2 1/8" diameter Tesla coil form?
John Asop
The Tesla coil I'm going to construct requires a 2 1/8" diameter form.
Bert, you pointed out the disadvantages of using cardboard the other day so
I wanted to ask if you or anyone else knew of a plastic form of this size
that could be obtained cheaply? I've checked common PVC outside diameters,
but none are 2 1/8".
Thanks,
John
Bert Hickman
Hi John,
Fortunately, Tesla coils do not require a high degree of precision to
obtain good performance. As long as you can tune the primary circuit to
resonate at the same frequency as the secondary/topload, the system
should work fine. You can use common 2" PVC pipe (2 3/8" OD) or low cost
extruded acrylic tubing (2" or 2 1/4" OD) with no problem. The OD will
only be slightly different than the cardboard tube specified. Here's an
example of extruded acrylic tubing from a plastics supplier:
http://www.tapplastics.com/shop/product.php?pid=141&PHPSESSID=2009012415293522976085
If you use PVC, make sure that you get solid PVC, not foam core, in
order to maintain good dielectric strength. Acrylic will slightly
provide better resistance to arc tracking from corona. If you use the
same number of secondary turns the secondary will resonate at a slightly
higher (2") or sightly lower (2 1/4" or 2 3/8" OD) frequency because of
the difference in secondary inductance, but this should not be a big
problem.
Which design are you using? Do you have a URL? Will it be a spark gap
switched, vacuum tube, or solid state driven coil?
Bert
--
***************************************************
We specialize in UNIQUE items! Coins shrunk by huge
magnetic fields, Lichtenberg Figures (our "Captured
Lightning") and out of print technical Books. Visit
Stoneridge Engineering at http://www.teslamania.com
***************************************************
John Asop
Unfortunately, that plastic alternative looks too expensive so I may have to
either go with the closest PVC size or the cardboard as are original in the
plans. What I am trying to build is called the "Iannini Transverter Coil"
which is essentially a Tesla coil that is part of plans to build an x-ray
generator from Information Unlimited. The x-ray part doesn't interest me,
but I thought it would be easy to just build the coil in Tesla form. I've
never seen Iannini's plans for this published anywhere on the web, but the
coil is remotely similar to the x-ray generator coil that appeared in I
think an Amateur Science publication from the 1960's. Anyway, I can share
the specs with you:
The transformer is a 6 KV neon with a 2400 pf 20 KV doorknob and stove bolt
gap. The primary is 5.5 turns of 1/4" close wound copper tubing. The
secondary is to be wound on the cardboard form, 2 1/8 OD x 1/16 wall x 13"
long, but the 420 turns of enamel wire will cover about 9" of the length.
This secondary is then inserted in a 3" sch 40 PVC pipe, secured, and then
filled with oil and sealed. The primary of copper tubing is to be wound
around this 3" PVC.
The reason I had hoped to stay within the original dimensions is that I had
already purchased the capacitor, which was a bit expensive plus I wasn't
sure how well the secondary form would fit within the 3" PVC if I changed
dimensions too much. Also, I am unsure what happens to the resonant
frequency upon filling with oil. My understanding is that it decreases.
John .
"Bert Hickman" <bert-h...@comcast.net> wrote in message
news:ieSdnQWrvMukNebU...@giganews.com...
Bert Hickman
Your description sounds like its a variant of a horizontal bipolar Tesla
coil. In this design, the primary winding is centered around the
secondary. You develop bipolar high voltage output that's 180 degrees
out of phase on each end of the secondary. Sometimes the center of the
secondary is grounded.
Filling the space between the secondary and primary with oil is likely
intended to reduce corona in Iannini's design. Paradoxically, this
approach may actually increase corona between the primary and the 3" PVC
pipe. Simply increasing the spacing between the primary and secondary
(with NO oil or PVC in between) should reduce/prevent corona. You can
also "tap" the primary (select the number and fraction of turns) to
provide a method of tuning.
What is your intended application?
Bert
John Asop
> Hi John,
>
> Your description sounds like its a variant of a horizontal bipolar Tesla
> coil. In this design, the primary winding is centered around the
> secondary. You develop bipolar high voltage output that's 180 degrees out
> of phase on each end of the secondary. Sometimes the center of the
> secondary is grounded.
Good guess, Bert, but the primary is wound around the base of the secondary
with the 3" PVC of course in between.
> Filling the space between the secondary and primary with oil is likely
> intended to reduce corona in Iannini's design. Paradoxically, this
> approach may actually increase corona between the primary and the 3" PVC
> pipe. Simply increasing the spacing between the primary and secondary
> (with NO oil or PVC in between) should reduce/prevent corona.
All the plans say about the oil is that it is optional, but adding it will
increase power and prevent breakdown after extended use.
You can
> also "tap" the primary (select the number and fraction of turns) to
> provide a method of tuning.
>
> What is your intended application?
I was just going to use it as a standard, fairly low power coil. I've never
built one that uses oil and was curious to try it out. These were the first
plans I came across that provided enough details to fascilitate accurate
construction. I've built regular non-oiled coils in the past, but not this
kind.
John
Bert Hickman
OK - even simpler - the "Iannini Transverter Coil" is actually a common
Tesla Coil with oil.
Since you have built other Tesla coils, this coil is really no different
except for the headaches associated with filling/keeping the mineral oil
from seeping out. Many coilers have built similar/larger coils with oil
immersed secondaries. Some have used cast PMMA outer tubing to make very
pretty secondaries - you can see the internal winding through the oil
along with optical magnification of the winding. Here is an example of
an oil-immersed secondary made by coiler Terry Blake at a NY Teslathon
in 2003:
http://www.tb3.com/tesla/teslathon2003/tb_tc/pages/TB_0073.htm
http://www.tb3.com/tesla/teslathon2003/tb_tc/pages/TB_0096.htm
http://www.tb3.com/tesla/teslathon2003/tb_tc/pages/TB_0097.htm
An oil-immersed secondary can indeed operate at a slightly higher
voltage stress/length, slightly higher coupling factor (without getting
racing sparks between portions of the winding). Because of the higher
dielectric constant of the oil, the coil also will operate at a slightly
lower frequency than an identical secondary operated in air. Based on
the results from other oil-immersed coils, maximum spark length may be
slightly better than similar air-insulated coils.
BTW, for improved performance, you may wish to use finer wire and at
least double the number of turns. Double the number of primary turns as
well. The coil will operate at a lower frequency, and the primary peak
current will be lower. This will contribute to more efficient operation
and higher output.
Good luck and best wishes,
Bert
--
***************************************************
We specialize in UNIQUE items! Coins shrunk by huge
magnetic fields, Lichtenberg Figures (our "Captured
Lightning") and out of print technical Books. Visit
Stoneridge Engineering at http://www.teslamania.com
***************************************************