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Dielectric
> Could someone post a dielectric chart?
update 8/1/1995
Compiled by Ed Harris
174 W 18th Ave
Columbus, OH 43210
New inclusions to the old stuff:
Info on magnet wire coatings!
>From all the discussion on this group about building ones own capacitors
and what types of materials make good coil forms, I became interested in
obtaining some hard (or semi-hard) data on different types of polymers. I
was also interested when someone (?) asked whether ABS was a good material
for coil forms - I had no idea. It seems that it is much preferable to PVC.
I thought I'd share the results of my library searches:
First, I'd like to list some of the plastics with their chemical name and
their abreviations. Trade names are listed if they are well known.
chemical name abreviation aka notes
------------- ----------- --- ------
polyethylene PE polythene-British!
CH2-CH2 monomer
HDPE High density PE
LDPE Low density PE
polypropylene PP replace one H in PE
by CH3
polyvinyl chloride PVC replace one H in PE
by one Cl atom
polyvinylidene chloride CPVC PVDC replace two H in PE
by two Cl
polystyrene PS replace H in PE by
a benzene ring
polyvinyl flouride PVF replace H in PE by
F atom
polyvinylidene flouride PVDF Kynar repace two H in PE
by two F atoms
*wire wrap insul.
polymethyl methacrylate PMMA Plexiglas
Lucite
Perspex (British)
polytetraflouroethylene PTFE Teflon replace all H in PE
by F atoms
polychlorotrifloroethylene PCTFE Kel-F replace 3 H in PE
with F one with Cl
polyamide 6 PA 6 Nylon 6
polyamide 66 PA 66 Nylon 66
polyamide-imide PAI Torlon
polyurethane PUR
polycarbonate PC Lexan
Polyacetal POM Delrin
polyethlene terephthalate PET Mylar co-polymer of PE
cellulose actetate butyrate CAB Butyrate
cellulose nitrate CN "Laquer" *typical constituent
laquers
acrylonitrile-butadiene-styrene ABS Cycopac ter-polymer of
polystyrene
* warning Jim Oliver says
this name may apply to
may many diff materials
polyimide PI Kapton
polyvinyl formal ? Formvar wire coating
OK, there are zillions of others, but these are the ones I picked because I
heard of them before...
A couple of comments: Notice that there are many polymers which share a
common structure with polyethylene, all that changes is replacing one or
more of the H atoms in (PE) with some other atom or group of atoms. Then
there are plastics which are called co-polymers or ter-polymers. A co-
polymer is just taking two different monomers and sticking them together in
a unit cell before polymerizing. Example: PET. Likewsie, a ter-polymer is
just sticking three monomers into a unit cell and then polymerizing. A very
common example is ABS which is used as sewar and drainage pipe.
Now for the useful stuff. What are the electrical properties of some of
these polymers? The most useful properties in my mind are the dielectric
constant (or permittivity), the dielectric strenght, and the dissipation
factor. All of these properties are dependent on temperature and frequency,
but amazingly they also depend somewhat on the actual thickness of the
material (as in thin films).
----A couple of notes:
All three properties mentioned above depend on frequency, but it turns out
that for many non-polar polymers (ie PE) that the dielectric constant and
dissipation factor do not depend much on frequency. I'll show some data for
some of the plastics I could find. However, nobody seems to have data on
the frequency dependence of the dielectric strength. It is best just to
assume that this was done at DC.
One property which is not well known for polymers is that the breakdown
electric field or dielectric strength (VOLTS/INCH etc...) depends on the
actual thickness of the film. Typically, as the film gets thinner, the
dielectric strength goes up!!! For example, LDPE has a strength of 800volts
per mil at 80 mils, but this goes up to 1400volts/mil at 20mils!!
Polystyrene exceeds even this! I have personally done measurements on LDPE
which show DC breakdowns of 3000Volts/mil at 2mils...
Finally what is dissipation factor? It is a measure of how lossy the
material is to alternating electric fields (as in Tesla coils and tank
capacitors). It is defined by
Ir
--- = tangent (delta) = DF
Ic
where Ir is the resistive or dissipative current and Ic is the capacitive
or displacement or reactive current. Delta is the phase angle between
these currents (in the complex plane). Another expression which contains
the same information is the Power Factor. For those familiar with this term
they are related by:
PF=DF/SQRT(1+DF^2)
For small DF, then PF is approximately equal to DF. Obvisously, one would
like to have DF as small as possible for low loss, high Q systems. In fact,
for the purposes of approximation, the Q of a capacitor with low DF or PF
is simply Q=1/DF=1/PF
Absolute power lost in the system is:
1. goes up with the square of the voltage gradient (electric field)
2. goes up linearly with the volume of the dielectric in the field
( make your coil forms thin)
3. goes up linearly with increasing dielectric constant
( don't use barium titanate primary caps!)
