Does anyone know what the 'compensator' circuits of portable spot
welders is and how they achieve their objective? I know (from adverts)
that they are supposed to compensate for slight contamination of the
sheets with oil and paint and are recommended for use with galvanised
sheet - but haven't a clue how they do it.

I've just acquired a "SIP M2 Spotmatic" (labelled M22 !) with
compensator, and sure enough it seems to have no problems with light
oil and galvanising but WHAT is the compensator doing?????? The works
look the same as my broken spot welder - just a wacking great single
turn on a mains transformer with a timer added.

Puzzling !

AWEM