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Re: [TCML] Secondary Coil Form
Hi Jim,
Yes, I agree, the problem of how much moisture a scrap piece
may have absorbed lying in a mud puddle is likely the biggest
issue in this situation. As for my aforementioned Green Monster
form, this issue was successfully sidestepped by the fact that
I purchased it new and by the foot from a local plastic suppli-
er. A little pricey ($5 or $6/ft, I believe, around ~2003), but
worth the cost to get exactly what I needed and to pretty much
avert the absorbed moisture problem.
David
----- Original Message -----
From: "Jim Lux" <jimlux@xxxxxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Thursday, September 13, 2012 5:46 PM
Subject: Re: [TCML] Secondary Coil Form
On 9/13/12 7:24 AM, David Rieben wrote:
I suppose there always is some risk of obtaining PVC with conductive
trash in it, since the industry specs don't require pristinely pure
materials for the intended application. However, It seems from the
collective data from fellow coilers that the actual level of risk of
electrical failure is quite small and manageable. I, for one, have never
had any issue with the PVC piping material that I have used in all of my
TC forms over about 20 years of actual coiling. As a matter of fact,
until I "knew better", I never even bothered cleaning off the printed
lettering from the surface of the pipe before winding it. I am currently
using gray 12" PVC duct pipe (thinner walls than sch. 40) for the sec.
form of my Green Monster coil and it's been performing *pretty much
flawlessly for about 8 years now. (I did have one flashover that damaged
it and caused me to have to facilitate repairs, but I attributed this
more to not wiping down its surface from dust or possible moisture after
i
t sitting
idle for months than to any conductive impurities in the PVC material.) I
noticed that Ed Wingate would wipe down the extra coil of his huge maggie
before firing her off and I've since employed a "pre-fire" wipe down as
normal setup for firing off my coil now. So far, I've had no more
secondary failure since doing this.
David
I would agree with you that it's not a big risk.. a bigger problem is the
water that might have been absorbed when that big piece of pipe was
sitting in a puddle.
Even bigger surprise is foam core that looks solid (e.g. ABS DWV..the
"foam" has such tiny bubbles you can't see them except with
magnification).
But even in that case, the voltage stress along the secondary isn't huge.
Figure 400kV or so spread over 2 ft. that's <20kV/inch.
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