Re: insulating oils.
OK, looks like it's time for me to re-cycle my post on
oils for Tesla Coil Caps. For many of you this will be
old-hat, but for the sake of the newbies I am posting
it again anyhow :)
Fr. Tom McGahee
> From: Tesla List <tesla-at-pupman-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: insulating oils.
> Date: Friday, June 25, 1999 6:07 PM
> Original Poster: "Michael J. Veach" <veachm-at-sunyit.edu>
> What kind of oil is best for very high voltage tesla-type stuff? I need
> some transformer oil, but I've heard it's 300 bucks a gallon. I need 100
> gallons, so as you can guess I'm worried about price.
> Mike Veach.
Certain questions tend to come up again and again on this list, and
the topic of oil for capacitors is one of them. In the interest of
gathering and presenting as much information as I could find on this
topic, I present this post in the hope that it will be found useful
by some. It includes parts of posts by Richard Quick, Mike Hammer,
Ralph Down, and many other coilers on the Tesla List (including
myself). I have not marked down who is responsible for what here,
simply because my clip file of data from which this was assembled in
many cases has only the data, and not the name of the person who
posted it. I hope no one is offended by having their name
inadvertantly left out.
If you have additional comments to add to this modest compendium,
please e-mail me at tom_mcgahee-at-sigmais-dot-com and I will try to keep
this compendium as up-to-date as I can. If I get any significant
e-mails I will repost the updated version when appropriate.
Please note that large sections of this post were taken from posts
originally sent to the Tesla List by many different people. So if
some of the paragraphs sound awfully familiar, it may just be because
it is based on sometheing *you* sent to the Tesla List.
As I have said before, the really good stuff gets recycled again and
Beginning of Discussion on Oil
Coilers use oil to reduce corona and increase High Voltage insulation
in such applications as Capacitors and Transformers.
Mineral oil is a rather generic term given to a whole class
of light oils. There are literally dozens of types.
Veterinary grade mineral oil can be had rather cheaply
in agricultural areas. Sold in 2 and 5 gallon pails.
Pure USP or veterinary grade mineral oil will work fine. The price
varies based on purity and quantity. You can get USP mineral oil at
any pharmacy for less than $2 a pint. While that seems reasonable, it
is much better to buy whatever you use by the gallon or five gallon
container if you want to get a really reasonable price.
Some coilers have even used mineral oil that had a fragrance added.
In *general* try to stay away from all forms of additives, because
you just don't know what properties they bring when used for High
Buy the Transformer Oils from oil distributors. Just tell them you
need a good transformer oil that is relatively inexpensive. Many
prefer transformer oil over mineral oil because it is specifically
made for insulating high voltage, has ALL water rigorously removed,
and is a very THIN oil, so it penetrates MUCH better than mineral
Whenever possible, go for the Transformer Oil rather than the generic
Mineral Oil. The thinner the oil the better, as thick oil makes
bubble removal harder.
Texaco, Mobil, Conoco, and many others also make transformer oil, but
I don't have any specific info on these products in my files (yet).
Some coilers have used refrigeration oil and silicone oils. Ralph
Down used SUNISO refrigeration oil (bought from local refrigeration
repair shop for $30 for 4 litres.) He was pleasantly surprised to
find that the high dielectric constant of this oil actually DOUBLED
the capacitance value of his homemade capacitor.
Coilers have used drugstore grade mineral oil and animal grade
mineral oil. Animal grade oil is sold as livestock laxative.
Those in agricultural areas can find it easily enough, but
city types might have a problem.
For what it's worth, I built *my* capacitors with Exxon Univolt 61. 5
Gallons cost me $34.50. That turned out to be a most reasonable price
for an EXCELLENT true transformer oil. The dielectric constant of
this stuff was almost exactly the same as the polypropylene that I
was using. By the way, when I did my yellow page searches, I was
quoted prices ranging from $34.50 to $48.00 for the exact same
product. So check out multiple sources before buying!
As to using stuff like motor oil, well, it has been done. Read the
label. Go for the stuff that has the LEAST amount of additives. Most
motor oils are too thick. Go for the lightest weight oil you can get.
Remember, you want the stuff to infiltrate every nook and cranny of
your capacitor. Something the consistency of molasses isn't going to
do you much real good!
In general, stay away from food oils. They tend to go rancid and have
too much water content.
