Re: Induction heating in toroid / short circuit of secondary

• To: tesla-at-pupman-dot-com
• Subject: Re: Induction heating in toroid / short circuit of secondary
• From: "Antonio Carlos M. de Queiroz" <acmq-at-compuland-dot-com.br> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
• Date: Sat, 25 Dec 1999 19:59:56 -0700
• Approved: twftesla-at-uswest-dot-net
• Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

Tesla List wrote:

> The idea is to see what power gets wasted heating the toroid.  Consider
> this:  If you hook a small flashlight bulb across a toroid gap, and you get
> no or little glow from the filament, then very little power is being wasted
> in the torroid.  On the other hand, if a 100 watt light bulb burns out, then
> we have a torrid torid, and we should all think about using gapped toroids.

The effect of the induced currents in the toroid is the effect of a 
shorted turn loosely coupled to the secondary (an to the primary too).
It just reduces slightly the equivalent secondary inductance, and reduce
the voltage gradient along the top turns of the secondary (Due to the
decreased impedance there caused by the coupling. Benefical?). 
Significant currents may circulate around the toroid, but probably 
much larger currents cross the toroid to feed streamers and sparks.
And remember that even with a gap, a conventional toroid has large
conductive surfaces immersed in the RF field of the coil, and so
would have a similar effect even if not completing a loop, due to the
induced eddy currents. 
Remember the idea of litz wire? If we conclude that a continuous 
toroid wastes energy, a solution may be a terminal composed of several
small rounded sections (metal foil disks glued to a nonconductive
base?) interconnected in a way that doesn't form loops. 

Antonio Carlos M. de Queiroz

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