Re: CD 942 failure - Found it!!

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

Original poster: Terry Fritz <teslalist-at-twfpowerelectronics-dot-com>

Hi John,

Ipeak = Vfire x SQRT(Cp / Lp)

If:

432 x 4 = 12000 x SQRT(2) x SQRT(66.7e-9 / Lp)  Then Lp = 6uH

So you would have to have less than 6uH of inductance in the primary to 
reach the peak current limit of the caps (assuming I did the math right...).

I think you have 6 5/8 active primary turns with in inner diameter of 8 
inches and 1/2 inch pitch so the outer diameter is 8 + 6 5/8 x 1/2 =  11.3 
inches.

 From the spiral coil inductance formula at:

http://home.earthlink-dot-net/~electronxlc/formulas.html#spiral

We get:

(6.625 x 4.825)^2 /  (8 x 4.825 + 11 x 3.3) = 13.64uH

So you should have had only half the caps rated peak current.  There should 
not have been any problem at all...

But, you are still getting a 1/4 tubing primary real hot with a 1440 watt 
NST which is unusual and the caps sure seem to have current damage.  I 
wonder if something strange is going on with your NST?  We might consider 
putting a current meter in series with it just to check.  I could send you 
a (Tesla coil hardened) current meter if you need.

Cheers,

         Terry






At 05:27 AM 3/9/2004, you wrote:
>Hi Malcolm,
>
>There is no safety gap across the cap bank.  I would assume low inductance
>considering the small number of turns I am tapped at.  Add another toroid,
>and move out a few more turns?  I could use one anyway.
>
>Thanks,
>John
>
> > Two possibilities spring to mind: the coil has a very low primary
> > inductance, or there is a safety gap connected directly across the
> > caps that is firing?
> >
> > Malcolm
> >
> >