PORTABLE HEAT-MAINTAINING AND WARMING FOOD TRAY

• US 3,622,753 A
• Filed: 08/14/1970
• Issued: 11/23/1971
• Est. Priority Date: 08/14/1970
• Status: Expired due to Term

• Current Assignee: Frank Kahn, Ruth F. Lax
• Original Assignee: Frank Kahn, Ruth F. Lax
• Inventors: Lax, Ruth F., Kahn, Frank
• Primary Examiner(s): Mayewsky, Volodymyr Y.
• Application Number:
  US05/063,793
• Time in Patent Office: 466 Days
• Field of Search: 219/448-449,268,464,482,488,519,451-453 320/36,2
• US Class Current: 219/446.1
• CPC Class Codes: A47J 36/2483 with electrical heating means

Abstract

A heat-maintaining and warming food tray is provided having a self-contained power source. The device includes a heatable plate to the underside of which a plurality of strips of heating tape are secured. The power source comprises rechargeable batteries which are connected to the heating tape via switching means. The switching means disconnect the strips from the power source when the output voltage of the battery falls below a predetermined voltage.

Claims

1. A warming device having a self-contained power source, said device including a heatable plate, said plate having secured thereto in heat exchange relation therewith at least one strip of heating tape, said power source comprising rechargeable batteries, switching means connected to said power source for connecting said heating strip to said power source for heating said plate, said switching means including means for automatically disconnecting said strip from said power source when the output voltage of said batteries falls below a predetermined voltage.

2. The warming device of claim 1 wherein said heatable plate is comprised of a heat-conductible metal.

3. The warming device of claim 1 wherein said rechargeable batteries are comprised of nickel-cadmium batteries which are connected in serial.

4. The warming device of claim 1 wherein said switching means comprises an electric circuit including a relay, a first transistor which is responsive to the output voltage of said batteries and a further pair of transistors which are controlled by the output of said first transistor and which control the current in the coil of said relay, said relay including a plurality of contact elements for connecting said batteries to said circuit and to said heating tape, said contact elements being closed to connect said batteries to said circuit and to said heating tape as long as said relay is energized, and said contact elements being opened to disconnect said batteries from said circuit and said heating tape when said relay is deenergized, for completely open circuiting said batteries when said relay is deenergized, whereby to prevent disruption of the batteries by current drainage during extended periods of disuse.

5. The warming device of claim 1 wherein said heating tape comprises a plurality of resistive strip heaters which are secured to the bottom surface of said heatable plate in heat exchange relation therewith, said strips being provided over substantially the entire surface of said plate.

6. The warming device of claim 1 wherein said heatable plate is encompassed by a peripheral frame which is comprised of a nonheat conductive material to minimize loss of heat from said plate.

7. The warming device of claim 1 in which said plate is horizontally disposed at the top thereof and said heating tape is secured to its lower surface, said warming device further including a housing disposed below said heating plate for containing the power source and all of the electrical circuitry utilized between said power source and said heating tape, said housing further including thermal insulation blocks which are supported immediately below said heating plate to prevent downward dissipation of the heat at said plate into said housing.

8. The warming device of claim 1 and further including a resistive means which is selectively connected serially to said heating tape, said resistive means enabling a longer period of heating when connected serially to said heating tape, said resistive means being secured to the bottom surface of said heatable plate in heat exchange relation therewith to enable the heatable plate to capture the heat of said resistive means.

9. The warming device of claim 8 wherein said resistive means is of elongated shape and is disposed in heat distributive relation with respect to said heatable plate.

10. The warming device of claim 1 characterized in that a manual switch is provided for selectively connecting said batteries to said switching means and to an external direct current source for charging said batteries.

11. The warming device of claim 1 wherein said batteries are assembled in serial as a unit package capable of being selectively electrically connected to the circuitry of said warming device and to be removed therefrom.