Re: [TCML] rotary gap disk

[bartb <bartb@xxxxxxxxxxxxxxxx>]

Hi Phillip,

Well the large NST current helped quite a bit. Still, it's one of the 
largest dwell times I've looked at (1.6ms). For 240 bps operation, this 
would be a problem, but 120 bps should is probably ok. If the psu was 
any smaller (or cap larger), the dwell time might cause problems. But 
with rsg's, hard to say what the problem was. This is just one of many 
aspects. But considering the small disc size and slightly large cap 
size, it simply adds to the probability. There's also the fact the cap 
is sized for full resonant charging, so this would have allowed the cap 
to charge rather quickly between bangs and could also have been part of 
the issue. We would have to spice this one to really look at it.

Take care,
Bart

Phillip Slawinski wrote:
> Bart,
>
> I just measured the disc, it has a 5" diameter.  My cap size is .05uF, and
> when I used that gap I was running the whole setup with a 12kV 240mA NST.
> The performance was nothing to write home about, but then again It was not
> the worst run I've ever had.
>
> On Sun, Nov 30, 2008 at 16:30, bartb <bartb@xxxxxxxxxxxxxxxx> wrote:
>
>   
> > Hi Phillip,
> >
> > One thing I didn't point out is that dwell time affects are psu and cap
> > dependent. Same problems can happen in large discs also. But more likely in
> > smaller disc sizes given the typical psu and cap sizes used. I have no clue
> > what psu, cap size, or disc size you used, so my comments are more of a
> > condition that is possible. Worst case is a small psu current, small disc,
> > and relatively large cap. I'm not sure if you were in this territory, but
> > thought I would throw it out there as food for thought (though you may
> > already realize this aspect).
> >
> > Bart
> >
> >
> >
> > bartb wrote:
> >
> >     
> > > What can happen in a small rotary is that the electrode mechanical dwell
> > > time can become excessive, up to the point of the cap charging and
> > > discharging a time or two during the mechanical dwell. This can cause a
> > > problem with steady firing voltages and so it tends toward a chaotic voltage
> > > at each break. Actually, in this situation, it helps to have a bit larger
> > > gap to prevent these occurrences. But as the disc is larger in diameter, the
> > > dwell time reduces linearly. A 10" rotational diameter would have 1/2 the
> > > dwell time as a 5" rotational diameter. As the diameter of the disc is
> > > increased, it doesn't take long before a tight gap is ideal (as tight as is
> > > mechanically sound). It's simply another cool aspect to larger rotational
> > > diameters. Of course, the stresses on the disc increase with larger
> > > diameters, and another good reason to use G10 or G11 as an insulated disc
> > > (at least for hobby coils).
> > >
> > > Regards,
> > > Bart
> > >
> > >       
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