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

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

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi Paul,

Wow cool!  I never stop being amazed at your programs :-))

I see MandK was not accurate for the two coils being close, but got better
with some distance.  I am pretty impressed this fast test got to within
3%!!  I am sure that is the error of placing the coils across the stick and
the coils are not perfectly flat circles perfectly in parallel.  I did test
the caps to within 0.5% and the signal generators and scope's accuracy is
very high in this case.

I am not sure what happened to the 1 inch measurement, but lots of
possibilities... ;-)  I was really just trying to quickly check if this
idea worked at all.  I didn't try too hard for accuracy but I naturally try
not to screw things up too bad ;-))

For the anti-parallel case.  Does that really hurt the coupling to the
secondary coil?  I want a really low primary inductance but I still need
good coupling to the secondary coil.  If two primary coils are run in
anti-parallel, I "think" that will really reduce the coupling to the
secondary?  If not, I could get up to about 40kHz for Fo!  But I have to
watch the primary current too since it is all being switched through thin
little layers of expensive silicon.  However, if I can get the Fo frequency
higher it makes the secondary coil easier.  I just got like 15,000 feet of
#28 wire for it!!  I am just on the edge of a practical size.

I will try to retest this with the anti-parallel case too tomorrow (must
get ready for coiling meet tonight :-))  I can't say how nice it is to have
programs and models to figure so much of this thing out!  I am not sure it
even could be done without them.

"IPT" is fine with me :-))  I can also tune with a variable number of
primary caps too.  I am not sure which way I will go but the dual primary
thing seems to have many advantages and is fairly simple.  I suppose I
could have 10 primaries with a cap and IGBT for each one, but that may be
"too" much.

Cheers,

	Terry





At 08:54 AM 7/28/2002 +0100, you wrote:
>Terry,
>
>You wrote:
>> Space (in)      Fo (kHz)        L(uH) (0.2uF)
>> 0.5             480             0.55
>> 1               481             0.55
>> 2               526             0.46
>> 3               551             0.42
>> 4               565             0.40
>
>> These measurements probably have a generally high error ;
>
>They look pretty good to me.  Something went a bit funny with
>your 1" measurement, I think.  Acmi calculates:
>
>dist|L1 uH|L2 uH| M uH|La uH|Fa kHz|Lb uH|Fb kHz
> 0.5|0.689|0.689|0.443|0.566|   473|0.123|  1015
> 1.0|0.689|0.689|0.323|0.506|   500|0.183|   832
> 1.5|0.689|0.689|0.254|0.471|   518|0.217|   763
> 2.0|0.689|0.689|0.208|0.448|   532|0.241|   726
> 2.5|0.689|0.689|0.173|0.431|   542|0.258|   701
> 3.0|0.689|0.689|0.146|0.418|   551|0.271|   683
> 3.5|0.689|0.689|0.125|0.407|   558|0.282|   670
> 4.0|0.689|0.689|0.108|0.398|   564|0.291|   660
>
>which agrees to 3% or better except for the 1" reading -
>your measurement seems well off the curve there.
>
>La and Fa are the inductance and Fres of the combination in
>parallel.  Lb and Fb are for the combination in anti-parallel.
>
>Note how you get a much wider tuning range with the anti-parallel
>version - but the differential voltage between corresponding points
>of each turn is high in this case, so close separation might be
>limited.
>
>> VMIPT
>
>How about IPT - interactive primary tuning.
>
>> ...MandK, realizing that it was never made to do this type of
>> stuff
>
>acmi was, here's the input file for the above output.
>
>; 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
>
>primary1 {
>   radius 11.5/2"
>   height  0.0
>   conductor 3/8/2"  ; wire radius
>   turns 1
>}
>primary2 {
>   radius 11.5/2"
>   height  d"
>   conductor 3/8/2"  ; wire radius
>   turns 1
>}
>
>show d as "dist" format "3.1"
>
>L1 = self(primary1)
>L2 = self(primary2)
>show L1*1e6 as "L1 uH" format "5.3"
>show L2*1e6 as "L2 uH" format "5.3"
>
>M = mutual(primary1, primary2)
>show M*1e6 as "M uH" format "5.3"
>
>; a = parallel, b = anti-parallel
>La = (L1*L2-M*M)/(L1+L2-2*M)
>Lb = (L1*L2-M*M)/(L1+L2+2*M)
>
>show La*1e6 as "La uH" format "5.3"
>show 1/(2*PI*sqrt(La*C))/1000 as "Fa kHz" format "3.0"
>
>show Lb*1e6 as "Lb uH" format "5.3"
>show 1/(2*PI*sqrt(Lb*C))/1000 as "Fb kHz" format "3.0"
>
>
>--
>Paul Nicholson
>--
>