need some help here!

To: "'Tesla List'" <tesla-at-pupman-dot-com>
Subject: need some help here!
From: Tesla List <tesla-at-stic-dot-net>
Date: Sun, 1 Feb 1998 14:48:31 -0600
Approved: tesla-at-stic-dot-net

----------
From:  Bert Hickman [SMTP:bert.hickman-at-aquila-dot-com]
Sent:  Saturday, January 31, 1998 4:01 PM
To:  Tesla List
Subject:  Re: need some help here!

Tesla List wrote:
> 
> ----------
> From:  Greg Rollins [SMTP:trig-at-ptw-dot-com]
> Sent:  Saturday, January 31, 1998 1:09 AM
> To:  'Tesla List'
> Subject:  need some help here!
> 
> Hi Tesla group,
> >    I have this Tesla coil unit that I have to get up and going.  It's one
> of the "Information Unlimited" coils and I blew up the Xformer. The size of
> the secondary coil is 12" tall by 3" diameter wound on pvc form driven by 6
> turns of #12 wire. The transformer is the is the question.
> 
>        I need to pick up a 6KV 20ma Xformer which has to fit in the
> original metal case.  Since it's one of these "Information Unlimited" Tesla
> coils, the original dimensions were   5.5" by 4.5" and stands 5" tall
> single output terminal with the trans case acting as the other terminal
> ground.  I'm also using a .005 uf cap across the trans with an RF choke.
>    My question is this;
> >       What if I increase the trans to 12kv and 30ma or 6kv and 30ma what's
> going to happen to the cap values?   where can I find the matching cap?
> What is the math equations to figure the difference in cap size?     HELP,
> HELP,
>                          Greg

Greg,

You may have a problem locating a 12KV 30MA trannie that will fit into
the footprint of the original transformer. Also, increasing the
transformer voltage will probably require you to change the tank cap to
a higher voltage unit so that you won't destroy it as well. 

The approximate maximum size tank capacitance that can be driven off a
neon transformer is a function of the transformer's voltage, current.
and line frequency. This is found by calculating the output impedance of
the trasnformer, and then setting this equal to the capacitive reactance
of the tank cap at line frequency. For example, if you have a 6000 volt
20 mA trannie, it's estimated output impedance would be:

   Z = E/I = 6000/0.020 = 300,000 Ohms (mostly inductive)

We now want to find the capacitance that has this amount of capacitive
reactance at line frequency. Let's assume line frequency (F) is 60 Hz.
We want to set Xc = Z (above).

   Xc = 1/(2*Pi*F*C) = 300,000 Ohms (capacitive)
      = 1/(377*C)

Solving for C (in pF):

   C = 10^12/(377*300000) = 8842 pF
 
Knowing E (volts), I (mA), and F (Hz), we can show this in one simple
equation:

   C = 159.2*I/(F*E)    uF
 or
   C = 1.592e^8*I/F*E)  pF

Now for 6000 V, 30 mA or 12000 V, 30 MA transformers:

                      Approx. Tank C: 
             (mA)    (50 Hz)   (60 Hz)
     Volts  Current  C (pF)    C (pF)
    ======  =======  =======   ======= 
     6000     30     15900     13260
    12000     30      7960      6630

Hope this helps, Greg!

-- Bert --