RE: Effective Resistance

["Malcolm Watts" <M.J.Watts-at-massey.ac.nz> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

An intriguing post:

On 16 Aug 00, at 8:02, Tesla list wrote:

> Original poster: "John H. Couture" <couturejh-at-worldnet.att-dot-net> 
> 
> 
> All -
> 
> In Tesla coil design the effective resistance (Reff) and the Q factor are
> unknowns and must be found indirectly. The (Reff) is related to the Q factor
> by the equation
>     Reff = 6.283 * Fres * L/Q
> 
> The Reff is not the same as the AC Resistance (Rac). I have never seen these
> two resistances calculated for a particular TC where all of the parameters
> were shown so I am using  as an example the JHCTES Ver 3.1 program default
> coil. If you have downloaded this program you can obtain the necessary coil
> parameters by changing only one input parameter. That parameter is the
> secondary terminal which should be changed to zero then press calculate.
> That will give you the necessary resonant frequency (Fres) and other
> parameters needed below.
> 
> The AC resistance (Rac)  of the secondary coil wiring is found by the method
> shown in the Tesla Coil Design Manual. For Fres = 270 KHZ the equation is
>    Rac = Rdc * Mft * y factor
>    Rdc = 26.7 ohms/Mft    Mft = 1000 ft (1571 ft)
>    y factor = 1.25 from TCD Manual Fig 8 page 9-4

How was that "y factor" arrived at?
 
>    Rac = 26.7 * 1.57 * 1.25 = 52.4 ohms

 
>    Q factor = Fres/BW
>    BW = Bandwidth = 6 KHZ (from scope)
>    Q factor = 270/6 = 45
> 
>    Reff = 6.283 * Fres * Lcoil/Q factor
>    Reff = 6.283 * 270000 * .0354/45 = 133.45 ohms
> 
> The 133.45 ohms agrees closely with the graph Fig 7 in the TCD Manual. In
> this example the Reff is 2.55 times the Rac.
> 
> Many Radio books including Terman and Henney show several ways to find the Q
> factors and the Effective resistances of radio tuned circuits. However,
> these methods can also be used for Tesla coils. You may want to make these
> tests with your coil(s) to see how they compare when using the above
> calculations as a guide.

Do they show the Rac of which you speak? (Bet = no).

Reff IS the AC resistance (or ESR).

What possible good does it do introducing yet another factor 
which isn't even used? 

Regards,
Malcolm
 
> Please post your results on the List so others can learn how to design Tesla
> coils..
> 
> John Couture

 
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