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Simple Rules for Producing Longest Sparks Using Minimum Power Input


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From:  FutureT-at-aol-dot-com [SMTP:FutureT-at-aol-dot-com]
Sent:  Thursday, August 13, 1998 5:49 PM
To:  tesla-at-pupman-dot-com
Subject:  Simple Rules for Producing Longest Sparks Using Minimum Power Input

 All,
 
 These rules may be helpful for some who may wish to experiment
 with sync-gaps at low break rates.  In a recent posting, I showed the
 better efficiency I obtained using these methods.  It is important to
 have a well matched system when using sync-gaps.  These rules are
 based on my 42" and 64" spark TC's.  It should be possible to scale
 the results up or down, by following these rules.  These rules are just 
 a rough guide, and some slight non-linearities may be seen with up or
 down scaling.  Results will be affected by transformer losses, design
 techniques, etc.  These rules are based upon a square law for power
 versus spark-length scaling, which seems to fit well with empirical
 results.
 
 1.  Select desired spark length in inches.
 2.  Divide by 2.5, this gives the desired toroid dia.  (approx)
 3.  Divide the desired spark length by 10, this gives the desired toroid
      thickness.  (approx)
 4.  Power input (watts) = (spark length/1.7)^2   (approx)
 5.  (Watts/120BPS)/1.5 = Joules/bang   (the 1.5 factor covers losses)
 6.  Minimum rating for transformer = power input (watts) from (4) above,
      for non-shunted transformer.  (approx)
 7.  Voltage on capacitor, Vc = input voltage times 2.22 times transformer
      nameplate rms voltage rating, for resonant charging with some losses
      thrown in.    (approx)
 9.  Capacitor size;  C = 2 J/Vc^2  (joules from (5) above) (approx)
 10.  Spark gap;  synchronous rotary, 120BPS.
 11.  Primary and secondary coils;  use traditional designs.
 12.  Inductive ballast; adjustable as needed.
 
 Let's try an example, and aim for an 80" spark.  80/2.5 = 32" toroid dia.
 80/10 = 8" = toroid thickness.  (80/1.7)^2 = 2215 watts.  (2215/120)/1.5 =
 12.3 Joules/bang.  Minimum non-shunted transformer rating = 2215watts.
 Voltage on capacitor, (assuming 14.4kV transformer), Vc = 14.4kV * 2.22 
 = ~32kV.  Cap size = (2 * 12.3)/32^2 = 0.024uF.

 For a small coil, aiming for a 20" spark:  20/2.5 = 8" toroid, 20/10 = 2"
 toroid thickness.  (20/1.7)^2 = 138 watts.  (138/120)/1.5 = .77 Joules
 per bang.  Minimum non-shunted transformer rating = 138 watts.  Voltage
 on capacitor, (assuming 10kV transformer), Vc = 10kV * 2.22 = 22.2kV.
 Cap size = (2 * .77)/22.2^2 = 0.003uF.

 For a tiny TC, aiming for a 5" spark:  1/2" by 2" toroid, 8.65 watts, .048
 joules/bang, assuming a 6kV transformer, Vc = 13.32kV, C = .00054uF.
 
 It is unknown if these rules will track "linearly" down to the small TC
 levels above.

 Enjoy!
 
 John Freau