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Re: [TCML] Racing sparks - question


Adjusting coupling actually changes the RATE that energy transfers between primary and secondary LC circuits. While reducing the coupling also slightly reduces the amount of energy transferred, this is a secondary effect due to system losses. Increasing the coupling reduces the "ringup" (or energy transfer time) from the primary to secondary, and vice-versa. Coupling that is too high can also cause coil performance problems due to quenching failures in the primary gap. For an excellent description of coupling and its roles in TC operation and quenching, see these sections on Richie Burnett's site:


A given secondary/topload can safely absorb energy at a limited rate. When this rate is exceeded, flashovers begin to occur between various regions of the secondary. These flashovers may span only a few inches, or may occur across the entire winding. Although racing sparks originally plagued only spark gap switched systems, it can also appear in certain configurations of SSTC's as well.

When coupling is too high, abnormal high voltage differentials are created which can induce racing sparks to jump across portions of the secondary winding or even across the entire winding. There is some evidence that racing sparks are created when higher frequency modes of oscillation are excited within the heavily-coupled resonator. Coils with a uniform protective overcoat tend to survive higher coupling better than uncoated coils. Coated secondaries will capacitively "spread out" and distribute the energy at the the ends of racing sparks over a larger area instead of poking holes and arcing/melting at specific points on the winding.

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Joe Mastroianni wrote:
> So as we are not quantifying spark production and measuring our
> success by objective energy output measurements - if it looks cool
> and nothing detonates and everybody is safe, then we have succeeded
> as coilers - far as I can tell in this eclectic hobby of ours.
> I guess reducing the k works, though to me it's the same as running
> it at a lower voltage on the variac.
> Cheers, Joe

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