General thoughts for later use.

At this point i have a decent spot welder base. I plan to add a controller which will give me ratio-metric power factoring via mains cycle counting. All that means is that the controller will turn on the transformer for a given number of cycles. My research shows that anything between 15 and 45 cycles is
normal. So that will be one of the parameters. Hold time is also an important parameter. This is likely to be rated in cycles as well, not sure of the range yet but i suspect that it will be a factor of ten if not more when compared to the power cycles.

The controller will consist of some pretty basic electronics. There will be a main power switch that must be mechanical. The secondary power will be switched from the mains through the mechanical switch via a solid state relay. At this point i am undecided on the type of relay. Namely that is Zero Cross or Random. I'll put forth a little more research here. The controlling factors are peak load and reactance. All i have are 25 amp SSRs so i may need to find something a little tougher for this job.

Also, the large currents which flow through the upper vice-jaws are very likely to have a lot of electromagnetic leakage. EM provisions should be assumed between the joystick hand piece and the controller(if not the entire controller assembly)

The controller will be nothing more than a Atmel Attiny2313 flash Microcontroller. This particular controller has more than enough Sram and Flash program for this project. I plan to use a 4x20 led backlit character lcd module. Industry standard type hard wired in nibble mode. 

The joystick has 8 buttons. This should allow for easier menu navigation for setup and use of the spot welder controller. 

Button Functions we be:

(Menu Use)
Up
Down
Left
Right
Ok(trigger)

Program weld(trigger)
Manual Weld(Upper Trigger)

with two possible reserved buttons depending on how i interface to the internal 74165 parallel load serial shift register. It may be easier to drop a button so that exact serial bit positions can be known at all times.

The system will also need a fan to help cool the welding transformer. 

A side note here, it would be nice to find some sort of small load sensor that could be mounted below the joystick hand piece. Even if it were mechanical it would be better than nothing.