Re: overcoupling

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

Original poster: FutureT-at-aol-dot-com 

Lance,

I get the impression that this is your first coil.  Overcoupling can cause
racing sparks along the secondary, causing burned spots on the wire,
or even destruction of the secondary coil and form.
The degree of coupling that can be tolerated by any coil depends on the
input power and break-rate.  A conical primary does not automatically
cause overcoupling.  Rather it depends on how close the primary is to
the secondary and other factors.  Consider a 30 degree primary that is
14" I.D., and 28" O.D..  Such a primary is likely to overcouple to your
12" dia secondary.   Now consider a 30 degree primary that is 22" I.D.,
and 36" O.D..  Such a primary is unlikely to overcouple to your 12"
secondary.  In fact the coupling may be a little loose and the secondary
may need to be lowered below the primary plane a little.  And you are
correct, you can always raise the secondary
to reduce the coupling to an acceptable amount.  I generally use
flat primaries for my coils these days.  Awhile back, I used to use 15
degree conical coils.  Generally the best degree of coupling is found
by trial and error by raising or lowering the secondary until the best
spark output is obtained free of racing sparks and primary to secondary
flash-overs.

John