Re: efficiency, turns vs. BPS, was 15" coil project

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <FutureT-at-aol-dot-com>

In a message dated 10/21/01 3:45:57 PM Eastern Daylight Time, 
tesla-at-pupman-dot-com writes:

>  Exactly.  Someone with experience and adequate
>  equipment really needs to write a paper on how wire
>  gauge/turns etc. affect coil efficiency...hint..hint.
>  
>  -Brett

Brett, all,

Anyone who does these comparison tests must keep
in mind that the break rate must be considered in all 
this.  Using a higher break rate, permits a smaller cap
to be used, which immediately raises the surge
impedance.  In such a case, increasing the number
of turns may give less of a benefit compared to a low
break rate system.  A low break rate system demands
a large cap, which in turn tends to lower the surge 
impedance and increase the gap losses.  Therefore,
a low breakrate system may benefit more from using
more turns of a thinner gauge wire.  This may even help
to explain why some folks have not seen much of a
benefit when they used a thinner wire in some small
coils.  These coils may have used a static gap, with
a small cap, and may have been running at high
breakrates.  As the surge impedance is increased more
and more, a point of diminishing returns will be found for
a given coil configuration.  As the surge Z is increased
even more, the overall efficiency will decrease due to the
rising wire losses.  Once the surge Z is reasonably high,
making it higher won't help much, and may even reduce the
efficiency by causing massive wire losses. 
I've found the best overall efficiency of
the spark growth at low breakrates.  This forces me
to use thin wire with many turns, for the best overall
results in my coils, which tend to use a low breakrate.
Richie B. used 200 bps for his coil, and still saw a 10%
benefit when he used 1500 turns, so I guess there's a 
range of breakrates which still benefit.  I haven't really
done much comparison work in varying the number of
turns for a high breakrate coil, but I just wanted to point
out these breakrate vs. number of turns considerations, 
which I've never seen mentioned much before.  Also,
a high breakrate coil uses a smaller bang size, so this
too reduces the wire losses.  It may be such factors,
which help to permit high breakrate coils to work as well
as they do.  It is possible that some high breakrate coils 
may not show much benefit from using more than 1000 turns
or so, if their surge Z is high already.

Cheers,
John Freau