Re: [CAD_CAM_EDM_DRO] PC ports, Encoder resolution and EDM PSU info

dave engvall wrote:

> > Tim Goldstein wrote:
> >
> > > played with EDM by hooking up a 48 V 10 amp transformer through a
>
> > > bank of power resistors and then a cap.
>
> It is my understanding that one really needs a base voltage of about
> 28-32 V at reasonable amperage plus a spike of approx 90 V to
> breakdown the dielectric.
> I've done a little fooling around but after modeling the process using
> the POCO CD am convinced that one need a good supply with
> var. pulse freq.
> If anyone has plans for a supply I'd give it a try. I have a handful
> of 15 A igbt to try on something.

I made a mini-EDM system for burining out taps, etc. I did a couple
broken taps
using about 30 VDC, a 30 Ohm resistor and about 3 uF of capacitor right
across
the EDm electrodes. There might be a small spike from the inductance in
the wire,
but the behavior I saw was an arc that repeated about 50 - 100 Hz. So,
I believe
the cap drains energy into the arc, the arc is suppressed by the EDM
fluid, the
resistor charges the cap back to near the raw DC supply voltage, and
then the
EDM fluid breaks down and a new arc forms.

There were no semiconductor switches at all, and it worked quite well.
Now, you
might be able to get stable cutting on a much wider electrode, or faster
cutting
with electronic switching of the arc, but it is not necessary to make
the process
work. This may well be necessary for wire EDM, to prevent welding the
wire
to the work, or just burning it away.

Jon