Hello everybody,
I recently discovered that rewinding the high voltage transformer for a microwave oven magnetron is easily done with common tools and common building wire. I followed the directions I found on a few sites that were about doing this procedure to use the converted transformers for making homebrew welders. So the information can be used to make high current supplies for running vapor deposition emitters, spot welders, stick welders and many other needs. At first I followed the instructions to the letter but then deviated somewhat in that I tried larger wire for the secondary windings. The result was I could run the transformer at higher amperage levels and have the secondary winding insulation survive the heating. For my purposed of heating emitters made from tungsten wire I need only power the transformer for less than a minute at high amperage levels so heating to the secondary is kept a tolerable levels. Of course I tried fan cooling and it helped reduce the secondary winding temperature but it is really only needed for run time of a few minutes or more. Please see the URLs for techniques on removing the original high voltage secondary windings without cutting the core as this is a major time and frustration saver. I'll try posting some pics of my work too.
http://www.geocities.com/aaawelder/ http://www.geocities.com/aaawelder/140amp.html http://www.instructables.com/id/Build-a-Microwave-Transformer-Homemade-Welder/ http://www.dansworkshop.com/electricity-and-electronics/homebuilt-arc-welder.htm I also found some information about using copper sheet metal for the new secondary but I haven't tried it yet.
http://tech.groups.yahoo.com/group/edsworkshp/files/mot/Roy
