parallel secondary coils

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

Original poster: "Chris Swinson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <exxos-at-cps-games.co.uk>

Hi all,

I did some testing with 2 coils in the primary.  Before I started I thought
that 2 identical coils in parallel would only half the resistance of them.
Latter I found out that each coil was 30mH and when in parallel they both
went down to 15mH. I was surprised about this but it does explain a few
things.  For one the tune point altered which was un expected. It jumped 3
or 4 turns on my primary tap.  I checked this out on my scope and found
frequency of the 2 coils in parallel was almost double.  It makes me wonder
if any more spark length could be gained this way purely on the basis of a
higher running frequency ?

It also makes me wonder how the Cself would alter with parallel coils ? I am
not sure how to work that out perhaps someone could shed some light on this
for me..  Lower resistance can only be good also. Apart from the Cself value
( I really don't know what would happen about this ) I would expect to then
build 2 double length coils, link them in parallel for the same inductance
as a smaller single coil. The simple idea then is double the turns on the
coil, Indeed inductance would be the same as a smaller single coil,
frequency would be about the same, Apart from Cself, if we assume that would
be the same, would the coil actually give more output power ?

I have a few coils where I built them in pairs to try this out. Though its
hard to work around when the Cself is a unknown factor.  So far my results
show maybe a 20% increase in output though there could be other factors at
work which I am not aware of.....  It does look possible to do this, I
wonder if anyone else has tried this type of thing ?  One slight problem in
doing this is that the 2 coils arc to each other from the sides of the
coils, so insulation becomes a bit of a problem. For my tests I am using a
large 2 foot primary so I can have a good space between coils on test. The
only reason for the big primary is to loose power on purpose so I don't have
to deal with meter long arcs going everywhere.  It does of course help as I
can space the coils a foot apart to stop arcs between them.

I tried to see if they were been coupled more to the primary being closer
than 1 coil. Its hard to say but it looks like in actual fact when they are
next to one another the arcs seem to be more. When I know a little more
about what people think I will try some more tests. Of course my in
construction flat coil prevents testing at the moment but I can try again
soon enough :)

Cheers,
Chris