Re: [TCML] using smaller caps

[bartb <bartb@xxxxxxxxxxxxxxxx>]

Hi Clive,

The recommended value is LTR for a static gap, so I assume that is what 
you'll be using. With that said, the static gap is self limiting on the 
voltage. If the cap is charged quickly, the bps will climb, but the 
voltage should "on average" not exceed it's breakdown setting. However, 
if something goes wrong (say an electrode freaks and pops off), well 
then bad things can happen and the transformer is at risk, or say if 
there are missed firings, the cap can be charged to a high voltage with 
the same results. The gap setting is important on the static gap to 
ensure it doesn't exceed a breakdown voltage greater than the 
transformer output. It's also necessary to ensure a backup is used in 
the event of some failure (safety gap).

If the cap is really small, you may not get much out of it. Many coils 
run STR. NST coils however are so easily damaged that much emphasis goes 
into protecting them, including the recommendation of a Terry Filter, 
running LTR, and staying away from resonance.

I think you'll be ok if you set the gap to the transformer. But, I 
haven't ran STR on an NST, so take that into account. It will be 
interesting to hear what others think.

Take care,
Bart

Clive Hansen wrote:
> Hello All,
>    Is it okay to run a coil with a cap of low capacitance? I am using 
> a 15kv 450va supply and JAVATC says a 5.5nf cap will resonate and a 
> 7.4nf cap would be ideal. I have a cap made from tin foil covering 
> overhead transparency sheets which I do not know the capacitance of. I 
> assume it is quite low, and I know it is good at 30kv. Will running 
> the coil with this small cap risk damaging the nst? I assume the 
> streamers will be much shorter in length, but it is a small coil (3.5 
> inch diameter), and I just want to demonstrate the concept to a 
> friend. Also, I am considering building a party cup cap with HDPE 
> disposable party cups and foil. Does anyone have experience with this 
> or a formula for calculating the capacitance of this type of cap?
>
> Thanks,
> Clive

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