US 3750082 A
The invention relates to a plug assembly for a small refrigerating unit or the like which plug assembly is equipped with one or more PTC resistors. Thermally loaded, ceramic resistors such as PTC resistors are generally brittle and have the characteristics of a substantial temperature expansion coefficient while being relatively weak structurally. The plug assembly accommodates one or more PTC resistors with a resistor holding device in which resiliently biased electrical contacts hold the resistors firmly in fixed positions while permitting the resistors to expand freely upon being heated without incurring stresses which would cause breakage.
Claims available in
Description (OCR text may contain errors)
United State Patent 11 1 Petersen et al.
1451 July 31,1973
I PLUG ASSEMBLY WITH RESISTOR lnventors: Poul Petersen, Havnbjerg; Hans Kristian Pedersen, Nordborg, both of Denmark Assignee: Danfoss A/S, Nordborg, Denmark Filed: June 15, 1972 Appl. No.: 263,121
, US. Cl 338/220, 338/232, 338/260,
Int. Cl. H0lc 1/02 Field of Search 338/220, 316, 232, 338/320, 260; 339/147 R, 147 P References Cited UNITED STATES PATENTS 9/1929 Dublier 338/220 X 5/1948 Johnson....., 338/220 2,960,673 11/1960 Young 3381220 X Prim ary Examiner- E. A. Goldberg Attorney-Wayne B. Easton [5 7 ABSTRACT The invention relates to a plug assembly for a small refrigerating unit or the like which plug assembly is equipped with one or more PTC resistors. Thermally I 12 Claims, 7 Drawing Figures v 1 PLUG ASSEM'BLY WITH RESISTOR.
This invention relates to a device for making contact with and holding thermally loaded ceramic resistors,
particularly PTC resistors.
On the one hand, ceramic resistors evidence an appreciable temperature expansion coefficient, and on the other, they possess only limited structural strength. Accordingly they are brittle, especially at higher thermal loads, for instance beyond 100 C. If heating or cooling proceeds unevenly, they easily shatter and this is also the case when their heat expansion is being opposed by the holding or fastening device.
This invention is directed to the object of providing a simple device of economical construction of the kind initially described or specified, which will allow holding ceramic resistors reliably and which will permit making contact with them, without danger of destroying them, even for high thermal loading.
According to the invention, this problem is solved by aconstruction in which the resistor body is mounted by its middle into an opening or hole corresponding in outline to the resistor. The resistor is a rigid disc made of heat resistant material and is held by friction or tension on both faces, which run about parallel to the plane of the disc, by the abutting electrical contacts.
In this arrangement, the resistor body is supported at its midpoint and any radially directed stresses occurring at the girth are appreciably less serious than at the ends because it is at the ends that breakage under load may easily occur." Further,- it is sufficient if the resistor body is loosely fitted or mounted into slotted plate in order to allow for radial expansion. In such case the resistor will be maintained in its position by the tension or pressure from the abutting electrical contacts. Axial forces are sufficient for the latter purpose as long as they do not exceed the resistors elastic limitllnthe case of heat expansion, the contacts, which are only pressure applied, may yield. The resistors surface is largely exposed to ambient air so that an even heating or cooling of the surface is achieved thereby.
It is a further advantage if only the faces of the resistor are ground or polished and if differences in tolerances or dimensions of the periphery of the resistor, which remains unpolished or unground, are compensated by suitable selection of the shape or size of opening in the disc. Three different perforated discs as a rule will suffice to accommodate the tolerance ranges of such disc like resistors, if they are of circular cross section, since loose fitting in such perforated discs presents no drawbacks or inconveniences.
Further it is recommended that each face of the resistor be provided with two contacts shifted in position with respect to one another, and that the position of shifting on one face as regards the other face differ by an angle preferably 90. A kind of gimbal or Cardan suspension is achieved thereby, which ensures a particularly reliable holding-in the preforated disc.
Though it is advantageous in many cases that the resistor be held by spring-loaded contacts from both sides or faces, it is enough nevertheless if the resistor is held by at least one spring loaded contact pressing against one face and friction holding the other face againstat least one rigid contact.
Further, two parallel perforated discs each with one resistor may be placed within a common housing or case. This parallel arrangement requires only minor in- 2 crease in space requirements. As desired, one or two resistors may bemounted within one housing.
In such a case, it is recommended that interconnected spring loaded contacts be mountedbetween-the resistors and that these be friction held against rigid contacts also interconnected. This makes possible a parallel connection of two resistors in a small space. Such construction is desirable when the total resistance should be smaller than the smallest resistance which can be manufactured as a single PTC body.
Another embodiment of the invention consists of a housing in'two' parts that are interconnected, one of which at least is provided with a groove for accepting the perforated disc. Upon connecting those parts, the perforated disc will be securely held. This allows very simple assembly.
Further, grooves or slots may be provided in the center of the housing and additional grooves or slots on the housings two sides. A perforated disc may be inserted in the center groove and two rails supporting the contacts may be inserted in the additional grooves. It is also possible to place two perforated discs in the additional Hence the housingmaterialmight be of any arbitrary material.
. A particularly well suited material for the perforated discs is a glass-fiber reinforced aromatic. polyarnide; Other fiber-reinforced synthetics too are useful.
In another embodiment, the housing forms the extension of a plug for an encased refrigerating unit, the PTC resistor being the starter mechanism for the single phase asynchronous motor of the unit and the contacts abutting the faces of the resistor being connected electrically with two plug-contactsinside the housing. This eliminates the necessity of specially fastening the housing. This results in compact construction. The arrangement according to the invention permits temperature loads as high as C or even higher.
