Terminal Post Assembly for Lead Acid Batteries

(1) Field of the Invention

The present invention relates generally to lead/acid batteries and, more particularly, to an improved terminal post assembly for lead/acid batteries in which the conventional cast lead connecting pad which connects the battery post with the threaded terminal has been replaced by a prefabricated connector formed of a lightweight material having high current capacity and creep resistance.

(2) Description of the Prior Art

The present invention is primarily intended for and will be described in conjunction with a lead-acid aircraft battery. This type of battery generally comprises a plastic interior casing containing lead and lead-oxide plates immersed in an acid electrolyte. The lead and lead-oxide plates within the casing are interconnected and includes a lead electrode post which projects through the cover of the casing.

External terminals for the battery are generally molded into a rather large lead plug which includes an opening in one end thereof for receiving the electrode post. The terminal is connected to the post through the lead member by melting the lead of the post and the lug together.

Some types of batteries include a wall upstanding from the cover forms a well which surrounds the opening in the cover through which the electrode post extends. The lead casting is placed around the electrode post within the aforementioned well and the two lead pieces are welded or soldered together with the lead melting and generally filling the well. This lead casting gives a high electrical resistance between the terminal and the post. The instantaneous peak power or current carrying capability is therefore diminished from what the battery is theoretically capable of producing.

Further, the lead castings (2 for each battery) provide an additional 4 ounces of weight to the battery. This extra weight is important, particularly in aircraft batteries. Further, the terminal to the lead casting connection is weakened because of lead's tendency to creep. Thus terminal connections formed in this manner often become loose after several months of usage. This can create a hazard in that arcing may occur and could lead to a fire or loss of power. Obviously in an aircraft this is highly dangerous.

Thus, there remains a need for a new and improved terminal post assembly for lead/acid batteries which has increase current carrying capacity while, at the same time, is lightweight and creep resistant

The present invention is directed to an improved terminal post assembly for a lead/acid battery of the type including a casing enclosing a plurality of lead plates connected together and immersed in an appropriate acid. The assembly includes a battery cover forming a part of one of the top or side walls of the battery casing. A lead electrode post is connected at one end to the plates of the battery and the other end extends through an opening in the surface of the battery cover.

According to the present invention, a non-lead connector is attached to the end of the electrode post which extends through the surface of the battery cover. In the preferred embodiment, the connector includes a substantially flat base member having an aperture therein in one end for receiving the electrode post and a boss member extending upwardly from the other end of the base member and having a threaded bore therein for receiving a bolt to attach an electrical cable for conducting the electricity produced by the battery.

In the preferred embodiment, the connector is formed from a creep resistant copper alloy such as bronze, brass or copper-nickel. These materials exhibit lower resistance, higher conductivity, and lower creep than lead. Specifically, a connector constructed according to the present invention and formed from one of these materials is capable of carrying greater than about 1100 amps without failure. In addition, the density of these materials are less than about 80% that of lead which provides important weight savings.

A terminal is attached to the non-lead connector and receives an electrical cable for conducting the electricity produced by the battery.

Further in the preferred embodiment, a conductive transition layer is formed between the lead electrode post and the non-lead connector to help provide better physical, electrical and chemical connection between the post and the connector.

The connector itself includes: (a) a substantially flat base member having an aperture therein in one end for receiving the other end of the electrode post which extends through the surface of the battery cover; and (b) a boss member extending upwardly from the other end of the base member and having a bore therein for receiving a terminal adapted to receive an electrical cable for conducting the electricity produced by the battery. The base member includes a reservoir surrounding the aperture to provide an increased surface area to which the lead from the post may attach. The boss also includes flats on opposite sides thereof to provide a gripping surface while the terminal is tightened to avoid stress on the connector/post interface.

It is therefore an object of the present invention to provide an improved electrode post/terminal connection which has a higher current carrying capability.

It is another object of the invention to provide a connection of the type described which is less likely to fail because of arcing resulting from creep as is the case with lead connections.

It is still another object of the invention to provide a connection of the type described which is lighter in weight.

It is yet another object of the invention to provide a unique connector to accomplish the above connection which is a copper alloy.

These and other aspects of the present invention will become apparent to those skilled in the art after a reading of the following description of the preferred embodiment when considered with the drawings.

FIG. 1 is a perspective view illustrating a completed battery constructed in accordance with the present invention;

FIG. 2 is an enlarged perspective of one corner of the battery, illustrating the well which is formed in the cover for the reception of the terminal support connector;

FIG. 3 is a perspective view of the support connector itself;

FIG. 4 is a perspective view similar to FIG. 2, except the cover of the battery has been placed on the casing with the electrode post extending through the opening in the cover and the support connector has been assembled into place in the well surrounding the post in preparation for the soldering operation;

FIG. 5 is a perspective view similar to FIGS. 2 and 4, except illustrating the connector and electrode post immediately after the soldering operation; and

FIG. 6 is a perspective view similar to FIGS. 2, 4, and 5, except illustrating the completed terminal installation with the potting material applied.

In the following description, like reference characters designate like or corresponding parts throughout the several views. Also in the following description, it is to be understood that such terms as "forward", "rearward", "left", "right", "upwardly", "downwardly", and the like are words of convenience and are not to be construed as limiting terms.

Referring now to the drawings in general and FIG. 1 in particular, it will be understood that the illustrations are for the purpose of describing a preferred embodiment of the invention and are not intended to limit the invention thereto. As best seen in FIG. 1, a lead-acid battery, generally designated 10, is shown constructed according to the present invention and intended primarily for the aircraft industry. Battery 10 includes a casing 20 which contains the electrodes, connectors, and the battery post. Cover 22 is placed onto the casing 20 with the battery post 30 (not shown in FIG. 1) extending through cover 22. A terminal support well 24 (FIG. 2) is formed by an upstanding wall 26 which surrounds the opening 25 through which the electrode post extends and forms a well for receiving the terminal support member and the terminal.

