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Re: Tesla Coil Q Factors



Tesla List wrote:
> 
> ----------
> From:  John H. Couture [SMTP:couturejh-at-worldnet.att-dot-net]
> Sent:  Monday, August 24, 1998 11:57 AM
> To:  Tesla List
> Subject:  Tesla Coil Q Factors
> 
>   To All -
> 
<SNIP>

Q = 6.283 x F x L    Q = Vs/Vp       Q = 3.1416/ Log Dec

<SNIP>
>   With real coils the secondary voltage Vs increases when the input wattage
> is increased. This means that in the equation Q = Vs/Vp the Q Factor would
> increase with an increase in wattage. However, with real coils just the
> opposite happens. The Q Factor decreases as the wattage increases. I show a
> graph in one of my books of this relationship where the Q Factor decreases
> with an increase in the wattage. To my knowledge there is nothing in the
> present literature that shows why there is this apparent discrepancy with
> the equations.
> 
<SNIP>

John,

The first equation is not quite right - it should be:
       Q = (6.283 * F * L)/Reff
where Reff is the combination of AC resistance in the circuit due to
resistance, skin effect, winding proximity effects. As you indicate,
determining the Q's of the primary and secondary circuits in a sparking
coil is tougher, but can be estimated by looking at waveforms and
back-calculating. 

However, output voltage is not directly relatable to input wattage,
although you will see a degree of correlation: larger systems tend to
use larger tank caps and higher primary voltages, and need more power to
achieve similar breakrates. Output voltage is more directly a function
of bangsize and system losses, since disruptive coils do not build-up
secondary energy from bang to bang. Sparklength is another matter...

I'm not familiar with Q = Vs/Vp - how was this equation derived? 

-- Bert --