Re: spark length formula needed*

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

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

Subject: spark length formula needed*


> Original poster: "J Whyte by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<xoom321-at-hotmail-dot-com>
>
> Is their a way of determining spark length via mathmatical formula.

yes and no.. In a uniform field, spark length is fairly proportional to
voltage: 31 kV/cm, roughly. In the real world, though, where fields are
non-uniform, there isn't a simple relationship between voltage and length.
Hence the popularity of empirical tables for sphere and rod gaps, where
someone has made careful measurements of both distance and voltage under
well controlled, repeatable conditions.

For tesla coils (which have very non-uniform fields!), spark length is
affected by a lot of things other than voltage.  The amount of charge that
can be stored on the top load, the breaks per second, and the energy in the
primary all factor into it.  A complicating factor is that once the spark
starts to develop, the effective capacitance of the topload changes, etc.

A rule of thumb developed by John Freau is that the length of a tesla coil
spark in inches = 1.7 * SQRT( primary Volts * primary amps).



>
> I am suspicious of the TC calculator: I keep getting 226" (18.83 ft) for
> spark length for a quadruple MOT power supply with a 115 nF as my tank
cap.

Yes, that would be a bit long.....