Patent Publication Number: US-2007119839-A1

Title: Heat dissipation platform

Description:
This application is a continuation of U.S. patent application Ser. No. 10/617,121 filed on Jul. 11, 2003 and entitled “HEAT DISSIPATION PLATFORM,” the entirety of which is incorporated herein by reference. 
    
    
     BACKGROUND  
      The present invention relates to the art of electric arc welding and more particularly to a heat dissipating platform for the output switches of the power source used in an electric arc welder.  
     INCORPORATION BY REFERENCE  
      An electric arc welder often employs an inverter having high speed switches to create an AC output. Output switches driven by the rectified output of an inverter create either an AC or a DC welding operation. A power source with such output switches is disclosed in Stava U.S. Pat. No. 6,489,592, incorporated by reference herein as background information. The output switches from the inverter can be operated in an AC mode or a DC mode for either a positive or a negative welding operation. This technology is background to the present invention, which relates to a heat dissipation platform to balance the heat of the output switches. This novel platform employs heat pipes as manufactured by Thermacore, Inc. of Lancaster, Pa. Such a device is shown in Rosenfield U.S. Pat. No. 5,076,352 and in an Internet publication entitled Heat Pipe Design. Both of these publications are incorporated by reference herein to show the structure of a heat pipe of the type used in practicing the present invention.  
     BACKGROUND OF INVENTION  
      In an electric arc welder having an inverter power source and output switches to convert between AC and DC welding as shown in Stava U.S. Pat. No. 6,489,592, the output switches and parallel snubbers create a substantial amount of heat. In the past, these switches were mounted on a heat dissipating platform with a heat sink having fins through which air is circulated. With the advent of the AC output switches and the use of these switches as a positive or negative chopper, previous heat platforms have not been capable of balancing the heat generated by the spaced output switches. It is advisable that the switches be maintained at the same temperature for consistent operation. In opposite polarity operation the duty cycle of the switches can vary between 0% and 100%. Thus, it is difficult to balance the heat between the two switches. The platform heretofore used did not solve this problem and did not balance the heat at the switches especially in DC operation. Such previous heat dissipation platform has not been successful and resulted in lower efficiency of the output switches.  
     THE INVENTION  
      The present invention relates to a novel heat dissipation platform for the output switches of an inverter power source used in an electric arc welder. This platform comprises a conductive plate with the first and second parallel surfaces. The output switches are mounted onto the first surface and are closely spaced from each other in a given direction. The object is to balance the heat between these two output switches, especially when they are operated in the DC mode. In accordance with the invention, a plurality of parallel heat pipes are embedded between the surface of the conductive plate and extend in the same given direction as the spaced direction of the output switches. In this manner, the parallel heat pipes equalize temperature between the two switches, even though one of the switches is operated at a substantially higher power than the other switch. In accordance with another aspect of the invention, a heat sink of high heat conductivity material with a thin mounting plate is located on the second surface of the conductive plate and includes integral, parallel fins protruding from the mounting plate and extending in the same direction as the spacing between the output switches. This platform construction has been successful in equalizing the temperature between the output switches, even when the switches are operated at substantially different power levels. When one or the other of the output switches is used to create a DC output welding mode, the platform quickly dissipates heat and still maintains a temperature balance between the two switches.  
      The primary object of the present invention is the provision of a heat dissipation platform that can equalize the temperature between two output switches in an electric arc welder driven by an inverter power source.  
      Still a further object of the present invention is the provision of a heat dissipation platform, as defined above, which platform includes a conductive plate having a plurality of embedded heat pipes.  
      These and other objects and advantages will become apparent from the following description taken together with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       FIG. 1  is a wiring diagram showing the output switches in an electric arc welder as generally described in Stave U.S. Pat. No. 6,489,592;  
       FIG. 2  is a schematic layout drawing showing two switches as illustrated in  FIG. 1  with two heat dissipation platforms of the type used in the prior art;  
       FIG. 3  is a side partially cross-sectioned view of the preferred embodiment of the present invention;  
       FIG. 4  is a cross-sectional view taken generally along line  4 - 4  of  FIG. 3 ; and,  
       FIG. 5  is a view similar to  FIG. 4  showing a further modification wherein a fan is used to force air toward the heat dissipation platform of the present invention. 
    
    
     PREFERRED EMBODIMENT  
      An electric arc welder, as shown in Stava U.S. Pat. No. 6,489,592, is represented as welder A in  FIG. 1  wherein an electrode E and workpiece W represent the output of a welder. A power source, in the form of an inverter  10 , provides a positive voltage at terminal  12  and a negative voltage at terminal  14  are connected to opposite ends of center tapped choke  20 . The center tap  20   a  is connected to electrode E. The electrode and workpiece W with ground  16  form the welding circuit. In accordance with the Stava disclosure, choke  20  includes sections  22 ,  24  so that output switches Q 1  and Q 2  can be operated in unison for AC welding, or separately for DC welding. Each of these output switches includes associated components, such as snubbers, and are in the form of a substantially large area package. As shown in  FIG. 2 , output switches Q 1 , Q 2 , are normally mounted on separate heat sinks  30 ,  32  each of which has a platform  34  in the form of a thin conductive plate  36  having depending, laterally extending fins  38 , best shown by cutaway of platform  30 . The fins extend in the direction between switches Q 1 , Q 2  to balance the temperature between the two switches, especially during AC welding. To enhance the cooling effect of platforms  30 ,  32  it is common to use a fan  40  blowing through fins  38  in an effort to balance the temperature T 1  at switch Q 1  on heat sink  30  with T 2  at switch Q 2  on heat sink  32 . Since the heat generated at the output switches varies according to the polarity and duty cycles and the associated components, platforms  30 ,  32  do not effectively balance temperatures T 1  and T 2 .  
      Novel platform P is shown in  FIGS. 3 and 4 . The platform does balance the temperatures of the output switches Q 1 , Q 2  located at locations x and y, respectively. These two switches are essentially as close together as the package containing the switches will allow. This results in a spacing z between the switches Q 1 , Q 2 , which distance is the direction of spacing between the switches. Platform P is provided with a unique conductive plate  50  having an upper surface  52  on which the switches are mounted at locations x, y and a lower parallel surface  54 . Between these surfaces there are a plurality of elongated, embedded heat pipes  60  mounted in semi-cylindrical recesses  70 ,  72  in portions  74 ,  76  of plate  50 . The recesses can be in the upper surface of plate  50 . The heat pipes are standard products and are sold by Thermacore, Inc. of Lancaster, Pa. They include internal wicking in a vacuum containing a slight amount of fluid. Such heat pipes equalize the temperature between locations x, y of surface  52 . In another embodiment of the invention, plate  50  is a single piece and the holes for the heat pipes are drilled through the plate. In other embodiments, the heat pipes are flat or rectangular in cross-section. Heat pipes  60  extend in direction z to equalize the temperature between locations x, y. In accordance with an aspect of the invention, lower surface  54  of plate  50  is provided with a standard heat sink  80  comprising thin mounting plate  82  and downwardly extending, parallel spaced fins  84  extending in the direction z. It has been found that this novel platform equalizes the temperature of switches Q 1 , Q 2  especially in unbalanced AC operation at widely varying duty cycles. As shown in  FIG. 5 , fan  90  is used to blow air through fins  84  in a direction perpendicular to plate  50 . In practice, two fans  90  are used and are positioned below both location x and location y in  FIG. 3 . In this use of the present invention, heat sink  80  is sometimes divided into two heat sinks one at location x and the other at location y.  
      Various modifications and arrangements of the components constituting platform P can be made in accordance with the invention as defined in the following claims