Re: Primary size

["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 6/8/02 3:23:06 PM Eastern Daylight Time, tesla-at-pupman-dot-com
writes:

Rick,

I don't think you want to use a small value cap, because then
you'll need a higher break rate to get enough power throughput.
A high breakrate doesn't seem to be as efficient as a lower
breakrate.  However the sparks may be hotter using the high
breakrate.  The coil may also have a more interesting sound.
So there are certain advantages using a high breakrate.  In
any case, you probably don't want to go over 400 or 500 bps,
because there doesn't seem to be any advantage.  So figure
that the smallest cap you'd want to use is one that will give the
proper power throughput (basically joules per bang times
the bps) for 400 or 500 bps.  If you want to use a low breakrate,
then figure the desired power throughput for 120 bps or so.
So the previous calcs set your limits for the cap value.  The
primary turns, inductance will fall into place as needed, based
on the secondary parameters of size, inductance, etc.  If you
use a too thin wire on the secondary, the losses may be too 
high.  But if you use a too-thick wire on the secondary, then
the spark gap losses may be too high, so it's a compromise.
There's a range across which not much difference will be seen.
I've gotten better results using about 1500 turns on the secondary,
than using 650 turns.  

I don't know of the optimal relationship between primary diameter
vs. secondary height.  I prefer the primary to have a small diameter,
so the toroid sparks are less likely to arc inward and strike the
primary.  These parameters will affect the coupling, but you can
adjust the secondary height to fix that.  None of it seems to
be too critical.  I don't think the optimals are known yet.

Cheers,
John


>
> Hi list,
>
> Primary tank resonance is a function of the coil and cap in that as the
> primary
> coil becomes larger, more inductance, the cap must decrease in value to
> remain
> at the same resonant frequency. So it seems that a larger primary coil may be
> advantageous in regard to the cap size needed. But there has to be limits and
> optimums. I would assume there has to be an optimum in the relationship of
> secondary height and primary diameter. So my question is what are these
> limits
> and optimums?
>
> Rick W.