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Re: [TCML] Choosing a Cap Size

Hey Michael...

I guess some of the considerations needed for choosing a cap for a 14.4 10KVA piggie are as follows:

1 Peak voltage that can occur if the trannie/cap do go resonate ( LTR caps are big for piggies) 2 Inductor/current limiter design ( EI core with adjustable plate, split variac etc.) 8 - 20A available (20 - 50%)
3 being satisfied with limited streamer length

For example, a piggie running at 14,400 Vac with 42 amps in will create a peak voltage of about 21,000V. Safe voltage rating for the cap should be in the 42 -50KV range. A cap resonate at the input voltage and amperage ( 240/42 // 14.4/.695) will be a whopping .128 uF at 50KV. A STR cap is still going to be about .100 uF or less at 50 KV, and a LTR cap would be .334uF at 50 KV for a rotory gap. Most people running piggies are running STR caps... the disadvantage is that one never "sees" the full potential of the piggies ability. The advantages are, the cap should become completely charged with proper gap settings giving one the biggest bang per charge.

Since you plan on running at reduced amp input and using an Async rotory, a cap in the .05 -.03 uF range should work nicely.

If you could, go to this website and use JavaTC to help configure your coil and power issues.


Bart has put this together and it is awesome!

Scot D

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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