Re: EDM home brew units ?

> There is a formual that relates surface area to amps. more amps
> allows a larger surface area. more amps in a smaller area does not
> offer any benifits.

There are usually guidance values on max current densities for the
various electrode materials but they are still quite high values.

For a pulser unit then the power delivered per spark is proportional
to the current. Energy delivered per spark assuming there is a zero
ionization delay is:

E = Vo.Ton(Vs-Vo)/Rl

where
Vo = operating voltage (average gap voltage maintained by servo system
Ton = on time
Vs = supply voltage
Rl = limiting resister.

the quantity Vs-Vo/Rl is the current which can be increased by
reducing Rl. You can think of the servo system as being an
adjustment of the gap resistance such that Vo is maintained at the
required level (or within limits).

With an RC system R dictates charging time and hence pulse rate and
also provides an absolute short circuit current limit however the
energy delivered is controlled by the operating voltage and the
capacitance.

> At some point, you no longer spark, but arc and then the process is
>lost.

At that point the gap should be increased increasing Rg to keep the
gap voltage where it needs to be however if you cut faster than your
flushing can handle it will all go to pot.

> An active circuit to charge and spark is desired. no reason why one
> could not have 3 caps, each discharging in a round robbin fashion
> while the others are being charged.

So you apply a fully charged cap to the gap, what do you use as your
feedback to the control? Normally it is derived from the voltage
that the gap brakes down and starts discharging the capacitor.

Graham