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Re: main caps and rsg's vs static gaps

In a message dated 4/12/99 2:52:00 AM Pacific Daylight Time, tesla-at-pupman-dot-com 
writes:

Robin,  my comments follow:

> Hi to everyone from Oz!,
>  
>   I have been reading the 'list' and the archives for some time and have
>  got some questions of my own that have probably been in before however,
>  
>  1) I have been slowly assembling parts for a coil and have a 13800kv
>  0.36 A pole pig (5KVA). Now according to wintesla I require a main cap
>  of 0.083uf - this is a big cap!. I have made a flat cap of 0.026uf using
>  1.5mm aluminium plates and 1.5mm ldpe. I don't fancy my chances using 3
>  of these caps in parrallel to approach the required capacitance required
>  and still withstand the peak voltages generated. Ques is  - Is the cap
>  value determined by the ability of the transformer to fully charge it
>  based on a static gap the will fire 100 bps, (OZ = 50Hz). If so, would
>  building a rotary gap allow me to fully charge a smaller value cap,
>  (i.e. 3x0.026uf in series = approx 0.01uf but better voltage capacity),
>  and allow me to fire the cap much faster than 100bps thereby still
>  allowing me to fully utilise the KVA rating of my transformer.

If you are building a Tesla coil with a distributition transformer power 
supply, you do not need to be concerned with resonant charging systems.  In 
fact, I had a resonant charging condition accidently with my 5 kva power 
supply and destroyed some expensive caps.  Your transformer will output at 
least twice the rated current and more with no trouble.  Depending on on your 
primary ballast, you could probably get 750 ma out of that transformer 
easily.  Design the primary cap value for whatever you need for resonance 
with the primary coil to match the secondary with topload.  I have a 6.0" 
diameter secondary and started out with .025 mfd for a primary cap and am now 
using .05 mfd. 
>  
>  2) If so, a) will using a smaller cap X say 400 bps give me a comparable
>  result, (spark length etc), as compared to larger cap x 100bps?
>               b) Is there any effect on the resonance of the primary in
>  using a smaller cap x faster breakrate as compared to the static gap
>  alternative?
>               c) Is there a formula for this, i.e. rsg's + transformer
>  ratings + cap and resonance?

With a heavy duty power supply like yours, a larger primary cap will give you 
better performance.
>  
>  3) with reference to rsg's , this implies from my point of view anyway
>  that for part of the input waveform there would be insufficient voltage
>  across the sparkgap to initiate a firing. i.e. instead of charging for a
>  full half wave there would be multiple chargings/firings per half cycle
>  - what happens near the point where the waveform passes through zero
>  potential?
>  

Yes, you will need a rotary gap.  Once you get the coil running, you can 
experiment with rotary gap speeds and note the effect on spark length.  I 
have found that my system likes increasingly higher rotary gap speeds.  These 
transformers put out so much current that I have not found an upper limit on 
disk speed where performance starts to drop off.  I am concerned about the 
beating that the cap must be taking however.

>   My apologies for what may seem basic questions, I would sincerely like
>  to thank the many contributors to the list as you have already saved me
>  countless wasted hours on a project I have spent a long time on already.
>  
Have fun with your project.  Ed Sonderman

>   Kindest regards
>  
>   Robin Copini,
>   Adelaide South Austra