Hi Steve Thank you very much for your reply,

Once the clamps are on, are you not regulating the airline feeding the cylinders ? I suppose the tips will mushroom over time though, a factor you can't monitor.....

No, In present design no provision to regulate the air going into the cylinders however there is mechanical NO type pressure switch which can sense the minimum threshold pressuer and react. True.. Tip mushroom can't be monitored I have a counter in software which counts number of welds done after redressing and flashes warning after set counts are reached.

If you are going as sophisticated as you seem to be, why not go the whole way and build an inverter ? There will be loads that are imposed on your proposed ac line system that you will be unable to compensate for under some circumstances, unless your welding cycle is many mains cycles long, whereas with an inverter, you can use the reservoir energy.

Only the PID part is going to change in new design, rest of the things will be same. I am not designing a completely new system but want to implement PID in my machines. My machine with the said current specification are already in operation at several places without any need of an inverter as a reserviour. Bi-Phase AC line is enough to feed the required current.

Thanks & Regards,
Prahlad Purohit