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Re: Capacitor Size and BPS



Original poster: "David Rieben" <drieben@xxxxxxxxxxxxxxx>

Hi Curt,

The size of your capacitor will be determined not
only by the size of your transformer and its ability
to readily recharge the capacitor after each discharge
cycle but also by the chosen BPS. 120 BPS is not the "magic" number BTW, unless you're intending
upon running in synch mode (assuming 60 Hz mains
frequency). For our friends in Europe with 50 Hz
mains service, 100 BPS would be the proper set-
ting for synchronous operation. Many pig coilers opt to run asynchronous with a variable speed DC motor driven rotory gap. Many find optimal BPS ranges in the 200 to 400 BPS range when running asynch. Obviously, you wouldn't be able to effective charge a larger capacitor as well running say 300 BPS as opposed to running 120 BPS with a given transformer size, so the synch rotary gapped coils (SRSG) often do employ a larger primary capacitor than an equally rated
asynch rotary gap driven coil. If you plan to operate your
5 kVA, 11" coil synch, I would suggest at least .1 uFd for
the primary capacitor size and you may want to go somewhat (but not a lot) smaller for the capacitor if running asynch, maybe
.05 to .075 uFd, depending how high BPS you intend to run.
Higher BPS doesn't offer as much energy per bang but since you're
firing more bangs per second, the total output power will still be
similar to the synch 120 BPS and the available power from the transformer is the limiting factor. Many coilers note increased spark length by increasing the BPS with an asynch driven coil, within reason. Emperical research has shown that there isn't any advantage by running BPS higher than 500 to 600 and the output
spark length actually begins to go down for a given input power
when BPS ranges are pushed beyond that. Besides that, very high
BPS rep rate is VERY hard on the primary capacitor ;^0

Also, because of the relatively large size of capacitor that would
be required for LTR with a pig transformer, many pole pig coilers keep their primary caps smaller than resonant (STR), even when running synch. With a 5 kVA, 14.4 kV pig, Bart Anderson's Java Tesla coil designer program shows .167 uFd as LTR for a SRSG driven coil and a "mere" .096 uFd as LTR for a sta-
tic gap driven coil, although a static gap would not be a good idea
for processing that much power (BIG quenching problems).

Good luck with your project and keep us informed of its progress.

David Rieben


----- Original Message ----- From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Friday, December 23, 2005 1:43 PM
Subject: Capacitor Size and BPS


Original poster: "C. Sibley" <a37chevy@xxxxxxxxx>
I'm trying to get a better understanding of the
appropriate size capacitor for a Pole Pig driven coil.
 Obviously a larger capacitor will give a bigger bang,
but too big will charge too slowly and may not achieve
120 BPS.  As I understand it, 120 BPS is the magic
number, anything lower essentially means charging
cycles are missed and total power transfer is less?
Correct me here if I'm wrong...
So I'm seeking advice on capacitor size for a 5KVA 11"
Coil.  Any advice?
Thanks,
Curt.