Re: larger than resonant (fwd)

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Original poster: List moderator <mod1@xxxxxxxxxx>



---------- Forwarded message ----------
Date: Fri, 1 Jun 2007 11:43:27 EDT
From: Mddeming@xxxxxxx
To: tesla@xxxxxxxxxx
Subject: Re: larger than resonant (fwd)

---------- Forwarded message ----------
Date: Fri, 01 Jun 2007 05:54:39  -0400
From: Scott Bogard <teslas-intern@xxxxxxxxxxx>
To:  tesla@xxxxxxxxxx
Subject: larger than resonant

Hey  everybody,
Can somebody explain to me the advantage to  using a "resonant" or 
"larger than resonant" tank capacitance?  I seen  coils get huge sparks using 
LTR and also very small tank capacitors, so what  is the point?  Thanks.
Scott Bogard.

Hi Scott,
 
For a beautifully illustrated, well-written explanation of resonant rise,  
it's uses and abuses, see:
 
_http://www.richieburnett.co.uk/resonant.html_ 
(http://www.richieburnett.co.uk/resonant.html) 
 
The very short version is this:
    When a cap is chosen such that the supply  transformer and the cap form a 
resonant circuit at the supply frequency, the  output voltage can be 
significantly higher than the supply voltage. If the spark  gap misses a firing 
occasionally, it can be 10 to 20 times  higher. It's just a question of if the 
insulation in the transformer will  breakdown before the cap dielectric is blown 
through, or vice versa. Either way  is catastrophic failure on a time scale of 
milliseconds. In a well-tuned,  precision-adjusted system, there is some 
advantage to using a little resonant  rise to boost output, but for most neophytes, 
and a majority  of old-timers, it's courting disaster. 
    The preferred method is to use a cap above (LTR) or  below (STR) this 
value so that you do not get the destructive in-phase  build-up in case of a 
missed firing. LTR is the preferred way to go for static  gaps, where the firing 
rate is fairly fixed, because the cap is not maxed  out, and STR is usually 
used with rotary gaps where the break rate can be  controlled and set higher than 
the supply frequency for more, smaller  bangs per second. 
 
Hope this helps.
 
Matt D.
 
 
 
 



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