Re: Secondary Coil Problems

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

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

Hi Nolan,

The "little" shocks from the secondary are apparently from a piezoelectric
effect in the coil's insulation.  Even if you were to completely discharge
it, it will recharge again.  I sometimes just rub my hands over the
secondary to sort of "get it over with".  That drains most of the charge
but a little still comes back.  A damp towel would probably do it but that
gets the coil wet so you can't run it again for awhile.  I guess most of us
just live with it.  It does show the coil is basically wroking well.

Primary to secondary arc over is not a coupling problem.  Racing arcs that
go up and down the secondary are caused by over coupling.  In your case,
there does not seem to be enough clearance between the primary and
secondary (.9 inch).  I would try wrapping the bottom of the secondary with
plastic sheeting or some other insulator.  That should fix it.  My coils
have 1 inch spacing and I don't get arc over, so I am a bit surprised that
your coil is arcing.  Be sure there are no sharp edges that would tend to
promote arcing.  Also be sure the bottom of the secondary is well grounded.
 Preferably with a thick wire going a short distance to a ground rod.
Maybe the base of the coil is going to high voltage.  Your 7.5kV
transformer really should not be arcing this distance.  But in any case,
the plastic insulation should fix it.

The turns on a coil, I start at the beginning of the wire and when I make
one circle around to get back to the beginning that is one turn.

Your coil is powered by a 450 Watt transformer (7500 x 0.060).  The formula
for best case arc length is:

in = 1.7 x SQRT (power) so   1.7 x SQRT (450) = 36 inches.  That is if
everything is absolutely perfect.  Your 13 inch coil is probably too short
to get that far before the arcs hit the primary and such but there is
plenty of room for improvement.  Your larger coils should get there.

Your cap size is perfect and everything else sounds good from a casual
glance.  I would search around and tap it for the longerst arcs.  That will
be easy once you get the arcing fixed.

Hope this helps.

Cheers,

	Terry
 




At 08:52 PM 12/27/2001 -0500, you wrote:
>    Hello this is Nolan I have been working in 3 new tesla coils, a 6.65in
>coil and a 4.5in coil.  I just finished my Mini coil the specs are Secondary
>diameter 2.375 in by 12.75in wound with Awg 28 caped on each end and it was
>baked, Primary flat coil made from solid Awg 6 ground wire 7.75 turns inside
>diameter 4in spaced 0.25in apart, Toroid length is 9.5in and 3.375 height
>made from flexible Al tubing wrapped 3 times in Al tape, Cap is 0.03uf rated
>at 35kv,  Spark single static gap set at 0.17in, power supply is a 7.5Kv
>60ma Franceformer.  Well my problem is that I was trying to find out were to
>tap the primary and I thought that I had it taped at 5.34 turns and I was
>getting multi streamer of the toroid about 3in long. I was getting some arc
>over between the primary and secondary, so I made sure the cap was
>discharged and the toroid, I began to unscrew the secondary to adjust the
>coupling when I got nipped 3 or 4 times by energy left in the windings on
>the secondary coil. It felt a little harder than when you run your hand over
>a TV screen.  Then I decided tap the primary one whole turn, and the
>streamers went from 3in to about 10in but I was still getting a little arc
>over.  So I went to adjust the coupling and I kept getting nipped by the
>secondary, so what I want to know is how to stop getting shocked by the
>secondary coil? and how can I prevent arc over? and how do you figure out
>the turns on a coil, do you count the first turn as one whole turn around or
>what? What is the max spark length I should get out of this system? Also
>were should I tap it at and any tips or suggestions that would help are
>greatly appreciated.  Thank you very much!
>
>Sincerely,
>Nolan Moore
>