US2558798A

US2558798A - Electrical resistor

Info

Publication number: US2558798A
Application number: US55193A
Authority: US
Inventors: Meivin A Thom
Original assignee: Individual
Current assignee: Individual
Priority date: 1948-10-18
Filing date: 1948-10-18
Publication date: 1951-07-03
Anticipated expiration: 1968-07-03

Description

July 3, 1951 M. A. THOM 2,558,798

' ELECTRICAL RESISTOR Filed Oct. 18, 1948 INVE'N TOR. j eZz/mflfZom mo m,

Patented July 3, 1951 UNITED STATES PATENT OFFICE ELECTRICAL RESISTOR Melvin A. Thom, Brighton, N. Y.

Application October 18, 1948, Serial No. 55,193

This invention relates to an electrical resistor, with particular reference to the type of unit including a wire resistance element wound upon a porcelain or another electrically insulating core, and it has for its purpose to afford a structure of small size that is compact and capable of withstanding large electrical loads and high temperatures without fracture or excessive heating.

More particularly the invention has for its purpose to afford a construction that lends itself to being mounted on a metal chassis in a small space, and so constructed that the heat generated by the resistance wire is easily and quickly dissipated.

A still further purpose of the invention is to afford an eflicient and durable construction of practical and economical manufacture that is especially useful for electronic installations in airplanes and other applications where conservation of space is highly essential and where it is necessary for a resistor to have a high currentcarrying capacity so as to conduct such currents as may be required without the parts becoming excessively heated or without causing fracture, damage, disintegration or lessening the efficiency of the resistor.

More specifically, the invention has for its purpose to provide a housing of metal or other heatconducting material within which the resistor is mounted in such a way as to be effectively insulated therefrom electrically, the metal housing being attachable to a metal chassis or support and the resistor being mounted therein in such a way as to conduct away and dissipate a large part of the heat generated by the current passing through the resistance element, so that the surfaces of the metal housing and the surface of the metal chassis adjacent to the housing do not become excessively heated, and the resistor is protected from fracture or damage that might otherwise result from electrical overload or excessively high temperatures.

To these and other ends, the invention consists in the construction and arrangement of parts that will appear clearly from the following description when read in conjunction with the accompanying drawings, the novel features being pointed out in the claims following the specification.

In the drawings:

Fig. 1 is a plan view of an electrical resistor constructed in accordance with a preferred embodiment of the invention, and showing the housing attached to a chassis or supporting plate;

3 Claims. (Cl. 201-67) Fig. 2 is a. view in side elevation of the same;

Fig. 3 is a vertical sectional view taken centrally of Fig. 1, and

Fig. 4 is a view in end elevation.

The invention is illustrated in connection with an electrical resistor of the type and construction disclosed in copending application Ser. No. 31,236, filed June 5, 1948, now Patent #2,524,550, issued October 3, 1950, which embodies a generally cylindrical electrical resistor including a wire resistance, not shown, and having an exterior contour such as shown in Fig. 3, including a cylindrical central portion I of lesser diameter, cylindrical end portions 2 of greater diameter, and conductors 3 extending centrally from the ends of the resistor, it being understood that the resistor is covered with an electrically insulating silicone varnish, shellac, plastic, resin, or other suitable material entirely surrounding the cylindrical surfaces of the resistor and its ends around the conductors 3, so that the porcelain core or body and interior of the resistor is effectively sealed against moisture. I

Such a resistor is limited in the load it will carry depending on its size, and in order to accommodate the maximum loads required, it is necessary to employ much larger resistors than desirable in order to prevent excessive heating, fracture, or other damage. It is essential and important to provide for greater heatdissipation than heretofore possible in order to employ a resistor of small size while carrying maximum electrical loads, and to accomplish the resistor is mounted within a housing of aluminum, or other metal or suitable heat-conducting material, which is constructed for attachment to a metal chassis or support and acts to dissipate readily and effectively the heat generated by any load towhich the resistor may be subjected.

Accordingly there is provided an integral, rigid housing of aluminum or other suitable metal or heat-conducting material, provided at its upper portion with a cylindrical longitudinally extending opening 4 within which the resistor such as previously described, or other suitable resistor, is located, the housing preferably including a curved top affording a relatively thin top wall 5 above surrounding the resistor and between it and the metal housing, such insulating material being applied in such a way as to avoid the possibility of any air pockets or voids remaining in the spaces surrounding and between the resistor and housing.

