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Re: [TCML] Choosing a Cap Size

If you have not yet wound the coil, use the largest dia you can.  With my
0.1 caps I always use 16" dia sec.  Sometimes up to 24" dia for even better
The 16" dia also works very well with a .06 uF cap.

Large inductance is the key and the inductance of a resonant transformer
goes up as the square of the radius of the sec coil.

Dr. Resonance

On Mon, Oct 27, 2008 at 6:33 PM, bartb <bartb@xxxxxxxxxxxxxxxx> wrote:

> Hi Michael,
> For a pig, consider power when thinking about Cp sizing. Power is directly
> related to spark length and to other components. Most pigs are STR mostly
> due to the cap costs for such a high cap size, but also, the energy across
> the gap is another factor probably not realized since costs keeps us at bay
> (most of the time). If an LTR type cap were used with a 14.4kv/10kva piggy
> or bigger, the energy at the gap would be tremendous and then the rotary
> would need to be built to handle this power. With power in the rotary comes
> "costs" (once again). And even after all the money was spent, do you have
> the facility to run the darn thing? These are the factors to look at in my
> opinion.
> I would keep it around 0.1uF to 0.13uF at max. 0.1uF is running at 1.3 x
> Cres STR, so slight resonant charging is occurring. At 0.13uF, 100% resonant
> charging is occurring. For this, the caps in my opinion should be designed
> for 2.5  to 3 x Vp or maybe higher. This would put out the best spark
> lengths, but you do risk pig and cap death in this condition. The 0.1uF is
> smarter for maximizing cap energy along with reducing resonant charging and
> keeping costs down to a manageable level (including keeping energy down to a
> manageable level. i.e., 20j versus say 70j).
> DC's advice on the rotary sounds perfect to me for the 0.1uF size. This
> will allow powerful spark lengths making good use of your available power
> without going overboard. Also, I'm not sure of the coil size you are
> planning to adapt the pig to, but the coil size is another factor which may
> play into the cap size. Hopefully, it's in the 10" to 12" diameter range. If
> you plan for the 2 to 5 kva range, then consider between .05uF and .08uF. As
> a matter of fact, it might be wise to build it with roughly .05uF now, and
> then later build a duplicate cap to put in parallel when the RSG is ready.
> Take care,
> Bart
> Michael Robinson wrote:
>> Hi All,
>> I am about ready to start adapting my coil to run with pig power, but
>> I have a question regarding the size of Cp.  The "rules" for finding a
>> cap size for for a NST are pretty well defined, but I'm having a hard
>> time figuring out what to use on a pole pig coil.
>> What parameters are used in finding the optimal Cp?  Should I use the
>> transformer's ratings, or the actual power I'll be running it at? (ie.
>> it is a 10 kva pig, but I'll most likely run it between 2 and 5 kva)
>> I'd like to go STR to save on cash, but how low can I go while still
>> maintaining decent spark length?  I will be running a blower gap, and
>> moving to ASRSG as time and money permits.
>> Thanks for any advice,
>> Michael Robinson, KE7AQL
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