Re: Few questions about large coils

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

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <FutureT-at-aol-dot-com>

In a message dated 6/2/01 11:49:15 PM Eastern Daylight Time, tesla-at-pupman-dot-com 
writes:

> 2. Would DC be better to run my coil? I'd need almost 700 BPS without the
>  resonant kick I could get with AC to raise my firing voltage that extra 
4kv,
>  for the same throughput. I don't really like this because MMC calc seems to
>  tell me that high BPS is hell on caps and I want this thing to last for 
> quite a
>  while. Comments?
>  3. I'm leaning towards a flat primary, because I have had great success 
with
>  flat primarys on smaller coils. But the primary on this coil wouldn't have 
> much
>  affect on the top turns 4.5' away, unlike most of the smaller coils I've
>  constructed. Would a sloped primary be better? 
>  4. If I get everything right on this coil (which probably won't happen at 
> first
>  light) John Freau's famous formula tells me I could get upwards of 18 feet 
> of
>  spark off this thing (YEAH!!!). Does this NST type formula hold well for 
big
>  coils?
>   
>  Jason Johnson

Jason,

I'd probably go with the flat primary.
To me, DC operation is not worth the effort, and I don't like very high
bps very much.  DC is good using 3 phase power though, as in
Greg Leyh's coil.  I actually designed my formula for any type of
Tesla coil, and it happens to work for NST's too as long as the
true input wattage is used for the calc.  With pigs or potential
transformers, the input VA works well too.  The formula (which I'll
mention for newbies is;  

  Spark length (inches) = 1.7*sqrt input power (wallplug watts)
  (or input VA)

examples:
Richard Hull's Nemesis TC gave a 15 foot spark with 11kVA input.
  The formula gives 15.86 feet

Kevin Eldredge's Biggg Coil gives a 24 foot sparks with 30kVA input.
   The formula gives 24.5 feet

John Freau