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Re: Primary coil
Tesla List wrote:
>
> Subscriber: gchristo-at-clt.mindspring-dot-com Fri Jan 17 22:40:14 1997
> Date: Fri, 17 Jan 1997 11:43:29 +0000
> From: Chris Gardner <gchristo-at-clt.mindspring-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Re: Primary coil
>
>
> This is a really wonderful post, Thanks to the author and thanks for
> reposting. As a novice I feel that there are some areas that may be
> obvious to the experienced coiler, yet to me are a little grey, if
> anyone (including RQ) would care to clarify I would be most
> appreciative;
>
> Most of my confusion is centered around the physical charactersitics of
> the primary -
> is there an optimal ratio of the diameter of the first (inner) turn of
> the primary to the diameter of the secondary? (for pancake and inverted
> conical primaries)
Chris, this in a way can be different for every system. The higher the
power level the greater the spacing, in general. The quality of the
secondary insulation is also a factor here. I can give you two examples
that may help. My running coil has a 8" diameter secondary with an 11"
I.D. on the primary, which is bare copper 3/8" tube. It worked very
well, generating sparks in 80"inch range. I used particular care with
the secondary, winding on an acrylic form and applying two coats of Behr
Super Build 50 polyurethane coating. I would highly recommend this
product, but it works best if yout rotate the secondary during curing.
I never had any sign what so ever of arcing between the primary and
secondary. On a lower power system you might be able to go a bit closer
with the spacing, just keep your eyes open for any arcing. On my coil
under construction which is bigger I'm using 2 3/4" spacing per side
between primary and secondary.
> Is the 'angle of attack' of the connecting leads from the primary tank
> circuit to the primary coil a factor?
Not really. Safety comes first. Keep them as sort as possible. I
chose to mount my capacitor and spark gap system directly under the
primary and this was done for two reasons. First, it made for a
relatively compact system and second these parts were protected from
arcs by the strike rail. Maybe I'd better define the strike rail. You
should install a turn of copper tube about 2-3" above the largest
diameter of your primary. It should be an open turn, i.e. witha 2" gap
or so between the ends . Then ground it to your system RF earth
ground. This will then absorb any strikes coming down from the toroid
and help minimize the stress caused by a direct primary hit--that
doesn't do good things!
> If youve made a fifteen turn primary and you've taped it at turn 12.25,
> what part if any do the remaining 2.75 turns play in the system? Is it
> advantageos to trim them if youve decided to make it a permanant setup?
I'd recommend just leaving them. If you get a bigger tranformer or
start trying larger toroids to get more spark, or make any change, you
might end up needing to retune the system. That extra turn or two is a
plus, not a minus. Just make sure the entire primary is well insulated
and protected. Many of the group use some type of plastic to
support/insulate the coil above a plywood or whatever structure.
> And this thought just sort of hit me from the blue.... has anyone ever
> posted any schematics of the types of EMF produced by each basic primary
> goemetry? is there somewhere I could look it up? My ARRL handbook only
> shows cylindrical coil fields.
I just saw some conversation on something that was posted to do this--I
think--unfortunately I missed the actual posting. Maybe someone could
provide the file name at the ftp site?? I don't have it.
>
> Thanks to all
Good Luck Chris
Chuck Curran