Re: parallel secondary coils

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

Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi Chris,
           I am following your expts with interest. Please understand 
that I am not trying to be picky but would like to see a scientific 
reason if higher frequencies produce longer sparks. In my experience, 
the opposite has been true but that I do not attribute to frequency 
itself - more to the properties that low frequency coils have such as 
a generally higher primary surge impedance with correspondingly lower 
gap losses.
 
On 30 Apr 2002, at 19:19, Tesla list wrote:

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

<snip>
> If 2 coils works better than one than why not ? a lot of things also as you
> rightly point out, though if it works better ( for what ever reason ) then
> it could be a good thing to look into. There are far to many variables for
> my simple brain to work out with this idea which is why I posted the
> experiments I did.

The question is, why should they? The problem is, which particular 
variable or variables are behind the difference you are observing. 
You are altering more than just frequency. 
> 
> 
> 
> >      But there is also another interessting issue. How close together
> > were your secondary coils positioned. If they were very close
> > together, the inductance may not have dropped quite so radically. One
> > would expect two identical uncoupled inductances to give a total
> > inductance of half if they were connected in parallel.
> >
> 
> I did have them connected at one point in parallel. If inductance is lower
> then thats a alteration which will effect the tune point.  Will be higher
> frequency which could be better for longer sparks.  I tried them about
> 1.5foot appart and just a few inches appart. closer the better, but as I
> stated arcs between coils become a problem. Connecting them in parallel did
> seem to work the best.  I wounder if there will be 2 frequencys at work
> since both coils are not 110% in tune. Though I dont think this is possible
> since it should act as a single coil since they are shorted together top and
> bottom.  Couldn't the EM off one coil compliment the other ?

That brings up an interesting point. Since the two secondaries are 
coupled to one another, there will be transfers of energy between 
them, just as there would be between primary and secondary. Beating 
is almost certain to be present. That alone might account for the 
observed arcing between them.
 
> 
> >
> > That's an interesting series of experiments. But I think you'll agree
> > that there is a plethora of variables at work. In the end, what is
> > the esl and esc of the setup with just one coil and with two, however
> > they are positioned?
> >
> 
> I will have to work values out again, I know the inductance of 1 coil is
> 30mH, together they are 15mH, capacitance I think was about 30 for 1 coils,
> I don't know how it would be effected with 2 coils in parallel, maybe double
> Cself ?  Closer together could only be better as they are more in the middle
> of the primary giving better coupling than coils which are placed lob sided
> in the primary.  Note that the primary is 2foot inner dia and the coils are
> only 6.2" in dia so I get a big scope of area to move the coils around in.
> I think some more tests are in order for this setup and better measurements.

I realized last night that the self capacitance is not simply going 
to be an additive thing because of the proximity of the coils to one 
another. I suspect there will be shades of shading. In fact the whole 
setup would be a most interesting one to model. The number of 
variables present is interesting to say the least. Perhaps I might be 
tempted to drag some of my coils out of limbo and set them up in a 
similar fashion to take some measurements. I have been missing my 
ozone fix lately.

Regards,
malcolm