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Re: Capacitor

Original poster: "Dr. Resonance" <resonance@xxxxxxxxxx>

These blue "glassmike" caps will not work for RF Tesla coil duty --- they are DC filter capacitors and will fail in short order at RF frequencies. You need extended foil pulse duty rated capacitors designed for RF (high freq alternating currents) work.

Dr. Resonance

Original poster: "Hajdrowski, Leo T." <leo.hajdrowski@xxxxxxx>


The capacitor I'm using is made by Plastic Capacitors, Inc. of Chicago.
It's a type 'OF' HV Filter - Glass Container. It's a hermetically sealed
plastic dielectric with mineral oil.  It's 9" long by 1 5/8" diameter.
It's .02MFD and 30KVDCW.

Yes, the other X-Ray capacitors were .11MFD in parallel at 90KVDC! Very
Very Large!

I adjusted the spark gap to fire continously with the greatest gap
spacing - I'm not using any additional air for quelching.  I tuned the
primary by adjusting the tap that produces the longest secondary spark.

One end of the secondary coil wire goes to the top torroid and the other
end to a pipe pounded into the ground.

I just don't get that HV high frequency corona; as I said before, the
output looks just like a step-up transformer!


-----Original Message-----
From: Tesla list [mailto:tesla@xxxxxxxxxx]
Sent: Monday, July 03, 2006 11:51 AM
To: tesla@xxxxxxxxxx
Subject: Re: Capacitor

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


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.


----- 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?
>-----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
>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
>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
>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