AC from DC Welder
Thanks again shortbus=, as usual great info for me, I'm no expert. I've attached a schematic in a .pdf document. The DC welder input is across the top and bottom of the bridge, the output for AC welding is in the middle of course. I programmed the PIC to output PWM 20-90%, dead time, and 30-300Hz from the bridge. I tried the circuit using DC input from several power "bricks" and checked the AC output, it looked great, nice square wave with pk-pk 2x the DC input, and I even used it to burn up some wires and resistors to check that the power was getting through, it was. Then it worked with 30A welder DC input on Aluminum, the weld looked clean, i.e. it was clearing the metal, for about 30 seconds or so until M3 cooked!
I realize the 3x9V batteries are not ideal, but this is proof of concept for now, (and is still not proven actually), before I take further steps to make it more permanent.
The next step for me I think, is to get MOSFET's that will not burn up? But maybe there's another problem, the 9V batteries are not strong enough to drive the mosfets.
I researched some voltage pumps and such, but it makes the circuit much more complex. I'm thinking to connect two 9V's in series for each of the gates, I think that will do it. Either that or get power mosfets with logic level Vgs, but these are expensive like $8 each. Cheaper to use 6x9V's I think.
What do you think of the entire concept, I can't find any other posts on the internet where anyone has tried this...
Thanks!