US 3227983 A
Description (OCR text may contain errors)
Jan. 4, 1966 M. J. BRAUN 3,227,983
STACKED RESISTOR Filed Aug. '7, 1963 "all,"
IIIIIIIJUIIIJ INV NTOR.
BY w. W
K .1 ATTORNEY.
United States Patent 3,227,933 STACKED RESISTOR Marinus J. Braun, Bradford, Pa, assignor to Air Reduction Company, Incorporated, New York, N.Y., a corporation of New York Filed Aug. 7, 1963, Ser. No. 300,555 2 Claims. (Cl. 33821) This invention relates to resistors and more especially to that type of resistor that is used as a surge resistor; for example, in the circuits of automobile horns; but the resistor of this invention can be used in a wide variety of combinations where it is desirable to have a resistor of known and substantially constant resistance value.
It is an object of the invention to provide an improved stacked resistor in which resistance elements are stacked together in end-to-end relation and with means for holding them in their stacked relation with one another. The resistor can be given any selected resistance by adding resistor elements to the stack; and the stack has any length as desired and affords N resistance where N is the sum total of the resistance of all of the individual resistance elements of the stack.
Another object is to provide an improved resistor, of the character indicated, and with the individual resistor elements constructed and stacked so that the resistance of the stack is independent of the pressure on the individual elements. The resistor of this invention withstands high surges and maintains the proper resistance value thereafter. By providing conductive, low electrical resistance coatings on both end faces of each individual resistor element of the stack, the flow of current is dissipated to minimize hot spot-s.
The stacked resistor of this invention lends itself to the construction of stacked resistors having total resistance values that are accurate within close tolerances, and that can be assembled with the resistance value necessary to test new circuits.
Other objects, features and advantages of the invention will appear or be pointed out as the description proceeds.
In the drawing, forming a part hereof, in which like reference characters indicate corresponding parts in all the views;
FIGURE 1 is a side elevation, partly broken away and in section showing a resistor element made in accordance with this invention;
FIGURE 2 is a view similar to FIGURE 1 but showing a modified form of the invention;
FIGURE 3 is a view, mostly in section, showing another modified form of the invention;
FIGURE 4 is a View similar to FIGURES 1 and 2 showing still another modified form; and
FIGURE 5 is a sectional view taken on the line 5-5 of FIGURE 1.
FIGURE 1 shows a resistor made up of a plurality of individual resistor elements 12. Each of the resistor elements 12 is of similar ring shape and there is a coating 14 on the annular surface at both ends of each of the individual resistor elements 12.
The individual resistor element-s 12 are preferably made of a compressed resistor mixture consisting of carbon powder and a binder and these resistor elements can be made in accordance with the process disclosed in the Krellner Patent 2,903,666. In accordance with the disclosure of that patent, the coating 14 on the end faces of each individual resistor element 12 is made of powdered copper molded simultaneously with the body of the resistor. While this is the preferred construction, the coatings 14- are representative of material of high electrical conductivity bonded to the high resistance material of the individual resistors 12.
3,227,983 Patented Jan. 4, 1966 This construction obtains a widespread and large area of contact between the inner faces of the resistor elements 12 and the coatings 14. There is, therefore, no substantial change in the resistance of individual resistor unit 12 when there is a difference in pressure exerted against the surfaces of the coatings 14. Because of the good electrical conductivity of the coatings 12, and the smooth faces on these coatings, there is good electrical contact between successive individual resist-or elements 12 and the resistance between them is independent of the pressure with which they are held together.
The individual resistor elements 12 are all similar in construction and none of them has any terminal for leads connected with it; but the stack of resistor elements has terminal pieces 16 at each end clamped against the coating 14 of the end elements 12. Each terminal piece 16 has a washer portion 18 with an opening through it similar in size to the openings through the individual resistor elements 12; and each terminal piece 16 also has a lead portion 21) to which conductors are connected for joining the resistor 10 with an electric circuit in which it is to be used.
