RE: [TCML] Suggestions for a mini-TC?, transformer

["Jim Mora" <jmora@xxxxxxxxxxx>]

Hi Jason,

There is a nice transformer on Ebay 6500v 20ma 140190900763 probably one end
ground.
Jim

-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
Of Jim Mora
Sent: Monday, December 24, 2007 4:00 PM
To: 'Tesla Coil Mailing List'
Subject: RE: [TCML] Suggestions for a mini-TC?

Consider building a pair of coils configured as a Twin Tesla Coils.  Each
coil acts as a counterpoise to the other, and grounding of the bottoms of
the connected secondaries can be a connection to your power line ground.  As
long as the sparks are between the two secondary toroids, very little
impulse current will flow in your ground connection.  And as a bonus, you
can achieve roughly 1.4 times the spark length for the same power a single
coil would use!  It might take two shoe boxes ...

-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
Of Jason Goodman
Sent: Monday, December 24, 2007 12:41 PM
To: Tesla Coil Mailing List
Subject: [TCML] Suggestions for a mini-TC?

I'm thinking of trying to build a very small spark-gap-style tesla  
coil: something with a secondary perhaps 1 inch in diameter and 6  
inches long, topped with a toroid about 4 inches across.  The whole  
thing should fit in a shoebox, and ideally throw sparks about 4-6  
inches.  One hell of a desktop toy for the office!

I played with JavaTC a little, and it looks like something with the  
following specs should work:
Toroid: 1 inch minor, 4 inch major diameter
Secondary coil: 1 inch diameter, 6 inches long, 30-AWG wire, 500 turns
Primary coil: flat coil, 10 AWG, 5 turns, min diameter 3 inches, max  
diameter 7 inches
Primary capacitor: 0.0012 uF
Resonant frequencies tuned at 2.3 Mhz

If I want sparks 4-6 inches long, I read from this list that length =  
0.85 sqrt(power), so power should be about 50 watts.
To easily exceed the breakdown voltage of 30 kV/cm in air near the  
toroid, I need to get the toroid up to about 100 kV.

I've got several questions about other aspects of the coil:

1) What voltage should the primary circuit be designed for?  Just kind  
of vaguely scaling things down from the sort of coils I've seen here  
and used before, I figure something like 1 kv should be sufficient,  
and will keep the components reasonably small and compact, but I'm  
just guessing.

2) What should I use for a power supply?  To deliver 50 watts of  
power, I want something in the ballpark of 120 V, 1 A on the supply  
side, and 1 KV, 100 mA charging the tank capacitor.  This seems kind  
of overpowered to me, but what do I know.
    a) anyone know of a transformer with vaguely this sort of spec?
    b) If not, can I make one?

3) With such a low voltage in the primary circuit, I'm thinking I'll  
have trouble building a reliable spark gap.  Would a solid-state  
switch (IGBT or SCR) make more sense in this circuit?

4) This needs to be a desktop plug-in model, so I can't exactly ground  
it using a stake in the earth.  Given its smal size, will I be able to  
filter it enough to be able to hook the secondary up to the mains  
ground line?
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