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Mutual Inductance (was Flat Primary Winding  next question)

To: "'Tesla List'" <teslaatpupmandotcom>

Subject: Mutual Inductance (was Flat Primary Winding  next question)

From: Tesla List <teslaatsticdotnet>

Date: Sun, 21 Jun 1998 23:46:14 0500

Approved: teslaatsticdotnet

From: terryfatverinetdotcom [SMTP:terryfatverinetdotcom]
Sent: Sunday, June 21, 1998 12:13 AM
To: Tesla List
Subject: Re: Mutual Inductance (was Flat Primary Winding  next question)
Just for clarity,
The coil in case A has the following parameters:
PRIMARY
15,000 volt 60 mA neon input (variac controlled)
17.05nF primary cap
8.84 inch avarage radius flat spiral primary of 1/4 inch tubing.
5.67 inch wide coil section
Lp = 118.4 uH
Fo = 112.0 kHz
SECONDARY
5.13 inch radius
1000 turns
33.33 turns per inch
0.02002 bare wire diameter
Ls = 75.4 mH
Cself = 16.68 pF
Ctop = 10.10 pF
The JHCTES program gives a K of 0.21 and m = 602.04 uH.
Mark's program gives a K of 2.01 and m = 635.96 uH.
The actual K is 0.2069 and m is 618.19 uH.
The thing I really like about Mark's program is that it predicts K for
various coil heights.
My coil will not quench well with a K of 0.21. I have to raise the coil
about 2 inches to get a clean quench.
Mark's program very accurately predicts the K at various heights. The
JHCTES program omits this input because of "lack of emperical data" (page
111 Tesla Coil notebook). Perhaps John could add this feature to JHCTES??
Terry Fritz
At 08:09 PM 6/20/98 0500, you wrote:
>
>
>
>From: John H. Couture [SMTP:couturejhatworldnet.attdotnet]
>Sent: Saturday, June 20, 1998 3:01 PM
>To: Tesla List
>Subject: Re: Mutual Inductance (was Flat Primary Winding  next question)
>
>
> All 
>
> The mutual inductance of a Tesla coil is important because it is the major
>parameter that connects the two magnetic circuits of the primary and
>secondary tank systems. Mutual inductance can be used to find other
>parameters including the important K factor or coupling of the coils.
> K = Lm / sqrt(Lp x Ls)
>
> It is always interesting to compare different methods of finding TC
>parameters like the mutual inductance. Mark has listed below the mutual
>inductance he has found for different primary coil arrangements. To compare
>his data using the JHCTES program I came up with the following for System A:
>
> Pri cap = .031 uf Pri spiral avg rad = 9.0 ins Width = 5.7 ins
>
> Sec rad = 5.14 ins Turns = 1000 TPS = 33.33
> Bare wire dia = .020 Sec term = 40 pf
>
> Some of the outputs
> Pri ind = 135 uh Pri turns = 15
> Sec ind = 76.3 mh K Factor = .20
> Op Freq = 77.86 KHZ Mut Ind = 656 uh
>
> Keep in mind that small changes in the inputs can make large changes in
>the outputs when solving for mutual inductance. The pri cap in the inputs
>can be used to change the pri turns. Coilers who have the JHCTES program may
>want to try other changes to see how they affect the mutual inductance.
>
> To my knowledge the only TC program available today for the coiler that
>solves for the mutual inductance is the JHCTES program. The Corum program
>has mutual inductance as an input not an output. The JHCTES program uses an
>algorithm based on an equation in Terman's Radio Engineering Handbook.
>
> One advantage of Mark's program is that it provides more detail of how the
>primary bathes the secondary as you go up the sec coil. To do this with the
>JHCTES program requires additional calculations on the part of the program
>user. If much of this work was to be done it would be better to write a new
>program and incorporating Terman's equation.
>
> John Couture
>
>
>
