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Re: Toroid = shorted turn ?
<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.