaded shaft406. Or the opening424, which is now on a side adjacent to the threaded shaft406, may instead be on the side opposite the threaded shaft, where the inset portion414is now located, in which case the shaft410of the stud would be orthogonal to the shaft406of the metal terminal402. Designers of ordinary skill in the art will recognize a number of ways in which the landing pad402may be machined to receive the base422and shaft410of the stud408without departing from the spirit of this disclosure.

Once inserted into the landing pad402, the insulated steel bolt408may be captured or mechanically locked in the bolt base receptacle404. In an exemplary embodiment, orbital riveting, a mechanical bottleneck, a secondary lock, or other means are employed to mechanically lock the bolt408to the metal terminal402.

The fuse426of the single bolt fuse assembly400includes a cylindrical opening428, a shaft receptacle, for receiving the shaft410of the stud408. In an exemplary embodiment, once the insertion of the shaft410through the fuse is complete, the single bolt fuse426is disposed atop and adjacent to a top surface of the bolt base receptacle404, as illustrated in the cutaway view ofFIG. 4C. Further, both the unthreaded portion416and the insulated portion418of the shaft410are disposed within the shaft receptacle428of the single bolt fuse426. In an exemplary embodiment, the shaft410is insulated from a bottom portion of the fuse terminal, ensuring that the bolt will not conduct the fuse element (not shown) within the fuse426. The insulation may be higher than is shown. In an exemplary embodiment, the threaded portion412of the shaft410extends to the top of the fuse426. In an exemplary embodiment, the insulating layer/portion418and the insulating washer420of the single bolt fuse assembly400isolates the center bolt408from the fuse426. The single bolt fuse426may also be known as a coaxial fuse, as the two terminals that are connected by the fuse element are actual coaxial. That is, their holes are concentric and placed in different (parallel) planes. This is in contrast to some fuses which have a linear shape with the fuse element in the middle, with a terminal on each side.

Similar to other fuses, the single bolt fuse426includes within its housing a fusing element (the intentional weak link that breaks upon the occurrence of an overload event, such as overcurrent, overvoltage, or both), connection means for connecting the fusing element to terminals (ensuring that the fusing element is part of a closed circuit), and fusing powder. This part of the fuse426containing the fuse element is known herein as the fuse element housing. In an exemplary embodiment, the shaft receptacle428is isolated from the fusing element housing. The fusing element housing of the single bolt fuse426may thus be thought of as an annular housing, shaped like a rectangular donut, with the shaft receptacle428being both physically and electrically isolated from the fusing element housing.

Atop the fuse426, the single bolt fuse assembly400includes the female battery or power cable430, which includes a cable432and a high-current electrical (ring) terminal436. The cable432attaches the fuse426at one end to a circuit or device to be protected (not shown) while the threaded shaft406of the landing pad402attaches the fuse at the other end to virtually any electrical component that has a hole through which the landing pad may be threaded, enabling the electrical component to be electrically connected to the fuse426. The threaded portion412of the stud408is fed through the ring terminal436, and the female battery or power cable430is attached to the assembly by an optional washer438and a nut440. In the illustrations, the nut440is a flange nut, but a regular nut may also be used as long as torque loosening is avoided during use of the assembly400. In the single bolt fuse assembly400, the washer and the nut are not part of the current path, and so need not be insulated. This means that, if lost, the optional washer and nut may be replaced without compromising the operation of the fuse426.

The low-resistant landing pad402lets current flow through the fuse426and the battery or power cable430. The steel insulated bolt408guarantees a high torque to fix the assembly400without being involved in the electrical flow.

FIGS. 5A-5Care perspective cutaway illustrations of a single bolt fuse500suitable for the single bolt fuse assembly400, according to exemplary embodiments. A cover portion502, when removed, reveals a fusing element506disposed to one side of the fuse500. A shaft receptacle504is for receiving an insulated shaft, such as the shaft410described above. The shaft receptacle504is both physically and electrically isolated from the fusing element506.

