Re: More Tuning/Debugging -- Success!

Tesla List wrote:
> >From ccurran-at-execpc-dot-comThu Aug 29 22:52:41 1996
> Date: Thu, 29 Aug 1996 20:18:54 -0500
> From: Chuck Curran <ccurran-at-execpc-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Re: More Tuning/Debugging -- Success!
> Hello All:
>         First a Thank You to Malcom and Jim for their thoughts on likely areas
> to look for my system problem.  I believe I have located the "BUG", it
> was the rotary gap.  One of the two pillow blocks supporting the main
> shaft had never been fully tightened during the original assembly.  They
> came looser and created a significant problem.  Yea, dumb as a bag of
> rocks is an acceptable comment!  Knocked the Lovejoy shaft coupling back
> about 3/8" along the motor shaft.  The good news is no real damage was
> done, except for needing a total realignment.  That is now done and I'm
> in the re-assembly stage of activity.
>         My original spark output was not real good, when power input is
> considered.  After putting in the new analog meters I beleive that I had
> about 4000 watts in and about a 6 foot spark out max .  I examined my
> primary/secondary coil placement visually and the first or lowest
> secondary turn is exactly even with the extreme top of the primary
> copper tube.  I never had even a hint of an arc from anywhere along the
> secondary to anything else.  I feel I could afford to raise the primary
> for a small increase in coupling, without smoke occurring!.  I designed
> the primary so that I can raise it with nylon spacers.  My first thought
> was to fire things up again and verify I'm back to where I was with the
> repaired rotary, then raise the primary 1/2" for some more coupling.
>         I would appreciate any comments on where others have found the primary
> secondary coupling point to work out the best,relative to the bottom of
> the secondary.  How far up?  I realize every system will be
> significantly different, but comments would still be of interest.
> Thanks in advance for any comments
> Chuck


Glad to hear you didn't have a catastophic failure on your rotary!!
You may want to measure the coupling coefficient of your coil and then
adjust it to be closer to a "sweet spot". You'll need a signal or
function generator and a pair of bright LED's soldered in parallel back
to back (cathode of one to anode of the other). A frequency counter will
improve the accuracy of the measurement. With your coil normally
positioned with toroid attached, disconnect the secondary ground, and
connect the functtion generator to the base lead through the LED's.
Disconnect any safety protection inductors or bypass capacitors. You
should only have the tank capacitor, primary, and sparkgap connected.
With the sparkgap OPEN, increase the frequency of the signal generator
until the LED's lights the first time. Adjust the ouput level of the
generator so that you can clearly see the "peak" brightness. Record the
frequency. This will be the center or "ring down" frequency (FC).

Now put a jumper across the sparkgap. This should place your primary in
series with you tank cap. Slowly reduce the frequency of the signal
generator until you see the LED's light. Record the frequency (FL).
Increase the frequency until you see the upper peak (FH). The coupling
coefficient can now be estimated as (FH-FL)/FC. Earlier work by a number
of people on this list has shown that certain coeffients of coupling
will result in better performance. These correspond to points where the
beat frequency (FH-FL) correspond to an integral number of cycles of the
center frequency. The corresponding values for k for these "sweet spots"
are 0.28, 0.22, 0.18, 0.153. 
You can also do it by trial and error. From a practical standpoint, you
should be able to slowly increase the coupling coefficient until you
begin to see evidence of overcoupling. After changing coupling, always
carefully increase operating power levels while observing the coil in a
dark room for any evidence of flashovers or corona where not wanted.
Overcoupling generally shows up as flashovers from the top part of the
coil to a lower portion, or to the primary or strikerail. Also, if you
raise the primary too high you may also see flashovers between the
innermost primary turn and the secondary or from the top of the
secondary winding to either the primary of the strikerail. The former
can be protected against by adding some polyethylene sheet between the

As you increase the coupling, your gaps will take more of a beating. I
have a configuration similar to yours, and have my primary about 1"
higher than the bottom of the secondary winding. I'm seeing a k of about
0.215. The epoxy-coated secondary runs very nicely at this level with no
evidence of any breakdown/corona.  If you can reach 0.21 - 0.23 range
and can keep your sparkgaps quenching you'll have a hot performer!

Safe coilin' to ya!

-- Bert --