Re: calculating copper plate indutance (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Thu, 20 Sep 2007 21:35:44 -0700
From: Ray von Postel <vonpostel@xxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: calculating copper plate indutance (fwd)

Hi Chris:

I think you will find the equations you need for the inductance of 
coils of various shapes, but wound with strip instead of round wire, in 
"Radio Instruments and Measurements" Circular C74, U.S. Department of 
Commerce, National Bureau of Standards 1937.  This is out of print  but 
your local library can probably get it for you as an inter-library 
loan.

An in-print source is:
Grover, Frederick W. "Inductance Calculations", ISBN  0-48649577-9,
Dover Phoenix Editions
Dover Publications Inc., 31 East 2nd Street, Mineola, N.Y. 11501

You can get it from Dover  or Amazon. Both are on line.  It is probably 
the best source for this kind of information although many people have 
published simplified methods of making the calculations which work 
within limits.  There is a pirated reprint of the Grover book.  It is 
poorly printed in S.E. Asia, even worse bound, and several times the 
price of the Dover edition.

An other source is  Langford-Smith, "The Radiotron Designers Handbook" 
also long out of print and with very little information on your 
subject.

The equations you are looking for involve extensive use of tables so it 
impractical to do much more than point you to the source.

The commonly used equations for inductance of coils do not calculate 
true inductance.  They calculate "current sheet inductance" which is 
that of a solenoid wound with infinitely thin conductor with infinitely 
thin space between the turns.  To get the true inductance you can apply 
"Rosa's Correction" but unless you are working in a standards 
laboratory there is little point since it such a small amount.  I 
notice that in Circular C-74 the current sheet inductance is first 
calculated and then that is corrected for round wire.

Three shapes of coils have been commonly wound with flat strips,  First 
is the helix with the strip wound like on a spool of tape. The second 
is the "pan cake" or helix with the strip wound on edge and third is 
the solenoid with the strip wound like a tape.  Which is best when 
comparing the same inductor wound with strip or wire?  According to Dr. 
Terman it is easier to get tighter coupling between two coils using the 
first method than if it is wound with round wire.  What causes this I 
have no idea. Otherwise, there is no practical electronic advantage. 
However, you can wind a solenoid with the strip on edge using a very 
minimum of sporting structure.  No form is used, just bars of 
insulation to keep the turns in place.

Hope this helps.

Ray


On Sep 20, 2007, at 3:37 PM, Tesla list wrote:

>
> ---------- Forwarded message ----------
> Date: Thu, 20 Sep 2007 23:11:43 +0100
> From: Chris Swinson <list@xxxxxxxxxxxxxxxxxxxxxxxxx>
> To: Tesla list <tesla@xxxxxxxxxx>
> Subject: calculating copper plate indutance
>
> Hi all,
>
> I am thinking about using copper strips for my primary, however I 
> can't find
> how to work out the inductance. The only online calculator I can find 
> is for
> solid wires.
>
> Or is there a simple way to convert a area to a wire dia ?  The planed
> copper area will be 2" wide( or 50mm) , 0.8mm thick. Can that be 
> crunched
> into a solid wire dia ? Also I am not sure if the inductance would be 
> the
> same from a plate to a wire anyway ?
>
> Trying to keep inductance and resistance down to a minimum. Even though
> copper tube is the norm, I am wondering if 50mm of copper sheet will 
> greatly
> reduce the inductance and resistance ?  I think it has to ? The larger 
> sheet
> area should work better at higher frequency's due to skin effect ?
>
> I know some will say its not worth going for copper plate over copper 
> tube,
> though I am using low voltages so even a few milliohms can cause a 
> serious
> reduction in power. Inductance I want to keep low also. I calculated 
> at 10V
> input the turn off spike would be 2KV into about 2uH. Really want to 
> keep it
> below 1uH if possible. Though like I said I am not sure if plate will 
> be
> better or worse then wire. I think overall it should be better ?
>
> Cheers,
> Chris
>
>
>