FIG. 6is a perspective illustration of a configuration600featuring the single bolt fuse assembly with an electrically isolated bolt400connected to a relay602, according to exemplary embodiments. The single bolt fuse assembly400is connected to the relay602by the threaded shaft406of the landing pad402. The relay602includes a threaded hole (not shown) for receiving the threaded shaft406, thus establishing an electrical connection between the relay602and the fuse426. The configuration600may further be connected to an electrical circuit or device via the female battery or power cable (such as female battery or power cable430inFIGS. 3A and 3B). The configuration600is merely illustrative. The single bolt fuse assembly400is designed to connect between 1) any electrical device that includes a threaded hole for receiving the threaded shaft406of the landing pad402and 2) any electrical device or circuit that is electrically connected using the female battery or power cable.

Single bolt fuses, such as the prior art single bolt fuses described and illustrated above, feature M6, M8, and M10 sized threaded holes for connecting with M6, M8, and M10 insulated studs, respectively. However, the single bolt fuse assembly400may be designed with a threaded shaft of any size, sized to fit with a single bolt fuse having a hole of a similar size. The examples herein are not limited in regard to the size of the threaded shaft or the threaded hole.

FIG. 7is a flow diagram illustrating a method700of assembling a single bolt fuse assembly with an electrically isolated bolt, such as the single bolt fuse assembly400described and illustrated above. For clarity, the reference numbers of the single bolt fuse assembly400are given in parentheses, though the method steps may apply to other configurations of single bolt fuse assemblies. The bottom rectangular-cube-like portion of the steel stud (408), known as the base (422), which is insulated, is inserted into the bolt base receptacle (404) of the metal terminal (402), known as the landing pad, which is sized to receive the insulated base (422). The shaft (410) of the steel stud (408), some of which is also insulated, fits flush against an inside edge of the inset portion (414) of a top surface of the bolt base receptacle (404) (block702). Optionally, the base (422) can be secured inside the bolt base receptacle (404), such as by orbital riveting, mechanical bottleneck, secondary lock, or other means (block704).

The shaft (410) is next inserted through the receiving aperture or shaft receptacle (428) of the single bolt fuse (426) until the fuse is disposed atop the bolt base receptacle (404) of the landing pad (402) (block706). At this stage, the insulated portion (418) of the shaft (410) is partially inserted into the receptacle (428). The ring terminal (436) of the female battery or power cable (430) is positioned over the shaft (410) of the stud (408) until the ring terminal (436) is flush against the top surface of the single bolt fuse (426) (block708). Finally, the washer (438)), if present, and nut (440are disposed over the shaft (410) of the stud (408), and secured tightly thereon (block710). Alternatively, the shaft (410) of the stud (408) is secured by a nut having an integrated washer, such as a flange nut, a trilobate nut, or other type of nut that can be used without a washer.

FIGS. 8A and 8Bare illustrations of a single bolt fuse800and a single bolt fuse assembly kit810, respectively, according to exemplary embodiments. Customers may want to assemble a single bolt fuse assembly, such as the single bolt fuse assembly400(FIGS. 4A-4C) or a configuration, such as the configuration600(FIG. 6) for connecting a single bolt fuse to an electrical device. Accordingly, the manufacturer may provide a variety of single bolt fuses for purchase, and, separately, may provide a variety of single bolt fuse assembly kits. Or the manufacturer may provide a kit including the fuse with the assembly. Thus, the single bolt fuse800(FIG. 8A) may be purchased as a standalone device, with the customer determining the specifications, such as current ratings, voltage ratings, and the like, to for their particular application. Separately, the customer may purchase a single bolt fuse assembly kit810(FIG. 8B) containing the metal terminal802(landing pad), steel bolt including insulated base804, optional washer806, and nut808, which is properly sized for the single bolt fuse. In particular, this means that the shaft of the steel bolt804will fit through the hole of the single bolt fuse. The customer will likely already have the female battery or power cable (e.g., threaded battery or power cable430inFIGS. 4A and 4B), as this component may be part of the circuitry or device in their possession. Thus, in one embodiment, the female battery or power cable is not part of the assembly kit810. Alternatively, the manufacture may sell the single bolt fuse800along with the assembly kit810.

While the present disclosure makes reference to certain embodiments, numerous modifications, alterations and changes to the described embodiments are possible without departing from the sphere and scope of the present disclosure, as defined in the appended claim(s). Accordingly, it is intended that the present disclosure not be limited to the described embodiments, but that it has the full scope defined by the language of the following claims, and equivalents thereof.