"John Albers" wrote in message
m...

Also, I have questions few about the relaxiation oscilator circuits
used for EDM. Why do they need a capacitor. The voltage across the
capacitor is the same voltage as the power supply. Therefore the
power supply wired directly to the spark gap should create a spark.
Or is there a difference in trying to create a single spark and trying
to create a cont. arc?

You need the capacitor to get a sufficient rate of current flow, through the
ionized channel, to sustain the channel and to do the work. The required
instantaneous current flow is very high -- far more than the internal
resistance of your transformers would allow.

Somewhere around here I have an article I wrote on EDM for American
Machinist, 25 years ago, that explains some of the things you're probably
looking for. It's 16 pages of magazine text and it's dated, but the basics
haven't changed. It was used by vo-techs and some EDM manufacturers as a
basic text on the subject years ago.

If I can find it, I'll scan it and send it to you. It's still copyrighted by
McGraw-Hill so I can't post it anywhere. Remind me in a few days if I
haven't gotten to it.

--
Ed Huntress
(remove "3" from email address for email reply)