Re: Spark length vs. toroid size (was RE: Newbe Question)

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Malcolm Watts" <m.j.watts-at-massey.ac.nz> 

Hi Steve,

On 14 Apr 2004, at 11:51, Tesla list wrote:

 > Original poster: "Steve Conner" <steve.conner-at-optosci-dot-com>
 >
 >  >My 3.5kW tesla coil
 >  >uses 4" PVC and is capable of 6-8 foot arcs depending on the toroid
 >  I use.
 >
 > That's interesting that your output changes by 2ft depending on the
 > size of the toroid. Is the toroid the only thing you're altering or
 > are you using a bigger bang energy too?
 >
 > Do others find that changing the toroid size makes such a big
 > difference?

Well yes, but there is a catch. If the primary cap and gap firing
voltage remains the same, the primary surge impedance goes up as the
terminal gets bigger in order to retune the system. Subsequently,
primary efficiency climbs somewhat. I did exactly this to one of my
coils and the result was a 20%+ increase in spark length.

     It is often not simple to attribute a performance increase or
decrease to any single factor (unless for example, one changes the
airflow through the gap without changing anything else). Change one
parameter and more often than not, others also have to be changed to
compensate in some way.

     To address the original question about using a 12" pipe at 1kW, I
say go for it. Use as high a primary energy as your power supply will
allow while keeping a minimum breakrate at 2Fmains. to get the best
results.

Malcolm

 > The reason I ask is because I'm hoping to get 6ft+ sparks from the
 > OLTC II by sticking a bigger toroid on and upping the tank
 > capacitance. Recent findings suggest that I'm being too nice to my
 > IGBTs.
 >
 > (eg Greg Leyh's IGBT modulator work, and this Review Of Scientific
 > Instruments paper
 >
 > http://depts.washington.edu/rppl/papers/multi%20megawatt%20solid%20sta
 > te.pdf
 >
 > where they drive 400A IGBTs at 3000A)
 >
 > Steve C.
 >
 >
 >