Re: [CAD_CAM_EDM_DRO] EDM capacitors and voltage

turbulatordude wrote:

>Hi all,
>
>I'm still working on the EDM project and have to make a decision on
>which way to go.
>
>>From what I have read, the work performed is measure in joules. the
>higher the joules, the faster the work.
>
>If I go low voltage, I need a higher capacity cap(s) Using the
>formula from the Build an EDM, it is
>work(joules)=0.5 x capacitance X ((voltage)^2)
>
>That said, a 700uF cap at 85 volts is roughly the same as a 100uF at
>311 volts. (220 x 1.414 = 311)
>
>Seems decent caps of high ratings are hard to find. a Motor run
>capacitor is easy to find, are rated in high voltages, should work
>but are limited to about 50uF in capacities.
>
>

Is this an RC EDM, or does it have a pulser? 700 uF at 85 V will blow
the work and electrode
to bits with an RC EDM. I did some tap burning using 3 - 6 uF at about
30 V. I admit it was
pretty slow. Some time I have to build a pulser.

>If anyone knows of a good source for caps, please let me know.
>McMaster Carr offers poly-metalized motor run caps for around $19.00
>per 50uf@370V. stock # 7602K38
>
>Have I got this right ? am I on the right track ? does higher
>voltage create any problems ? I'm hoping to avoid some shocking
>discoveries.
>
>

What are you using for EDM fluid? Water will electrolyze above 40 - 50
V, unless you have
a way to keep it VERY pure. Hydrocarbon fluids will withstand much
higher voltage, but you
generally have the risk of fire with them.

Jon