Re: AC wire resistance with proximitry effects

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Malcolm Watts" <m.j.watts@xxxxxxxxxxxx>

Hi Bart,

On 8 Oct 2005, at 22:46, Tesla list wrote:

> Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>
>
> Hi Gerry, All,
>
> Replying to myself I guess. I went ahead and measured Q on my 8.5"
> secondary.
>
> The precise coil specs are 8.4375" x 39.75", 1,789 turns, 24 awg,
> closewound.
>
> F1 = 112.9 (kHz). Javatc predicted 112.68, so only 0.19% error. I then
> tuned generator to half power points (via low-z amp). Fhigh = 113.1
> Flow = 112.7
>
> So, Q = F1/(Fh-Fl) = 282.25
>
> Fraga = 311.94 = 9.52% err
>
> That is the best overall prediction I have ever calc'd! If the Fraga
> holds well with other coils, then Fraga will likely become the best we
> have.
>
> My coil here was a bare coil Q measurement out in the backyard away
> from everything. A 30" square counterpoise was used as ground. I use
> of course all the great tools that Terry Fritz has designed (planewave
> antenna for the scope measurements for the half power points, low-z
> amp for a low impedance signal, and a digital frequency meter to
> attain the fine frequency differentials). The coil was setting on a
> 15" hdpe bucket. The antenna was about 15 feet away from the coil with
> height about equal to the top of the coil. I and the equipment was
> even further. All this allows for high Q measurements. Note that
> without a good digital readout of the frequency. I wonder if the extra
> 10% error lies in the dielectric (white pvc former).
>
> Anyway, just wanted to share that measurement.
>
> In 1995, Malcolm measured a lot coils Q. The coils h/d ranged from 5
> down to 1 or less I believe. He also measured bare and loaded coils.
> Loading the coil certainly drops Q. Thus, when we run our coils with
> the toroid installed, and in vicinity of the primary coil, our
> secondary Q is much lower than a bare coil measurement. Smaller h/d's
> will increase Q, but my coil is pretty normal (4.71:1). However, the
> turns on this particular coil is higher than the norm. I sure wish I
> had the coil specs to go along with those measurements Malcolm made.
> Malcolm, I don't know if you have anything logged on those coils, but
> it would certainly be neat if you did. ;-)

I recently bundled all the measurements I made up in one file and
sent it to Terry to put somewhere on hot-streamer (Terry ? please ?)

     While the Q of some coils will drop with top loading (L/C ratio
is degraded) others will see an initial rise in Q as the topload
takes the burden of being a topload off the top coil turns (thereby
forcing the top turns to add to the effective inductance). There is
no doubt a general rule which could be derived to show which coil
types and shapes this occurs with but deriveing such a relationship
was beyond the scope of accurately measuring a bunch of coils. I hope
there is some useful data in there for you. I doubt that I will ever
have access to facilities to make those kinds of measurements again.

Regards,
malcolm

> Something I didn't explain in the previous post was that I typically
> measure Q of the coil as a whole, not just a bare coil. I don't run a
> bare coil, I run a loaded coil. However, for the purpose of this
> exercise, I thought a bare coil is the right place to start.
>
> Oh, btw, I checked Les and Ces in the equations. It's worse and has
> twice the error. As Fraga, Terman, Gary, etc. all compare and base
> their equations from Medhurst, it actually makes sense that the least
> error would occur with Ldc and Cdc in their particular equations.
>
> Anyway, just wanted to share those measurements.
>
> Take care,
> Bart
>
> Tesla list wrote:
>
> >Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>
> >
> >Hi Gerry,
> >
> >Fraga is looking "real".  Have you checked your coils predictions
> >with Fraga? I'm showing a Q of 207. My high turn 8.5" coil is showing
> >a Q of 155. If memory serves, that's close to measurement. I'm trying
> >to dig up my misc. Q measurements (scattered via emails, hand written
> >notes, etc.). Anyway, could only get on the internet for a second,
> >but wanted to mention that. I still need to do a lot of verification
> >with the equation and values as I did it rather quickly. But, it
> >certainly ballparked well.
> >
> >Take care,
> >Bart
> >
> >Tesla list wrote:
> >
> >>Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>
> >>
> >>Hi Bart,
> >>
> >>After looking at the Fraga equation again, it does look and L and C
> >>directly. It uses the product of L and C by virtue of the frequency
> >>needed for skin depth.  Your Les and Ces are the frequency
> >>determining equivalents that are suppose to be accurate to like 1%.
> >>How accurate are Medhurst C and Wheeler L in predicting the correct
> >>frequency.  I doubt there will be any significant difference
> >>especially since f gets sqrt'd which will cut the error in half.
> >>
> >>Gerry R.
> >>
> >>>Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>
> >>>
> >>>Also, with Fraga, Gary used Medhurst C and L. I wonder how it plays
> >>>out with Ces and Les in place of Medhurst? As a matter of fact, I
> >>>wonder how well a lumped effective L and C would work with all the
> >>>equations? They probably won't change a great deal (but, I haven't
> >>>looked at that).
> >>>
> >>>Take care,
> >>>Bart
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