RE: K Factor & Mutual Inductance

        RE: K Factor & Mutual Inductance
        Fri, 11 Apr 1997 07:35:27 +0000
        "John H. Couture" <couturejh-at-worldnet.att-dot-net>
        Tesla List <tesla-at-pupman-dot-com>

At 03:33 PM 4/10/97 +0000, you wrote:
>        RE: K Factor & Mutual Inductance
>  Date: 
>        Thu, 10 Apr 1997 07:54:36 -0400
>  From: 
>        Heinz Wahl <hwahl-at-jtc-campus.moric-dot-org>
>    To: 
>        "'Tesla List'" <tesla-at-pupman-dot-com>
>        You state that the R is effective, not DC or AC. Why can't you
>measure the R of the coil, calculate the XL, at the
>expected frequency of operation, and use the result to find a ballpark
>Q? Could you elaborate on effective R?

 Heinz -

 When you say "measure the R of the coil" I ibelieve you mean the DC
measurement. Many coilers calculate the Q factor as you describe and
Q factors in the hundreds and sometimes thousands. These high Q factors
not be verified by tests that are properly performed.

 The best way to get the calculations and tests to agree is to build
different coils and test them for Q and XL. The effective R can then be
found. You can then make a graph of the results that can be used in
before anything is built.
 The Q factor is important because it it should be optimum if the spark
is to operate properly. Too great a Q factor will interfere with the
duration. I do not know of anyone who has ever made these tests.

 The true nature of the Q factor can be elusive as I show in the Tesla
Notebook. The Q factor is tied to the log decrement by a famous constant
ratio (pi). The Q factor is also equal to 1.364 times the number of
to reduce to 10% amplitude. It is obvious that this has an effect on the
spark gap firing. If this was better understook coilers would have less
problems with their spark gaps.

 John Couture

Hi John, All,
>>Have you ever tried the formula Q = sqrt( L / C ) / R.
>> ----------------------------------------------------
>  Barry -
>  I have never seen the above Q factor equation before. What would you
>for R? In the usual equation   Q = X/R   where X = 6.283 F L  the R is
>effective resistance, not DC or AC.  The only way to find the R is to
>use a
>value for a typical Q and X and solve the equation for R. The Q factor
>the K factor is easily found by tests after the TC is built, however, at
>design stage these two factors are difficult to determine. 
>The basic nature of Q for Tesla coils has to do with the energy stored
>the field of the coil and the energy dissipated. The Q factor also
>resonant rise in voltage and other electrical effects. It is also
>interesting that Q involves other phenonmena such as in the swing of a
>pendulum and in horological science ( measuring time). 
>  John Couture