Re: Rolled LDPE cap ratings & over design

In a message dated 99-06-17 17:08:10 EDT, you write:

<< Original Poster: Ross <ross-o-at-mindspring-dot-com> 
> Hi,
> I have noticed several posts in the last few weeks on rolled LDPE cap
> failure.
> Most of the posts seem to hint that any singe 60 mil cap will be
> instantly destroyed by > 12KV.
> Just for reference, I am running (2) .060" LDPE caps in parallel for a
> total capacitance of .027 uF.
> I am powering them with (2) 12/60s running off 140V from the variac.
> These 2 caps have at least several hours of run time with no failures
 <<yet>>.  My RQ style gap is currently at .180".  I plan to move it to
> .210" at the So Cal Teslathon (I have more caps).


Since your spark gap spacing is reasonably close, this will prevent
the voltage from ever going too high, but if someone were to use a
wide gap spacing, or use a rotary, then they'd have problems.
> Lord knows that I am not disrespecting safety factors and sound
> engineering practices, I just want to tell the new guys that this has
> worked for me.  Other issues that sometimes get a little caught up in
>the hype are variac ratings, grounding issues, and secondary coil form
> preparation.
> 1.  I am running a 10A variac at 15-20A with no problems at all.  I
> usually run 1-3 mins and then cool for several minutes.  ( My R-C-R
> filter is the component that requires cooling, not the variac! )

> 2.  My 8' ground rod seems to work nice, although I have a buddy that
> routinely comes over and forgets to hook up his ground wire and gets
> results similar to mine (40-50 inch arcs from a couple of NSTs).
> 3.  My secondary is 6" SDR that has been sanded, baked, coated, wound,
> and coated again.  It is identical in performance to another secondary
> that was only wound and coated once with a really thick epoxy coating.
> I'm not sure that drying and coating makes any measurable differences on
> NST driven coils.  Has anyone ever made any quantitative measurements on
> this?

I doubt that baking or coating has any effect esp on a plastic form,
but I never did direct comparisons (I never baked any coils.  I use
either no coating, or just a thin coating to hold the wire in place).

The thing about coiling myths, is you can't kill 'em (I've been trying).

John Freau
> Making arcs in Huntington Beach, CA
> Ross Overstreet