Re: Variable Mutual Inductance Primary Tuning (VMIPT Sorry :o)))

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

Original poster: "Paul Nicholson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <paul-at-abelian.demon.co.uk>

Terry,

> For the anti-parallel case.  Does that really hurt the coupling
> to the secondary coil?

Yes!  I just realised.  The B field of the primary is strongly
confined in the anti-parallel case.  Along most of the length of
the secondary the field from the two primaries almost cancels and
the overall coupling is very low.  Acmi gives

dist|L1 uH|L2 uH| M uH|La uH|Fa kHz|  Ka|Lb uH|Fb kHz|  Kb
 0.5|0.689|0.689|0.443|0.566|   473|0.14|0.123|  1015|0.01
 1.0|0.689|0.689|0.323|0.506|   500|0.14|0.183|   832|0.02
 1.5|0.689|0.689|0.254|0.471|   518|0.15|0.217|   763|0.03
 2.0|0.689|0.689|0.208|0.448|   532|0.15|0.241|   726|0.03
 2.5|0.689|0.689|0.173|0.431|   542|0.16|0.258|   701|0.04
 3.0|0.689|0.689|0.146|0.418|   551|0.16|0.271|   683|0.05
 3.5|0.689|0.689|0.125|0.407|   558|0.16|0.282|   670|0.05
 4.0|0.689|0.689|0.108|0.398|   564|0.16|0.291|   660|0.06

where Ka and Kb are the parallel and anti-parallel coupling
coefficients respectively.  Guess you can forget the anti-
parallel arrangement then, except perhaps as an 'off-axis'
tuning inductor.

The input file is now

; ACMI input file for Terry's parallel primary.
; See http://www.abelian.demon.co.uk/acmi/ 

C = 0.2e-6             ; Primary cap value - Farads
d = [from 0.5 to 4 step 0.5]  ; Range of separations - inches

h = 0    ; Height of mean primary plane above
         ; secondary base - inches

primary1 {
   radius 11.5/2"  height  h+d/2"
   turns 1   conductor 3/8/2"  ; wire radius
}
primary2 {
   radius 11.5/2"   height  h-d/2"
   turns 1   conductor 3/8/2"  ; wire radius
}

show d as "dist" format "3.1"

L1 = self(primary1)   show L1*1e6 as "L1 uH" format "5.3"
L2 = self(primary2)   show L2*1e6 as "L2 uH" format "5.3"

M = mutual(primary1, primary2)  show M*1e6 as "M uH" format "5.3"
La = (L1*L2-M*M)/(L1+L2-2*M)  ; Parallel case
Lb = (L1*L2-M*M)/(L1+L2+2*M)  ; Anti-parallel case

secondary {
   radius 8"
   height1 0
   height2 40"
   conductor 26 awg
   turns 40*63         ; 63 tpi for 26 awg
}

M1 = mutual( primary1, secondary)
M2 = mutual( primary2, secondary)

Ma = (M1*(L2-M)+M2*(L1-M))/(L1+L2-2*M)  ; Parallel case
Mb = (M1*(L2+M)-M2*(L1+M))/(L1+L2+2*M)  ; Anti-parallel case

Ls = self( secondary)   Ka = Ma/sqrt(La*Ls)   Kb = Mb/sqrt(Lb*Ls)

show La*1e6 as "La uH" format "5.3"
show 1/(2*PI*sqrt(La*C))/1000 as "Fa kHz" format "3.0"
show Ka as "Ka" format "4.2"

show Lb*1e6 as "Lb uH" format "5.3"
show 1/(2*PI*sqrt(Lb*C))/1000 as "Fb kHz" format "3.0"
show Kb as "Kb" format "4.2"

--
Paul Nicholson
--