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Re: [TCML] 6" Coil Sparks too short

If I can add my two cents here, the way to determine the relationship
between break rate, and input current, and cap size, is that you want your
spark gap to fire each time it is just over one time constant for charging
the tank capacitor (this will be around 70% charge).  This way you are
being current limited by your transformer, not your capacitor, and you
still develop a respectable enough voltage to make great sparks.  As long
as this method is used, your NST [should] be safe, in async mode, as
voltages shouldn't develop that can kill the transformer.  However, you
still need a terry filter and safety gap or transients and missed firings
can kill them (even the best designed system can fail, we shoot for a fail
safe).  At any rate designing your cap to work with 120BPS is safest, and
going LTR is safer still, as it keeps your voltage levels too low, because
of the whole time constant rule above, and missed firings just drain the
tank charge instead of building up dangerously.  Just use JAVATC to get all
those parameters lined up, and then I suspect your performance will be
fine, barring any quenching issues.  The way to do that is get your SYNG
going, and add capacitance until JAVATC says you are firing at 70%.  Good

On Thu, Feb 26, 2015 at 3:28 PM, deano <deano@xxxxxxxxxxxxxxxx> wrote:

> On Thu, 26 Feb 2015 08:00:32 -0800
> Kuba Anglin <kubaanglin@xxxxxxxxx> wrote:
> > Brandon, you say that I should be running 5-6 times my current rsg
> > setup. That seems very significant. What should my bps be on this
> > coil? Since this is my first rsg coil, I am not incredibly familiar
> > with rotary spark gap operation. If I simply added more electrodes to
> > my disc and tested the coil, would that be a good place to start?
> > -Kuba
> > 2) .80 BPS is way too slow.
> > 3) Running NSTs in asynchronous mode is one of the best ways to kill
> > them.
> > Matt D
> Hi Kuba
> When running NSTs you should be running at some multiple of line
> frequency, 120bps or 240 bps in synchronous mode. As Matt has said,
> running asynchronous is a great way to ruin your NSTs.
> Also in the spark gap picture I do not see a safety gap or a "Terry
> filter" both of which would help to prolong the life of your
> transformers.
> I see in the spark gap picture that the motor is a nice one, easy
> enough to disassemble for modification to synchronous operation. If you
> mill (or grind) four flats on the stator then it will be able to lock
> to the line frequency and run at 1800 RPM which with four electrodes on
> the spark gap rotor will produce 120bps (recommended). It appears you
> have "saddles" on the motor mount which will allow a rough adjustment
> of spark gap timing. The addition of a "John Frau phase shifter" will
> allow for "real time" phase adjustment.
> I would also recommend a safety gap across the rotary spark gap to
> catch missed firings, and yes, also a "Terry filter" to help protect
> the NSTs from over voltage.
> Another thing that is hard to tell from the picture, but the spark gap
> rotor appears to be clear. Hope you are not using acrylic or
> polycarbonate for that:-)
> One more thing I see in the spark gap picture is a lot of alligator
> clips. This is something that could also be contributing to poor
> performance.
> Best of luck in your endeavor
> deano
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