>At 07:29 AM 6/18/98 0500, you wrote:
>>
>>
>>From: Mark S. Rzeszotarski, Ph.D. [SMTP:msr7atpo.cwru.edu]
>>Sent: Thursday, June 18, 1998 2:49 AM
>>To: Tesla List
>>Subject: Re: Flat Primary Winding  next question
>>
>>Hello All:
>>Steve Young said in part:
>>><snip>
>>>I am wondering just how
>>>primary diameter affects coupling to the secondary. I envision the
>>>magnetic flux from a larger diameter primary will intercept more of the
>>>secondary than will a more compact primary, but I don't know the practical
>>>significance of such an effect. I would assume we should couple to as much
>>>of the secondary as possible to even out the secondary volts per turn
>>>distribution (implies large diameter primary).
>>
>>Consider three flat spiral primaries:
>>System A: inside diameter 12", outside diameter 23.34", N=15.125 turns
>>(Terry Fritz's primary)
>>System B: inside diameter 12", outside diameter 36.00", N=15.125 turns
>(match N)
>>System C: inside diameter 12", outside diameter 36.00", N=14.000 turns
>>(match Lp)
>> Assume each is coupled to a secondary which is 1000 turns of .02"
>>wire on a 10.25 inch diameter by 30 inch tall secondary, positioned such
>>that the bottom turn of the secondary is in the same plane as the flat
>>spiral primary.
>>
>>Results of mutual inductance calculations:
>>System A: Lp=131 uH Ls=76.3 mH M=636 uH K=.20
>>System B: Lp=151 uH Ls=76.3 mH M=614 uH K=.18 (same # turns as
System A)
>>System C: Lp=132 uH Ls=76.3 mH M=569 uH K=.18 (tried to match Lp of
>>System A)
>> Conclusion: you get slightly better coupling with the smaller
>>diameter primary. The current in the secondary is directly proportional to
>>M, so the small diameter primary may be advantageous. Of course, you could
>>wind a solenoidal primary and get even higher M, if you can hold off the
>>higher voltages.....
>>
>>>This leads to another thought. If the primary effectively couples mainly
>>>to the lower part of a 1000 turn secondary (e.g. the first 100 or so
>>>turns), then do we in effect have a 100 turn secondary feeding a 900 turn
>>>third coil?
>> One can examine the degree of coupling between the primary and
>>secondary by looking at the mutual inductance M between the primary and a
>>one inch tall segment of the secondary. In the example below, I looked at
>>the coupling between the primary and a secondary 10.25" diameter, 1" height
>>with 33.33 turns. The secondary coil is moved from 0" above the primary to
>>28" above the primary, near the top of the actual secondary. Here are the
>>results for System A and System C (which have the same Lp and Ls):
>>
>>Position M for System A M for System C
>> 0" 93 uH (100%) 64 uH (100%)
>> 2" 71 uH ( 76%) 53 uH ( 83%)
>> 4" 50 uH ( 54%) 42 uH ( 66%)
>> 6" 35 uH ( 38%) 32 uH ( 50%)
>> 8" 25 uH ( 27%) 25 uH ( 39%)
>> 12" 13 uH ( 14%) 15 uH ( 23%)
>> 16" 7 uH ( 8%) 9 uH ( 14%)
>> 20" 4 uH ( 4%) 6 uH ( 9%)
>> 24" 3 uH ( 3%) 4 uH ( 6%)
>> 28" 2 uH ( 2%) 3 uH ( 5%)
>> It is clear that the larger diameter primary bathes the secondary a
>>little higher up than the smaller diameter primary. Still, most of the
>>coupling is accomplished in the lower 1/4th of the coil height or so. So,
>>to answer your question, no, not 100 turns, more like 200 turns!
>> There are striking similarities between the magnifier configuration
>>and the conventional two coil system. Unfortunately, you generally lose
>>with the magnifier, unless you can build a really fast quenching series type
>>rotary spark gap to handle the higher coupling coefficient.
>>
>>Regards,
>>Mark S. Rzeszotarski, Ph.D.
>>
>>
>>
>
>
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