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Re: My new 6" coil

Hi Glenn,

Sit back, this is a long one.

>With a thick clear coat, they are real art.  What ga wire did you wind it with?
>How many turns?  At 6", that must have been quite a bit of wire.

I used 22 gauge with 954 turns.  The winding is 26.5" long.  That was a little
over 1500' of wire at about 3 pounds.

>If I am reading right, a syncronous type gap is the one to build.
>A syncronous motor will stay in step with the 60hz.  I read
>that the gaps should be timed so that they conduct on the
>"side" of the power wave rather than on the peaks so the
>condenser will absorb a full charge.  They also say the rotary
>should be run with a static gap in series.  Have you done any
>research on this?   I was at the local surplus store picking
>up some copper flashing and noticed that they had Bodine 3600rpm
>X 1/3hp motors.  I'll have to go back and see if they are sync.
>At 3600rpm, they probably are.

Ahhhh!  An interesting and very complex discussion can be had on this subject.
Where to begin.  Well first, syncronous gaps THEORETICALLY charge the capacitor
at the optimum point in the electrical cycle.  That much is true.  Buying a
syncronous motor is probably not enough to truly keep it syncronous.  A
syncronous motor is more likely to not lose any cycles.  It will probably drift
a little this way or that.  The people that I have heard that run these
syncronous units use feedback systems, encoder motors, tach generators, etc.,
etc.  This is EXPENSIVE.  It also will only give charging twice during a 360
degree cycle.  Since the capacitor's time constants are much shorter than
1/180th of a second, you are not getting full potential from your capacitor.
Most people have abandoned the use of syncronous gaps.  As a general rule of
thumb, the more charging cycles per second, the better.  If you study rotary
gaps carefully, you will find that power throughput goes up as breaks per second
increase.  I suggest you get the program ROTJIT and check it out carefully.  It
is enlightening in this area.  Keep in mind that the data in this program is
specific to a rotary gap only.  Read its technical manual carfully.  One thing
is evident is this program, the more breaks per second, the better the power
throughput and the easier it is on the system overall, especially the capacitor
and transformer.  The current and voltage bursts are evened out.  The gapping of
the rotary also becomes less critical as the breaks per second increase.

Now I would not have blindly trusted this program.  I had been discussing gaps
long before I laid my hands on ROTJIT.  This program explained observations by
Richard Hull ,Richard Quick, Ed Sonderman, and many others.  Changing nothing
else in their system, the faster they spin their gaps, the longer their sparks
become!  And you can take that to the bank.  Some guys are spinning them in
excess of 6000 RPM.

On those static gaps;  These are used for only 2 reasons.  First, they provide
an excellent place to improve quenching.  By using vacuum or air blast, the
spark can be "blown out" to keep the primary from bleeding back through the gap,
thereby increasing primary Q, hense better ringing.  (The faster spinning rotary
also improves the quenching tto.)  The second reason is to spread out the
voltage drop between many gaps instead of just one or two.  This means that less
wattage is dissipated at one point.  By doing this, the spark gaps all last
much, much longer without maintenance.

Here is an excerpt from the ROTJIT documentation:
------------start quote----------------
At one extreme, assume that if a voltage
gradient of 175 KV per inch appears across the electrodes then breakdown
will occur instantly.  Also assume the traditional value of below 76.2
KV per inch where the electrodes will not break down at all.  In the
band between these two values the electrodes will not break down
immediately, but after some unspecified period of time.
-----------end quote-----------------

There has been suggestions by some that 1 gap spaced at .020" to .030" should be
used per 1000 volts of the transformer.  This keeps the gaps from breaking down
very rapidly.  My experiments suggest that perhaps 1 or 2 less gaps should be
used than this rule of thumb suggests, assuming a 12000 to 15000 volt
transformer.  I suspect that I will have to reevaluate this when I finally go to
a high powered system this spring.  This is something you will have to
experiment with.  Don't forget to count your rotary as 2 gaps when considering
this.

Later,
Scott Myers