This invention relates to a multi-value motor run capacitor for an electric motor. More particularly, the invention relates to a multi-value motor run capacitor with a safety disconnect mechanism that interrupts the circuit between the motor and multi-value capacitor if the multi-value capacitor fails.
A distributor for electric motors currently carries several motor run capacitors of different values that must be stocked to fill the service chain. Service technicians and distributors must stock motor run capacitors of different values even though only a few values are high volume.
A motor run capacitor consists of a steel can or an aluminum can with insulator/connections on the top and with a capacitor element inside. The can is filled with oil or paraffin that acts as a moisture barrier and an electrical insulator for the capacitor element. The capacitor element consisting of two foil layers separated by an insulator (paper, Mylar, or other very thin insulating material). The foil(s) and insulating material are made in the form of a long sandwich 2 or 3 inches high and several 10's of feet long. The sandwich is rolled to form a cylindrical shaped capacitor element that has electrical connections to each of the two foils. The rolled capacitor element is typically 1 inch in diameter and 2 or 3 inches long. The rolled capacitor element is placed into the can and connected through two terminals on the outside of the can.
Dual capacitors are made with a similar construction, but one of the foil layers is separated to form two capacitor elements. An additional lead wire is connected to the third foil. A dual capacitor with asymmetrical capacitance values can be configured to create a three value capacitor by connecting the first element, the second element, or both elements in parallel.
Because a large portion of the cost of a motor run capacitor is in the can, the winding element, the packaging, and general handling, a single capacitor that can be configured to provide different values offers cost advantages over stocking multiple capacitors of different values.
A motor run capacitor having multiple values should also have a safety disconnect in case of failure either of the motor or the capacitor itself. When a failure occurs, heat and pressure may build up within the capacitor's can. Unless a safety disconnect is provided, the pressure may build until such time as the can ruptures creating a substantial hazard resulting from the spillage of hot oil from the can. Prior art safety disconnect mechanisms typically are located inside of the capacitor can. Consequently, disconnect arcing in the presence of high pressure oil vapor can lead to fire or explosion. The potential to arc is further exacerbated by the fact that the prior art safety disconnect mechanisms often rely on a slowly stretched link of wire. Single value capacitors and dual value capacitors likewise may experience the same failure mode as multi-value capacitors.
The multi-value motor capacitor with a safety disconnect mechanism of the present invention is constructed in a single can having a core with six capacitor elements. When the capacitor elements are connected to the electric motor in various parallel and serial combinations, the motor run capacitor provides virtually all of the popular capacitance values required. Therefore one SKU part number covers the majority of motor run capacitor applications.
The multi-value motor run capacitor comprises a cylindrical metal can with a sealable metal lid. A capacitive element with six sections, each section having a capacitance value, is positioned within the cylindrical metal can. One terminal of each of the six sections is connected to a common wire, and the other terminal of each of the six sections is connected to one of six section wires. The common wire is soldered to a common contact located in the center of the capacitor's metal lid. The center common contact is fixed to the metal lid, is fluid tight, and provides an electrical path from the inside of the metal lid to the outside of the metal lid. Each of the six section wires is soldered to one of six similar fixed section contacts spaced around the periphery of the metal lid. The section contacts similarly are fixed to the metal lid, are fluid tight, and provide an electrical path from the inside of the metal lid to the outside of the metal lid.
In order to provide a safety disconnect mechanism, the multi-value capacitor also includes an external insulator disk positioned adjacent the metal lid. The insulator disk has a center common terminal and six section terminals spaced about its periphery all respectively in alignment with the common contact and the section contacts in the metal lid. The center common terminal of the insulator disk is fixedly riveted to the center common contact of the metal lid. Spring elements form the electrical connections between the section terminals of the insulator disk and the section contacts in the metal lid. Lead wires to the electric motor are connected in various parallel and serial combinations to the common terminal and the section terminals of the insulator disk.
The metal lid is dished downwardly (concave) to provide an “over-center” pop-spring (hysteresis) action. When the metal lid is crimped onto the cylindrical metal can, the downward dish of the metal lid pulls the insulator disk, by means of the center rivet or post, toward the metal lid so that the spring elements are compressed between the section terminals of the insulator disk and the section contacts about the periphery of the metal lid to form electrical paths from the section wires through the section contacts to the section terminals.
If an overload condition occurs with respect to the capacitor and sufficient pressure builds inside the sealed metal can, the metal lid springs from its concave configuration to a convex configuration. The spring action of the metal lid causes the insulator disk to pop up and thereby simultaneously break the connection between all of the section contacts in the metal lid and the section terminals of the insulator disk. The safety disconnect mechanism of the present invention thus moves any arcing of disconnecting contacts outside of the can and away from the atmosphere inside the can that might be combustible. Further the spring action of the metal lid provides a rapid and simultaneous disconnection of all periphery terminals thereby reducing the risk of arcing.
The safety disconnect mechanism of the present invention also has applicability to single value as well as dual value capacitors.
