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Re: Disc Construction, and dwell
In a message dated 99-05-07 00:52:23 EDT, you write:
<<
> 1.) You make the assumption, that the arc start/stop takes up no dwell time.
> This is a major problem (I donīt have a solution for it, either), because
the
> arc will jump before the gaps line up and will continue after the gaps
> seperate.
Reinhard,
Are you suggesting that the arc fires for the entire time
that the gaps are lined up and also before and after for a little while?
I would suggest that the gaps usually quench much sooner, based
on when the bang energy is mostly gone. For instance if the
mechanical dwell is 400uS, the gap may actually fire for only 100uS
(just an example). Yes, the spark will jump before the gaps line up,
and in some cases, the gap may quench before the
electrodes even reach each other. Some books suggest that the
high pressure shock wave in front of the spinning electrodes helps
quench the spark as the electrodes approach each other ( I don't
remember which books it was, but I'm sure someone else does.)
Robert Jameson discussed the undesireable effects of a really long
mechanical dwell time, which can permit the gap to "re-fire" while
still aligned, (resulting in much wasted energy). Small caps can,
in certain systems, contribute to this undesireable state also.
> In order to consider this time "zero", you would have to incorperate a very
> high rpm motor and / or big disk diameter (the speed of the electrodes has
> to be VERY high). Otherwise, the arc time is much longer than your proggy
> suggests. Finding the time that the arc stays on (= time before alignment+
> time during alignment+time after alignment) isnīt that easy. It depends on
> electrode size (the larger the ROC, the faster the time is) and shape. I
> donīt know of any simple formula that will allow one to accurately calculate
> this (although the Sim guys out there probably could make a simulation to
> predict results),
Again, I think the gap quenches before the mechancal dwell is "used up".
How can the gap continue to fire when the energy is gone and the
cap is discharged, or am I misunderstanding what you are saying?
Depending on the purpose of the spreadsheet in question, I
would think that the difference between a zero dwell, and the true
dwell, might not affect the results that much, but again, this would
depend on what's being analyzed.
> 2.) What do you mean by center to center offset? Do you mean this:
> (use courier to view) >>
In the past, I tried a method of offsetting the electrodes by offsetting
the fixed, but not the spinning electrodes. My aim was to effectively
eliminate the mechanical dwell. This didn't help the quench since the
quench seems to be independent of mechanical dwell. In some cases,
this reduced the total power draw however, which suggests that I may
have been experiencing the re-firing that Jameson mentioned.
Cheers,
John Freau