Re: [TCML] Newbie questions

[Gary Lau <glau1024@xxxxxxxxx>]

Hi Peter,

I agree with others saying that there's no need to parallel MOTs.  They
already have more than enough current.

As far as your question about modeling the spark gap for Spice - it depends
on what your ultimate goal is.  There's no symbol that's already there and
ready to use, that will translate directly into an accurate simulation
model, if that's what you're asking.  You'd need to build up a model out of
lower-level components.  So your SPICE schematic won't look very much like
what's actually wired together.

For most simulation purposes, it's adequate to model the gap as a timed
switch with a fixed, low on-resistance.  It really isn't - the resistance
is dependent upon the current flowing at the time, but creating such a
dynamic model isn't trivial and I'm not aware of anyone who has done this
in the TC community, even though references to spark gap SPICE models are
easily found on the web.  But a simple resistive model is quite adequate
for understanding most primary-side behavior.

Many years ago I modeled my NST-powered coil in P-Spice and the model is
shown here:  http://www.laushaus.com/tesla/gapsim.htm

The interesting thing in this model is that the chaotic firing of a static
gap is nicely modeled.  The parameters of the 15/60 NST were determined by
Terry Fritz.  I can't advise you on how a MOT might be modeled.

For question 4 - a ballast might be used to limit the primary current drawn
by the MOT's (although I think that most users don't bother with MOT
current limiting).  Safety gaps are used to clamp transformer secondary
voltages to safe values, and this is unrelated to primary current limiting.
 I have no personal experience with MOT's, but I think that MOT's are
typically used without safety gaps, due to their lower voltages relative to
NST's.

Regards, Gary Lau
MA, USA



On Tue, Jan 10, 2012 at 5:58 AM, Peter Sutter <peter@xxxxxxxxxxxx> wrote:

> I am new to coiling and try to figure out how to build a Tesla Coil with
> the material I have available; which is:
>
> - a secondary coil of PVC tubing 160mm diameter, 73 cm high, wound with
> 1250 turns of .53 mm copper wire. JavaTC tells me that the resonant
> frequency is about 114 KHz.
>
> - about 8 m of 1/2 inch refrigeration copper tubing
> - a 6000V 30 mA NST
> - a 9000V 30 mA NST
> - several 2000 V 850VA Microwave oven transformers
>
> I would like to use the microwave oven transformers, possibly two in
> parallel with two voltage doublers, so I would get about
> 2000 * 1.41 * 4 = 11300 Volts peak and about 150 mA max current.
>
> Going through the calculations in JavaTC I notice that a bigger tank
> capacitor reduces the number of primary turns, so I try to get by with the
> 8 m of refrigeration tube. A tank Cap of .1 uF would require about 7 turns
> and a length of 6 meter, leaving some length left for tuning.
>
> Question 1: Are the above assumptions correct and would it work?
>
> Question 2: With the voltage doubler as described here
> http://scopeboy.com/tesla/**tc2schem.html<http://scopeboy.com/tesla/tc2schem.html>what Voltage and frequency would I enter in in the transformer section in
> JavaTC to calculate the transformer and the spark gap.
>
> Question 3: I am using geda gschem for drawing and would like to feed the
> data into spice. What could I use to symbolize the spark gap?
>
> Question 4: Is the charging reactor / ballast necessary to protect the
> MOTs or will a safety gap be sufficient to protect the MOTs?
>
> Thanks
>
> Peter
>
>
_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla