Re: [TCML] rotary gap disk

["Phillip Slawinski" <pslawinski@xxxxxxxxx>]

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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