Compactness is further achieved if that part of the housing in which the PTC resistor is located projects above the plug contacts allowing connection to the network or power supply.
The invention is further elucidated below by means of the illustrations and embodiments shown in the drawing:
FIG. 1 is an arrangement or device according to the invention, with a plug for a small encasedrefrigerating unit from the outer or front side.
FIG. 2 is a longitudinal section, partly as a side view,
FIG. 3 is a rear view of the arrangement of FIG. 1, with part of the housing removed,
FIG. 4 is a top view of the arrangement of FIG. 1, partly as a section,
FIG. 5 is an upper part of a modified embodiment of the arrangement illustrated in FIG. 3,
FIG. 6 is a longitudinal section through the arrangement of FIG. corresponding to an embodiment in FIG. 2, and
FIG. 7 is a top view of the arrangement of FIG. 5, partly in section.
For the embodiment shown in FIGS. 1 through 4, a PTC resistor 2 is held and electrically connected in housing 1 which forms the extension of a plug 3 for an encased refrigerating unit. Two housing parts 4 and 5,interconnected by means of a rivet or pin 6, are provided. The housing parts evidence shaped crosssections by means of which their respective location remains fixed and between which are located three sockets 7, 8 and 9 in an insulator on the case-wall for insertion of jacks. If necessary, the sockets may be provided with outwardly projecting lugs 10 for connection to the power. Another pair of lugs 11 is provided for ground.
Housing part 5 is provided with an enlargement 12 at the top, where the ventilation orifices l3 and 14 are located. I-Iousing parts 4 and 5 are provided with a center groove 15 and 16 each, and with additional grooves 17, 18 on both sides.
A disc 19 made of an aromatic polyamide (trade name: NOMEX) is inserted in the center groove 15,16 this disc being provided with an aperture 20. Resistor 2 is loosely placed in this aperture. Lips 21 of rails 22,23 engage the additional grooves 18; rails 22,23 on one hand are connected with sockets 8 and 9 and on the other hand they support spring-loaded contacts 24,25 or 26,27, which abut under the influence of friction the faces 28, 29 of resistor 2. Since perforated disc 19 is locked into position by grooves l5, l6, and since rails 22,23 are locked into position by the additional grooves 18 and the connection with sockets 8,9, theresistor 2 is reliably kept in place in opening of disc l9.
FIG. 2 shows that contacts 24 and 25 are shifted with respect to one another in the direction of line X. On the other hand, contacts 26 and 27 are shifted with respect to one another in direction of line Y, which lies at 90 to line X. In this fashion one obtains a gimbal or Cardan suspension of resistor 2 in perforated disc 19.
For the embodiment shown in FIGS. 5 through 7, the same housing as for the embodiment in FIGS. 1 through 4 is used. Therefore the same reference numerals are used to a large extent.
In this instance there are two perforated discs30 and 31, each supporting a resistor 32 and 33. Both perforated discs 30 are being guided in the additional grooves 5. of structural parts 4 and 5 An outer contact rail 34 runs in a U-shape along the inner surface of construction part 5 and is provided with 4 contacts 35,36 and 37,38 touching the outer faces of both resistors 32 and 33. Further rail 34 is connected to socket 8 via connecting rail 40. A groove 41 is provided in con- 7 struction part 5 for accepting rail 34. A rail.42 is emother. This again results in a gimbal or Cardan suspension or support of both bodies 32 and 33 in perforated disc 30,31. It will also be observed that both resistors 32 and 33 are connected electrically in parallel.
1. Circuit apparatus for mounting a thermally loaded ceramic resistor such as a PT C resistor, comprising, a housing having groove means, a disc member'made of a heat resistant material and being mounted in said housing, said disc member being mounted in said groove means and having a central opening, a resistor having a greater thickness than said disc member and a profile similar in shape to said opening, said resistor loosely disposed in said opening, said resistor having side surfaces generally parallel to said disc member, and spring loaded contact means engaging at least one of said resistor side surfaces to maintain said resistor in its mounted position.
2. Circuit apparatus according to claim 1 wherein only said resistor side surfaces are ground surfaces.
3. Circuit apparatus for mounting a thermally loaded ceramic resistor such as a PTC resistor, comprising a housing, a disc member made of a heat resistant material and being mounted in said housing, said disc member having a central opening, a resistor having a profile similar in shape to said opening and being loosely disposed in said opening, said resistor having side surfaces generally parallel to said disc member, and spring loaded contact means engaging at least one of said resistor side surfaces to maintain said resistor in its mounted position, said contact means comprising a pair of contacts for each of said side surfaces, the contacts of each said pair of contactsbeing offset with respect to each other and each pair of contacts on opposite sides of each pair of said surfacesbeing offset from each other by approximately 4. Circuit apparatus according to claim 1 wherein said contact means comprises spring loaded contact means engaging opposite ones of said side surfaces of said resistor. v v
5. Circuit apparatus according to claim 1 wherein said contact means comprises a friction loaded contact on one side of said resistor and a spring loaded contact on the other side of said resistor.
6. Circuit apparatus according to claim 3 including a pair of said disc members mounted in said housing in spaced parallel relation to each other, each of said disc members having a resistor mounted therein, said spring loaded contact means being between said resistors.
- 7. Circuit apparatus according to claim 6 including firction loaded contact means between the outer sides of said resistors and inner wall means of said housing.
8. Circuit apparatus according to claim 1 wherein said housing comprises mating parts with groovemeans in at least one of said parts, said disc member being disposed in said groove means and held in place solely by the joining of said mating parts.
9. Circuit apparatus according to claim 8 including