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Coiler Formers: a lossy mystery
Hi All,
I need some help:
Iīm getting ready to build my 8x36" (winding length) secondary. I want to wind
it with AWG 20. Is this okay or should I rather go for AWG 22 ? Using AWG 22
would get me above the 1000 turn number, tho. Also a coil wound with AWG 20
should have a better Q factor
Next problem:
I have the choice between a 20cm (~<8") PVC pipe and a 21 cm (~>8") PPS pipe.
Which one should I go for?
Not considering price or the fact that PVC reabsorbs water.
I would go for the PPS pipe, but no paint in the world will adhere to PPS
pipe.
(i.e to keep the wire on the fomer, etc)
Now, I know a lot of people say PVC is lossy. I had a look at some tables.
Material Table:
PVC: PPS:
------------------------------------------------------------------------------
---------
R1: >10^15 >10^16
R2: 10^13
-----------
K -at-1Mhz: 3.0 3.2
LF-at-1Mhz 0.015 7*10^ -4
kV/cm 350-500 595
VLF: 600
-----------
R1: Resistance "thru" the material
R2 Surface resistance
K: Dielectric constant at 10^6 Hz
LF: Loss factor at 10^6 Hz
kV/cm: Puncture voltage in kV per cm thickness
VLF: Leakage factor
To VLF: This number tells you something about the ability of the material to
prevent the voltage from "creeping" along the surface. Sorry, I donīt know the
english expression for this.
What immediately springs into mind (looking at the loss factor) is go for the
PPS pipe and trash the PVC stuff. But after some discussion with a friend of
mine Iīm not sure if it really matters.
Our reasons why:
Fact: the E-field goes from every turn of the winding to the base (or ground)
of the secondary.
Given the second fact that the material is about 5mm thick and the E-Field
lines are somewhere around 500mm "long", only about 1% of the E-field is
contained within the plastic itself. Virtually all TC components are going to
have loss factors of way more than 1%.
What would be of more concern to me is the surface resistance. Esp. as the
material gets older. (i.e. the surface resistance will go down). The table
doesnīt contain any number for weathered or aged material, so I couldnīt even
guess what the drop in numbers would look like.
It is quite clear that building a cap with PVC (as dielectricum) would be less
than desirable because in this case the 95% of the E-field will be contained
in the plastic sheet and only about 5% will be present in the oil and / or
surrounding material.
help wanted in germany to clear up the lossy mystery,
Reinhard