Re: [CAD_CAM_EDM_DRO] Re: high-performance EDM power supply

Graham Stabler wrote:

>It seems to me that a chunky DC supply a, chunky mosfet and a decent
>pulse generator to drive the gate would be a good start for
>experimentation.
>

The DC power supply doesn't have to be too sophisticated. 30 years ago
when I was copying every research article I could get on EDM, I sort of
decided that the power output from a 48 Vac @ 20 Amp transformer would
do the job. Note that the voltage would be around 65 Vdc. A couple
capacitors and a choke added on might be that chunky DC supply you mention.

What I found out during 6 months of collecting and reading articles is
that the spark (desirable) and arc (undesirable) sensing circuitry can
be quite sophisticated. Well, that was 30 years ago and there are
integrated circuits and solid state devices now that are far better.
Still, the sensing circuits are very important and these have to be
connected in some sort of feedback mode to the stepper drivers. The
current required is related to the surface area being eroded so a small
electrode doesn't need as much as a large electrode. It used to be that
the power supply would charge up a capacitor which would discharge
causing a spark. This capacitor doesn't have to be large, but it will
be expensive as it has to accomodate a very high cyclic discharge rate
if you are going to have any speed at all.

> Some lab pulse generators have frequency and duty
>cycle adjustment, and a simple PWM circuit is quite easy to make
>anyway.
>

I don't know much about electronics, but can this be superimposed on a
power supply/capacitor discharge circuit to efectively control the Hz
rate of spark generation? I am reminded of my Lincoln 175 Square Wave
TIG welder - the High Frequency is on all the time, keeping the arc
going. Wonder if that circuit would be of any benefit in EDM?

> I suppose it all depends how smart you want it to be.
>

Smarter the better, perhaps. But there is a minimum that we would want,
even as hobbyists. If you begin to go from plain die sinker to rotary
electrode with hollow electrodes and dielectric pumping on to wire EDM,
then that can get sophisticated.

JerryK