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Re: Capacitor

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

Leo,

The next thing that I would look at is the primary coil tuning
followed next by the spark gap design. Have you tuned the
primary coil to the secondary for maximum output spark
length? Also, how well built is your spark gap? Does it pro-
perly and efficiently dissipate the generated heat to allow for
proper and complete quenching? Also, I think Bart Anderson
mentioned in  previous post that he was assuming that your
stated ".2 uFd" rating of your 2 caps was a misprint and that
you actually meant to say that they were rated at ".02 uFd".
Is this correct?
The 30 kV DC rated capacitor can also be ran on AC although
not at the full rated 30 kV in AC volts. What's more important is
whether ot not your capmis rated for pulse discharge duty or
for filtering duty. Filter cpas aren't of much use for Tesla coils
as they are not designed ruggedly enough for the very high
discharge currents generated by the rapid charge/discharge
cycles of Tesla duty. Filter caps will quickly overheat and may catastrophically rupture from internal heat buildup in a 
Tesla coil.

David


----- Original Message ----- From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Monday, July 03, 2006 10:46 AM
Subject: RE: Capacitor



Original poster: "Hajdrowski, Leo T." <leo.hajdrowski@xxxxxxx>
Hello David,
As you suggested, I replaced the (2) big X-Ray capacitors with (1) .02
MFD, 30KVDCW capacitor.
I still get the same 6-8" spark w/o any corona on the torroid!
Since the capacitor is rated as DC, can I run AC?
Thanks.
Leo
-----Original Message-----
From: Tesla list [mailto:tesla@xxxxxxxxxx]
Sent: Tuesday, June 27, 2006 3:06 PM
To: tesla@xxxxxxxxxx
Subject: Re: Capacitor
Original poster: "David Rieben" <drieben@xxxxxxxxxxxxxxx>
Leo,
Larger than resonant (LTR) capacitance is a good thing, especially for
NST powered coils and even more so for NST powered coils that are
equipped with a synchronous rotary spark gap (SRSG). However, there are
limitations to this and .44 uFd is WAYYY too large of a primary ca-
pacitor for a 15/60 NST powered coil. I believe around
.02 uFd is a resonant capacitoance for a 15/60 NST trans- former and 2x
resonant size is considered optional for a stationary gapped NST powered
coil and 3x resonant for an SRSG NST coil. So with your stationary gap,
.04 uFd would be about as big as you would want to go with your coil.
Your capacitor is about 11x too large and even if you were to series the
2 caps instead of paralleling them, you'd still be at .11 uFd which
would still be nearly 3x to large! You should probably opt for the
Cornell-Dubilier
942 series snubber capacitors (.1 or .15 uFd each at 2000 volts) and
series-parallel how ever many you need to get the correct total
capacitance with a multiple-mini capacitor (MMC).
Also, I believe you'd be better off to take out your rectifier and just
run AC with this type of coil. DC powered coils require proper filtering
or else you're just running a half chopped off sine wave instead of true
DC and this would not be an efficient way to operate the coil.
I would also consider building a better multiple section stationary
spark gap with forced air cooling to aid in quenching or if you're
willing to take on an additional constructional challenge, go for a
SRSG.
David Rieben

----- Original Message ----- From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Tuesday, June 27, 2006 12:35 PM
Subject: Capacitor

>Original poster: "Hajdrowski, Leo T." <leo.hajdrowski@xxxxxxx> Hi All,
>One quick question.
>I just finished helping my son build a coil:
>15 kv, 60 ma nst with full wave rectification Secondary 10.5" x 30"
>#22GA wire Primary 3/8" 10 turns copper tubing flat coil - 1/2" spacing
>between winds 1" spacing between primary and secondary First windings
>of secondary approximately 1" above primary.
>Stationary spark gap with 1/4" spacing
>20 amp variac
>30" dia. Torroid
>(2) .22uf 90KV capacitors in parallel (They came from an X-Ray machine
>and are about 4" dia. X 18" long).
>We only get about an 8" spark and no corona.....it doesn't appear to be
>high frequency, more like a step-up xfmr.
>Is too much capacitance bad?
>Thanks...Leo