Re: strike rail mystery. (fwd)

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Original poster: List moderator <mod1@xxxxxxxxxx>



---------- Forwarded message ----------
Date: Fri, 1 Jun 2007 23:48:57 -0500
From: resonance <resonance@xxxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: strike rail mystery. (fwd)




In many cases, with classic Tesla coil setups, the experimenter forgets that 
a "variac" autotransformer effect occurs across the very high Q primary 
coil.  If you have an extra 3-4 turns hanging on the primary, e.g., your pri 
tap is in 3-4 turns from the end of the primary coil, very high potentials 
can exist across the end of the outer turn.

This is the principal that Tesla discovered when making his "magnifier" 
system.  This is, of course, not desireable in a classic coil system where 
you want the last tap usually within 1 turn of the end.  This is also why 
I'm a strong advocate of building a "scrap wire" primary circuit before 
laying on lots of copper tubing, tapping in 4-6 turns from the outer end, 
and then seeing 8-10 inch long sparks flashing from the last turn to 
anything grounded, or, worse yet, upwards along your secondary coil.

Keep the primaries as "tight" as possible to the required number of turns to 
prevent autotransformer voltage multiplication due to the very high Q of 
copper tubing primaries.

When Sloan built his 18 turn 1,000,000 Volt, 150 kVA, vacuum tube resonance 
transformer (I believe it was at Stanford), he applied only 15 kV input at 
150 kVA from the CW oscillator into a water cooled 2 inch dia. copper tube 
sec.  He tapped across the first 2-3 turns and developed a tremendous 
voltage multiplication due to the very high Q effect, i.e., a Tesla 
"magnifier" effect.

This Q multiplier effect is causing your strike rail flashovers.  Trim your 
pri properly and this problem will go away.

These effects along with overly tight coeff. of coupling (k factor) cause 
many the the "racing spark" problems.

Dr. Resonance


>
> To add to DC's statement, when the situation occurred in the beginning
> of this thread, the strike ring was arcing across the 3" gap. During
> those arc events, the ring was a shorted turn, so power did attempt to
> flow and energy was lost. But under normal circumstances, the ring is
> not much more than an external capacitance that is felt only slightly by
> the secondary. The primary feels the capacitance also but the large tank
> cap overwhelms any possible affect.
>
> Take care,
> Bart
>