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Re: The demonic Rotary spark gap

In a message dated 99-04-19 09:36:51 EDT, you write:

<< Original Poster: "christopher boden" <chrisboden-at-hotmail-dot-com> 
 
> Alright....I yeild. I shall attempt to build a rotary gap.
 
> I've seen a design for one on the Tesla Research site...I believe 
>it's in the pics for the Model 8 or 12. It looks like a motor 
> spinning a 10 or 12" phenolic disk with about 8 electrodes mounted 
> around the periphery. There's an electrode with terminal at either 
> side on the back (motor side) of the disk. And a shorting bar with 
> electrodes across the front of the disk.
> This looks to be the simplest type of rotary I've seen and I can 
> build one (after finding the right electrodes) in a couple hours.

Christopher,

You can make one simplification if you'd like, and that is don't use
the shorting bar, just use the two gaps on one side, rather than the
four gaps using both sides.  This is what I'm doing on my sync gap
coil.  I orginally planned to use the shorting bar with 2 gaps on each
side, but then i was too lazy to finish so I'm just using the gaps on
one side.  For higher powers, it's very advisable to use all four gaps
with the shorting bar, to cut down on gap erosion and help the
quenching.

> Here's the rub...
> 1 is it syn or a-sync? Which is better? Why?

One is not better or worse than the other.  They both have their
advantages and disadvantages.  Generally speaking, a sync gap
system is much less tolerant of design errors.  With async, you 
can simply vary your break rate to compensate for things.  I've
posted a lot about this issue in the past, it's in the list archives.

> 2 Electrode material? Brass, Tungsten? (For the 4th of july I was 
 thinking Magnesium ;-))

Tungsten is the best.  Stainless is not so good.  Brass is not so good.
I've heard that copper is OK.

> 3 What size disk, electrode, spacing, how many...etc ad nauseum..

This will all depend on the power handling capability needed, the
relative cap size, etc.

> 4 What effect will speed have on coil operation...faster/slower?
 
A higher gap speed will draw more power, and give somewhat longer
and brighter sparks usually, with a given cap size.  I prefer a larger
cap, with a lower break rate and have gotten better efficiency that
way.  Most folks (99%) use an non-sync rotary not a sync rotary.

> 5 What is the target speed for the motor? Should I make it a DC servo 
> with tight speed control? Or a constant speed AC and just plug it in?

You don't need a servo.  For a non-sync rotary, a universal motor will
permit easy speed adjustments as needed.  For a sync rotary, you'll
need a sync motor, or you can modify an induction motor for sync
operation by grinding flats on the armature (squirrel cage rotor).

John Freau


> 6 Will 2" Lexan be a good shield ? Should I have a single plate as a 
> shield or totally enclose this and have an air pump to keep the 
> oxides from tinting the glass.
 
> The Coronaphile
 
> Christopher A. Boden  >>