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Re: [TCML] Considering a new coil build...
Hi Travis,
Sounds like you have a few goodies on hand,
20 Awg would be fine, but you could go smaller. Is there a reason why
the h/d is under 4? If you used 20 Awg with a 30" winding length, you'll
get about 860 turns on it with simple single build. Consider 36" of
winding length at which point you could get 1030 turns on it. Of course
with smaller wire (like 22 Awg, you can get 1080 turns on a 30" length).
One thing to consider before going to far with the secondary is the cap.
With the pig, there will be no charging limitations for what you can use
with the coil. But big capacitance gets expensive. Also, due to the
inductances you'll see with your geometry and turns (with toroid
installed), the frequency will be relatively high. This will cause a
real limit on using a large cap as the primary turns will get quite low.
It's best to look at some scenarios first.
The lower you can make Fres, the higher a cap size you can use and still
keep the primary within a decent number of turns (and bigger bang).
Increasing h/d is an easy way to add turns and get the frequency down.
Smaller wire is another way to do it, so obviously a combination of both
is needed. I would like to recommend 34" winding length with 22 awg at
1225 turns (requires a 5lb spool). With your toroid (and since you
purchased two, I'm under the assumption that you would like to use
them), this would get Fres down to about 107kHz and with a .04uF cap
size, 10 turns on the primary. A .06uF cap would tune in a little over 8
turns. A .08uF is 7 turns.
As mentioned, the cap size is something you might want to look at first.
To design an MMC say .04uF is quite a task. For example, to build a
killer .04uF 60kV cap size, then 30 caps per string x 8 strings in
parallel. This is 240 caps and if caps were say $3ea, then $720. It only
gets worse with higher capacitance. You could also build a 30kV type
with 15 caps per string x 4 strings, but reliability gets questionable.
However, that gets down to $180. The problem here is what is available
at the voltage, capacitance, and their construction. Your probably
better off buying pulse caps.
Although you can cut one of the variacs and gap the core for a current
ballast, you might want to consider keeping the variac in tact and
finding an alternative means of ballast. I cut the core on one of my big
30A variacs, but many times wish I had gone a different route. The
ballast variacs rating will be the limit on the power you can process
and if you go over that, brushes will smoke (or worse, windings can short).
Take care,
Bart
Travis Tabbal wrote:
It's been a while, but I miss Tesla coiling. :)
I had purchased a number of useful parts before stopping years back, so
here's what I have and what I'm thinking. I'd love some thoughts from you
guys.
Power source: 10KVA Pig 14.4KV
Control: 3 giant variacs (I forget the rating). I planned to use 2 to
control voltage and modify one for inductive current control. They are
currently stacked with a motor drive for the brushes. I planed to remove the
motor and one of the variacs. The other 2 will remain ganged up and I'll
move the shaft by hand with a big plastic wheel or something. There may be
better ways to handle this bit. I might be able to obtain an old arc welder
for the ballast.
Cap: MMC. To be determined. Ideas welcome.
Secondary: 8" diameter ~30" long. What do people use as a form for these big
coils? I was thinking of drying some Sonotube or other cardboard tube and
coating with laminating epoxy or even just polyurathane. Or I could get
ambitious and try to make a fiberglass tube by adding a release agent to the
sonotube so I can slip the fiberglass off after curing. Considering AWG20
magnet wire. Works out to about 1000 turns. Need a source for that much wire
in one spool. The 11lb spools on EBay and such are too small. I need about
15lb if I'm figuring right.
Primary: Copper tube spiral. Probably .25". Need to run the calcs to get the
number of turns.
Gap: Async RSG. I'm thinking to try to build one with .25" G-10 and tungsten
electrodes. About 8" diameter. Construction tips welcome. Particularly
holding the flying electrodes in place. I'd like to have it be speed
controled, so I can vary break rate around a bit. Even if it's not realtime
adjustable.
Topload: I bought 2 8"x24" spun toroids in a group buy years ago. Still in
the box. It's a shame not to use them. They are so pretty. :)
I also have some RFI filters for the pig I think I bought on the list.
Note that I don't have a machine shop, though I do have a decent tool
collection both power and hand types. So I can't do fancy stuff like
machining electrode holders from bar stock. :) I can drill and tap it with
some acuracy, but nothing too special. No lathe or mill. :)
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