[Prev][Next][Index][Thread]
Re: additional transformers [rolled caps]
From: Peter Electric[SMTP:elekessy-at-macquarie.matra-dot-com.au]
Reply To: elekessy-at-macquarie.matra-dot-com.au
Sent: Saturday, August 02, 1997 5:01 AM
To: Tesla List
Subject: Re: additional transformers [rolled caps]
Tesla List wrote:
>
> From: Robert W. Stephens[SMTP:rwstephens-at-headwaters-dot-com]
> Reply To: rwstephens-at-headwaters-dot-com
> Sent: Thursday, July 31, 1997 4:05 PM
> To: Tesla List
> Subject: Re: additional transformers [rolled caps]
>
> > From: Peter Electric[SMTP:elekessy-at-macquarie.matra-dot-com.au]
> > Reply To: elekessy-at-macquarie.matra-dot-com.au
> > Sent: Thursday, July 31, 1997 6:15 AM
> > To: Tesla List
> > Subject: Re: additional transformers [rolled caps]
> >
> > Tesla List wrote:
> > >
> > > From: richard hull[SMTP:rhull-at-richmond.infi-dot-net]
> > > Sent: Wednesday, July 30, 1997 1:27 PM
> > > To: Tesla List
> > > Subject: Re: additional transformers
> > >
> > > >Just though I'd throw in my two bobs worth after having blown up a few
> > > >rolled poly caps!
> > > >
> > > >All of mine failed at the edges (even being under oil) so I reckon the
> > > >secret is to put big overlaps between the plastic and the Al plates i.e.
> > > >at least an inch or more. Also here the thick poly sheet is bloody
> > > >expensive! so use multiple sheets of 8 mil concreters plastic,
> > > >preferably the clear stuff but if all else fails use black plastic with
> > > >engine oil! It ran ok on my coil for more than 3 months.
> > > >
> > > >Cheers,
> > > >
> > > >Peter E.
> > > >
> > > >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,
Do you advocate using several serial connected stages in the one, rolled
poly cap or several separate caps connected in series?
Peter E.