Wil,
Your VTTC is probably drawing more than 700 watts.
MOT's are slightly current limited but not much.
You can get more current by removing the shunts,
but you have to be careful not to damage the windings
if you remove the two shunts.
Using a doubler (level shifter) you'll still be running
half wave, but you'll get higher voltage and therefore
longer sparks.
I use the formula:
spark length inches = 0.5*sqrt input watts,
to figure the spark length from a VTTC. If you're
drawing 1200 watts then with a level shifter maybe
you'll get 17" sparks.
It's pretty standard to always want longer sparks
but if you build a 100kW VTTC it can be very
scary sounding when it's running. You can reduce
the input power requirements by running in staccato
(pulsed) mode.
Due to spark loading/tuning/voltage issues, VTTC's have
trouble breaking out of a toroid without a breakout
point, and if you tune it to break directly out of a
toroid it will give shorter sparks
than otherwise. Also running without a breakout
point stresses the tube more. When there's
no spark breakout the primary voltage goes
higher. A toroid should be used, but with a
break-out point.
VTTC current draw should be controlled by
using a higher grid leak resistance value rather than
by limiting the MOT. This will increase the efficiency
of the circuit by reducing the tube conduction angle.
Cheers,
John
-----Original Message-----
From: William Howard <snakeprior@xxxxxxxxx>
To: tesla <tesla@xxxxxxxxxx>
Sent: Sun, May 18, 2014 4:24 pm
Subject: [TCML] Maximum arc length from 700w VTTC?
Dear Group,
I've got a dual GU81M setup running from a 700W MOT (from a 700w oven). I
am not using a voltage doubler so I am running of half a wave (waiting for
parts).
My tank is 100pf 20kV. Windings are 20 feedback 60 primary 1mm wire.
Secondary is about 800 turns on 60mm form of .5mm wire.
I get 20cm arcs and the MOT heats up and trips out my 10A board after 1
minute. I run 3 100W fans and a 12v 20A filament transformer off the same
board.
I wanted to know what is the biggest arc if properly tuned I will get out
of 700W?
Also I noticed not placing a arc out point on the topload tends to cause
arcing on the primary side. Why is this? If properly insulated could I run
a toroid? Or would it blow my mot up?
Also if I wanted to current limit could I use a ac capacitor in series with
the hv out? Is there a calculation for capacitance and current flow or do
I need a ballast.
Here is a video of it running:
http://m.youtube.com/watch?feature=youtu.be&v=N9l8mqj8zZE
I'm a novice and this is my first ever tc.
I have noticed one thing tho I seem to always want bigger arcs is this
normal or will I end up building a 100kw unit and still be unsatisfied?
Cheers!
-Wil
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