Note in FIG. 2 that there is a locating pin 28 provided on the bottom wall or floor 27 of well 24 at the end of the well opposite the opening 25. This locating pin will be used to position the terminal support connector 40 properly within well 24 as will be described hereinafter.

The electrode post 30 is best shown in FIG. 4. Post 30 is formed substantially of lead and includes a portion which extends above the surface of the body member 42 of the terminal support connector 40 for reasons which will be described hereinafter. There is a relationship between the extent to which post 30 extends above the surface of body member 42 of terminal support connector 40.

Turning now to FIGS. 3 and FIGS. 4, there is illustrated in FIG. 3 the preferred embodiment of the terminal support connector 40 which includes generally a base or body member 42 and a boss 50 extending upwardly from the surface of base 42 and one end thereof. Base 42 includes an aperture 44 slightly larger in diameter than the electrode post 30. A recess or reservoir 46 is provided in base member 42 around aperture 44 for reasons to be described hereinafter.

Boss 50 includes a threaded opening or bore 52 which ultimately receives the threaded terminal 60 such as a bolt or stud. Boss 50 also includes two parallel sides or flats 54, 56 which provide a gripping surface to hold the connector support 40 while terminal is tightened without causing stress on the connection between the support connector 40 and the softer lead post 30. The connection between the lead post and the connector is very fragile because of the nature of lead, therefore with the present invention, the battery connections can be made without causing stress at all on the lead post/support interface.

The material from which the connector is made is extremely important. First of all, it must be a non-lead material. Lead is not a good structural material in that it tends to creep, and it is much higher in electrical resistivity (20.65 m ohms/cm) and lower in its current carrying capability when compared to other conductors (9.6 .mu.ohms/cm for bronze and 1.7 m ohms/cm for copper). Lead is also much denser (11.34 g/cc) compared to other metallic materials (8.92 g/cc for copper) which are much higher in conductivity and provide better creep resistance. For example, copper alloys such as brass and bronze, as well as copper-nickel, tellurium-copper, and beryllium-copper alloys provide an excellent material for connector 40. The preferred material is bronze.

It should be noted that preferably one end of the connector 40 is larger than the other. The connector therefore is not elliptical but asymmetrical along the longitudinal axis. This facilitates proper positioning and assembly of the connector during the manufacturing operation, as well as reducing weight. However, symmetrical shapes may be appropriate in some applications.

Such non-lead connectors exhibit about a 30%-50% increase in current carrying capability for typical terminal sizes and are able to carry at least 800 amps and preferably approximately 1100 amps before failure, compared to about 700 amps for lead. These materials are also approximately 2 ounces lighter (less than 80% the density of lead) than the lead castings previously used. The connector may be formed of powdered metal, stamped, machined, cast, or forged.

Finally, the boss 50 includes a small opening 58 in the bottom wall thereof which registers with the locating pin 28 in the bottom wall of well 24, so that the connector may be easily placed in the well in the proper position for final assembly.

To complete the assembly, the cover 22 is placed on the casing 20 with the post 30 extending upwardly through the opening in the cover. An O-ring (not shown) is placed around the electrode post 30 and positioned down in opening 25. The O-ring may be formed of any appropriate material such as an acid resistant rubber or polymeric material. The O-ring prevents leakage of the epoxy potting compound which is to be applied next down into the inside of the casing 20. At this point, a small amount of potting should be applied around the electrode post 30 and in the bottom of well 24. The battery should be charged at this point, because the sulfuric acid used to charge the battery will generate an environment of acid mist.

It is undesirable to have the terminals and terminal connector assembled at this time, because the acid mist will attack brass, bronze, copper or silver containing items in the area.

Once the battery is charged, the connector 40, is placed within the well with the opening 44 extending around electrode post 30 and the small hole 58 being placed over the locating pin 28 on the floor of well 24. Preferably, the support connector 40 is first plated or dipped in silver, gold, platinum or their alloys to provide a non-corrosive surface which ensures better connection between the electrode post and the terminals. Additionally, the seat area of the reservoir 46 also is dipped or coated with tin over the silver layer to provide better attachment between the lead and silver plated connector. Tin alloys extremely well with both lead and silver or even gold (should gold be used for the terminal plating). Thus, there is provided a transition layer between the brass connector and the lead electrode post. A first component of the transition layer is a copper protecting, non-corrosive coating such as silver or gold. Secondly, there is a layer of tin to provide better compatibility between the lead of the electrode post 30 and the silver plating of the connector 40.

The connector 40 is then soldered to post 30. During the soldering operation, the lead heats and melts. The volume of lead extending above the surface of the base member 42 is just sufficient to ensure that the reservoir 46 is filled with lead. Because of the reservoir configuration in the base member, there is more surface area for the lead to attach to, and therefor a better bonding result is attained. Finally, additional epoxy potting compound is used to fill the well 24 substantially level with the upper extremity of the wall 26. The terminal 60 may be later attached by the customer at the time the battery is installed.

Certain modifications and improvements will occur to those skilled in the art upon a reading of the foregoing description. By way of example, a terminal in which the terminal connector is formed in such a way as to mate with a quick disconnect cable instead of a threaded member. Also, an assembly in which the terminal connector is integrally molded into the battery cover in order to provide precise location and orientation, and eliminate secondary manufacturing operations. It should be understood that all such modifications and improvements have been deleted herein for the sake of conciseness and readability but are properly within the scope of the following claims.