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Multi-layered Secondary HELP!!




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From:  Bert Hickman [SMTP:bert.hickman-at-aquila-dot-com]
Sent:  Monday, February 16, 1998 12:43 AM
To:  Tesla List
Subject:  Re: Multi-layered Secondary HELP!!

Tesla List wrote:
> 
> ----------
> From:  Zuma [SMTP:mwise-at-ns.sosis-dot-com]
> Sent:  Sunday, February 15, 1998 1:58 AM
> To:  tesla-at-pupman-dot-com
> Subject:  Multi-layered Secondary HELP!!
> 
> I am considering making a very small portable tesla coil. But before I
> do this I need to clear up how I am going to wind the secondary. First
> of all I am planning on making a secondary coil with these demensions,
> 3.25"o.d. x 9.75"height giving it a 3:1 ratio. I know this sounds way
> too small but hear me out. I want to make a multi layered secondary,
> basically to increase the pf, mh and lower the frequency. I want to have
> three layers to the coil, but I don't know if the windings have to be
> three seperate windings wound one on top of the other or if it needs to
> be one continuous winding. I would think that having a continuous
> winding would be what I need, but I want to make sure before I biuld it.
> I also would like to know how well the magnet wire would hold up to
> having that many windings over each other, it seems like it would put a
> voltage strain between the windings. I was planning on insulating each
> of the windings with about 2 layers of polyethylene tape or high
> dielectric strength electrical tape. The winding I am considering starts
> at the bottom winds to the top, then I insulate it and wind back down to
> the bottom, insulate again and wind to the top and coat it in
> polyurethane. Does this sound right or should I wind one layer then the
> next layer and then the last layer, each not being connected to the
> others and then all three connected to ground and the three on top all
> connected the terminal. Which is right or will they both work??
> 
> Chris

Chris,

Making a multi-layer coil is only practical if you wind one layer
directly over the previous one, and connect them in parallel at the
ends. Winding to the top, then back down will not work irrespective of
what you use for insulation between the layers. Although it's not
obvious, when you wind one layer above the other, you'll have virtually
no impact on in the coil's inductance or self-capacitance. The only
advantage is that you now have a coil which has less resistance (DC and
AC), and thus higher Q. 
If you want to increase the inductance in order to reduce it's operating
frequency, use a smaller diameter wire, since the inductance is
proportional the the number of turns squared. For example, if you
close-wound 30 AWG magnet wire instead of 24 AWG, the inductance will
increase from about 4.6 mH to 11.2 mH, and the self-resonant frequency
will drop from about 1.05 MHz to about 670 kHz. Adding a 12" x 3" toroid
will get you down to about 380 kHz. Going to #30 or even #32 will lower
it even further to about 305 kHz or 245 kHz.

Safe coilin' to you!

-- Bert --