Re: Effective Resistance

["Barton B. Anderson" <tesla123-at-pacbell-dot-net> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Hi John, Malcoom, 

Tesla list wrote: 
>
> Original poster: "Malcolm Watts" <M.J.Watts-at-massey.ac.nz> 
>
> 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




My undestanding is that Reff is a resitive component because it draws in-phase
current from the AC voltage source. It includes skin effect, eddy currents,
hysterisis losses, I2R losses, and any other effect which causes a "resistive"
loss. I don't understand how there can be a stand-alone component termed "Rac".
Does it describe a particular condition such as a calc to seperate one of these
"resistive" components from the rest? 

Bart