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Re: Rotaty popping, (Was Re: commercial cap failure)



> Original Poster: "Jon Rosenstiel" <jonr-at-pacbell-dot-net>
>
> <snip>
> Ed,
> Jon Rosenstiel here. We corresponded a few times via email, ( Re:
> Sonderman's Saga). Your above comment in regards to explosions or
backfires
> in the rotary made a light go on. With my system, (6" x 28" secondary,
5kVA
> 14400V pig and 120bps srsg), I notice every once in a while, (particularly
> above 230Vac in), a sound like a car door slamming shut. I usually shut
down
> and check for visitors, but never find any!
> Other than the infrequent car door slamming sound my coil runs fine,
always
> nice and smooth, but  I have this nagging feeling  that something's not
> quite right. I think that I'm getting too much "inductive kick" from my
> welder ballast. The reason's that I think I'm getting too much "kick" is
> that:

> 1. Any amount of parallel resistive ballast kills coil performance.

Are you putting the resistors in parallel with the inductive ballast?
If so, try putting around 0.25-0.5 ohms in series with the ballast and
see if you still have the same problem.  This will help take out some
of the inductive kick and produce a smoother running coil.

> 2. Coil performance is better with the welder on "low" range. Let me
> explain; The welder that I'm using for ballast is a old Sears 185A model
> that has a low and high current socket on the front panel, (along with the
> variable inductance core).  I would think that I would be able to input
more
> current, (and get longer sparks), using the high range socket.

On the lower current range (higher voltage), you have more turns around
the core of the transformer.  This in turn provides more current limiting,
thus putting the inductive ballast closer to the range that you need.  The
same thing would happen if you used say 100 turns around a core and needed
150 turns for your ballast inductor around a gapped toroidal core (such as
from
a large variac).

> This is what
> happens when a Jacobs ladder is connected.  I figured the same would
happen
> with my coil connected. It doesn't. My coil has best output on low range.
> When I select high range the input current stays the same and to get the
> same sparks I have to turn up the input voltage.


The Jacobs ladder works better because you need raw current for it to
produce longer, hotter sparks.  On the lower current setting of the welder,
you have less turns (lower voltage) and less inductance or current limiting
capability.  This is in some contrast to the tesla coil that needs a certain
amount of inductance (to limit the current through the transformer) to
enable the gap to quench.  If you don't have enough inductance on the
primary side of the transformer, the gap won't quench well.  In this
case (same as when you try it on the high current side of the transformer),
you will have what I called "arc follow".  Arc follow is where the rotary
gap
doesn't quench, and the arcs follow the contacts as they spin around.  I've
seen arcs follow the contacts for about 1/4-1/3 of a revolution on the
rotary
disk.  When you have arc follow, the performance of the coil will greatly
diminish.


> I think that next time I run my coil I'll install a safety gap across the
> srsg and observe the firing of the safety gap while trying, 1:Parallel
> resistive ballast, and 2:Low and high range on the inductive ballast,
> (welder). I think that if I'm getting a lot of "inductive kick" the safety
> gap across the srsg will fire easier, (or more often).


A safety gap across the rotary is a good idea.  The series ballast
resistors will aide in reducing the inductive kick and produce a
smoother running system.


>  I will also try to watch the srsg closer to see if I can see any flashes
of
> light associated with the "car door slamming" sound.  With 6' sparks
flying
> around it's pretty hard concentrate solely on the gap. Maybe I need to
have
> my coiling buddy come over so there are two of us to observe things.

I'm speculating that the popping is coming from a reignition of the arc on
the rotary spark gap (as I'm interpreting that you presently don't have any
safety gaps across either the capacitor or the rotary gap).  If you don't
already have one, try a series (in series with your rotary gap) static gap
using a vacuum cleaner motor.  Also, put the arc through one side of the
disk (through one set of contacts) and then out the other side.  This will
give you 4 "dynamic" gaps + your additional series vacuum static gap.  This
would quench the rotary very well and should give you a really good
performing coil.


> I'm chicken to wire the safety gap across the cap because when I once did
> the cap failed just as the safety fired.
> Maybe a coincidence, but I'm not pushing my luck!
>
> Regards,
> Jon

Hope this helps!

David L. McKinnon
D&M's High Voltage