Re: Of Resistors, First Light, and SparkGaps

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

Original poster: "Mike Novak by way of Terry Fritz <twftesla-at-uswest-dot-net>" <acmnovak-at-email.msn-dot-com>

Hi Simon,

Your resistors are acting as self-safety gaps. Just choke down the real
safety gap and you won't have a problem. However, this does limit the
bangsize of the system. You'll have to use a larger cap to achive a higher
power level rather than increasing gap distance. I'm really not a big fan of
heat in tesla coils (no pun intended). When it comes to using resistors in
filter circuitry, I've decided to massively over-engineer mine. I'm using a
series-parallel combination of high power resistors to achive a larger
degree of heat-dissipation and voltage distribution. I just bought 40 15
watt resistors from ebay. Each are rated at 1.2kOhm, so I'll be using 3
strings of 6 resistors in series to get a total resistance of 2.4K per leg.
This, combined with a safety gap, and 1.1nF bypass cap will make this a
nealy indestructible filter circuit. Also, I've decided to mount everything
on a sheet of CE phenolic (formerly known as bakelite) which has a temp
range from -30 to 200 deg C... Not too bad if the thing gets struck by an
arc and decides to go nuclear.
"Overkill" is my specialty :-D
Till next time,

-Mike


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> Original poster: "Terry Fritz" <twftesla-at-uswest-dot-net>
>
> Hi Simon,
>
> At 08:44 AM 12/23/2000 -0500, you wrote:
> >
> >Hi all.
> >
> >Well, the days has finally arrived, I'm ready for first light.
> >Before I do, I have just a few questions.
> >
> >1] The 100W Resistors in the NST Protection unit. For RE. to the
question,
> >you might want to look at:
>
>
http://au.rs-c.dk/servlet/dk.stibo.module.ShowModuleServlet?moduleId=5124333
>
> >Although they are heatsinked, they get pretty darn hot quite quickly [~1
> >min] to the point where they are almost too hot to touch.. Is this ok? If
> >you look at the picture, you can see that there is not much space between
> >the connecter and the heatsink. This is causing some problems; if I tap
my
> >sparkgap at too many gaps, it just arcs from connector to heatsink on the
> >resistor. [This is despite insulating taps [which I didn't expect to do
> >much] and HDPE [which I though would] Any Ideas? I have got some silicon,
> >do you think that would do the trick?
>
> I would not recommend the metal encased types like this since arcing to
the
> case may be a problem.  However, just be sure that the cases are floating
> and let that silicon flow freely :-))
>
> Don't worry about the heat.  Those resistors normally run super hot.  I
> think they are rated to 200C!!  The ceramic versions can hit 350C!  They
> are just little space heaters...
>
> Great luck on your first light!!
>
> Cheers,
>
> Terry
>
>
>