Each of the seven terminals on the insulator disk has an individual insulator cup formed around the terminal.
Further objects, features and advantages will become apparent upon consideration of the following detailed description of the invention when taken in conjunction with the drawing and the appended claims.
Turning to
One terminal of each of the six capacitive sections is connected to a common wire 22, and the other terminal of each of the six capacitive sections is connected to one of six section wires 26. The common wire 22 is soldered to a common contact 24 located in the center of the capacitor's metal lid 14. The center common contact 24 extends through the metal lid 14 and is fixed to the metal lid 14 by means of a common contact seal 30. The common contact seal 30 is fluid tight and insulates the common contact 24 from the metal lid 14. The common contact 24 provides an electrical path from the inside of the metal lid 14 to the outside of the metal lid 14.
Each of the section wires 26 is soldered to one of six section contacts 28 spaced around the periphery of the metal lid 14. The section contacts 28 extend through the metal lid 14 and are fixed to the metal lid 14 by means of section contact seals 32. The section contact seals 32 are fluid tight and insulate the section contacts 28 from the metal lid 14. The section contacts 28 provide an electrical path from the inside of the metal lid 14 to the outside of the metal lid 14. The section contacts 28 terminate in contact surfaces 34 on the outside of the metal lid 14.
The multi-value capacitor 10 also includes an external circular insulator disk 40 positioned above the metal lid 14. The insulator disk 40 and the metal lid 14 comprise a safety disconnect mechanism 8. The insulator disk 40 has a center common terminal 42 and six section terminals 44 spaced about its periphery all respectively in alignment with the common contact 24 and the section contacts 28 in the metal lid 14. The upper end of the common contact 24 is fixedly connected by means of a solid, conductive rivet or post 36 to the insulator disk 40 and the associated common terminal 42. Section springs 48 are fixed to the section terminals 44 and form the electrical connection between the section terminals 44 of the insulator disk 40 and the section contacts 28 in the metal lid 14 by the springs 48 resiliently engaging the contact surfaces 34 of the section contacts 28.
As previously noted, the metal lid 14 is dished downwardly (concave) to provide an “over-center” pop-spring (hysteresis) action. When the metal lid 14 is crimped onto the cylindrical metal can 10 to seal the metal can 10, the downward dish of the metal lid 14 pulls the insulator disk 40, by means of the common contact 24 and the solid conductive post 36, toward the metal lid 14 so that the section springs 48 are compressed between the section terminals 44 of the insulator disk 40 and the section contact surfaces 34 of the section contacts 28 around the periphery of the metal lid 14 to form an electrical path between the section wires 26 and the section terminals 44 on the outside of the insulator disk 40.
Each of the seven terminals 42 and 44 on the insulator disk 40 has an individual insulator cup 50 formed around it as shown in
If an overload condition exists with respect to the capacitor, pressure builds inside the sealed metal can 12. Once a predetermined pressure has built within the sealed metal can 12, the metal lid 14 springs from its concave configuration (
The safety disconnect mechanism 8 may also be used in connection with a single value or a dual value capacitor. For a dual value capacitor, the common contact 24 and the common terminal 42 have the same construction as the multi-value capacitor 10. Instead of six section contacts 28 and six section terminals 44 provided in the multi-value capacitor 10, the dual value capacitor has only two section contacts 28 and two section terminals 44 mounted on the periphery of the metal lid 14 and on the periphery of the insulator disk 40 respectively. For a single value capacitor, the common contact 24 and the common terminal 42 have the same construction as the multi-value capacitor 10. Instead of six section contacts 28 and six section terminals 44 provided in the multi-value capacitor 10, the single value capacitor has only one section contact 28 and one section terminal 44 mounted on the periphery of the metal lid 14 and on the periphery of the insulator disk 40 respectively. Alternatively, the single value capacitor may have a solid nonconductive post positioned at the center of the metal lid 14 and the insulator disk 40 and between the metal lid 14 and the insulator disk 40. The solid nonconductive post replaces the common contact 24, the solid conductive post 36, and the common terminal 42. For the alternative design of the single value capacitor, the common contact and the section contact and the common terminal and the section terminal are mounted on the periphery of the metal lid 14 and on the periphery of the insulator disk 40, respectively.
In another embodiment of the present invention shown in
In another embodiment of the present invention, an additional gas or liquid with a high pressure/temperature ratio is used to fill the metal can 12 to force disconnection at a predetermined temperature. In another embodiment of the present invention, the dished lid 14 may be made of or may incorporate a bi-metal element to force temperature dependence for disconnection instead of pressure dependency for disconnection.
While this invention has been described with reference to preferred embodiments thereof, it is to be understood that variations and modifications can be affected within the spirit and scope of the invention as described herein and as described in the appended claims.
This application claims priority from U.S. Provisional Patent Application Ser. No. 60/968,110 filed on Aug. 27, 2007, which is incorporated herein in its entirety.
Number | Date | Country | |
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60968110 | Aug 2007 | US |