HI all, I was pretty pleased with myself yesterday, I was looking at a 300 volt 200 amp SCR and thinking what to do with it when I saw a bank of old electrolytics I had lying around in the workshop BINGO!!! a capacitor discharge spotwelder!!. Anyway after wiring it all up in a jury rigged fashion I ended up with a solid state switched 240 joule spot welder. Just the thing for welding up those tungsten grids etc, any way it worked like a champion welding up to 1/8" steel wire without any problems as fast as the caps would charge. At this point I tried to weld a couple of 5 cent pieces together and the caps suddenly would not charge as I had shorted the SCR, which brings me to the point of this post: does anyone know of a good way to switch really high currents?.
All I can think of is a large bank of parallelled mosfets which would be less prone to thermal runaway than bipolar transistors or some kind of spring loaded switch that has a liquid contact of salt water (no mercury). I am using 5x 80 000 uF powerlytic caps at 40 volt rating (35 v power supply) which if I remember rightly give 245 joules but I can subsitute 3300 uF 375 volt caps which would store 230 odd joules each if some kind of triggered tube will work at that voltage
Created on Monday, February 19, 2001 3:09 AM EDT by Mark G Harriss