RE: Rotary Gap Construction? (part two)

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Matt Woody Meyer by way of Terry Fritz <twftesla-at-qwest-dot-net>" <meyerml-at-stolaf.edu>

first and foremost- thanks to all of you for your help with my SRSG
questions.  I'm still a bit new at coil construction and you've all been
most helpful.  I'm sure I'll have several more questions throughout the
engineering process. :)

Thank you again so much for all your help... the gap was the part of the
coil that I didn't quite understand last time around, but I think I've got a
much better grasp on it now.  Still, a few more questions:

Again, the caps I'm using are both rated at .018uF, and are rated up to
3600W apiece and will be wired in parallel, so C1+C2=TC=.036uF total
capacitance of the take circuit.  The primary is fed off of two 15000V 60mA
transformers (I think this is what I'll go with, else it will be 1 15kV 60mA
and 2 12kV 30mA transformers.  I understand that the minimum firing rate
that I'd like is at least 120Hz (120 fires/second)... do I want to go higher
than this, or will this achieve maximum voltage in the primary circuit?

How many gaps do I want to use?  I know that I will need a minimum of two
using a SRSG, but I've seen several people use four.  Probably like
everybody out there, I'm striving for maximum arc length, so is two or four
better?

My original idea was to hook up the coil using two outlets, one to power the
motor, the other for the coil... however, I see that this can goof up the
tuning in consecutive runs (gap may not be aligned with the current).  What
I'm thinking of doing now is wiring the circuit so it only runs off of one
outlet.  On my "control panel", I am thinking of setting up two switches...
one for the motor (running separate from the variac) and then the HV circuit
(running through the variac).  The motor circuit would be controlled
independently of the HV circuit, but must start up first in order to apply
the HV circuit.  This works, right?

Lastly, I've heard that I should use a bleeder circuit in the tank so as to
discharge the capacitors while the system is off... does anybody have any
suggestions for this?  I'm still young (21), and I really don't feel like
dying for some time, especially after dropping thousands of dollars on this
education (practically sold my soul to St. Olaf) :)

Thanks again, I really appreciate everything!  Also, thanks for the
protection circuit suggestions. :)
><>Matt Meyer

ps: please feel free to e-mail me directly about anything.
meyerml-at-stolaf.edu

><>  ><>  ><>  ><>  ><>  ><>  ><>  ><>  ><>  ><>  ><>  ><>  ><>  ><>
Matt "Woody" Meyer         Ellingson 120       507-646-2883 (CUTE)

St. Olaf College Physics Major
St. Olaf Admissions Tour Co-Coordinator
2001-2002 Ellingson Hall Residence Life Junior Counselor
><>  ><>  ><>  ><>  ><>  ><>  ><>  ><>  ><>  ><>  ><>  ><>  ><>  ><>

-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Thursday, March 21, 2002 5:39 PM
To: tesla-at-pupman-dot-com
Subject: Re: Rotary Gap Construction?


Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<Esondrmn-at-aol-dot-com>

In a message dated 3/20/02 4:19:32 PM Pacific Standard Time,
tesla-at-pupman-dot-com
writes:


>
> Hello hello,
>     My last coil used a static spark gap with marginal results at best, so
> I'm
> planning out a means of building a rotary gap.  Since many of you seem to
be
> experts in construction, I was wondering if anybody would mind throwing in
a
> few engineering suggestions.  I'm open to anything, and have a substantial
> budget to work with.  I'm looking around for 2400-4800rpm variable motors
> (most of them I can just control the angular velocity with a variac,
right),
> I'm assuming that this should be enough if I have about 6-8 presentations
> every rotation.
>
> What I'm having difficulty with, as of now is:
> 1) My idea calls for using a conductive circle with bolts attached as the
> electrodes.  I would then have two stationary electrodes (one at the 9:00
> and one at the 3:00 position).  The problem I see in this is that the
> charge, as it passes through the metal disc, will also partially hit the
> motor.  This is bad.  Is there a way to, say, using electrical tape, wrap
> the circle around the center with tape, or would this not work?
>
> 2) This would be slightly more complicated, but I suppose I could use a
> belt, run off the motor and connected to the electrode plate, thus the
motor
> would be insulated from the electrode plate.
>
> 3) I'm also worried about the heat from the sparks melting the bolts... I
> don't think those viewing the demonstration would appreciate a "hot dross
> bath"... is there something (like tungsten?) that I should coat the
> electrodes in?
>
> As of now, I'm looking at the following for my setup:
> a combination of the following transformers:
> One 15kV 60mA neon
> Two or three 12kV 30mA neons
> Combination of the above... suggestions welcome here too.
> Everything through a 20A 0-120V variac.
>
> 2 .018uf capacitors (in parallel)
> 12 turn flat primary spaced 1/2"
> 8" x 32" secondary, 24AWG topped with a 14x4 aluminum toroid (may build a
> larger toroid).
>
> The circuit is in the simplest design... Vac through primary transformer
in
> parallel with main spark gap. (two chokes to protect transformer).  Tank
> circuit standard.
>
> Thanks much, I'm still fairly new to coil construction, so I apologize in
> advance for my ignorance :).  Strangely enough, none of the professors
here
> have had much HV experience, so I'm more or less on my own with this
> project.
>
> ><>Matt Meyer
> meyerml-at-stolaf.edu
>
> ><>  ><>  ><>  ><>  ><>  ><>  ><>  ><>  ><>  ><>  ><>  ><>  ><>  ><>
> Matt "Woody" Meyer         Ellingson 120       507-646-2883 (CUTE)
>
> St. Olaf College Physics Major
> St. Olaf Admissions Tour Co-Coordinator
> 2001-2002 Ellingson Hall Residence Life Junior Counselor




Matt,

Your coil project and design sound fine.  I would not recommend using chokes
for transformer protection.  They do more harm than good.  I would suggest
instead using Terry's protection system, it seems to be popular.  I use only
resistors in series with the H.V. supply lines, between the transformers and
the spark gap.

For the synchronous rotary, you really need a synchronous motor.  Either
manufactured that way, or modified armature to make is synchronous.  The
rotor
itself does not need to be conductive.  It is easier to manufacture if it is
not.  Mine is 1/2" thick phenolic with four brass electrodes with tungsten
faces on them.  I bought the motor, rotor and electrodes from Bill Wysock
(on
this list).  Then I made a mounting base and electrode holders and completed
the project.  You can see this gap at my web site:
http://members.aol-dot-com/esondrmn/index.html

Good luck, Ed Sonderman