Re: [TCML] RE: Splicing wires - Secondary Coil

[Steve Ward <steve.ward@xxxxxxxxx>]

Dan, It sounds like what you are suggesting is that this delta Z will cause
a reflection (as if the secondary was a transmission line, which it can
behave as at high enough frequencies, but not so much at Fres) which then
causes the circuit to oscillate at some higher frequency mode.  But the
impedance of a little solder joint and having 1 turn have a small air gap
around it has gotta be tiny, like 1%-5% or something (maybe much less),
which isnt enough to overcome the very strong feedback signal that is at the
right mode.  If you are going to make your point #2, i demand to see some
measurements (or even simulations, or even supporting math), otherwise i
dont believe it for a second.  Of course i have seen the instability during
ground arcing of a SSTC, but that really is a BIG change in impedance which
DOES cause the mode of the system to change.  And this was always with
secondary coils that didnt have any splices in them, so we cant blame it on
that.

The worst thing about a splice is that it might leave a raised sharp edge.
Cover it with enough insulation (varnish, epoxy, whatever you like) and
avoid air bubbles in the insulation near the surface of the copper, and
provided you arent really over-stressing your secondary, its probably just
fine.  The higher permittivity of the insulation vs air helps to reduce the
localized E-field, basically making a sharp point look more blunt on the
boundary to the air, which lowers the chances of corona forming.

Steve

On Sat, May 1, 2010 at 6:46 AM, McCauley, Daniel H <
daniel.h.mccauley@xxxxxxxx> wrote:

> Tom,
>
> Thats a very good question, and there are two answers.
>
> 1.  If you are running a coil thats MANUALLY tuned, then its perfectly okay
> to splice the wires together.  I've done this many times from small high
> frequency coils using 34 AWG wire to large pole transformer coils using
> 20AWG secondary wire.
>
> 2.  If you are running a self-resonant (antenna or current feedback based)
> coil, then it is NOT recommended to splice the wires.
>
> The reason for this is that with a self-tuning system, there will be some
> impedance discontinuity at the point of splicing.  And the self-tuning
> feedback network has a high probability it will detect this continuity and
> tune the coil accordingly making that discontinuity the node where voltage
> is maximum.  What happens next is that your coil is now tuned at that point,
> and high voltage peaks and destroys your secondary at the splice point.
>
> This is one of the drawbacks with self-resonant systems.
>
> Which makes me think, maybe some sort of notch filter in the feedback
> network would prevent this.   Hmmmm . . . sounds like an idea!
>
> Daniel McCauley
> http://www.easternvoltageresearch.com
> DRSSTC, SSTC, Flyback Kits and Components!
>
>
>
>
>
>
> Alright folks - suppose you are in the middle of winding your secondary and
> the magnet wire snags and brakes. Or maybe you need 2000' of magnet wire and
> all you can find are 1000' spools. Or ... etc
>
> Let's just suppose that you can't get a continous piece of wire for your
> secondary coil. What do you do? Can you splice magnet wire effectively and
> not hurt the electrical integrity of your coil? What are good techniques to
> splice single strand copper wire?
>
> Thanks,
> Tom
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