RE: Voltage determination

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

Hi John,

On 25 Jul 00, at 18:49, Tesla list wrote:

> Original poster: "John H. Couture" <couturejh-at-worldnet.att-dot-net> 
> 
> 
> Bart -
> 
> It is a well known fact that the secondary coil inductance affects the
> length of the output spark. This is the main reason that 1000 turns are used
> instead of 100 turns for a Tesla coil. The 1000 turns gives more inductance
> and longer sparks. Of course there are many other design considerations. The
> theoretical equation is
>    Vs = Vp sqrt(Ls/Lp)
> Note that when Ls is increased the secondary voltage Vs is increased which
> in turn increases the spark length. The factor I used is non linear and
> obtained from empirical data and using mathematical regression.

In order to increase Ls you *have* to change something else if 
tune is to be maintained, whether it is decreasing Cs 
(physically smaller coil, hence smaller wire, hence higher 
secondary losses), increasing Cp (in which case you'd have to 
lower Vp in order to retain an identical Ep = same Vout) or 
increasing Lp (in which case the impedance ratio is the same = 
same Vout). I think it is unrealistic to simply attribute 
increased sparklength to a change in one variable only when in 
reality others change or must be changed as well. The 
foregoing arguments assume negligible losses in the primary 
which isn't true either and then of course any modification to 
either coil affects k. Not so simple I would say.

Regards,
malcolm



> Empirical Tesla coil design is a complex combination of many parameters
> involving both theoretical and empirical equations. The Tesla coil output
> spark length equation is obtained from empirical data and subject to many
> variations.
> 
> John Couture
> 
> --------------------------------
> 
> -----Original Message-----
> From: Tesla list [mailto:tesla-at-pupman-dot-com]
> Sent: Tuesday, July 25, 2000 11:13 AM
> To: tesla-at-pupman-dot-com
> Subject: Re: Voltage determination
> 
> 
> Original poster: "Barton B. Anderson" <tesla123-at-pacbell-dot-net>
> 
> Hi John,
> 
> Couple questions below:
> 
> Tesla list wrote:
> >
> > Original poster: "John H. Couture" <couturejh-at-worldnet.att-dot-net>
> >
> > How about using the following equation that takes in the most important
> > conditions that affect the output spark? One advantage of using factors is
> > that you do not need to know the efficiencies. The factors are based on
> > empirical data.
> >
> >   Spark length = W*Vp*Ls*B
> >
> >  W = Input watts
> >
> >  Vp = Factor for Tesla primary volts
> >
> >  Ls = Factor for secondary inductance
> >
> >  B = Factor for breaks per second
> >
> > The JHCTES program uses a similar equation.
> 
> 
> 
> How is the secondary's inductance important to spark length? I can see it's
> importance to Fr, but not to spark length (power processing maybe?).
> Inductance
> is a factor that naturally increases with coil size - size generally means
> more
> power applied and therefore greater spark length. Is it possible that
> inductance here is mistaken as a factor due to naturally occuring mechanics?
> Maybe not, I just haven't seen a reason Ls would be thought of as a major
> factor to spark length, and if it is, I'd like to know why?
> 
> The equation would suggest just increasing Ls to gain spark length. I'm sure
> you didn't mean the equation in that way. Maybe you are referring to a
> higher Q
> secondary?
> 
> Thanks,
> Bart
> 
> 
> 
> 
>