Such electrically insulating material preferably comprises a woven sleeve 1 of fiber glass or other suitable insulating material that is positioned and fits snugly around thecentral portion 1 of the resistor before the latter is inserted into the metal housing, the flexible woven glass sleeve 1 being cut of proper length to just fill the space around the central portion 9 of the resistor, and the flexible glass sleeve I may be temporarily held in place by winding a glass or other thread 8 that will stand high temperature therearound, after which a flexible insulating sleeve 9 is fitted over the sleeve 1 and the enlarged ends 2 of the resistor, the flexible sleeve 9 being also preferably of woven fiber glass or other suitable efectrically insulating material and of a size to fit snugly around the sleeve '1 and ends of the resistor and approximately the length of the resistor.

After the sleeves 'l and 9 are assembled, the resistor with the woven fiber glass sleeves in position is dipped or the sleeves otherwise saturated with resin varnish, plastic, or other electrically insulating material such as Dow Corning 993, a silicone varnish manufactured by the Dow Corning Corporation, Midland, Mich, to saturate the fiber glass sleeves thoroughly and form a slight coatin I thereover. After permitting the fiber glass sleeves to air-dry at room temperature for one-half hour to a point where the saturated varnish is in a tacky state, the resistor is inserted into the cylindrical opening of the metal housing, the diameter of the opening being such that the resistor with the sleeves assembled thereon and saturated as described will fit snugly and occupy substantially the entire space within the opening, following which the resistor is baked at a temperature of 250 C. for about four hours to drive off every particle of air from the mass of insulating material composing the cylindrical sleeves and the saturating material surrounding the resistor and to cure the saturating material, so that the space between the resistor and metal housing is entirely free from air and i filled solidly with insulating material such as glass and with the saturating material.

The ends of the resistor are then coated or sealed with silicone varnish or other suitable electrically insulating material, as indicated at M, which surrounds the conductors 3 and occupies the area over the ends of the resistor between the conductors 3 and the surrounding metal housing, which projects slightly beyond the ends of the resistor and surrounding insulating sleeves as shown clearly in Fig. 3.

It will be understood that the opening that is formed in the metal housing is of a diameter to accommodate properly the resistor and surrounding insulating sleeves with the plastic material saturating the latter so that when the resistor unit is inserted into the opening within the metal housing, it fits tightly therein, and the sleeves l and 9 are selected of a size so as to fit closely around the resistor and to fill the space between the cylindrical surface of the resistor and the surrounding surface of the metal housing.

Beneath the cylindrical opening that receives the resistor, the metal hOllSing includes a relatively thick base portion I2, the sides of which are substantially parallel as shown. The base 62 preferably has a width at least as great as the width of the housing at its upper portion where the resistor is secured in the cylindrical opening. and the base or lower portion l2 of the housing preferably terminates in lateral flanges l3 provided with openings I4 to receive screws 15 for attaching the housing to a metal chassis or support l6.

With this arrangement, a resistor having an actual length of approximately 1'' and a maximum diameter of approximately will withstand electrical loads that otherwise would require resistor of approximately five times the size. A resistor such as shown, without the metal housins, will reach a temperature of 250 C. when carrying a 5 watt current load, and it is not possible with resistors as heretofore constructed to mount a resistor on a metal chassis in electronic installations, but the resistor must be suspended by brackets, whereas with the present structure, the resistor can be mounted directly on a metal plate or support, and a current load of 10 watts produces a temperature on the metal housing of only 40 C. as compared with a similar resistor without the metal housing producing a temperature of 250 C. when carrying a load of 5 watts. With the present structure, a current load of 20 watts produces a temperature in the housin of only C., and a current load of 30 watts produces a temperature in the housing of only 119 C.

With resistors as heretofore constructed, a rated current load of 30 watts has required a resistor unit 3" long and /8" in diameter, whereas the present structure occupies a space approximately one-fourth that size and with a current load of 30 watts produces a high temperature on the outside of the housing of only 119 C., compared with 250 C. for a 30 watt unit, free air rating of conventional type, operated at full load. The structure therefore possesses superiorities and practical advantages that have not been possible with any of the resistor constructions heretofore available.

