RE: [TCML] Q,,question

["Lau, Gary" <Gary.Lau@xxxxxx>]

I don't agree that stranded welding cable is comparable to Litz wire, or a good choice for a primary.  In common stranded wire, every strand is electrically in contact with the adjacent strands.  Due to skin effect, if current is flowing through a strand on the interior of the bundle, it will want to flow outward to the outermost strands.  But to do so, the current must pass through the surface of each intervening strand, subject to surface oxidation and resistance.  As bundles are generally comprised of multiple twists, this may result in many trips through surface oxidation, incurring significant losses.  That's the reason that Litz wire must be made of insulated strands - to keep current from hopping between adjacent strands.

I performed extensive testing and comparisons between various primary conductors - Litz, stranded, solid, and ribbon.  See http://www.laushaus.com/tesla/primary_resistance.htm.  I tested only AC resistance, as opposed to actual performance in a Tesla coil.  While not 100% conclusive, I believe the data supports my previous paragraph.  Relating to the value of Litz wire, it's important to note that the Litz wire I used was comprised of strands thicker than what is recommended for the upper end of the frequency spectrum that I measured AC resistance at.  At below 100KHz, my Litz was the hands-down winner.

Regards, Gary Lau
MA, USA

> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> Behalf Of resonance
> Sent: Wednesday, December 05, 2007 9:11 PM
> To: Tesla Coil Mailing List
> Subject: Re: [TCML] Q,,question
>
>
>
>
> Litz wire would be ideal for the primary if it were not necessary to tap.
> It's a nightmare to properly tap and get solid connection to all strands.
>
> Fine stranded copper welding cable works good and is easy to tap.
>
> The best option, really, is copper tubing.  It's hi-Q, easy to tap, and you
> can use larger diameters if you need less resistance.
>
> Dr. Resonance
>
>
>
> ----- Original Message -----
> From: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>
> To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
> Sent: Wednesday, December 05, 2007 6:53 PM
> Subject: Re: [TCML] Q,,question
>
>
> > Hi Paul,
> >
> > I would expect higher losses due to proximity currents. Most primary's
> > have a good deal of spacing minimizing those currents, but if we were to
> > bundle everything together, those particular losses would certainly
> > increase. So in that respect, I think the single copper mass is more
> > efficient.
> >
> > Take care,
> > Bart
> >
> > Paul Bidmead wrote:
> >>
> >> Gents
> >>
> >> I may be stabbing in the dark but i have a theory to share with you all
> >>
> >> with my experience with high frequency power supplies and with skin
> >> effect prevalent would it feasible to use multi-filar enamel wire for the
> >> primary
> >> that being said would it not be wise to use lets say around 10 - 12
> >> strands of 0.8mm dia or whatever is needed to get same approximate copper
> >> cross section required therefore the skin effect is reduced to a
> >> percentage or each strand rather than a percentage of a single copper
> >> mass
> >>
> >> not sure if i explained it clearly but my 2c worth anyway
> >>
> >>
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