[TCML] Re:Pros and cons
dexterlabs at dcemail.com
Tue Dec 15 13:24:53 MST 2009
But,the question here isn't how long arcs can tesla transformer
(of any type) generate for optimum BPS rates and fixed powers.
The question is rather how long arcs tesla transformers can generate
given output voltages and resonant frequencies!
I asked the question before for aprox 100 kV output and nobody knew
to answer (except Dr.R who suggested lenghts around 4 ft).
At least I found the material relevant for VTTCs below 100 kV and 500 kHz.
Do you see why is operating frequency important for VTTCs?
I guess the most "voltage efficient" VTTC frequncy is between 200 kHz and 400 kHz.
In VTTC coiling higher frequencies (>500 kHz) are not desirable
becouse the coil parts start to consume more power (overall efficiency drops)
,and frequencies below 50 kHz develop too high output voltages causing coil
For SGTCs or DRSSTCs I have got no clue except the resonant frequency is
--- futuret at aol.com wrote:
From: futuret at aol.com
To: tesla at pupman.com
Subject: Re: [TCML] Re:Pros and cons
Date: Tue, 15 Dec 2009 14:16:08 -0500
I'm thinking that a coil which has a rather small bang size for the physical size
and toroid size, may need a higher break rate for best results, just to bring it
into the sweet spot. At low break rates, the spark may be barely breaking
out, and barely coalescing, etc. I do think that large coils tend to be somewhat
more efficient in general. It would be interesting to greatly increase the bang
size of Greg's coil, and then see what breakrate is best, and if the spark
length still grows well with increases of breakrate. The toroid size is a factor
in these issues too. Once the spark length reaches 3 or 4 times the toroid
diameter, the sparks have a much harder time growing longer. With a small
bang size, a higher breakrate is needed to grow the spark to 3 or 4 times
the toroid diameter. At that point the spark length is maxing out pretty
much anyway, based on toroid size. Much of what we see regarding
the performance of coils at various breakrates may have a lot to do with
the toroid diameter. For example if the bang size of Greg's coil was
greatly increased, then his coil would probably give long sparks at a
much lower breakrate. Then if the breakrate was increased, the sparks
might not grow very much. However if a much larger toroid was installed,
then the spark length would again increase more as the breakrate was
increased. It's a matter of matching the input power to the toroid size
basically (within some acceptable range of breakrates). In a totally
optimized system, a lower breakrate around 120 to 150 bps is probably
still best.... at least that's my guess.
From: Steve Ward <steve.ward at gmail.com>
To: Tesla Coil Mailing List <tesla at pupman.com>
Sent: Tue, Dec 15, 2009 1:36 pm
Subject: Re: [TCML] Re:Pros and cons
Glad you could chip in here a bit, i was having trouble finding any good
references for coils with discharges much longer than the top voltage would
suggest. More comments
On Tue, Dec 15, 2009 at 5:54 AM, Dex Dexter <dexterlabs at dcemail.com> wrote:
> Large SGTC:
> I was quite amazed when Greg Leyh (who designed it) told me it could
> put out 25 ft long discharges during outdoor 25 kW /350 BPS operation.
> Since the coil is DC charger powered ,the bang size from bang to bang
> is constant and is somewhere between 70 and 75 Joules (only).
> As can be seen this is a big coil which probably has something like
> 140...150pF secondary effective capacity.With 100% efficiency and no loss
> peak secondary voltage would be aprox 1 MV.Some Dr.Resonance's resarches
> indicate that in reality most sparking SGTCs peak at about 65%-75% of
> their max possible voltage without loss.
> Therefore,max voltage for this coil is about 650..750 kV.
Greg also said the best BPS rates given input power are somewhere between
> 100 and 350 BPS (what you with your 250 PPS DRSSTC observation confirmed).
Yes. I find that spark length does not grow much vs the linearly growing
power consumption after about 250bps. Now that speaks strictly of length,
not the impressive impression that the coil makes operating at higher BPS
still! The sparks become very frantic and wild and often appear brighter,
either because they really do have higher peak channel temp, or just the
integrated photons from higher rep-rate. But much longer, they are not.
> I suppose he has experimentally reserched such things in a great detail.
You'd think it might be trivial, but with a BIG coil, you have to supply
lots of power to research really high break-rates! I just dont trust my
semi-conductors to handle dissipation in huge excess of the original design.
> So,the questions like how good this coil would perform at say 1200 BPS
> and fixed bang size of 75 Joules are quite interesting.
It would be. Im curious if Greg has that capacity?
> I wouldn't bet the arcs would be much longer.
Probably not really. But something interesting happens when running a coil
at much lower bang energy than designed for. I find that i can go from
having a few inches of sputtering corona, to a 1+ foot long solid streamer
by exceeding something like 500BPS. When i originally noted this behavior,
i thought it suggested something: Bigger (energy) sparks require less BPS.
But as of yet, i have not had any real confirmation on this. The reason i
suspected it was because spark length seems to follow an energy-squared
trend, but the channel volume does not seem to be a length-squared type
trend (if the channel was just a wire, then its volume is just linear vs
length). Leading to the next point...
> They would be thicker and bushier instead I think.
Yes, i think i agree. It might be nice to capture some fast shutter
pictures of a coil operating at both low BPS and really high BPS with Ebang
being the same, and spark length remaining within say 15% of nominal. As
mentioned, the high BPS sparks *appear* more frantic and bushy, but its hard
to say if thats just because there are more sparks, or if each bang produces
a spark channel with many more branches. A fast shutter photograph
capturing just 1 or 2 spark events would possibly settle this question.
> Too low output voltage and bang size despite great power input.
> Do you (dis)agree?
I agree that these 2 characteristics will make for a poor "Freau factor".
For instance, Mr. Conners large OLTC that was discussed previously seemed to
lack bang energy, and it could not make up for this fact with higher BPS.
He gave up on that machine when he saw the results from my larger DRSSTC at
the time making about 2X the spark length with maybe only a little more
input power, and at much lower BPS.
Despite this, Greg's 120L02 coil seems to claim excellent performance
despite requiring higher (than ~120) BPS to achieve it. Most of my systems
have optimal Freau Factor's at around the 150BPS mark, and while spark
length increases beyond that (up to 250BPS), input power increases faster,
lowering the Freau Factor. This suggests that bigger coils like Greg's, are
maybe just more efficient spark producers. Maybe i can further prove this
to myself next year.
> > Yes, the 74J i see is just the peak energy stored in the primary
> > in Finn's case. Indeed the real spark energy (time integral of the spark
> > power during 1 spark event) is certainly higher than 74J (unless of
> > he is recycling nearly all of his primary energy, i doubt it).
> > There is something unusual about Finn's system, at least compared to mine
> > (which is a bit smaller, but similar spark length). My primary current
> > only 1300A when using a 1.25uF tank capacitance at 35khz. I calculate
> > for comparison) that the peak primary energy is only 14J in this case
> > the true bang energy!). The best sparks were about 12 feet in length but
> > surely not at a low 67bps! I think i see peak performance at about
> > The DC bus power consumption is about 6.5kW in this case or about
> > (so nearly 2X the peak primary energy). When you compare this to other
> > topologies you can see the benefit in reduced peak current/voltage
> > of your primary components, with of course the trade-off that the
> > lower current/voltage persists for a longer period of time.
> > Steve
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