Re: Graphite spark gaps (fwd)

---------- Forwarded message ----------
Date: Thu, 30 Apr 1998 11:05:06 +1200
From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: Graphite spark gaps (fwd)

Hi Aric,

> Date: Wed, 29 Apr 1998 09:22:02 -0400
> From: Aric C Rothman <Aric_C_Rothman-at-email.whirlpool-dot-com>
> To: Tesla List <tesla-at-pupman-dot-com>
> Subject: Graphite spark gaps
>      Has anyone had success using graphite electrodes in a static spark 
>      gap?
>      I've built one using hexagonal pieces of artist's graphite (approx. 
>      1/2 inch across, 6B grade (alot of C, little binder)).  I tried it out 
>      by connecting it across the series-connected secondaries of two 
>      microwave transformers.  It produced a fierce, bright spark.  The 
>      spark was so hot it ignited the wood base of the spark gap assembly.  
>      I've read that graphite has a negative temperature coefficient (as it 
>      gets hotter, its resistance goes down).  This property would appear to 
>      make it a great choice for static spark gap material.  Other than the 
>      mechanical problems associated with using graphite (fragile, can't be 
>      soldered or welded), are there any reasons why graphite would be a bad 
>      choice for Tesla coil use?

The negative resistance characteristic is an inherent property of 
sparks (ionized matter). Graphite is a terrible choice. It is 
designed to ablate, it has more resistance than copper etc and you 
can see the power being lost in the gap :(  The ideal gap issues no 
light, no heat and no sound, just conducts as though it wasn't there.