Re: Power versus Spark Length

From: 	Greg Leyh[SMTP:lod-at-pacbell-dot-net]
Sent: 	Sunday, July 13, 1997 10:46 PM
To: 	Tesla List
Subject: 	Re: Power versus Spark Length

John Freau wrote:

> Recent work with disruptive coils, and old work with tube coils, suggest
> that the power required for a given spark length follows (more or less) a
> simple direct square law.
> Two coils were built, each optimized for its input power level.  One drew
> 680 watts and gave a 42" spark, the other drew 2100 watts and gave a
> 65" spark.   The tube coil results followed a similar trend.
>   watts (wallplug)           spark length
>        10.6                           5 1/4"
>        42.6                         10 1/2"
>        170                             21"
>        680                             42"   (actual)
>      2100                              65"   (actual)
>      8400                             134"
>       33.6 kW                       268"   (22 feet)
>       67.2 kW                                 (30.8 feet)
>      134.4 kW                                (44 feet)
>       537.6 kW                               (88 feet)

Your curve appears to fit amazingly well to a number of widely spaced
data points, both empirical and calculated.

Two data points that I compared to this curve:

 watts (wallplug)   spark length

      28.5kW            ~22'     TC in Austin TX, with improved primary ckt
      5.1 MW            270'     From design set for a twin 85' coil system

This squared relationship makes sense if the following statements are true:

A)  The arc's current density remains constant as the current increases.

B)  The arc's total consumed power is proportional to its volume.

C)  The arc can be modeled as a long thin cone, where its base diameter 
    is proportional to the square root of its length.

D)  The arc length is proportional to the output voltage.