Re: strike rail mystery. (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: List moderator <mod1@xxxxxxxxxx>



---------- Forwarded message ----------
Date: Sun, 03 Jun 2007 12:14:35 -0700
From: Barton B. Anderson <bartb@xxxxxxxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: strike rail mystery. (fwd)

Hi Scott,

The unused turns of a coil (variac, primary, whatever) form an 
autotransformer. Primary currents and voltages are high but usually only 
a few unused turns are there. I expect there is more to the phenomenon 
with primary's than a simple continuous wave autotransformer action 
occurring. Back emf and resonances might be part of what causes 
problems. I had arcing to one of my coils from the strike ring to unused 
turns. I only noticed the situation in photo's and it was predominate 
when a topload strike hit the strike ring. Against all good wisdom, I 
quit using strike rings years ago. I'm not saying it's a good idea to 
not use a strike ring, I'm simply saying I don't. The reason I don't is 
because I get less strikes down towards the primary when I don't have a 
strike ring. That means to me that I have less risk of component failure 
due to a downward strike. Many have argued otherwise. But, I have never 
had a problem ==== yet. <big grin>.

Take care,
Bart

Tesla list wrote:

>Original poster: List moderator <mod1@xxxxxxxxxx>
>
>
>
>---------- Forwarded message ----------
>Date: Sun, 03 Jun 2007 01:34:45 -0400
>From: Scott Bogard <teslas-intern@xxxxxxxxxxx>
>To: tesla@xxxxxxxxxx
>Subject: Re: strike rail mystery. (fwd)
>
>I have always wondered what happened in the unused turns of a primary, I 
>always just assumed there was little or nothing in there, I guess this 
>assumption was very false!  My coils do have several unused turns on the 
>primary, which I will probably trim off after I finally settle on a top 
>load, but my primary did not arc to anything.  My Strike rail arcs to a 
>grounded wire, namely the disconnected lead to the RF ground.  Unless it is 
>surface tracking from my primary, to the wire, and then arcing to a floating 
>capacitance, the primary is not the culprit, otherwise, I don't see how it 
>could be.  The strike rail is not a complete turn, so I don't think it is 
>transformer action, but perhaps it is simple magnetic induction of a wire in 
>a changing magnetic field?  Any thoughts on this?
>Scott Bogard.
>
>
>  
>
>>From: "Tesla list" <tesla@xxxxxxxxxx>
>>To: tesla@xxxxxxxxxx
>>Subject: Re: strike rail mystery. (fwd)
>>Date: Sat, 2 Jun 2007 16:11:39 -0600 (MDT)
>>
>>Original poster: List moderator <mod1@xxxxxxxxxx>
>>
>>
>>
>>---------- Forwarded message ----------
>>Date: Sat, 02 Jun 2007 14:59:48 -0700
>>From: Barton B. Anderson <bartb@xxxxxxxxxxxxxxxx>
>>To: Tesla list <tesla@xxxxxxxxxx>
>>Subject: Re: strike rail mystery. (fwd)
>>
>>Hi DC,
>>
>>Excellent advice! Your right, if there are several unused turns, there
>>is a proximity issue from the strike rail to the nearest winding of
>>which may have a multiplier effect due to the number of turns unused
>>    
>>
>>from the actual resonant tap point. Excellent advice!
>  
>
>>Take care,
>>Bart
>>
>>Tesla list wrote:
>>
>>    
>>
>>>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
>>>>
>>>>
>>>>
>>>>        
>>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>      
>>>
>>    
>>
>
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