Re: 60 vs. 30 ma

Subject:      Re: 60 vs. 30 ma
       Date:  Wed, 04 Jun 1997 06:37:06 -0700
       From:  Bert Hickman <bert.hickman-at-aquila-dot-com>
Organization: Stoneridge Engineering
         To:  Tesla List <tesla-at-pupman-dot-com>
 References:  1

Tesla List wrote:
> Subject:   60 vs. 30 ma
>   Date:    Mon, 02 Jun 1997 18:39:14 -0500
>   From:    Tedd Payne <tpayne-at-netnitco-dot-net>
>     To:    Tesla List <tesla-at-pupman-dot-com>
> Here's another "what if".  Suppose I have a well-designed Tesla coil
> using a 12KV/30ma neon transformer, .005 uF cap, appropriate torroid,
> RQ-style gaps, primary with more than enough turns, and the coil
> produces an 18" discharge when optimally tuned.
> Now suppose I replace the 12KV/30ma transformer with a 12KV/60ma unit.
> I'm wondering how much the performance will be improved by the higher
> current transformer combined with little or no other changes.  My
> questions:
> 1. How likely is it that any part of the whole system would be damaged
> by the higher current?
> 2. What increase in discharge length could I expect by changing only the
> primary tap location?
> 3. What increase in discharge length could I expect by changing the
> primary tap location in conjuction with using a larger torroid?
> Thanks!


1. Little chance. Overvolting typically blows up TC elements, not
over-current. If you've "tuned" your system with the "optimal" or
"maximum" tank capacitor (many of the TC design programs provide the
capacitance value which does this), you'll actually be resonating the
neon's inductance and tank capacitor at 60 Hz. In this case, a 60 ma
transformer may tend to withstand the higher secondary currents more
reliably IF you don't overvolt the system by opening the gaps too

2. Not clear. The primary tap only facilitates tuning of the primary
circuit. Loosely speaking, a "tuned" system will have the same operating
frequency for both the primary and secondary. To the extent a tuned
system runs better, it will always produce better output than if not
tuned. However, the degree of improvement is a function of the overall
"Q" of the system - a poorly designed coil, with lossy cap, losy
primary, poor gap, etc may show little change WRT to tap position since
it's tuning range is so broad. 

3. Again, the primary tap position is a tuning aid. If you add a larger
toroid, the added self-capacitance of the toroid lowers the secondary
systems's resonant frequency. The primary must then be tapped to a
larger number of turns so that it now resonates to the new, lower,
frequency. Generally, when you lower the frequency, you also lower some
of the losses from skin-efect in both the primary and secondary

If you've also increased the radius of curvature of the toroid, you'll
increase the point at which streamer breakout occurs (the "hold-off
voltage). The combination of a higher hold-off voltage, combined with
added top capacitance usually improves overall spark length and tends to
generate a single channel streamer rather than simultaneous smaller
streamers. This tends to significantly improve coil performance,
particularly for high Z secondaries - however, your specific mileage may
vary! :^)

Safe coilin' to you, Ted!

-- Bert --