Re: Toroid selection

["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 8/10/01 6:37:47 PM Eastern Daylight Time, tesla-at-pupman-dot-com 
writes:

> Original poster: "G by way of Terry Fritz <twftesla-at-qwest-dot-net>" 
<bog-at-cinci.rr.
> com>
>  
>  Hello all,
>  
>  Is there a way to determine maximum toroid size in the design stage? 
>  I have designed an MMC and secondary for a MOT coil, but to use them 
>  with a de-potted 15/50 NST, I would need a 55 pF toroid. While I 
>  won't have a problem building a toroid in this size, I would like to 
>  know if it will breakout before I buy the MMC caps and are committed 
>  to a frequency range.
>  
>  Thanks!!
>  Gregory

Gregory,

Yes, you can calc the largest toroid size that will breakout
for your coil.  But the calc is a ballpark figure.  Many factors
go into the calc, such as:  MMC value, break-rate, secondary
size, type of spark gap, safety gap spacing and design, 
input voltage (normal, or 16% over).

If I understand you correctly, you're saying that you need
a 55pF toroid to place the coil into proper tune.  But you can
easily retune it by changing the tap point on the primary, for
a larger or smaller toroid, so I don't see
any problem with just building the coil, and trying the 55pF
toroid, and if it doesn't breakout, simply retuning the coil for
the new toroid size.  Or are you saying that you want to
avoid the job of building various toroids?  How did you 
determine that you need a 55pF toroid?

John Freau