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Re: Toroid Design

Tesla List wrote:
> 
> Original Poster: Esondrmn-at-aol-dot-com
> 
> In a message dated 12/19/98 6:35:39 PM Pacific Standard Time,
tesla-at-pupman-dot-com
> writes:
> 
> <<
>  Ed,           -snip-
> 
>  You definately need a larger ROC toroid - 8" or 10" (perhaps even 12")
>  should work. Be forewarned, however, that the increased breakout voltage
>  will place significantly more voltage stress on your 6" coil, and you
>  may begin to get interturn flashovers. I presently use an 8" ROC on a
>  system that delivers only 65" streamers, and get excellent field control
>  and single-root streamers. I also went through a 4", two 6", before
>  settling on the 8" ROC toroid in the processs!
> 
>  For ease of construction and low cost, flexible aluminum ducting can't
>  be beat. Aluminum ducting is available in these diameters, but you may
>  need to go to a heating/ventilation supplier. I got my 8" material at a
>  Home Depot, but it was the largest they stocked.
> 
>  Safe coilin' to you, Ed!
> 
>  -- Bert --
>   >>
> Bert,
> 
> Maybe I will try an 8" x 50" toroid made out of aluminum ducting
material.  I
> am familiar with the smaller diameter variety that I used to vent my dryer.
> It comes in what looks like short lengths all scrunched together and you
just
> pull it out to the desired length to use it.  Is this the same material?
Any
> tips on how to make toroids out of it?  It seems like it wourd be quite
> fragile - if dropped or banged into something, it will dent correct?  Can
you
> repair the dents?  If I can get 8" diameter material, I would cut out a 32"
> diameter circle of .25" thick acrylic and wrap the ducting around it then
> cover the center with aluminum tape.
> 
> I sure don't want to overstress my 6" coil and destroy it.  How do you know
> when to stop this madness?
> 
> Ed Sonderman

Ed,

There's several different kinds of ducting material out there. One kind
(which sounds like the material you used on your dryer) has a spiral of
springy wire with either a metalized mylar or very thin aluminum foil
wrapped around it, and an 8' length is scrunched down to abot 4" long.
You DON'T want this stuff. The right material is more like a thinwall
(0.005"?) aluminum bellows that's fairly stiff and is shipped somewhat
compressed. The 8" diameter material I purchased was about 2-2.5 feet
long, but would stretch out to about 7-8 feet. It will dent if you poke
it hard enough or drop the toroid, but otherwise is pretty robust. 

It's also very easy material to work with. I used a small piece of
rolled galvanized steel (also in the heating and ventillation section)
about 3" wide to fit tightly in an open end, putting it about 1/2 way in
and then taping it in place with aluminum tape. I slipped the end of the
next piece of ducting over the 1 1/2" that stuck out of the other duct,
and taped the joint, and then carefully smoothed out any protrusions.

I used a couple of 14" pizza pans spaced about 3" apart via three 2" PVC
pipes for my center, but for a larger center I'd use the same approach
that Chuck Curran recommended by using some 1" aluminim foil covered
insulation board used in home construction. It's cheap and light weight.
Just remember to make good electrical contact between both the top and
bottom foil layers and the toroid. You'll nd up with a toroid that's
light wieght, works great, and is very inexpensive. Heating and
ventillation suppliers should carry the ducting material in up to 18"
diameter.

Good luck, Ed, and let us all know how the bigger toroid works!

-- Bert --