Optimal Quench Tests

To: tesla-at-poodle.pupman-dot-com
Subject: Optimal Quench Tests
From: Tesla List <tesla-at-stic-dot-net>
Date: Sun, 30 Mar 1997 22:37:15 -0600
Approved: tesla-at-stic-dot-net
Subject: 
        Optimal Quench Tests
  Date: 
        Sun, 30 Mar 1997 19:56:25 -0500 (EST)
  From: 
        FutureT-at-aol-dot-com
    To: 
        tesla-at-pupman-dot-com


All,

I set up a small 360 VA (12kV, 30ma neon) coil for quench testing. 
Steady
first notch quenching was achieved at k = .11, k = .12, and at k = .18,
spark
length was 36". 

Specs are as folllows;     Primary is #12 standed pvc ins, 15 degree
inverted
cone, tapped at 33 turns  (448uH).  C = 0.007uF, polypropylene. 
Secondary is
6- 1/2" by 23" plastic form wound with #28 formvar, L = 108mH.  Resonant
frequency without toroid is 130 kHz, with toroid is probably about 100
kHz or
so.  Toroid is 4" by 17" aluminum dryer duct.  Gap is a 120 BPS
synchronous
12 point super-series quench rotary (the spark snakes through 12 gaps
during
each firing).  There are 12 spinning and 12 stationary electrodes, all
electrodes are 1/8" dia. stainless steel.  Motor is 3600 rpm, 1/10 HP
salient
pole design with ~7" rotor.  Six of the gaps are "offset".  Maximum
voltage
applied to the Tesla coil transformer is 125 volts.

First test:       Secondary was set at 2 1/4" above center of primary, k
=
.11, spark was 36"  and quench occured at first notch.  Quench was
monitored
using a solid state o-scope in the next room with an antenna type
pickup.  To
obtain the 36" spark, it was necessary to attach a small aluminum foil
"bump"
to the toroid to force it to emit from that point only.  Without the
bump,
multiple streamers formed but were shorter.  Ringdown was near-linear,
and
took about 40uS.  First notch quenching was achieved for 2 to 3 foot
spark.
 At lower power levels (1 foot spark length), the gap quenched
intermittently
on 1st notch since the coil was not loaded enough, and too much energy
reflected back from the sec. to the primary. 

Second test:       Sec. was set at 1 3/4" above pri, k = about .12,
results
were the same as in first test.

Third test:      Sec. was set at  1 1/2" above pri, k = about .13,
results
were similar, but gap quenches mostly on the first notch but
occasionally on
the second.  Spark may have appeared slightly stronger, but still just
reached 36"

Forth test:     Sec. was set at 1 1/8" above pri, k = about .15, still
quenched on first notch most of the time, but a second toroid streamer
formed, so sparks were shorter.   Probably a slightly larger toroid
would be
helpful.

Fifth test:      Sec. was set at 1/4" above pri, k = about .18, quenched
at
second notch, and the multiple streamers were strong, but not quite 36".
 Racing sparks started to appear on the secondary at this k value.

Sixth test:     Sec was set at 9/16" above pri, k = about .18, quenched
steadily at first notch.  Here I no doubt "hit" the exact (.18) needed
magic
k value.  In some of the above tests, I no doubt "passed by" some of the
exact magic k values, I'll have to go back and check in smaller sec.
height
adjustment increments of 1/4".    No racing sparks occured.  Multiple
streamers were strong but did not hit 36" but hit 35- 1/2" one time.  A
slightly larger toroid would probably reduce the number of streamers and
give
a longer spark.

The next test will be to try for k = .22, but to accomplish this, I will
have
to lower the secondary 1/2" or so below the primary.  Failure to quench
here
on the first notch will cause my secondary coil to be destroyed by
racing
sparks.  The primary/secondary as presently physically configured,
cannot
couple tighter than k = .22.  I may also try using a smaller capacitor
with a
higher rotary break rate for comparison, but this may destroy the neon
transformer.     Comments welcomed.

Towards optimal coiling,

John Freau