The resistor elements 12 are secured together in FIG- URE 1 by a bolt 22 made of material which is a non-conductor of electricity, such as nylon. The bolt 22 has a head 24 which provides a shoulder for clamping the terminal piece 16 against the top coating 14 of the uppermost resistor element 12. There is a nut 26 threaded over the lower end of the bolt 22, and this nut 26 clamps the lower terminal piece 1 6 against the coating 14 on the lowermost individual resistor element 12. The nut 26 is screwed up tight enough to hold all of the resistor elements 12 and the terminal pieces 16 secured in assembled relation with one another and with the contacting faces of the various parts under substantial pressure.
There is always uniformity in the resistance across the confronting coatings 14 of the successive resistor elements 12, but even though the individual resistor elements are made by the same method and with the same amount of material, there are manufacturing tolerances which produce some differences in the resistance through the carbon mix between the coatings 14 of the different resistor elements 12. In order to make resistors having accurate values of resistance, individual resistor elements are initially sorted and grouped according to precise resistance tolerances. When a resistor of a given value is to be assembled, the resistor elements are selected which add up to the total resistance desired for the particular resistor.
For example, if the individual resistor elements 12 are designed to have a resistance of four ohms each and four resist-or elements are selected which produce a total resistance of only 15.8 ohms, then the fifth element or the resistor shown in FIGURE 1 must be selected from a group having a resistance of 4.2 ohms in order to have the resistor with a final resistance of exactly 20 ohms.
Although the resistor 10 is shown with individual resistor elements 12 which are of the same size, the invention can be made with resistor elements of different thickness for example, a resistor could be made with one resistor element having a resistance of 8 ohms and three resistor elements having individual resistances of 4 ohms each in order to produce a resistor having an overall resistance of 20 ohms.
FIGURE 2 shows a resistor 30 which is similar in construction to the resistor 10 shown in FIGURE 1 except for the clamping means. Individual resistor elements 12 are indicated by the same reference characters as in FIGURE 1, and so are the coatings 14, there being no difference between the individual resistor elements in FIGURES 1 and 2. The terminal pieces 16 are also the same.
In place of a bolt made of electrical insulating material, FIGURE 2 uses a metallic bolt 32 and in order to prevent this bolt from short-circuiting the terminal pieces 16, the resistor has bushings 34 made of electrical insulating material. Each of these bushings has an opening through it for passage of the bolt 32 but the bolt is considerably smaller than the opening through the resistor elements 12 and the terminal pieces 16. The openings in the bushings 34 are of substantially the same diameter as the bolt 32 so that a head 36 of the bolt provides a shoulder for clamping the bushing 34 against the uppermost terminal piece 16. The bolt 32 has a nut 38 for clamping the lower bushing 34 against the lowermost terminal piece 16 and for holding all of the individual resistor elements 12 together in assembled relation with one another and with the terminal pieces 16. I In order to center the bolt 32 and the terminal pieces 16, each of the bushings 34 has a portion of reduced diameter extending through the openings in the terminal pieces 16 and into a portion of the length of the end resistor elements 12. An insulating sleeve covers the bolt 32 between the bushings 34.
FIGURE 3 shows a resistor 40 which has individual resistor elements 12 similar to the resistor elements 12 as shown in the other figures but without any hole extending through them. The individual resistor elements 12 are solid cylinders. They have a coating 14' over their upper and lower faces and this coating is similar to the coating 14 of FIGURES l and 2 except that its area is more extensive since it covers the area of a circle instead of an annular end face such as is formed by the ring shape of the resistor element 12.
The resistor elements 12 are surrounded by a sleeve 42 of electrical insulating material and there are terminal pieces 16 at opposite ends of the resistor 40; but these terminal pieces 16 contact with electrical conductive discs 44 instead of being clamped directly against the coating of the resistor elements.
