Re: [CAD_CAM_EDM_DRO] EDM Controller Qustion

James Stevens wrote:

> In searching the archives and other sources, I understand the basic controls of the EDM as follows:
>
> 1 - Measure voltage when electrode discharges
> 2 - If V < desired gap voltage, move electrode up (too close)
> 3 - If V = desired gap voltage, don't move electrode
> 4 - If V > desired gap voltage, move electrode down (too far away)
> 5 - Goto 1
>
> This is just a simplification but is sufficient for my question.
>
> When you build your own power supply, you have a capacitor at the output. This is what you measure (V). When you purchase your power supply, what do you measure? Can I assume that there is also a capacitor at the output of the power supply that I can measure the same way?

This will be true for simple, RC EDM systems, only. More sophisticated EDM uses electronic
switches of some sort (that would be MOSFETs, now) to turn the discharge current on and
off.

> Also, for any usefull work to be accomplished, there must be power (P=V*I). If there is high voltage and no current then there is no power. If I'm using a shunt resistor to measure the voltage, and a voltage is measured, then there will be current (I=V / R). Likewise, if I try to measure current with the shunt resistor, and a current is measured, then there will be a voltage (V=I * R). Do I need to worry about this or does measuring one validate the other?

EDM is accomplished by thousands of tiny discharges, but the pulse current is
fairly high. I would assume I was getting over 100 A pulses with my little RC
setup, when the average current was about 1/4 A. You don't really need to
measure both I and V for control of electrode advance. With a switched EDM
power supply, it would most likely have isolated digital outputs to advise the
control what was happening. It needs that, anyway, to control the current
pulser.

Jon