Re: Dwell time, etc

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: FutureT@xxxxxxx 

In a message dated 4/2/06 1:18:06 PM Eastern Daylight Time, 
tesla@xxxxxxxxxx writes:


> Original poster: dest <dest@xxxxxxxxxxxxx>
>
> Hallo John.
>
> > Original poster: FutureT@xxxxxxx
>
> >It must be realized that the spark-gap arc quenches well before the
> >elecrodes pass each other by.  There is often no correlation between
> >actual quench times and mechanical dwell times.
>
> >Generally, rotaries do not quench by pulling out and stretching the
> >arc to promote quenching, rather, the arc quenches while the
> >electrodes are still lined up.  In some cases, the arc will quench
> >before the electrodes even line up...they will quench as the
> >electrodes are still approaching.
>
> then what`s the point in using series rotary at all - only in reducing
> heating of each flying electrode? but this is a wrong way - you can
> achieve the same result just by increasing the number of electrodes, so
> you don`t introduce additional air gap which is bad thing (coz this
> means additional losses).


Dmitri,

There is usually no point in using a series rotary from a quenching
(dwell) point of view.  So yes, only the heating of each electrode is
reduced.  Although it's true that additional air gaps increase
the losses, the effect may be minor.  I did some tests and
compared the spark length using a sync rotary, compared
to a triggered sync static gap.  The triggered sync static cap
had about a 5/8" spacing.  Yet the coil gave the same spark
length as when using the rotary.  It's possible the voltage
was able to go higher using the triggered rotary.  I don't think
I checked that aspect.  So maybe this was compensating
for the greater losses.  In still another test, I ran my TT-42 coil
with a 2 gap series rotary, and then added 2 more gaps to
make it a 4 gap series rotary.  The spark length was the
same in either case.


> series rotary doesn`t decrease the dwell time, right?


Not for small or medium coils.  Possibly for very large coils.


> it`s written here:
> http://www.lod.org/Projects/electrum/construction/pages/rtarygap.html
>
> "with 8 gaps in series, the effective opening speed of the gap system
> is mach 3.2"
>
> you want to say, that this gap system is nonsense and just waste of
> materials and power, and it can be done in _much_ smaller volume with
> absolutely same performance, coz "opening speed" have no significance
> at all?


You must have missed the part in one of my recent posts in which
I mentioned Greg's coil.  I agreed with Greg that his series rotary
may be helping his quenching because he has a large coil.
This permits the mechanical dwell time to be similar to the
actual optimal quench time.  It is only under such conditions
that the opening time becomes important.  Also at very
high powers it may be harder to quench, so such opening
speed may become a factor.  But again, this seems to work
only on larger or very low frequency coils so things are able to work
out well from a timing aspect.

My comments the other day were geared more towards the
typical small or medium coil in which the opening speed is not
a factor.

John


> -----
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