# Re: [TCML] Primary design question for minimum radius

```From your description it sounds like a somewhat similar technique is used for HV conductors on utility poles above 100 KV. They are called bundled conductors. Two or more small-diameter conductors are placed closely in parallel to simulate the diameter of a larger conductor. The larger simulated diameter reduces corona losses.

Steve White
Cedar Rapids, Iowa

----- Original Message -----
From: "Terry Oxandale" <toxandale@xxxxxxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Tuesday, May 5, 2020 10:03:47 PM
Subject: Re: [TCML] Primary design question for minimum radius

Okay,
Gary, thanks for the link. I studied the information you shared, especially the last sentence. I didn't quite "get it" until I studied it in detail, and read the description again, realizing that your double primary was an upper primary spiraling inward until the end of that coil was connected to the lower coil's end, that spiraled back out and hence the separation of the two, and shorter turns for each one. This was very different from my assembly, which is:
My double primary has two (or more) identically wound coils placed on the same form, directly on top of each other, thus touching each other continuously (in theory) throughout the entire length of the primary winding, and in essence would be a single coil that has a cross-section that resembles the number 8 throughout its entire length. The attempt was to increase the surface area while not increasing the footprint of the primary form.
Terry

On Monday, May 4, 2020, 04:42:31 PM CDT, Gary Lau <glau1024@xxxxxxxxx> wrote:

I believe I recall that with ribbon conductors, the current flow is
concentrated at the top and bottom edges and the copper in the middle is
mostly wasted.  Some time ago I performed an experiment to compare primary
losses for various primary coil geometries, including ribbon, tubing, Litz,
and various other things.  The copper ribbon was unrerkable in terms of
losses.  See  http://www.laushaus.com/tesla/primary_resistance.htm

That aside, I can't imagine how to keep 3 spirals of tubing aligned with
each other and tapping it.

Regards, Gary Lau
MA, USA

On Mon, May 4, 2020 at 5:25 PM Terry Oxandale <toxandale@xxxxxxxxxxxxx>
wrote:

>
> I'm rebuiding my primary (and other parts), with the intent of using a
> larger diameter tube (going from 1/4" to 3/8"). It would be very convenient
> to use the same primary footprint I'm currently using, and feel I could do
> this with the larger tubing, but would like to have some margin of unused
> turns for flexibility in components.
> So my question to the group relates to primary turn stacking. I'm
> considering stacking 2 to 3 layers of 1/4" tubing (to resemble a ribbon
> versus a single, larger diameter, round conductor) into each slot of the
> structure. Looking at increase power, efficiency, etc, and think this may
> be a way to keep the radius constrained, while improving the performance.
> Thoughts and experiences of this from the group?
> Terry
>
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