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Original poster: "Dave Halliday" <dh@xxxxxxxxxxxxxx>
Been reading this thread and everyone's advice has been good.
I wanted to say that you really need to examine your Tesla Coil as a
"system" and not just a capacitor, some coils of wire, a top load, a
spark gap and a transformer.
_Every__single__component_ in this system needs to be matched to each
other and playing at "tuning" one part of it when one of the other
components is so totally mismatched will lead to component failure and
As far as I know, list members do not have a financial stake in
Cornell-Dubilier -- we are all recommending these because they work and
they work so incredibly well for the price that anything else really
should not be considered.
You may balk at the $40 cost but that is a couple hours overtime at
work, a meal or two more eaten at home instead of at a restaurant, a
couple neighbors lawns mowed, etc... and figuring the amount of time
that you are spending trying to fit a square peg into a round hole, is
your personal time really worth that little?
You may tell yourself that you are learning and getting educated but
this is not really the case if you are blindly ignoring the decades of
collected experience of other list members.
Sorry for the rant but as long as you continue using a cap that isn't
rated for your coil, you will not get good results.
> -----Original Message-----
> From: Tesla list [mailto:tesla@xxxxxxxxxx]
> Sent: Monday, July 03, 2006 7:11 PM
> To: tesla@xxxxxxxxxx
> Subject: Re: Capacitor
> Original poster: "David Rieben" <drieben@xxxxxxxxxxxxxxx>
> I hate to be the bearer of bad news, but that capacitor
> that you describe is obviously a filter duty type without the
> internal extended end foil terminals and will probab-
> ly fail rather quickly in Tesla service. And you don't want to be
> anywhere around when a glass cased cap decides to "go ballistic"!
> Does the outer case of it get significantly warmer than ambient
> temperature when you operate your coil? That's a sure sign of
> destructive dielectric heating
> and a hermatically selaed glass-cased cap + internal heating =
> KABOOM! Like I stated before, what you really need is the proper
> number of Cornell-Dubilier 942C series snubber caps that are rated
> around 2,000 volts and .1
> uFd or .15 uFd each. If you series-parallel enough of these
> type of caps for the proper range of voltage and capacitance
> for your coil, they will prove pretty near bullet proof in your
> circuit. I think Richardson Electronics? sells these although
> they usually have a minimum order of like 30 or something
> like that. List member D.C. Cox aka Dr. Resonance often has
> these type of caps in stock for around $3 each. I'm sure he can
> fill you in more on the details. Bottom line, the wrong type of
> capacitor can cause dismal performance and can die a premature death
> in your Tesla coil.
> David Rieben
> ----- Original Message ----- From: "Tesla list" <tesla@xxxxxxxxxx>
> To: <tesla@xxxxxxxxxx>
> Sent: Monday, July 03, 2006 2:22 PM
> Subject: RE: Capacitor
> >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"
> >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?
> > >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