The resistor 40 has a C-clamp frame 4-6 and has a screw 48 which threads through the upper portion of the C-clamp frame and which presses a clamping plate 50 against the upper terminal piece 16. This clamping piece 50 can be made of metal, like the rest of the C-clamp frame 46, because there are discs 52 of electrical insulating material between the C-clamp frame 46 and the terminal pieces 16 to prevent short-circuiting by the C- clarnp.
The screw 48 is turned to force the clamping piece 50 downward so as to clamp the terminal pieces 16, discs 44, and individual resistor elements 12' together between the clamping piece 50 and the insulation disc 52. The screw 48 is tightened so as to maintain firm contact between the clamped parts and the screw is then locked in position by a lock nut 54.
FIGURE 4 shows a resistor 60 which is made up of individual resistor elements 12 identical with those used in FIGURE 3 and with terminal pieces 16 which are the same as in all of the other figures. The resistor 60 has the individual resistor elements permanently secured together by bonding their confronting, high conductivity coatings 14' to one another. The terminal pieces 16 have their confronting faces bonded to the faces of the endmost resistor elements 12' of the stack so that all of the parts of the resistor 60 are permanently connected together by electrical conductive bonding to hold the parts in assembled relation. Although this form of invention requires no clamping element, it still has the advantages of being made up of individual resistor elements which can be selected for their specific resistance so as to obtain the resistor 60 with an overall resistance value of close tolerance.
The terminal pieces 16, which are preferably made of sheet metal, can be stampings, or can be made by any other inexpensive method.
The preferred embodiment of the invention ha been illustrated and described, but changes and modifications can be made, and some features of the invention can be used in different combinations Without departing from the invention as defined in the claims.
What is claimed is:
1. A surge resistor comprising a stack of individual resistor elements stacked together in end-to-end relation, clamping means pressing against opposite ends of the stack and holding the individual resistor elements in assembled relation, each of said resistor elements comprising a cylindrical carbon body and integrally formed metal end portions, said metal end portions being simultaneous 1y molded with the carbon body whereby the electrical resistance of each of the resistive elements is independent of physical pressure of the clamping means against the stack, the width of each of said resistor elements being at least twice as great as the height of each of said resistor elements, each of the resistor elements having an opening therein, electrical terminal means adjacent to and electrically contacting each end of said stack, and said clamping means comprising a bolt made of material that is a nonconductor of electricity, said bolt passing through said opening in each of the resistor elements and holding the electrical terminals and individual resistor elements in assembled relation.
2. A surge resistor comprising a stack of individual resistor elements stacked together in end-to-end relation, clamping means pressing against opposite ends of the stack and holding the individual resistor elements in assembled relation, each of said resistor elements comprising a cylindrical carbon body and integrally formed metal end portions, said metal end portions being simultaneously molded with the carbon body whereby the electrical resistance of each of the resistive elements is independent of physical pressure of the clamping means against the stack, the width of each of said resistor elements being at least twice as great as the height of each of said resistor elements, each of said resistor elements having an opening therein, electrical terminal means adjacent to and electrically contacting opposite ends of said stack, said clamping means comprising a metal bolt enclosed by bushings of material that is a nonconductor of electricity, said metal bolt and bushings being inserted through said openings for holding the electrical terminals and individual resistor elements in assembled relation.
References Cited by the Examiner UNITED STATES PATENTS 513,126 1/1894 Meredith 338115 860,997 7/1907 Steinmetz 338330 1,663,810 3/1928 Morse 338-101 2,289,791 7/1942 Loftis et a1. 338327 X 2,496,743 2/1950 Neild 338105 2,502,489 4/1950 Sparklin 338-101 2,822,452 2/1958 Neild 338-105 2,870,307 1/1959 Milliken et a1 33821 2,903,666 9/1959 Krellner 338330 2,914,742 11/1959 Heath 33821 FOREIGN PATENTS 764,693 1/ 1957 Great Britain.
RICHARD M. WOOD, Primary Examiner.