Re: How much DC on your mains ?
Back in the '60s, I went on a short course on Process Control, my interest being in firing pottery. We had a tech rep gave us a talk, he was from a US company, West I think, maybe Leeds and Northrup. Anyway, part of his talk was of power control of electric furnaces. No longer big saturable reactor / tapped transformer, but thyristor control. However, he cautioned us that many manufacturers were using phase angle firing, which upset the mains as it only fired on one part of the positive going waveform, and as such "screwed up" the mains supply. Their particular controller, however used something called "Cycle syncopation" and this was wonderful, not affecting the mains.
I suppose this was an early example of zero crossover switching. If I go and dig out my notes, I may still have the product sheet he gave us all.
Les
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