Re: LTR MMC Question - "Geek Group" caps

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

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

In a message dated 4/25/01 7:34:27 PM Eastern Daylight Time, tesla-at-pupman-dot-com 
writes: 


>
> Original poster: "Bill Vanyo by way of Terry Fritz <twftesla-at-uswest-dot-net>" < 
> vanyo-at-echoes-dot-net> 
>
> OK, so I think I'll go with MMC for my under-construction first coil, 
> and am considering the Cornell-Dubilier 942C (aka  "Geek Group") caps 
> (0.1uF or 0.15uF, 2000Vdc) for their high capacitance to cost ratio, but 
> I'm having trouble figuring out the string length (caps in series) and 
> how many strings I need.  Ideally, I'd like to be able to run with 
> either two or three 15/60 NST's, and want to use an LTR cap size, so I 
> think I need to be able to get 0.03uF and 0.045uF from the MMC. 
>
> Question 1: How critical is the exact cap value when using an LTR cap? 
> For instance, can I use 0.05 with three 15/60's? 
>
> Question 2: How many strings, minimum, do I need, for adequate current 
> handling (with three 15/60 NST's, for instance)?  I remember reading 
> more strings is better, but with these caps, more strings quickly means 
> much longer strings just to keep the capacitance *down* to where you 
> want it, and it gets costly again. 
>
> Anyway, here are some of the options I was considering: 
>
> A) Using 0.15uF caps, 3 strings of 10.   
>   2 strings = 0.03uF, 3 strings = 0.045uF. 
>   Quite cheap, but seems pushing it voltage (20KVdc) and current (?) 
> wise. 
>
> B) Using 0.15uF caps, 5 strings of 15. 
>   3 strings = 0.03uF, 5 strings = 0.05uF. 
>   30KVdc seems quite adequate.  Will 5 strings handle the current with 
> three 15/60 NST's?   
>   And will 0.05uF be a good LTR size for three 15/60's? 
>
> C) Using 0.01 caps, 6 strings of 13. 
>   4 strings =  0.030uF, 6 strings = 0.46uF 
>   26KVdc - adequate?, less than $150 - not too bad, good match to the 
> capacitances I think I need.




Hi Bill! 
       A Tesla coil is like a big bug zapper. It's the "pests" that fly in 
without asking questions that get Zapped. If no questions were asked, there 
would be no need for a list. The minimum voltage rating should be 1.414 X 
tranny label output voltage.  15/60 NST means 21.6 KV min. So you are in the 
OK zone with options B or C. When you can afford more replacement caps, then 
you can try pushing the limits of voltage ratings. I would still use a safety 
gap across the cap package,  because "compost occurs". 

Matt D.