But never be afraid to experiment on a *small* scale. Make up a small
flat plate capacitor consisting of just two plates of relatively
small size and EXPERIMENT. Determine the breakdown voltage yourself,
if you have to. The bottom line is not whether all the bigwigs would
use it, but does it work for *you*? And if you find a good reasonably
priced source for Castor Oil, please let the rest of us know about
it! (Castor Oil has a nice high dielectric constant, more than double
the value of transformer/mineral oil).
All of the following oils have been used successfully by coilers on
the Tesla List.
Tulco Snaplube 100
USP Mineral Oil (Laxative) (available at any pharmacy).
Veterinary Grade Mineral Oil (Laxative)
Commercial transformer oils are excellent! Examples would be:
Shell Diala-X or Shell Diala-AX
Esso VoltEsso 35
Exxon Univolt N60
Exxon Univolt N61
Exxon Univolt 33
r-Temp (Paraffinic - Best for capacitors, but more expensive)
There are many other brands of silicone oil
Some coilers have used LIGHT GRADES of Motor Oil successfully
Use ones with least number of additives.
Those of you who are scroungers at heart might want to try your local
power utility. Some people have had success getting a couple of
gallons of transformer oil from their local power company cheaply or
High Voltage transformer oil is used in power distribution
transformers and also in x-ray machines.
When looking to locate a source for *any* item, the FIRST thing is to
use the yellow pages of your phone book. In this case you would look
under OIL. Find the advertisements that specifically mention
transformer oil. Try these first. Call at a time of day when the
person working there is not going to be too busy. That way they will
be more inclined to spend some time talking to you on the phone.
Some people on the other end of the phone will be very knowledgeable
and helpful. Other persons won't have much of an idea of exactly what
you want unless you give them specific information such as "do you
carry Exxon Univolt 61 transformer oil?" Remember, sometimes the
person at the other end of the phone knows more than *you* about the
topic you are discussing (which at the moment is transformer oil, not
Tesla Coils). If it seems like the person is pretty knowledgeable,
then you might divulge the purpose for which you want to use the
transformer oil... you might be surprised and find that he can give
you something even better than what you were asking for.
Besides checking out the Oil Suppliers and Distributers, you might
also discretely try to find out what KIND of customers the Oil
Suppliers are supplying all this transformer oil to. You can
sometimes get one of these customers to sell you something less than
a full five gallon container at their cost (which is usually going to
be LESS than what the supplier quoted *you*, because many customers
buy the stuff 100 gallons or more at a time.)
It is often quite useful to tell people what you are going to use the
oil for. This is especially true if you go some place in person. Take
along some pictures of a Tesla Coil in operation. If you don't have
any good pictures of one of your own coils, download one of somebody
else's magnificent coils and use *that*. Depending on a great many
factors, you can often get the person you are talking to to either
sell you the stuff at cost, or give you a small amount for free.
Below is a copy of a table produced by Richard Quick some time ago.
It includes the dielectric constants and breakdown voltages
per mil of a number of substances, including several kinds of oil.
I could have cut this table down to just include oils, but the
table will have greater utility for all of us if it is kept intact.
Dielectric strength Puncture Voltage
Material K per Mil(0.001 inch)
Paper, bond 3.0 200
Paper, Royal Grey 3.0 200
* Paper, telephone, treated 2.5 - 4 200 - 250
Paper, Parafin Coated 2 -3.5
Paper, Kraft 2.2
Oil, Castor 4.67
Oil, Mineral, Squibb 2.7 200
Oil, Mineral 2.2
* Oil, Transformer 2.1 - 2.5 75
* Rubber, Hard 3.0 160 - 500
1 Rubber, Vulcanized 3.2 - 3.9
Fibre 5.0 - 7.5 150 - 180
