Re: eddy current with secondary coil

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Ed Phillips <evp-at-pacbell-dot-net> 

Tesla list wrote:
 >
 > Original poster: Bart Anderson <classi6-at-classictesla-dot-com>
 >
 > Ed,
 >
 > Were these measurements taken at resonance? Adding a topload will not
 > change the low frequency inductance, however, it definitely will change the
 > inductance at resonance. It has to. The induction is caused by the current
 > flowing through the secondary. At resonance, the current is not distributed
 > evenly, but occurs in uneven portions along the length of the secondary.
 > These circulating currents cause non-uniform induction in portions of the
 > winding. The induction can be very significant. On my small 19mH secondary,
 > the inductance at resonance drops to 14.3mH, however, when I add the
 > topload, the inductance at resonance increases up to 18.3mH. As far as I'm
 > concerned, that is significant.
 >
 > The topload definitely affects current distribution and must therefore
 > affect both inductance and capacitance. Because your measurements assume
 > otherwise, were there any low frequency measurements used? any? You said
 > that you and others have taken careful measurements with and without
 > topload. Will you explain the measurement method used?
 >
 > Take care,
 > Bart

	The accurate inductance measurements were made with a bridge running at
1 kHz.  I find that the resonant frequency calculated from the low
frequency inductance and Medhurst's capacitance tables agrees within a
percent or so with the self-resonant frequency without leads.

Ed