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Re: additional transformers [rolled caps]
From: Robert W. Stephens[SMTP:rwstephens-at-headwaters-dot-com]
Reply To: rwstephens-at-headwaters-dot-com
Sent: Thursday, August 07, 1997 12:21 AM
To: Tesla List
Subject: Re: additional transformers [rolled caps]
>
> From: richard hull[SMTP:rhull-at-richmond.infi-dot-net]
> Sent: Friday, August 01, 1997 5:52 PM
> To: Tesla List
> Subject: Re: additional transformers [rolled caps]
>
> A
> >> > >
> >> > >Peter,
> >> >
> >> > I recommended leaving a full 2" edge separation metal to edge of dielectric
> >> > in all rolled capacitors!
> >> >
> >> > Richard Hull, TCBOR
> >>
> >> Thanks for the info on that, I will go 2" on my future overlaps. It
> >> seems strange to me that sparks seem to travel much further along the
> >> surface of an insulator, no matter how clean it seems to be. Maybe this
> >> is due to microscopic impurities on the surface of the plastic?
> >>
> >> Another little trick that you probably have already figured out is to
> >> insulate the input connections to the plates by rolling a few layers of
> >> poly around them.
> >>
> >> Cheers, Peter E.
> >>
> >Peter, Richard, All,
> >
> >I had the same problem with a rolled poly cap I made once, and I
> >*was* using a 2 inch surround from the foil to the edge of the poly.
> >Dismantling the cap after the failure showed these burns distributed
> >all along the edge of the foil outwards into the poly.
> >
> >I had a chat with a capacitor engineer at Condesnser Products about
> >this phenomenon and was told that this is why HV capacitors are
> >generally not successful when one tries to apply more than 8-10 kV
> >across a single stage. He explained that the energy exchange between
> >the plate and the local surface of the dielectric becomes too violent
> >and just completely overstresses the dielectric causing it to
> >break down. Placing additional thickness of poly does not
> >significantly reduce this violent surface area exchange so you will
> >still get failures no matter what you do if you try to run a single
> >stage cap at 15 or 20 kV.
> >
> >FWIW
> >rwstephens
> >
> >
> >
> >Robert,
>
> This is the very reason I have stated even in tape #3 where the big rolled
> jobs are made that one should never run them at over 10KV. Series for more
> volts. In tape #8 where we build another type of poly cap, I note that 7-8
> KV is the max on the single unit. Nonetheless, many never headed my
> warning and blew out there caps almost immediately. Too many coilers rush
> to the 15,000 60ma neons and use a single capacitor unit. They will lose it
> sooner or later.
>
> The two inch boarder is minumum on caps used over 5KV per unit. Once aged
> and all the air is out I have run my single, big, rolled oil caps with 12KV
> neon transformers and luckily have never lost one. When working on maggeies
> #1-8 from 1990-1995 I used two of the big rolled jobs in series with a
> 14,400 volt potential transformer and never suffered a break down, but the
> stress was reduced on each unit by series stringing them.
>
> Since then I have used only professionally produced discharge caps. The old
> 1990 built rolled caps are still kickin' and are often used in snap setups
> for visitors, etc.
>
> Concomittant with the use of homemade caps is a sense of power input
> limitation in the form of break rate. Lots of folks kill these spartan
> units with 15,800 rpm 24 point rotary gaps!!!! Even 2 KV might blow them at
> that rate of delivery. Newbies always want the 20,000 volt transformers and
> turbine speed rotaries and wonder at the ease of destruction of their
> capacitors.
>
> There is rarely a real viable need for break rate over 360/second (maggies
> can handle more). If a rotary gap has more than 8 points, it will be a bear
> to quench well with out super high speed and attendant cap destruction.
>
> I have no way of knowing, but I suspect a lot of Good CP caps fell to the
> turbine rotary effect.
>
> Richard Hull, TCBOR
>
Richard,
You have shared some valuable pointers again for newbies here and
safety reminders for the rest of us. I can really appreciate how a
turbine break rate will destroy the best commercial capacitor but I
just wanted to say in reference to your 360 BPS suggestion that I
have personally found ~ 402.5 BPS (14 stud rotary wheel on a 1725 RPM
non-synchronous motor) to be really sweet. A wheel with 12 studs
yielding ~345 BPS was significantly less impressive in my MTC unit, all
things else being identically equal. I guess there is an ion channel
lifetime effect difference happening here that is better at the
slightly higher break rate of 400, but suspect a supply sinewave
filling factor or synchronizing benefit also as the break pulses 'walk' through
the 60 cycle mains phase in a slightly more concentrated manner.
The Twin system which I have recently built really comes alive in
this 400 PPS regieme, and is noticeably less remarkable at slower
rates, including attempts to set the non-sync DC rotary break motor
to run synchronously at 120 BPS (due to large wheel inertia and
variac control I can successfully ride the crest of the sinewave peaks for a few
seconds at a time). I subsequently have no intention to operate the
Twin at 120 BPS synchronous, nor any need to operate it's break rate
exceeding 402 PPS.
rwstephens