Hi Steve,
Frankly speaking I am not an expert in welding transformers. But I have seen these welding machines are taking current of the order of several hundred/thousands amperes through their primary winding without any invertor type reserviour Bi-Phase industrial line is enough for them. I am working as a designer for microcontroller based control card and my job is limited to designing a system that can monitor various paramters such as
- Current feedback through CT.
- Voltage feedback.
- Pressure switch [ Air pressure to cylinders ].
- Thermal switch [ Transformer overheat protection switch ].
- Water flow sensor [ Ensure cooling water flow through electrodes ].
- User Keypad.
- Foot switches.

and actuate appropriate solenoid valves to clamp, squeeze and forge the component. And also fire the thryristor appropraitely to achieve desired welding currents. And now In the phase 2 of my design I have to implement a
- PID control loop for thrysitor firing.
- GLCD to display current waveforms and support multiple Indian languages.
- Networked programming through RS422.

If you can please help me with PID stuff It will be great help. Rest I think I can manage.

Regards,
Prahlad Purohit