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Re: [TCML] Burnt Joint (Cap Bank)



For the same money I can get roughly 250% more PVCu tube from here:

http://www.pipestock.com/pvc/pvc-pipe/pvc-pipe-10-bar-metric/

So is there any real difference between acrylic and PVCu? What's the
electrical property of primary concern here, relative permittivity?

I'm still wondering about that volume resistivity figure I was given for
the PVCu... anyone able to shed some light on that one?

Or am I over-engineering this whole decision...? Is it just a case that any
old (pure) plastic will do a good job?


On 21 May 2013 08:50, Phil Tuck <phil@xxxxxxxxxxx> wrote:

> Use Acrylic tube from somewhere like this http://www.theplasticshop.co.uk/
> (no connection)
>
> I've used it for three secondaries (8", 6.5", 4") and it works ok without
> being too 'lossey'
> Need about 1/8 inch minimum.
> (Varnish 1 layer initially, so wire grips better)
> Phil
>
> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
> Of Mike Gray
> Sent: 20 May 2013 22:21
> To: Tesla Coil Mailing List
> Subject: Re: [TCML] Burnt Joint (Cap Bank)
>
> This is straying from the original topic of the thread, but follows from
> the story told and the general direction of the responses, so I'll post it
> here. Not sure what the general guidelines are for this, a lot of
> information pertaining to my situation is in this thread too...
>
> With regard to making a new, wider secondary coil, I've contacted a
> manufacturer of PVCu water drainage piping in the UK asking for the
> electrical characteristics. They have given me a comprehensive technical
> datasheet and whilst the electrical properties given are limited, it is
> enough to determine suitability:
>
> Volume resistivity: 1050 Ohms/cm3
> Breakdown voltage: 30 kv/mm
> Power factor: 0.02 at 800 Hz
> Dielectric constant: 3.4 at 800 Hz
>
> So for a 50cm tall secondary, the induced voltage from top to bottom would
> need to be greater than 30*500=15,000kv or 15Mv in order to cause
> dielectric breakdown. This should be fine...
>
> However I'm struggling with the volume resistivity figure. Not sure how to
> read it or convert it to a more useful figure. Surely the resulting
> resistance of some arbitrary volume, say 5cm^3, of the material would
> depend greatly on the geometry and dimensions of the shape in which it is
> formed? i.e. a long tube of small cross-sectional area vs a short tube of
> large cross-sectional area. So what does this figure really mean with
> respect to my secondary coil? Is it suitable?
>
>
> On 15 May 2013 18:48, Matthew Edwards <matthew.n.edwards@xxxxxxxxx> wrote:
>
> > I have used black HDPE from (tapplastics) on 3 coils for primary
> supports,
> > strike rail supports and base with no problems. And the best part is that
> > they cut to size "cheaply" which will save you some considerable time.
> >
> > Matt
> >
> >
> > Sent via the Samsung Galaxy NoteR II, an AT&T 4G LTE smartphone
> >
> > -------- Original message --------
> > From: Jim Lux <jimlux@xxxxxxxxxxxxx>
> > Date: 05/12/2013  1:34 PM  (GMT-08:00)
> > To: tesla@xxxxxxxxxx
> > Subject: Re: [TCML] Burnt Joint (Cap Bank)
> >
> > On 5/12/13 1:08 PM, Mike Gray wrote:
> > > Okay thanks for that - I'm not too bothered about transparency in the
> > > plastic, and it appears that the transparency will cost you extra, so
> > I'll
> > > go for some HDPE. Black probably, should look quite smart.
> >
> >
> > oops.. when it comes to HV, "black is bad"..
> >
> > A lot of times they use carbon black (a conductor) as the pigment.
> > You'd want to get a small sample and try it.  If it's a $5 cutting
> > board, that's easy. If you're ordering from a plastics distributor, get
> > the breakdown voltage specs, or have them send you a small sample for
> > testing.
> >
> > >
> > > Anyway before I order I need to know what minimum width I'm going to
> need
> > > on the sheet, and since I need to re-wind my secondary I will probably
> > make
> > > it a bit wider and taller. My current secondary, at 5.6cm diameter and
> > 27cm
> > > tall, only has approximately 600 turns... which should be more like
> 1000+
> > > yes?
> >
> > 600 is fine. It's really more about what the inductance and capacitance
> > are, relative to the series resistance.   Run one of the modeling tools.
> >
> > You're at 4.8:1 height/diameter which is fine. When people talk about
> > long and skinny, they're talking about those 30" tall by 3" diameter
> > coils wound on mailing tubes that were popular in the 60s and 70s.
> >
> >
> >
> >
> > >
> > > If I used a 4" diameter form for the secondary, and wound a 50cm tall
> > coil
> > > on that, that would give me just over 1000 turns. Are those dimensions
> > > suitable for me? My NST is 10kV, 50mA.
> >
> > Run JavaTC and find out.  You're right at 5:1 which is fine.  You might
> > want to look at reducing the number of turns. slightly bigger wire will
> > have less loss. Spacewinding (e.g. with monofilament between turns)
> > might be another idea.
> >
> > http://home.earthlink.net/~jimlux/hv/wheeler.htm
> >
> >
> > _______________________________________________
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> >
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> > Tesla@xxxxxxxxxx
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> >
> >
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