Re: Coil design questions.
In a message dated 12/1/98 11:05:25 PM Pacific Standard Time, tesla-at-pupman-dot-com
<< Original Poster: Travis Tabbal <bigboss-at-inquo-dot-net>
- Travis, my comments are included below: Ed Sonderman
I have built one coil from a book and got pitiful performance. After
reading here and on varrious websites I think I have enough info to start
again. I did just about everything wrong the first time so any info here
that can save me time/money would be appreacted.
6" dia 24" long PVC Secondary wound with 22 AWG for 888 turns. PVC sanded,
dried, and treated.
- sounds good, about the same as mine -
Inverse conical primary from 1/4" copper tube starting at 8" with .200
spacing and 30 degree slant
- I would suggest winding it flat, the saucer configuration adds nothing, and
using 3/8" copper tubing with 3/8" spacing if you can afford it. I think I
used about 70 or 75 feet for 14 turns.
Rolled poly cap(s) WinTesla says .0108 mfd should do it.
I was planning on using the design from the list archive page.
15kv 30ma Neon - ok for a start, get a bunch of them.
RQ Style static series gap - works well, I have two of them.
6A Varriac - keep your eyes out for a larger variac. This size will work
for two of the 15 kv 30 ma transformers in parallel (maybe three for short
runs) with pfc correction caps on them.
Topload of about 14 pf. - good start.
Now, this seems to fit, I was planning on using one rolled poly cap of the
design listed which with 90 mil poly should give me .0100 mfd according to
the docs, I was thinking to build two of them right off just in case. The
doc states that it will handle a coil with input of 15KV. - I built two of
these first and eventually built another one. Be careful of the voltage
ratings. I blew both of the first two of these that I made (made with only
one piece of .062 poly). Use an extra layer of poly cut the full width of the
cap but only about 2.0" wide under the bottom edge of the aluminum. Having
someone help you, roll the first turn of the cap, keeping everything straight
and aligned properly, now slide this extra piece of poly right under where the
bottom edge of the aluminum wants to dig into the poly. I am not sure I am
explaining this properly but you will understand when you actually get to that
For the poly, I think 90 mil is the way I should go. Are 3 30 mil layers
prefferable to a 60 and a 30 or otherwise? - I believe this is a good idea
and is what I would do next time.
For the oil soaking does layering oil soaked paper in with the poly sheets
help? If I do so that will affect the thickness of the dielectric. Is
replacing a poly sheet to compensate a good idea? I'm leaning against
this and would preffer to just parallel 2 of them if I do add the
paper. "better safe then sorry". - I also like this idea. Three layers of
poly with a sheet of paper between each layer and the foil would be very good
construction. I just made a sketch of this and it requires 8 layers of paper.
Has anyone out there done this? I think it would be very difficult to roll.
I don't have a vacuum pump and would preffer not to buy one. I can let
them sit for a while before use and plan to break them in with the NST and
varriac. I would preffer not to have them explode. :)
If the vacuum is that important any idea on where I can obtain a cheep
pump? - I did not have a vacuum pump. I just built them, filled them with
oil, let them sit for a couple of weeks - tapping on them and bouncing them
around a few times each day. Then broke them in using them both in series for
a while. The longer you use them, the more trapped air comes out. It is
important not to have a marginal design (voltage rating wise) and to "run them
in" slowly. At least that is my experience. Both of my first two caps failed
right at the first inside roll of the cap where the aluminum flashing
contacted (and apparently dug in) to the poly.
Any ideas where the primary will tune? I found a good price on a 50ft roll
of copper tube and don't mind using the whole thing if I need it. The
calcs I have from WinTesla and the spreadsheet on the archive page think I
can get 12-14 turns starting from 8 in. - I did not run the calcs, the
spreadsheet program should get you close.
For the topload, I was thinking of using the duct wrapped in foil method.
But the copper spheres mentioned on the list today calc to a higher
capacitance for a 6" then the torriod that I was planning. And it would
look cooler and be eaiser to work with. Is there a prefference on sphere
vs. torriod for this? - I would build a toroid. I think I started out
with one 5" x 18" toroid with this coil and now use one 5" x 30" and a 5" x
The transformer/cap match equations seem to think I want 60ma for this
size cap. Can I get by with 30 or should I go up to 60? I don't mind
limited performance for the first runs and I allready have the 30 ma
transformer from my previous efforts. Any estimates on performance either
way? Would putting another 30 in parallel overload my varriac? Do I need
PFC on this thing? :) - You can start with one 30 ma transformer. It won't
be long before you are adding more in parallel. I think you should get 3 to 4
foot sparks with one 15kv, 60 ma transformer.
For hookup wire I would like to use the 8 AWG power cable I use in my car.
It's very flexable and is made from thousands of tiny strands. I am
concerned about the insulation. Has anyone used simmiliar cable for the
connections on a coil? I would like to use it in the caps too, so
breakdown is important. Is encasing it in poly tubing a workable way to
prevent problems? I believe it's made by "Monster Cable". - I originally
used RG213 without the shield for all my primary hook up wire then changed it
to 3/8" copper tubing. Your #8 cable should be ok, just design it so that the
wire is routed a couple inches away from anything else. Obviously, the
insulation on that wire is only good for a few hundred volts.
For oil filling the caps I found a local jobber I can get Shell Diala AX
from for what seems to be a reasonable price ($25/5 gal). Is there any
problem using this oil in a cap? I've read on the list that it is a good
oil, I just didn't see anything saying what for. They tell me it's a
transformer oil, which seems to fit the requirement. Any idea how much oil
I need for 2 caps? - That oil should work fine. I originally bought 5 gals
of transformer oil and have built three caps and still have a gallon or two
For the neon protection network I need caps, where can I get some? :) What
exactly do I need for this? I found a doc thinking that the LC filter was
prefferable to RC. I don't really know and don't want to start a debate.
Any pointers? I need to keep the cost reasonable so please keep that in
mind. :) - There is indeed a lot of debate in this area. I would use a
ceramic type power resistor of 1k to 5k ohms in series with each high voltage
lead, locate the transformer(s) close to the spark gap and use nothing else.
My opinion only. I would use a safety gap across the output of the
transformers with a grounded center point and also use a safety gap across the
capacitor(s). Have fun, should keep you busy for a few weeks.
Thanks if you got this far, I'm a bit new and thought I should ask all the
questions I could think up in one message rather then flood the list with
posts over the next week. :)
Any thoughts on my proposed system would be welcome, even to say I'm an
absolute idiot. :) If you do that please provide somewhere to look for
more info though! :)
Saftey tips are great too, after shocking myself on the primary of my last
coil I'm pretty carefull now though. ;) I think I'll build a box for the
primary circuit this time.