From: richard.quick-at-slug-dot-org (Richard Quick)
Date: Sat, 30 Dec 1995 08:08:00 GMT
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Someone, I believe it was Lawrence Wang, asked me the other day
about coupling in Tesla coils. Being rather distracted I did not
take time to reply, so I thought I would briefly discuss this
Coupling in a Tesla system is basically the mutual inductance
between the primary and secondary coils. The mutual inductance
may be varied by changing the position between these two coils.
Separating the coils reduces the coupling factor, bringing them
closer together increases the coupling.
A coil system that is insufficiently coupled does process all of
the energy available from the tank circuit. This results in spark
discharges that are not as violent.
On the other hand a coil system that is overcoupled "splits".
Splitting is when the resonator (secondary coil) is overdriven
and is no longer able to resonate a clean signal. Parasitic 1/4
wave resonances become established in the coil. These "split"
frequencies are typically noted because they produce 1/4 wave
voltage peaks in the winding below the discharger. These 1/4 wave
peaks produce sparks that leap up and down the sides of the
secondary winding. If the coupling is not loosened up to stop the
coil from splitting, the coil will eventually break down, short
out, and destroy itself.
Part of the tuning process involved in peaking a coil system out
is adjusting the proximity of the primary and secondary coils to
achieve "critical coupling". Critical coupling is just that: the
critical amount of mutual inductance that produces the best spark
from the secondary discharger without the presence of parasitic
1/4 wave voltage peaks in the winding.
... If all else fails... Throw another megavolt across it!
___ Blue Wave/QWK v2.12