Re: RSG spacing.

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: FutureT@xxxxxxx 

In a message dated 4/9/07 3:29:09 AM Eastern Daylight Time, 
tesla@xxxxxxxxxx writes:

> Greetings everybody.
>    Ok, I just finished a Synchronous rotary spark gap, and I am
> having some difficulties getting it in phase (the motor is a modified
> induction type, and it is salient pole, and plenty powerful).  I
> adjust the phase by rotating the motor in it's mount, I got it "dead
> on" in my test rig with an OBIT and a salt water cap, but using my
> MOT array, it seems to usually be slightly out of phase, giving a
> periodic surging, about every 3 seconds or so which I can make much
> better by adjusting the phase, but rarely get perfect.



Scott,

the periodic surging is very strange.  It sounds to me like the
gap is not actually running synchronously for whatever reason.
Maybe the MOT system draws so much power it's pulling down
your line voltage below the voltage at which the rotary can lock
into sync.  But it's possible that your gaps are so wide, that
they can barely fire.  Your gaps are probably much too wide at
0.3cm on both sides.


The surging

> went away for a while, I believe because the fast start slid it
> slightly in its mount, and it was good for several runs, giving
> really good arcs.  Any tips for fine adjustment would be appreciated,
> but that is not actually why I am writing (and no, I do not really
> have time or money to build an electronic phase adjuster right now,
> but if you have plans for one that can handle a .5 HP 1800 RPM motor,
> I'll gladly tuck it away for later!).


Well I have the schematic for the electronic phase controller at my
website at

<http://hometown.aol.com/futuret.page3.html>http://hometown.aol.com/futuret.page3.html.

This controller will work with any motor.  Just adjust the phase capacitor
value to about 200uF or more or whatever is needed to give the
5volt max rise above input voltage across the motor at some
phase variac setting.  You don't want the voltage to rise more
than 5 or 10V higher than line voltage across the motor at
any variac position.  If you get no resonant rise, then use a larger
capacitor value.  the needed value can be somewhat critical.

>    My question, primarily, is why does the rotary gap spacing have
> to be so close, as is suggested on many websites.  I can understand
> this with an asynchronous, as the firings are all at different
> potentials so it would need to be tight for the lower potential
> firings, but with an SRSG, I would imagine for best quenching it
> would be smart to leave the spacing wider (although this makes
> phasing more difficult).


The concept of widening the gap to help quenching doesn't really
work.  You have to make the gap close enough so the coil runs
smoothly.  The rule is; the more power you're using, the wider
the gap spacing can be.  Also the more voltage you're using,
the wider hte gap spacing can be.  Always tune for smoothness.
Usually the gaps will not be more than 0.020" in any case.


Some people put a static gap in series, or

> have the electricity pass through 4 gaps on one disk, but it would
> make sense to me (I am not an electrical engineer however, just an
> MET in training) that since your "Q" goes down slightly with every
> gap, that you would want as few as possible, meaning 2 gaps (in
> series, as many as you like in parallel) would be best.


If you put gaps in parallel, one will fire first and take all the power,
so there's no advantage to putting gaps in parallel.  Yes, a couple
more gaps in series gives higher losses (lower Q), but in reality
it usually can't be noticed in the coil's performance.  But if the
coil needs the extra gaps to quench..... then that's much more
important than any losses involved.  The rule:  Quenching is
important, losses are less important.


I have run

> my gap, on 4 MOTS (I keep burning out the flanks, so I cut back for
> now from 6 to 4) very wide, about .3 cm on both sides, and closing
> the gap distance seemed to make phasing easier, but did not help arc
> length any.  Anybody care to shed some light on this?  Thanks.


If you run wide gaps, you'll get terrible results (rough running).
The gaps shouldn't be more than 0.020" wide, and you can try
them closer.

> Sincerely,
> Scott Bogard.
> P.S.  Am I correct in my assumption, that what the "Q" actually is,
> is the height of the resonant voltage rise (the huge spike on a
> voltage over frequency graph).  People throw around that little
> letter a lot, and it is hard to find a concrete definition, they are
> always either too complicated to understand for somebody with my
> background, or too simple to help me understand what it technically
> is, so that is my best guess (derived from both the complex and basic
> definitions).  Thanks a bunch.


Q represents the ratio of reactive energy to resistive losses.
Usually not something to worry about very much.   Other factors
tend to be more important.

John



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