Re: AC wire resistance with proximitry effects

["Tesla list" <tesla@xxxxxxxxxx>]

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. ;-)

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