Re: Toroid Eddy Current?

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

Original poster: "Barton B. Anderson by way of Terry Fritz <twftesla-at-uswest-dot-net>" <tesla123-at-pacbell-dot-net>

Hi Gary,

Since my last post on my toroid measurements, I made a few more experiments
this weekend. This
time, with the primary in place. The secondary Fr was unaffected (very
slight change). I've found
it interesting that the top of the secondary is greatly affected by top
capacitance, but as an
object decreases further down the secondary, the affect lessens and appears
to have little affect
after about half way down the secodary and beyond.

But regarding primary measurements, the secondary has a large affect. Terry
mentioned that the
secondary should be removed (for my experiments witht the tuner) and he was
absolutely right. The
primary was greatly affected by the secondary or any object near it,
including my own proximity. I
would expect the toroid depending on size "might" affect eddy currents, but
any object within
close proximity (i.e, secondary, caps, gap, "distance from the ground",
etc..) will have a greater
affect due to the typical heights of top terminals vs. other objects.

Just my intuition on the subject,
Bart A.

Tesla list wrote:

> Original poster: "Lau, Gary by way of Terry Fritz <twftesla-at-uswest-dot-net>"
<Gary.Lau-at-compaq-dot-com>
>
> Several months ago I performed an experiment to determine things which
> affect primary losses.  I charged my tank cap with a 9V battery and
> replaced the spark gap with an ultra-low Rds on-resistance MOSFET (0.02
> Ohms), driven by square wave generator to get a repetitive waveform.  I
> then scoped the logarithmic primary tank ringdown with NO secondary
> present.  When I placed large metal objects (like an NST or a sheet of
> metal) within about a foot from the primary I could see the ringdown
> time get shorter, indicating that eddy current losses were occurring.
> But nothing so distant as the toroid at it's normal position had any
> observable effect.  Bringing the toroid MUCH closer to the primary will
> of course result in the observed losses.
>
> That said, I didn't try any experiments with the secondary in place.  I
> don't know if the presence of the secondary would raise the "active
> field zone" to where the toroid could result in losses, and intuition
> suggests that it may.
>
> Gary Lau
> MA, USA
>
> >Original poster: "Ray Haynes by way of Terry Fritz
> <twftesla-at-uswest-dot-net>" <ray.haynes-at-home-dot-com>
> >
> >Doesn't the toroid form a single shorted turn that would dampen the
> >secondary by lowering the Q? It seems that the toroid is close enough
> to the
> >secondary to have an effect. An interesting test could be performed if
> >someone had a working coil with an identical spare toroid. That spare
> toroid
> >could be cut with a band saw radially toward the center stopping couple
> of
> >inches from the middle. Probably 3 or 4 (maybe more) equally spaced
> cuts
> >would be adequate and maybe dabs of epoxy to stabilize the cuts. Then
> >install the modified toroid, retune the coil and compare the results
> with
> >the original toroid.
> >
> >Maybe I'm off base but I have never seen this discussed and if the Q of
> the
> >material for the secondary coil form matters, seems this just might.
> >
> >Ray