From: richard.quick-at-slug-dot-org (Richard Quick)
Date: Tue, 12 Dec 1995 02:23:00 GMT
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Quoting gcerny-at-ix-dot-netcom-dot-com (Glenn Cerny):
> Thanks for the lead on the motors for a rotary.
> I will be ordering one of them. Guess that building
> one myself is the way to go. I do have a friend with
> a complete machine shop out back and can make use of it
> whenever. He is a nice guy, but always makes a multi-day
> project out of whatever 2 hour project I come over with.
> In other words, he is a good friend that has really followed
> my coil project with great interest, but is a super
> perfectionist and insists that things be done his way in his
> shop. I don't have a problem with being as close to perfect
> as possibly, but I don't think that the shop should have to be
> rebuilt every time someone walks in. Enough about my pal Mark.
These motors are good quality. This is nearly identical to mine,
if not a bit better. Plenty of torque and plenty of velocity.
Smaller motors can tend to "drag" when you throw the works into
the coil but a motor like this has plenty of inertia to overcome
voltage drops etc. The ball bearing design is commercial duty.
And the coils are wound with heavy enough magnet wire that even
an occasional arc through the "guts" from a kickback/flashover
will blow the $3.95 full wave bridge without hurting the motor.
> While I have your ear, found some interesting things while
> toying with my 4" coil. Its wound on acrylic with 22ga at 19"
> and embedded in behr50. Being a great radio hack, I took my
> function generator, freq counter and scope, and made a test of
> what was what with this coil. At 147. Khz I found a BIG
> resonance peak on the bare coil that was a PEAK. While tuning
> off a small amount, the peak diminished greatly.
> I also noticed that the coil was greatly disturbed in waveform
> amplitude by any object brought near while tuned off peak.
> When the coil was peaked, it made little difference. Note that
> this is for the bare coil sitting on my bench without any top
> capacitance. My function generator and counter were connected
> to the bottom or the coil, and the scope to the top.
This was the problem! You simply hit a resonate frequency, of
which there are many in the coil. Most are subtle, a few (like
the 1/4 wave peak) are not. The peak on the scope is registering
because of resonate rise in the winding which is picked up by the
probe connected to the top of the coil. This is not really the
best way to examine the electrical characteristics of the coil
using these valuable diagnostic tools.
What I prefer to do is to common ground the function generator,
scope, and frequency counter. I put a 1K resistor in series with
the output of the function generator and then feed the signal
directly into the base of the coil. I make my connection to the
frequency counter on the function generator side of the resistor.
On the coil side of the resistor I hook up the O'scope probe (or
in my case I just connect the center lead of the BIN coax).
With this setup the O'scope shows a drop in voltage when the
function generator output matches a resonate frequency in the
coil. The flatter the line in the scope, the more efficient
(higher Q) the resonate node. This is called "grid dipping".
Because the coil will show a very high impedance to non-resonate
frequencies, your dips will be quite noticeable. It is not
unusual to find several resonate frequencies, or dips, in a high
Since the same basic setup (grounded cases, 1K resistor in series
with the function generator output) is also used to "grid peak"
the primary circuit; I built a "little black box". I can plug the
BIN coax jacks leading back from the box into the diagnostic
equipment. Inside the box all of the ground leads are commoned,
and a 1K resistor is wired in series with the function generator
output. The frequency counter is connected before the resistor,
the O'scope is connected afterwards. The face if the "little
black box" has two, single conductor, female banana jacks in the
face: one red (signal) the other black (common ground). I have
two alligator clips soldered to a short (say three feet long)
lead wire with the male plugs soldered on the end. When grid
dipping secondaries only one plug is jacked into the box. When
grid peaking a tank circuit (where common ground is also
connected to the circuit) I jack in the second lead wire.
> Equipment used are a TEK 2235 scope, TEK CFG 253 generator, and
> a TEK 250 counter. I found these observations most interesting
> due to the sharp peak, the effects of obvious capacitance, and
> the low frequency that the peak occurred considering this is a
> bare coil.
You did not include the secondary coil physical characteristics
(coil diam., number of turns, etc.) so I can't really say what
you hit: but at both very low input powers (like from diagnostic
equipment) and at very high input powers (as in overloaded from
excessive coupling) secondary coils will exhibit 1/16, 1/8, and
3/16 resonate nodes. I have even seen some that looked like 32nd
fractional wave resonances.
I believe you said you have a copy of Tesla's COLORADO SPRINGS
NOTES. Look at the photo on page 326. I count nine different
coils all resonating on energy induced or base fed by one narrow
band signal generator. I also see two RF transmission lines...
There is more here than meets the eye! You picked up a hint of
this on the scope.
... If all else fails... Throw another megavolt across it!
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