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Re: parallel secondary coils

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

Chris: as I read your postings I wonder are your 2 coils inductive aiding or
opposing. I dont see that in your diccussion. I think it is important to
know what phase relationship your coils have.
  Robert  H 

> From: "Tesla list" <tesla-at-pupman-dot-com>
> Date: Tue, 30 Apr 2002 19:19:04 -0600
> To: tesla-at-pupman-dot-com
> Subject: Re: parallel secondary coils
> Resent-From: tesla-at-pupman-dot-com
> Resent-Date: Tue, 30 Apr 2002 19:52:21 -0600
> Original poster: "Chris Swinson by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> <exxos-at-cps-games.co.uk>
> Hi Malcolm,
>>> 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 ?
>> Perhaps - IF you eliminate ALL other factors you could demonstrate
>> such, at least for your particular setup. Why the reticence? In
>> changing the primary tap, you also changed the primary surge
>> impedance and the coupling constant as well. To work with the same
>> coupling constant obviously requires adjusting pri-sec coupling. But
>> first, you have to change the primary surge impedance back to what it
>> was originally. This is not so easy since you must have 1/4'd the
>> primary inductance to retune to 2Fc. In order to correct this, you
>> would have to drop the inductance of the primary by only half, then
>> drop Cp by half as well, then increase Vp (gap setting) to maintain
>> the bang energy and hope the gap doesn't behave any differently. The
>> further you dig, the more mind-bending it becomes. If you overlook
>> the surge impedance issue and get the coupling the same, you may have
>> some basis for comparison.
> 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.
>> 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'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.
> Chris