Re: eddy current with secondary coil

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

Original poster: Dave Lewis <hvdave-at-earthlink-dot-net> 


In my view, eddy current effects are a good reason to place your torroid
a few inches above the last turn on the secondary.   A conductive sheet
right over the top of the secondary looks like a shorted turn that is
magnetically coupled.  Putting some air gap between the last secondary
turn and the torroid loosens the coupling up so that its not an issue.

One way to visualize how much space you need is to imagine the magnetic
flux density within the center of the secodary as more or less evenly
distributed along the cross section.   Given that the area is pi*D where
D is the secondary diameter, you'd like at least that much area for the
flux lines to exit the top of your secondary and bypass the torroid
without compressing.  That would be a vertical spacing of at lease D/4.
Thats derived by equating the area of the secondary pi/4*D^2 to the area
below the torroid and last turn pi*D*X.

Dave Lewis




Tesla list wrote:
 >
 > Original poster: "Lau, Gary" <gary.lau-at-hp-dot-com>
 >
 > Space-winding a secondary coil will result in one with a higher Q, but Q is
 > simply not all that important on the secondary.  I suspect the
 > "requirement" of close winding a secondary is more from the lower (than
 > needed) inductance that is achieved when space winding.  Of course, one may
 > add more turns to compensate, but this changes the aspect ratio, so it's
 > difficult to make an apples to apples comparison.
 >
 > Gary Lau
 > MA, USA
 >
 > -----Original Message-----
 > From: Tesla list [mailto:tesla-at-pupman-dot-com]
 > Sent: Friday, October 03, 2003 2:12 PM
 > To: tesla-at-pupman-dot-com
 > Subject: eddy current with secondary coil
 >
 > Original poster: "chris swinson" <exxos-at-cps-games.co.uk>
 >
 > hi all,
 >
 > If the proximity effect of the secondary wires is causing higher eddy
 > currents within the wire, increasing reactance at high frequency, then it
 > would make sence to space the turns out on the secondary form so that more
 > energy will flow though the wire, which suggests higher output. Though this
 > can't be true since close turns is what is required ?
 >
 > Chris