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# 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 Note® 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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