The structure may be constructed of difierent sizes for varying capacities and with the resistor herein shown for a 5 watt rating, the opening in the metal housing has a diameter of and the metal wall above the opening a thickness of .07". The base below the opening is .483" wide at the top of the flanges and .984" wide at the bottom of the flanges. the flanges are 3% thick and the housing has an overall length of 1%", These are successful dimensions for a 5 watt unit and for a 10 watt unit, the holein the housing has a diameter of 5%"; the width of the base is .546" at the top of the flanges and 1.047 at the bottom of the flanges, and the overall length is 1.802", the other dimensions remaining the same as for the 5 watt unit.

With a 5 watt unit such as described above, a current of 80.2 watts was required to raise the internal temperature of the resistor to 251 C. whereas the same unit without the metal housing rose to a temperature of 250 C. with only 5 watts of current, and 15 watts would render the resistor useless.

While the invention has been described with reference to the particular method and structure shown and described, this appliction is not confined to the details herein set forth and this application is intended to cover such modifications and departures as may come within the purposes of the invention or the scope of the following claims.

I claim:

1. In combination, a rigid metal housing having an upper portion which has a longitudinal opening extending therethrough, a high-voltage electrical resistor having conductor wires extending centrally from the ends thereof, said resistor being mounted within said opening with the conductor wires extending centrally beyond the ends of said opening, said opening being of a size to fit closely about the resistor and the wall of said housing which surrounds said opening being of substantial thickness and entirely surrounding said opening, said housing having a base integral therewith for attachment to a support, said base having a greater thickness than said wall and being of a width throughout substantially as great as the width of said upper portion, and a body of electrically insulating material arranged around the resistor between it and the housing and entir'ely filling the space between the resistor and the housing and surrounding the conductor wires at the ends thereof adjacent to the resistor and covering the ends of the resistor.

2. In combination, a. rigid metal housing having a longitudinally extending cylindrical opening therethrough, a high-voltage electrical resistor of the type in which a length of wire is wound on a hollow cylindrical insulating body which has metallic caps at its opposite ends closing the ends of said insulating body and to which the opposite ends, respectively, of the wire are secured and which has conductor wires extending axially outwardly from the caps, said resistor being mounted-within the opening of the housing with its conductor wires extending outwardly beyond the ends of the opening. said opening being of a diameter to fit closely about the resistor, the wall of said housing entirely surrounding the resistor and being of substantial thickness, said housing having an integral one-piece base below said opening for attachment to a support, said base having a width throughout substantially as great as the diameter of said opening and terminating in oppositely extending lateral flanges, and a body of electrically insulating material arranged around the resistor and between it and the housing and entirely filling the space between the resistor and the housing and surrounding the conductor wires and covering the caps and sealing the ends of the opening.

3. In combination, a rigid metal housing having a longitudinally extending cylindrical opening therethrough, a high-voltage electrical resistor of the type in which a length of wire is wound on a hollow cylindrical insulating body which has metallic caps at its opposite ends closing the ends of said insulating body and to which the opposite ends, respectively, of the wire are secured and which has conductor wires extending axially outwardly from the caps, said resistor being mounted within the opening of the housing with its conductor wires extending outwardly beyond the ends of said opening, a cylindrical envelope of electrically insulating porous material arranged about the resistor between it and the housing, and a body of insulating material around said envelope and impregnated into said envelope and acting with said envelope to fill entirely the space between the resistor and the housing, said housing having a base integral with it below said opening, said base having a width throughout substantially as great as the diameter of said opening.

MELVIN A. 'I'HOM.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,092,790 Garrison Apr. 7, 1914 1,124,849 Brush Jan. 12, 1915 1,434,225 Rice Oct. 31, 1922 1,494,939 Abbott May 20, 1924 1,699,898 Lightfoot Jan. 22, 1929 2,146,509 Mucher Feb. 7, 1939 2,218,204 Marsten Oct. 15, 1940 2,227,931 Greenleaf Jan. 7, 1941 2,378,772 Hummel June 19, 1945 2,387,829 Burnham Oct. 30, 1945 FOREIGN PATENTS Number Country Date 342,223 Great Britain Jan. 29, 1931