RE: Primary coil configuration

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Lau, Gary" <Gary.Lau@xxxxxx>

Hi Hal:

How'd you manage to sneak an attachment past our moderator? ;-)

I don't think there's ever any reason to use a non-flat primary,
regardless of power supply or secondary size.  I've used flat primaries
with my 2" 4/20 mini coil and my 6" 15/60 coil, and I can adjust the
secondary height too low and get racing sparks or too high for not
enough coupling, for both.  It all comes down to getting the right
coupling, and NST and secondary size won't affect that to the point that
a conical primary is needed.

Speaking of coupling, after scanning your attachment for viruses, if I'm
interpreting it correctly, it looks like you have a PVC end cap at the
center of your primary for attaching the secondary.  This will force you
to locate the lowermost secondary turn at least a couple inches above
the plane of the primary, and this may be too high for optimum coupling.
I've found that the lowermost secondary turn wants to be roughly even
with the primary for optimum coupling, but one must always be prepared
to experimentally go up or down from that point, so you'll need to find
a means of mounting the secondary base below the primary base.

With your 15/90 power supply, if you do a good job optimizing things,
you may find that a 4" secondary is overpowered if you maintain the
usual 5:1 secondary winding aspect ratio.  This will result in
persistent primary strikes, and you'll soon want to build a bigger
secondary, just to get the top load further away from the primary.

Regards, Gary Lau
MA, USA


> Dr. Resonance,
>
> I am building my first coil.  It has a 4" secondary.  Just this
> afternoon I wound a flat primary for it and then read your
> email.  Will a flat primary not work with 4" coils?  I plan on
> powering it with 15KV, 90mA.
>
> []
>
>
> Hal in Tucson
>
>
>
> ----- Original Message -----
> From: "Tesla list" <<mailto:tesla@xxxxxxxxxx>tesla@xxxxxxxxxx>
> To: <<mailto:tesla@xxxxxxxxxx>tesla@xxxxxxxxxx>
> Sent: Wednesday, April 19, 2006 4:44 PM
> Subject: Re: Primary coil configuration
>
>  > Original poster: "D.C. Cox"
> <<mailto:resonance@xxxxxxxxxx>resonance@xxxxxxxxxx>
>  >
>  >
>  > If you run a 4 inch dia. sec coilform use a 15 or 20 degree
inverted
>  > cone primary.  If running a 6 inch dia. sec coilform use a flat
>  > Archemedian (expanding) spiral.  Overcoupling is a big problem for
>  > most beginning coil builders and it generates multiple headaches
like
>  > racing sparks, etc.  Keep it simple and it will work right the
first time.
>  >
>  > Use 1.3 to 1.5 x Cres for your MMC cap value and you will have a
nice
>  > performer.  The 6 inch dia. coil will give you better performance.
V
>  > = -L x dI/dt.  Inductance, L, is proportional to the square of the
>  > radius of the coil so bigger is better.  Use #26 AWG for a 6 inch
>  > coilform and #28 AWG for a 4 inch coilform.
>  >
>  > With a reasonably large toroid, ie, 20 x 5 or equiv. modern
>  > transmission line theory doesn't apply much to TC building.
>  >
>  > Dr. Resonance
>  >
>  > >Hi All,
>  > >    I'm in the process of designing my first coil.  I'm a junior
in
>  > > EE and it just caught my intrest while I was researching HV
>  > > transmission lines. I have a 15kV 60mA NST and I'm reading as
much
>  > > as I can about the rest of the design before I actually
> buy/build anything.
>  > >    My question is what is the difference between making the
primary
>  > > wind outward away from the secondary opposed to winding
vertically
>  > > keeping the windings all the same distance from the
>  > > secondary.  Also what does primary placement around the secondary
>  > > effect.  If I move the primary up to the middle of the secondary
>  > > what will that effect?
>  > >
>  > >~Farmer
>  >
>  >
>  >
>  >