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Re: [TCML] MOT stack replaced with PT, performance gone
Hi Mark, Ted,
That is interesting, and it sort of makes sense. To say what Ted did
in simpler terms, even though the power supply (whether MOTs or a
PT) ratings should not matter, and even though the power supply
theoretically does not effect the resonate frequency, well, it does... It
is a bit complex but think of the secondary of the power supply like an
inductor in parallel with the TC primary and tank cap, it won't effect Fres
of the TC secondary, but it will effect the primary tuning point. This
principal is what is behind "resonate charging" of the tank cap. And as
Ted said, MOTs usually have a high leakage inductance, so the Fres of the
primary at any given tap point will be more off from the theoretical value
than with the PT, which has lower leakage inductance, or maybe the other
way around... Does that make sense? If you scoped your primary before and
after you would probably see the same frequency with differant tap points
on differant transformers, due to the inductance of the transformers
themselves. I never thought about it that way, good call Ted... This also
solves a huge personal mystery for me, my best running coil ever ran at
like double the predicted turns of JavaTC, and it was a twin MOT coil with
no ballast, probably had huge leakage inductance being part of the tuning
On Fri, Jul 13, 2012 at 8:18 AM, SusaX2 X2 <susax2@xxxxxxxxx> wrote:
> Hi Ted, Scott,
> The PT is 100:6000V, so with a slightly overvolted input, voltage output
> should be about the same as with 4 MOT's.
> To get a higher power throughput I've doubled the flying electrodes, going
> from 200 to 400BPS. Did a run, still nothing..
> Leaving the theoretical approach for what it was, I tuned the primary tap
> inward. And here you go, the coil came back to life. With the MOT's, the
> sweet spot was between 5,5 and 6 turns. It started sparking again when I
> putting the tap a tad before the 5th turn. The sweet spot is now between 4
> 2/3 and 4 5/6 turns.
> I am pleased with the result, but I don't understand what is going on in
> reference to my calculation sheet. Please bear in mind my knowledge in this
> matter is limited, but I've coped with the steep learning curve so far.
> Since the secondary and topload are unchanged, Fres. should remain the
> On the primary side, Cp is unchanged. The primary 'L part' in the LC
> calculation has just become more complex, at least for me I guess.
> 2012/7/13 Tesla <tesla@xxxxxxxxxxxxxxx>
> > Greetings
> > An aspect I'd consider is resonance with the leakage inductance and the
> > primary cap in the MOT system. Magnetically Shunted MOT's will have much
> > higher leakage inductance ( I think at least 6Hy per MOT) than the PT
> > leading to significantly different dynamic charging of Cp with the PT I
> > think
> > Rgds
> > Ted in NZ
> > -----Original Message----- From: SusaX2 X2
> > Sent: Thursday, July 12, 2012 1:56 PM
> > To: Tesla Coil Mailing List
> > Subject: [TCML] MOT stack replaced with PT, performance gone
> > Hi,
> > recently my 4MOT-stack died and I replaced it with a PT.
> > I expected quite a performance gain, since it puts out twice the power of
> > the 4 MOT's.
> > But the completely opposite happened,
> > from streamers well over 1 meter to feeble 10cm sparks.
> > I also noticed the 200BPS SRSG fires very week, despite adjusting phasing
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