System and method of film capacitor cooling

Film capacitor assembly has a plurality of film capacitive layers for storing an electric charge. The plurality of film capacitive layers have a first metal contact and a second metal contact. A heat sink removes heat from the plurality of film capacitive layers. The heat sink is in thermal conductive communication with at least one of the first metal contact and the second metal contact. A dielectric material is configured to prevent a transmission of electric current through the heat sink from the plurality of film capacitor capacitive layers.

BACKGROUND OF THE INVENTION

This invention relates to a system and method for cooling a film capacitor.

A film capacitor has two or more layers of a dielectric material, such as plastic. The dielectric material is metallized by depositing metal using vacuum deposition or spray to make the material electrically conductive. The two layers are then rolled and compacted. The ends of the roll are sprayed with a metal to make the ends electrically conductive. These rolls are then placed in a housing, which may be sealed with an epoxy resin.

Due to the nature of the dielectric material, the film capacitor may be sensitive to heat. Often times, these capacitors are the most temperature limiting parts inside of a motor controller used in aircraft application or similar products. The location of the film capacitor within the epoxy resin may further adversely affect the ability of the film capacitor to eliminate excess heat. Consequently, the film capacitor may overheat. As electric storage demands increase, there is an even greater need for the removal of excess heat from the film capacitor.

A need therefore exists for a film capacitor assembly that easily and inexpensively eliminates excess heat and prevents overheating.

SUMMARY OF THE INVENTION

A film capacitor assembly has a plurality of film capacitive layers for storing an electrical charge. The plurality of film capacitor layers have a first metal contact and a second metal contact. A heat sink is provided to remove heat from the plurality of film capacitive layers. The heat sink is in thermal conductive communication with at least one of the first metal contact and the second metal contact. A dielectric material is provided to prevent a transmission of electric current through the heat sink from the plurality of film capacitive layers.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference toFIGS. 1 and 2, there is shown film capacitor assembly10.FIG. 1shows a perspective view of film capacitor assembly10, showing heat sink26extending from housing34. As shown inFIG. 2, also extending from housing are positive capacitor terminals16and negative capacitor terminals17.

Housing34contains a number of film capacitor rolls42. As shown inFIG. 3Aas known, each film capacitor roll42is created from a plurality of film capacitive layers14, made from metalized plastic layers, which are rolled to form film capacitor roll42having first end46and second end50. The plurality of film capacitive layers14form edges38at first end46and second end50. With reference toFIG. 3B, film capacitor roll42is then compacted by applying a compressive force in the direction of arrows B and C as shown. The compacted roll, film capacitor roll42, then has metallic spray applied to first end46and second end50to form first metal contact18and second metal contact22. Film capacitor rolls42have plurality of film capacitive layers14stacked along axis A as shown inFIG. 3B.

With reference toFIG. 4, film capacitor rolls42are then placed in housing34as shown. An epoxy resin40is placed around film capacitor rolls42to seal film capacitor rolls42against moisture. Housing34and epoxy resin40encase film capacitor rolls42. To remove heat from film capacitor rolls42, heat sink26is placed in proximity to at least one of first metal contact18and second metal contact22. Heat sink26should be placed close enough to one of said metal contacts18,22, here first metal contact18, to permit thermal conduction of heat from film capacitor rolls42. Heat sink26is a metal, such as copper or aluminum, extending out of housing34as shown inFIGS. 1 and 2, that permits thermal conduction of heat out of housing34. As a consequence, heat may be eliminated from film capacitor rolls42so as to prevent a build-up of heat in the film capacitor rolls42.

Because of the electrically conductive nature of metal of heat sink26, there is provided dielectric material30disposed between first metal contact18and heat sink26. Dielectric material30prevents the transmission of an electric current through heat sink26to prevent the leakage of charge. Dielectric material30is made of a thin sheet of polyamide plastic, such as Kapton™ made by DuPont or Silpad S™ made by Berguist. Dielectric material30is thin enough, say 0.005 inches or 0.127 mm, to permit thermal conduction of heat from film capacitor rolls42to heat sink26while thick enough to prevent the transmission of electrical current from film capacitor rolls42to heat sink26. In this way, heat may be transferred out of housing34without leaking electrical charge. Dielectric material30is glued to both heat sink26and first metal contact18with Armstrong 661 glue.

With reference toFIG. 4, plurality of film capacitive layers14are stacked along axis A. Heat sink26is located proximate edge38of film capacitor rolls42and arranged generally parallel to axis A. In this arrangement, heat may be transferred in the direction of arrow D, which is toward edge38rather than through each of the plurality of film capacitive layers14. This arrangement provides a more efficient path for thermal conduction of heat from film capacitor rolls42to heat sink26than attempting to transfer heat through a stack of layers of film.

With reference toFIG. 5, heat sink26is a rectangular shape extending along axis A across film capacitor rolls42. Other shapes can be envisioned without deviating from the teachings of this disclosure.

With reference toFIG. 6, as part of a motor controller for a vehicle, such as an aircraft, film capacitor assembly10may be mounted on cold plate54. Heat sink26is mounted on a thermally conductive mounting boss58, which itself is attached to cold plate54. As shown, there are three laminated bus bars, positive bus bar63, negative bus bar62and ground bus bar66. Each bar62,63and66is insulated from the other as known and mounted to cold plate. Negative bus bar62is screwed to metal screw67, which extends through positive bus bar63and is screwed to negative capacitor terminal17. In this way, electrical connections are created between negative bus bar62and negative capacitor terminals17. Screw67has electrically insulating washers69, preventing an electrical connection between positive bus bar63and ground bus bar66. Similarly, but not shown, positive bus bar63is electrically connected to positive capacitor terminals16and insulated from negative bus bar62and ground bus bar66.

The aforementioned description is exemplary rather that limiting. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed. However, one of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. Hence, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For this reason the following claims should be studied to determine the true scope and content of this invention.