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Re: Toroid = shorted turn ?



I just have to contribute my 0.02 as well.  Here's what I've observed in
my coiling.  It seems that a shorted turn on a secondary will heat up
quite nicely.  For example, when my 6" coil shorted out, there were
grooves around the entire coilform, so I don't think it was merely from
the arc heating.  

The other contradictory thing I observed was shorting out the strike rail
on the primary.  I thought I'd see what happens if there was the dreaded
shorted turn right over the primary.  Interestingly enough, I couldn't see
any difference between shorted and not.  

Chip

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 Chip Atkinson 
 http://www.pupman-dot-com 
 --- If I can't fix it, I can fix it so it can't be fixed --
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On Thu, 8 Oct 1998, Tesla List wrote:

> Original Poster: "R M Craven" <craven-at-globalnet.co.uk> 
> 
> <SNIP>
> 
> >>.  However, I would like to hear from anyone else who has investigated
> this.
> 
> 
> <SNIP>
> 
> >I have. If you measure the inductance of a coil with and without a
> >toroid on top the difference will be close to zilch. I once thought
> >the same as you. BTW, if the ring is a near perfect conductor, it
> >shouldn't absorb much energy at all.
> 
> <SNIP>
> 
> On a standard two-coil TC where the secondary has an aspect ratio of 3 or
> more, and coupling coefficient is low (a quarter or less,say),the average
> power coupled directly into the topload is indeed small. In this situation
> the "shorted-turn" losses of the toroid can be ignored.
> 
> If the coupling is increased between the primary and the secondary as might
> be the case in a valve powered TC, the proximity of the toroid to the
> primary is increased. A helical primary might couple relatively tightly to a
> secondary, but will also couple more tightly to the topload.
> 
> In this case, topload joule heating rises. However, another contributory
> factor is the rms power achieved in the primary. The peak power in a valve
> TC will generally be a lot lower than a spark-gap driven TC, but the average
> P will be relatively high for the size of secondary and the coupling. Thus
> the average P dissipated in the topload due to direct coupling to the
> primary will rise.
> 
> In short, it is not a problem to have a shorted-turn toroid in a typical
> two-coil system. It will become a likely loss mechanism in any TC where the
> distance from the primary to the toroid is small AND at the same time the
> average P is high.
> 
> In a magnifier where there is some field-shaping on the top of the secondary
> and there are high rep-rate primaries, it could become a problem. Has anyone
> with magnifier experience seen any toroid heating effects?
> 
> 
> Richard Craven, Malvern, England.
> 
>