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My cap is still alive! (forwarded, used wrong email)


>From - Sat Apr  3 13:58:41 1999
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Message-ID: <370605AF.D7B960DC-at-clara-dot-net>
Date: Sat, 03 Apr 1999 13:12:31 +0100
From: Alex Crow <alexcrow-at-clara-dot-net>
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To: Tesla List <tesla-at-pupman-dot-com>
Subject: My cap is still alive, thankfully!
References: <4.1.19990402223512.00a0cd20-at-verinet-dot-com>
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All,

The cap hasn't punctured at all it seems - the buzzing was just because it
was'nt clamped and the plates were vibrating a lot - there was a bit of a bang
on the final plate where there was a large air space btweeen the dieletrics,
but it only produced a little carbon that was easily wiped off (I painted all
the plates with oil as I built it). Being as it's still OK, I will take better
care of it from now on and find it a nice little oil bath! For 10KV operation
I'm going to need three more of these! Should be fun (yawn) building them -
300 plates in total!

Thanks for the help

Alex



Tesla List wrote:

> Original Poster: "Gregory R. Hunter" <ghunter-at-accucomm-dot-net>
>
> At 06:31 PM 4/1/99 -0700, you wrote:
> >Original Poster: Alex Crow <user-at-alexcrow.clara-dot-net>
> >
> >Dear All,
> >
> >I finished my first layered cap today, and decided to give it a test
> >run. I had oiled all the plates as I built it, and given it a quick duck
> >in a bath, but the testing was done 'dry' so to speak. I hooked the
> >thing to a variac and gapped the terminations about 1/4 inch apart for
> >safety. I turned up the voltage on the variac, and got really loud
> >sparks across the termination leads at only 20 volts in!
>
> Sounds like you punctured something.  The 50Hz buzzing sound is an arc
> inside your cap or transformer.  Testing a cap in this manner is very hard
> on components and is not neccessary.  The low loss, high-Q 50Hz circuit can
> instantly ruin caps and transformers unless your safety gap is set very
> narrow.  I had a similar experience testing a wine bottle capacitor with a
> 15kv NST.  I used no safety gap, and for a few amazing seconds, the HV
> actually jumped AROUND the ceramic output bushings to the case of the
> NST--a distance of over two inches.  Then the wine bottle punctured.
> Fortunately, the cheap, replacable bottle failed before my transformer was
> ruined.  Every wine bottle I tried failed within seconds.  Fortunately I
> had an entire case of wine bottles (L2.00 for a whole case at the Banham
> boot sale in Norfolk).  When I used them with my Tesla coil, I never
> experienced a failure.
>
> The best place to test a Tesla capacitor is in a Tesla coil.  Use a 50W /
> 1Kohm power resistor on each transformer bushing.  This will reduce the "Q"
> of the 50Hz circuit and limit excessive voltage rise.  Also, put your spark
> gap in parallel with the transformer so it can do double duty as a
> transformer safety gap.  Tune up the system at low power before giving it
> full power.  This will allow the Tesla coil to act as a load on the
> transformer & capacitor.  Output sparks will carry away the power output of
> your transformer so it can't flywheel back and forth through your cap in
> runaway resonance.  I assure you your cap/transformer combination will
> behave very differently when connected to the load presented by a tuned
> Tesla coil.  Testing your cap with only a transformer is almost certain to
> ruin the cap or transformer.  From what you've described, it sounds like
> you've already punctured something expensive.  Sorry Alex.
>
> Greg
>
> >Then I increased the gap to nearly half an inch, and got huge,,
> >deafening bangs at just about 32 volts input to my neon, which I worked
> >out was only just over 1300V on the output! I then gapped further, and
> >just past 35 volts in the gentle hiss from the cap lowered in pitch very
> >suddenly and got a lot louder - and no more sparks on the output.
> >I bumped up quickly to 45V in and still no spark, but the hum stayed the
> >same.
> >
> >To put it bluntly, this worries me. I have layered my plates with an
> >inch of gap on all sides - I was hoping this will be enough with 2 caps
> >in series across my 10kV NST. I have heard that others have been fine at
> >15kV with 1.5 inches of minumum inter-plate distance at the edges. But
> >if I can only get up to a fifth of the voltage on the input at most in
> >this 'damp' state (admittedly there are air gaps at the edges) can I
> >expect them to take 5kV each when they are fully flooded with oil? Is
> >this just a case of me being premature and should I wait until I have
> >run them in in my deep-fat bath before I get too worried? i know this
> >sounds like corona discharge drawing extra current from the transformer
> >and thus limiting the output, but will my corona be five times less
> >severe when there's no air left in the thing? Maybe it's doing resonant
> >charging (0.04uF on a 10kV, 150ma short-circuit current neon) and I'm
> >getting a serious voltage rise)?
> >
> >This cap took me two days to build and I don't want to go through it all
> >again!
> >
> >Any help would be deeply appreciated.
> >
> >Alex Crow
> >
> >
> >
> >
> >
> >
> >