Re: ABS Coil Form

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi Jon,

A common trick they do is to put carbon black into plastics to improve the
resistance to sun (UV) and general degradation of the plastic.  This leaves
the plastic conductive to high voltages which is poison for Tesla coils.
Thus, the use of black plastics is avoided.  The common black plastic
sheeting for gardens is terrible.  Be very careful of "outdoor" or "garden"
plastics that are black.  Many common black types of garden hose are very
conductive.  Even low voltages like 208VAC can give a shock if one tries to
use black garden hose (or black on the inside) as an insulator (guess how I
know this :-))

However, many ABS plastics are fine.  The black color is apparently not
from conductive carbon at all.  There are two "tests".

1.  Rub the plastic with your hair or your cat and see if it picks up a
substantial static charge.  If it does, that is a very good sign.  If the
plastic seem to have no static charges it is probably conductive.

2.  Rub the plastic on paper.  If it leaves a greasy black streak it
definitely has carbon in it.  If there is no mark at all then it probably
does not have carbon.  The non-conductive plastics are also very hard where
conductive types seem to have a soft greasy feel.

White plastics such as PVC or obviously free of carbon and that is why it
is such a common material in Tesla coils.

For a secondary,  "Sonotube" and other cardboard forms seem to have much
higher loss than any of the non-conductive plastics (we "think" from
absorbed water).  I estimate my Sonotube coil probably has 1 inch shorter
(out of 40 inch) sparks due to this loss.  Thus, form losses are
insignificant for plastics anyway.

The big hot streamer off the toroid is were 99% of the secondary loss is
just like it should be :-))  For tube or CW coils, you have to be a bit
more carful since they can overheat and melt if the form loss is too high.

Cheers,

	Terry


At 04:23 PM 6/11/2001 -0700, you wrote:
>Anyone know why ABS pipe wouldn't be a better coil form than PVC? I've
>heard it does not retain water like PVC... that'd reduce loss. Less loss
>== better power transmission. That's a good thing.
>-Jon
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