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Re: status report
Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>
Hi Justin,
Congrats on getting the coil operating! More comments interspersed.
Tesla list wrote:
Original poster: Just Justin <rocketfuel@xxxxxxxxxxxxx>
It lives!!!
I finally got to give it a go today and it's working! Such a great feeling
after all of this research and fabrication.
It's not working perfectly of course, and these are some of the issues
I'm having:
-Primary to Secondary arcing. I was able to stop this by raising
the secondary
but I'm afraid it's maybe too high for proper coupling. The primary inner
radius is about 1/2"-3/4" wider than the secondary (which is 2"
radius, 4" diameter).
The secondary starts about 2" above the primary now, although
there are a few
widely spaced turns that reach down to about 1" above the primary.
1" would be less sensitive to pri to sec arcing. Currently, there is
about 2" proximity because of the height differences, so the primary
is likely initiating to the lower spaced turns of the secondary. I
never space wind the lower end of the secondary myself.
-Tuning. I was noticing that it really wanted to arc primary to
secondary at about
5-6 turns, but didn't have the problem with less or more turns, so
intuitively this
seemed like it might be close to the tuning point. I'm going to
try using WinTesla
or another program to find out where I should be, given my components.
I did of course use Javatc to take a look. Your coupling is actually
low at 0.075. Your coil should run fine with the primary even with
the secondary (0.15 k, which is a decent k to start, not necessarily
a k you want to stay with). However, you may still need to get rid of
an inner turn to gain some pri to sec clearance. As it is now, it
should tune in at about 6 turns. I've got a similar coil I run with a
12/60 as well. Very similar actually and my primary (also similar) is
about 0.25" below the secondary.
-Spark gap. I'm not sure about the widths on the segments of my fan
blown spark gap.
Safety gap is set correctly and does fire occasionally when the
variac is 100%.
The total width is of course important, but different sized tubes,
material, environment, etc.. will have different total widths. You
can just run the spark gap itself with only the transformer to set it
properly (consistent steady firing).
-Toroid. I used Al tape to connect the Al dryer ducting (4"
diameter) to a 15" pizza
pan. I can see sparking around the tape when the sparks break out
to a grounded rod,
so it seems that the tape is not conducting terribly well.
Actually, the tape is conducting fine. The sharp edges of the tape
are creating breakout points, and you'll notice the breakout will
favor those edges. That's why it's nice to a have as smooth a toroid
as possible (to have control of the breakout).
-RF ground. I'm running in a warehouse with a concrete floor
currently, so the ground
is just a piece of copper lying on the floor. Haven't looked for
sparks there yet.
You might want to put down a counterpoise of some type (something
more than a piece of copper).
Take care and good luck during your tuning!
Bart
Specs:
PSU: 12kV 60mA NST
Spark gap: 6 segment 1" diameter x 6" length copper tubes, fan cooled/quenched
Cap: 30nF Maxwell pulse cap
Pri: 11 turns 1/4" copper tubing. Inner diameter: 5-6"
Sec: 18" of 24 guage magnet wire
Toroid: approd 4" minor diameter, 17" major diameter
Woohoo!
Justin