Originally Posted by
Binraker
Yes it is a little more complex. The idea is basically a mechanically actuated scratch start TIG welder with arc timer. The magic is in the timing. The order of actions is something like: turn on gas, wait a bit for it to flow and cover everything, start electrode retract (it will take a millisecond or 2 to get moving and we want to turn on the caps just before the electrode leaves the surface, wait a few milliseconds, turn on cap bank, wait the desired amount of weld time, turn off cap bank, wait a bit to allow the user to remove the item, turn off the gas and release the electrode. It's all millisecond stuff so its not fast but it is "fast" from a human point of view.
You can then select the charge voltage and arc duration to vary power and total energy supplied. If I had found it useful more I would have put in a number of parallel systems so that you could profile the voltage throughout the weld cycle and get a bit more control. you could also change the retract solenoid voltage to change the mean arc length or have a shorter retract distance so that full retract is at optimal to distance. or you could use an overlaid high speed high voltage ionising pulse to start the arc which will give more arc profile control but will limit your ability to weld into corners. There are numerous possibilities...
The switching of the cap bank needs to be fast (sharp edges) and low resistance so very careful selection of transistors required MOSFETs will do the speed but not the power so you really need an IGBT with a hard driving circuit to keep the speed up. this needs to turn on an off in 100us territory to stop the transistor dissipating too much energy. The inherent ESR and ESL of the cap bank with throttle the energy dump quite a bit so it will probably be the limiting factor.
If you want I will post all the details of my machine and the code if you want to build a copy of it as a starting point for your own investigations.
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