ElectroWin
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titanium dioxide dielectric for HV capacitors
a friend asked me to help him build a Tesla coil; it seems i need a 25 kV, 2200 pF capacitor for this. i cannot afford the $200 price tag, so i got to
thinking,....
could i make my own?
to be successful, i would have to sinter synthetic rutile powder, so i would need really high temperature. but what if i mixed like 80% TiO2 into some
Al2O3 and/or SiO2 powders? would that reduce the sintering temperatures to manageable?
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Twospoons
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The more usual dielectric would be polyethylene for home made capacitors. Its cheap, low dielectric loss, and readily available in sheet form. PET
('Mylar') sheet is often used too.
Helicopter: "helico" -> spiral, "pter" -> with wings
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Xenoid
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Check out the various sellers on ebay - search for high voltage capacitors tesla doorknob. Suitable capacitors can be had for $5, $10, $20 or so, the
normal procedure is to put several in parallel to increase capacitance or series for voltage, etc.
Do you really need 25KV, I would have thought 20KV at the most for NST based teslas.
I have a half-built tesla myself... must get around to finishing it!
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IrC
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http://www.ebay.com/itm/0047uF-15KV-High-Voltage-Capacitor-H...
2 in series is very close at 2,350 pF and 30 KV in rating, all for a mere $13.80 shipped. $5.50 ea plus $2.50 + .30 for mailing. He has 7 of the
.0047uF 15KV capacitors left.
"Science is the belief in the ignorance of the experts" Richard Feynman
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12AX7
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Film is easier than ceramic. Or glass, if you don't mind a lot of salt water around.
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AndersHoveland
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Capacitors are perhaps the easiest part of a Tesla coil to make yourself. You can use transparent projector film and sandwhich them with aluminum
foil. Each layer can hold up to 15kV before breaking down.
http://en.wikipedia.org/wiki/Transparency_(projection)
I think they are usually made out of HD polyethylene, which has a dielectric constant of around 2
[Edited on 19-4-2013 by AndersHoveland]
[Edited on 19-4-2013 by AndersHoveland]
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franklyn
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www.youtube.com/watch?v=g1SN3rMTFok
www.youtube.com/watch?v=pdYJgnWe40s
www.youtube.com/watch?v=RUlAy-7AgC0
.
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ElectroWin
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Quote: Originally posted by Twospoons  | The more usual dielectric would be polyethylene for home made capacitors. Its cheap, low dielectric loss, and readily available in sheet form. PET
('Mylar') sheet is often used too.
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Polyethylene dielectric constant is 2.25, i need about 100.
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ElectroWin
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okay, the bucket cap may do just fine; in fact, we have the bucket and the bottles, a box of salt is $1, i'll strongly consider it.
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watson.fawkes
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Where does this "need" come from? You can just
use larger plates as a substitute. Now "want" I can relate to, but unless you're going to get serious about technical ceramics, I don't see using
barium titanate as a short path to finishing a coil project.
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Morgan
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Teflon has some good qualities.
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ElectroWin
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ok, i just realized that if my chosen dielectric has much-greater dielectric strength than air, i can substitute high dielectric constant for thinner
plates. (ie: i should be comparing the product of the dielectric strength and dielectric constant, when choosing the capacitors)
also, though i seriously do want to get to creating my own ceramic capacitors, those turn out to be deprecated for tesla coils by geek group, who says
they tend to crack under mechanical stresses.
the bucket capacitor, described in the geek group video, looks like the cheapest.
thanks
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watson.fawkes
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| Quote: Originally posted by ElectroWin | | also, though i seriously do want to get to creating my own ceramic capacitors, those turn out to be deprecated for tesla coils by geek group, who says
they tend to crack under mechanical stresses. |
Mechanical stress isn't trivial in oscillating high voltage.
It the main reason that the DC rating for HV capacitors is five times or more higher than the AC rating on the same unit.
To be precise, it's not the mechanical stress that's actually the problem, it's the strain, which is to say it's not the force but the the motion. You
can get rid of the motion by prestressing the capacitor stack by clamping it down. Commercial capacitors don't (as a rule) have such clamps but rather
use alternate means to provide the pre-stress.
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Morgan
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I know this is primitive, but just a little salt water in an LDPE bottle held this nice little spark I made simply by rubbing a paper towel over a
piece of PVC tubing. Salt water makes a decent capacitor. Under it is a piece of 1/8 inch thick PTFE. On top of the poly bottle is a stainless steel
water bottle for the electrode. Probably not the design you are going for but I was really impressed by the simplicity.
Here's some tidbit I came across.
http://www.pupman.com/listarchives/1998/October/msg00790.htm...
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Twospoons
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have you been here : http://4hv.org/e107_plugins/forum/forum.php
Wealth of information, very helpful members.
Film (PE or PET) + Al foil, rolled and submerged in oil, is generally regarded as a good mix of low cost, simplicity and robustness.
[Edited on 23-4-2013 by Twospoons]
Helicopter: "helico" -> spiral, "pter" -> with wings
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