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Re: Combo Gap

In a message dated 10/7/00 11:49:48 AM Pacific Daylight Time, 
tesla-at-pupman-dot-com writes:

> Original poster: "BunnyKiller" <bigfoo39-at-telocity-dot-com> 
>  Hi All....
>  I've been kicking around an idea that I havent seen much talk about...
>  running a SRSG with a static gap in series.   The SRSG I currently use is
>  showing signs of wear -n- tear and I feel it is due to the high voltages
>  present at gap alignment timing. What is happening is that the disc is
>  begining to show arc marks before the electrodes fully align. ( slight
>  schorching on the disc before the electrodes)
>  Before I go and place a static gap in series with the SRSG, my question is
>  ....   will this aditional gap help in reducing the voltage gradient at the
>  RSG ( if my thinking is correct as in the multi gap, each additional gap
>  helps reduce the voltage across each gap)


Yes, this method will reduce the voltage gradient, and may also
help to prevent "re-firing" of the gap while the electrodes are still
aligned.  In the 120 bps small systems I'm running, extra series
gaps are not needed, but higher powered, high bps systems
with wide electrodes, and slow turning motors, may benefit from
series gaps.  If series gaps are used, the rotary electrode
spacing should be set very close otherwise the gap may fire
erratically.  The higher the input voltage, the more series gaps
can be tolerated.  The series gaps should be set quite close.
>  The possible downside to this idea I see so far is that by adding the
>  additional gap(s) this will (?) make the gap length longer and possibly
>  overvolt the cap?  I have watched the rotory gap at work and have seen the
>  gap spark "streach" to almost an inch on each side of the rotory electrodes
>  ( total length almost 2" ).

The cap voltage depends mostly on timing rather than spacing unless
the series gaps are too wide, causing firings to be skipped.  The
sparks should not stretch that much on each side of the rotary.  This
stretching is also affected by other things such as ballasting, and
possible "refiring" of the gap while the electrodes are still aligned,
if the electrodes are rather thick.
>  How about it people ??   do yall think that by adding an additional static
>  gap in series to a RSG will help reduce the scorching problem or am I just
>  getting ready to blow up the cap?

I'm assuming you're using an non-sync gap.  The extra series gaps
will tend to cause some of the lower voltage electrode presentations
that are at low points on the sine wave to fail to fire.  But as long as
the series gaps are not too wide, it shouldn't tend to destroy the cap,
provided the cap has a reasonable voltage rating.  THe series gaps
should not be set so wide that firings are skipped at electrode
presentations near the ac sine wave peak.  Not too many series
gaps should be used; just 3 or 4 close-spaced gaps.  Often it can
help to have some air blowing over the static gaps to keep them
cool also.

John Freau

>  Scot D