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Re: [TCML] Burnt Joint (Cap Bank)
On 5/21/13 11:34 AM, Mike Gray wrote:
For the same money I can get roughly 250% more PVCu tube from here:
So is there any real difference between acrylic and PVCu? What's the
electrical property of primary concern here, relative permittivity?
you don't care about epsilon in this application. And you don't really
care about dissipation either (unless you're using it in a capacitor as
dielectric). Terry Fritz made some measurements a few years ago with
secondaries wound on various materials, and there's really not much
What you really care about is breakdown voltage.
And that depends a lot on things that aren't controlled in, e.g. PVC
pipe. For instance, PVC pipe can have some amount of metal fragments in
it and still meet spec for plumbing. Not that it's very common, but it's
something to bear in mind.
And along the breakdown voltage subject.. Some kinds of tubing have a
foam core with solid skins (black ABS drain,waste, vent DWV pipe is like
this, as is some sewer pipe). The foam breaks down easier than the
solid plastic (less "stuff" in the way, and the bubbles create field
the concern about carbon black as a pigment has more to do with surface
resistivity. If you stick an ohmmeter probes on the surface and it reads
infinity, you're probably good to go.
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?
Any old plastic that doesn't have a lot of inclusions and debris in it
Fiberglass tubing works quite well, for instance.
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