Fibre, Red 5.0
Mica 4.5 - 8.0 3800 - 5600
Mica, Ruby 5.4 3800 - 5600
Quartz 3.8 - 5.0 1000
* Quartz (Fused) 4.2 150 - 200
Shellac 2.5 - 4.0 200 - 400
Spar Varnish 4.8 - 5.5
Steatite, low loss 5.8 150 - 315
Steatites (Magnesium silicate,etc)5.5 - 7.5 200 - 300
2 Cambric (Varnished) 4.0
Alsimag 196 5.7
3 Gutta Percha 4.0
4 Amber 3.0 - 7.0
Resin 2.48 - 2.57
Enamel 5.1 450
Mycalex 7.4 250
Silicone RTV 3.6 550
Wood 2.0 - 5.2
* Wax (Parafin) 2.1 - 2.5 250 - 450
Beeswax 2.9 - 3.0
5 Slate 7.0
Barium titanate(25 C) 1200
Bariam titanate 6000
Titanium dioxide 125
Cellulose acetate 3.3 - 3.9 250 - 600
6 Casein, Moulded 6.4
A Polytetraflourethylene 2.0
Aluminum oxide 8.7
Tantalum pentoxide 22
Glass 4.8 - 10 300
Plate Glass 6.8 - 8.4
Pyrex Glass 4.8 - 10 335
Window Glass 7.6 - 7.8 200 - 250
Cordierite ceramics 5.0 - 5.5 100
Magnesium titanate ceramic 12 - 18 150
Porcelain 5.1 - 7.5 40 - 280
Titanium dioxide ceramic 70 - 90 100
Titanium-zirconium dioxide ceramic40 - 60 150
Bakelite 4.4 - 5.8 300
Bakelite, Mica filled 4.7 325 - 375
Epoxy Circuit Board 5.2 700
7 Formica 4.6 - 4.9 450
Nylon (lowest values of 3 types) 3.2 407
PVC (rigid type) 2.95 725
Plexiglass 2.8 450 - 990
Polyethylene 2.2 - 2.3 450 - 1200
Polycarbonate (Lexan) 2.96 400
Polyethylene Terphthalate (Mylar) 3.0 - 3.1 7500
Polystyrene 2.5 - 2.6 500 - 700
Teflon 2.1 1000 - 2000
Air (dry air at 1 atm) 1.0006 30 - 70
* Air (20 atm, 19 deg. C) 1.0108 500
* Carbon dioxide ( 1 atm, 0 deg. C) 1.000985 36
Carbon dioxide (20 atm, 15 deg. C)1.020
* Hydrogen (1 atm,0 deg.C) 1.000264 26.1
Ammonia (liquid) 22
8 Carbon tetrachloride 2.24
9 Chlorinated diphenyl 6.5
Ethyl Alcohol (O C) 28.4
Ethyl alchohol (20 deg.C) 25.8
Methyl alchohol 33.1
Water (distilled) 80 - 81
* = Measured in Kilovolts per centimeter. All others are Volts
per mil (.001 inch) unless otherwise stated.
1 = Vulcanized means it has been melted, or heated in some
2 = Cambric is a finely woven white linen or cotton fabric.
3 = Gutta Percha is a rubbery substance made from the latex of
tropical trees and is used in insulation, waterproofing,
and dentist use it in thin sheets sometimes when working
4 = Amber is a hard, translucent, yellow, orange, or brownish yellow
fossil resin, used in making ornamental objects like jewelry.
5 = Slate is a fine grained metamorphic rock that splits into
thin smooth faced layers. Black Boards for writting are
made of this. Also used as roofing material in some areas.
6 = Casein is a white, tasteless, oderless milk and cheese protein
used in the manufacture of plastics, glues, paints, and food. The
word 'moulded' means it has been shaped by a mold.
7 = Formica is a trademark for any of various high-pressure laminated
plastic sheets of melamine and phenolic materials used for
chemical and heat-resistant surfaces.
8 = Carbon tetrachloride is a very toxic substance. It has also been
shown to cause cancer in lab animals. It is banned in most labs.
It is a liquid that was used as a strong solvent.
9 = Chlorinated diphenyl is a liquid dielectric that is used to
impregnate Kraft paper in small A.C. capacitors. This is a PCB
and may cause cancer, handle carefully.
A = Polytetraflourethylene films retain good properties even at 200
degrees Celsius (200 C).
atm = atmospheres (pressure of air at sea level is 1 atm).
deg.C = degrees Celsius.
Warning - Some liquids and gases listed may be explosive under the
right conditions. Many solids can catch fire and burn. Use
CAUTION and GOOD COMMON SENSE.
Note: Some books gave very different values for each substance so I
have given you the highest and lowest values reported. The
values will depend on the purity of the substance your using.
If you know your substance is very pure then use the higher
value reported. If you know your substance is contaminated or
of poor quality then use the lower values reported. If you have
unknown purity then use the average of the values given.
**** End of Richard Quick's Table
If you have anything to add to this compendium, please e-mail it to:
Hope this helps someone out there. File it away for later.
Fr. Tom McGahee