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Re: Scroungein' (fwd)
Hi Christopher, I added some comments below:
> Original Poster: "christopher boden" <chrisboden-at-hotmail-dot-com>
>
> Due to constant design changes and new ideas....not to mention a
> through flogging from Sam ;-) we are trying two seperate ideas.
>
> Project 1
> Design Goal: To produce 5' discharge from a 120VAC <20Amp input.
> Secondary size: 25" X 4"
> Secondary winding: 26 AWG? (any ideas?)
> Secondary form Schedule 40 PVC 4" pipe with glued on endcaps
> Winding method: Lathe....BIG lathe.
> Primary winding: 1/4" soft copper tubing
> Primary form: Flat helix?
> Primary size? Number of turns/spacing????? any ideas?
> Caps: Where can we get some? What size do we need? How long will they
> last? We need rock-solid-reliability.
> NST: 15KVAC -at- 30mA
> Variac: ? what size do I need 20A?
> Spark Gap:Static (no shrapnell) possibbly the Quick model
> Torus: ?? biggest possible?
> Anything else? What am I forgetting?
The secondary sounds ok. The cap size for your xfmr would be about
0.005uF, and the primary will need about 19 turns. The xfmr at 30mA is a
bit low for 5' discharges. I would consider at least 60mA and make the cap
0.01uF (primary then is about 14 turns). You should then get about 40 to
50 inch sparks. I would go with a 26pF top capacitance (26" x 4" toroid).
If you need rock solid reliability in a cap, then I would suggest a
manufacturers cap. Of course you do realize that nothing is rock solid in
a TC, especially caps?
> Prodect 2
> Coil Name: Thor
> Secondary size: 12" X 5' twin secondaries
> Secondary wire: 18AWG
> Secondary Form: 2 1X5" Sonotubes 1/4" Cardboard tubes
> Primary Wire: 3/8" Soft copper tubing
> Primary Size: ?
> Primary Form: Flat Helix
> Power Supply: 20KVA Pole Pig (Supplier?)
> Spark Gap: 4 Pole Async Rotary in a 1.5" Lexan Enclosure (ideas?)
> Control Circuitry:?? Ideas?
> Caps: Big... Ideas? Suppliers? MMC?
> Possible "Magnifier" setup insted of twin secondaries?
> Design Goal: Biggest possible discharge:
Now this sounds like a fun project! The sonotubes will work fine. Just
make sure you seal them inside and out. I like to use a thin absorbing
polyurathane to prep the coil, then later use spar varnish for the outer
coatings (flexible and goes on thick). When purchasing the tubes, measure
the diameter because they vary quite a bit from tube to tube. 18awg is a
good size to use for this coil size, but you'll need about 20lbs. per
coil. If you can get 20lb spools then it will be easy. If not, you can
drill a small hole and run both wire ends inside (sand, twist, solder,
snip, hot glue - works great). Then keep winding. You'll probably leave a
couple inches unwound on each end so you'll end up with about 1260 turns
if close wound (56" length).
It's difficult to guess your xfmr voltage/current, so I'll go with a
standard 16.8kv, 893mA (15KVA). If you matched your cap size to this xfmr
size, then you would need 0.141uF. The problem with this is 40J. Way too
much energy. So you MUST NOT go with a matched xfmr sized cap, but with
something less (way less). I'll cut it down to 12J (still a lot). This is
4 times less Joules and thus 4 times less capacitance. 0.04uF is 11.3J.
This would equate to 15.7 turns on the primary. I would go with 100kv
rated professional caps if I were you. Your cap is going to see 50kv quite
often at full voltage. These are big coils and your talking about 20KVA
potential. This equates to big sparks. Really big sparks if it doesn't
burn up first. You'll definately need a high grade rotary gap. You'll also
need to externally ballast the pig with some large inductance. I would
recommend big variacs with this (40 to 50A type). These are not easy to
come by. Also, the 20KVA xfmr is not really necessary since you can push
these transformers quite a bit above their ratings. A 10 or 15 KVA will do
just fine for your set up. The toroid size I would recommend is 67pF (12"
x 63" toroid).
> Both coils will be housed in a dediated "High Voltage" room.
> Room dimentions : 70' Long X 32' Wide X 23' High
> Raised wooden floor (concrete floor 3' below for 26' ceiling height)
> can be remooved if needed.
> Brick walls 3-5' thick
> Dual RF dedicated grounds to 10' Ground rods on 0AWG ACSR conductors.
> Concrete ceiling with 3' X 6" I-Beams every 3'
Sounds wonderful! I wish I had that kind of space.
> Power supply (Mains): 480VAC -at- 500Amp 3Phase to 100 KVA Stepdown (220)
>
> Control room will be next to the HV room with interlocks preventing
> the doors to the HV room being opened while the mains to the TC are
> energized.
> Both coils will require a key to arm the system and a button to be
> held to power the NST/pole pig.
> Thor will require 2 Keys 6' apart to arm the system and a button to
> arm the Pig.
Safety will definately be important with these coils. The 2 key idea may
be a bit more than I would go, but hey, to each his own. Whatever you do,
make sure you have a fire extinguisher around, seriously. I keep one handy
when running my coil (12.5" x 44", 10KVA, sonotube coil). As far as
control panel, I would use a low voltage setup which energizes the AC line
via relays or whatever. The current capability will let you know what you
can do. Make sure you use dual-trip breakers so that both legs of the
mains break at the same time.
> There may be a Faraday cage in the HV room for viewing, if this can
> be done with ABSOLUTE safety to persons/ cameras inside...any ideas?
I would just stay far far away to NOT get hit. You don't want to get hit
by this coil. A faraday cage is a good idea if you plan to be in stike
range.
Well, I could write for hours but that's all I had in me tonight. Lot's of
good questions. However, I'm better at a piece at a time than all at once.
Anyway, best of luck to you,
Bart