Re: Non-Linear Coil Winding Experiment. (and more tests!)

To: tesla-at-pupman-dot-com
Subject: Re: Non-Linear Coil Winding Experiment. (and more tests!)
From: Tesla List <mod1-at-pupman-dot-com>
Date: Sat, 18 Oct 1997 11:09:28 -0600 (MDT)
Approved: mod1-at-poodle.pupman-dot-com



---------- Forwarded message ----------
Date: Sat, 18 Oct 1997 11:08:28 -0600 (MDT)
From: Tesla List Owner <listown-at-pupman-dot-com>
To: Tesla List <mod1-at-pupman-dot-com>
Subject: Re: Non-Linear Coil Winding Experiment. (and more tests!)   



---------- Forwarded message ----------
Date: Sat, 18 Oct 1997 05:31:12 -0600
From: "Mark S. Rzeszotarski, Ph.D." <msr7-at-rabbit.INS.CWRU.Edu>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: Non-Linear Coil Winding Experiment. (and more tests!)  

Hello All,
        I agree that the resonant frequency of a loaded tuned circuit is in
fact sqrt(1/LC-(R/2L)**2).  The fact that resonant frequency is changing
substantially is probably explained by a combination of both changing
effective series resistance and distributed capacitance.
        Distributed capacitance consists of an "internal component" and an
"external component" according to Medhurst, who studied this extensively in
the 1940's.  The internal component is conceptually due to the difference in
potential between adjacent and nearby turns.  This voltage difference is
dependent on the AC resistance of the wire, since the potential is I x Rac.
This effect is most dominant in that part of the coil where high current
flows, or where Rac is large.  One can vary Rac by changing wire size (D.C.
resistance), operating frequency (skin effect), or winding pitch and/or coil
H/D (proximity effects).  
        The second component of distributed capacitance is the external
capacitance which is due to the fact that the mean potential between each
turn and earth represents an isotropic capacitance.  This effect is present
if one end of the coil is grounded to earth, which is, of course, the way we
normally operate tesla coils.
        The experiments demonstrate that by varying the effective series
resistance, significant differences in resonant frequency are obtained.  The
Q of the secondary is significantly improved if steps are taken to reduce
Rac in regions of the coil where the current is high (personal observation).
Whether it is Rac or Cdis or a combination of the two that is causing the
effect requires further investigation.  The end result is a higher Q coil.
Regards,
Mark S. Rzeszotarski, Ph.D.