4. generally increases with frequency
polymer dielectric dielectric dissipation
constant strength factor
50Hz / 1Mhz (Kv/cm) 50Hz / 1Mhz (x10^-3)
-------- ----------- ----------- -----------
LDPE 2.29 / 2.28 370 .15 / .08
HDPE 2.35 / 2.34 -- .24 / .20
PP 2.27 / 2.25 240 .40 / .50
PVC-plasticized 4-8 / 4-5 270 80 / 120
PS 2.5 / 2.5 200-300 .1-.4/.05-.4
ABS 2.4-5/2.4-3.8 ~400 3-8 / 2-15
PMMA 3.3-3.9/2.2-3.2 140 40-60/4-40
POM 3.7 / 3.7 400 5 / 5
PTFE 2.1 / 2.1 480 .2 / .2
PCTFE 2.3-2.8/2.3-2.5 550 1 / 20
PA-6 3.8 / 3.4 400 10 / 30
PA-66 8 / 4 600 140 / 80
PC 3.0 / 2.9 380 .7 / 10
PET 4.0 / 4.0 420 2 / 20
PI 3.5 / 3.4 560 2 / 5
PUR-linear 5.8 / 4.0 >300 120 / 70
PUR-thermoset 3.6 / 3.4 240 50 / 50
PUR-thermoplas 6.6 / 5.6 300 30 / 60
CAB 3.7 / 3.5 400 6 / 21
Silicone 3.6 200 5-13 / 7
Another comparison:
polymer Dielectric constant / Dissipation Factor (x10^-3)
100 Hz 1000 Hz 1 Mhz 10 Mhz
ABS 2.8/5 2.8/6 2.8/8 2.8/7
PMMA 3.6/62 3.2/58 3.1/40 2.9/33
PC 3.1/1 3.1/1.3 3.1/7 3.1/11
PE 2.3/.1 2.3/.1 2.3/.1 2.3/.1
PA-6 4.2/31 3.8/24 3.8/31 4.0/20
**************************************************************************
Magnet wire coatings from Phelps-Dodge:
All data pertain to 18 gauge magnet wires
Build= thickness of coating
Coating What's it made of Build DC
---------- ----------------- ----- breakdown
Thermaleze-T (TZT) polyester-imide 2.8mils 11kV
Armored Polythemaleze 3.05mils 11kV
(APTZ) modified polyester&
modified polyamide-imide
Imideze (ML) Aromatic polyimide 2.9mils 12kV
Formvar modified polyviynyl 3.0mils 10kV
formal
Sodereze modified polyurethane 2.9mils 8.5kV
Nyleze Polyurethane 2.9mils 8.5kV
& polyamide
* Note: for the dielectric breakdown - These numbers are much bigger than
for bulk materials because they are very thin coatings. As mentioned
previously, the breakdown field increases as the thickness goes down.
{a similar effect happens in gases and liquids and was studied by Paschen}
Anyway, here's the dielectric constant/DF numbers for these matearials:
Material Dielectric Const. / DF x 10^-3
1kHz 100kHz 1Mhz rating
TZT 3.7/5.6 3.56/16.4 3.58/21.5 3rd
APTZ 3.86/6.9 3.69/22.1 3.67/26.6 5th
ML 3.34/0.9 3.3/5.7 3.36/9.8 2nd to
teflon
Formvar* 3.6/11.2 3.41/25.2 3.37/28.4 5th
Soldereze 3.85/11.3 3.66/20.7 3.66/23.1 4th
Nyleze 4.07/19.7 3.78/27.1 3.75/27.2 6th
* This shows that Formvar is far from an ideal coating for magnet wire
used in Tesla Coils when compared to something like Polyimide coatings
References:
1. Polymer Engineering Principles, Richard C. Progelhof and James Throne
2. Plastics for Electronics, Martin T. Goosey
3. Handbook of Plastics in Electronics, Dan Grzegorczyk and George Feineman
4. SPI Plastics Engineering Handbook, Society of the Plasitics Industry
5. Electrical Engineer's Handbook, Pender - 4th Edition
6. Phelps-Dodge magnet wire product data
Plastics sources: probably best to check your local distributors, but there
is a mail order company called US Plastic Corp -at-800-537-9724 (catalog).
They have rod/sheet/tubing of PVC, PMMA, CAB, POM, PE, PS. Of particlular
note:
Butyrate tubing up to 6 " diameter * lower loss coil forms
Polystyrene tubing to 4 " dia * very low loss coil form
4x8ft LDPE sheet 60mil or other * Capacitors
... If all else fails... Throw another megavolt across it!
___ Blue Wave/QWK v2.12