Thanks John,
I felt it was just two as well, but as you point out, the ground strikes
loose the energy, otherwise the two gaps may have struggled with 50kW on
hand.
On the phase thing, I recall a video a while back where Kevin gave a guided
tour of the coil, but I can't find it on YT now.
In that video I thought he either stated, or it could be seen, that the
phase was done by a small motor rotating the main 5Hp motor (via a chain
set-up) rather than your own variac method, but it may well have changed
now.
Going back to the original issue of gapping, is the main source of power
loss, in the air / plasma interfaces, or in the actual plasma stream across
the gap itself. Obviously there are losses in both, but just wondering on
how much the length of the plasma stream influences the losses.
Is the Biggg still up and running out of interest, anyone know?
Phil
-----Original Message-----
From: Tesla [mailto:tesla-bounces@xxxxxxxxxx] On Behalf Of Futuret via Tesla
Sent: 21 October 2014 16:12
To: tesla@xxxxxxxxxx
Subject: Re: [TCML] Number of stationary electrodes & gap spacing in RSG
Kevin uses 2 spinning electrodes for 120 bps and a 5 HP motor. I think
he uses an electrical phase controller.
I agree on the "over-quenching" issue that you basically can't get
over-quenching with a rotary spark gap. If the TC loses power with
too many gaps, etc, then either the gaps are too hot, ruining the
quenching, or in many cases the spark has trouble firing across
so many gaps and fires only sporadically giving an uneven weak
streamer output. As the streamers get longer, stronger and more
numerous, the quenching will improve, almost regardless of the
gap situation. Basically you want to use up the energy by
producing big streamers, then there's less energy to feed back to the
primary and prolong the tank oscillations, and delay the quenching.
Theoretically speaking, with a super huge low frequency coil and
super fast rotary, perhaps the quench could be forced to some
degree. Grey Leyh's Electrum coil may have been approaching this
situation. It's a matter of mechanical dwell time versus optimal
quench time for 1st notch quenching (first full energy transfer to
the secondary).
John
-----Original Message-----
From: Phil <pip@xxxxxxxxxxx>
To: 'Tesla Coil Mailing List' <tesla@xxxxxxxxxx>
Sent: Tue, Oct 21, 2014 9:25 am
Subject: Re: [TCML] Number of stationary electrodes & gap spacing in RSG
Does anyone know what Kevin's Biggg coil uses gap wise? I know it's 100bps
sync rotary @ 3600rpm with I think STEEL electrodes (phase control by body
rotation)
Phil
-----Original Message-----
From: Tesla [mailto:tesla-bounces@xxxxxxxxxx] On Behalf Of Teslalabor
Sent: 21 October 2014 12:46
To: Tesla Coil Mailing List
Subject: Re: [TCML] Number of stationary electrodes & gap spacing in RSG
Hi David, Phil,
in the "over quench" thing I definitely have to disagree. I think, your
performance problems when using 4 gaps instead of 2 must have had some other
reasons. In my opinion, you never can have enough single gaps in a spark
gap. Have a look at the outstanding rotary gap, Greg Leyh has built many
years ago for the Electrum coil:
http://lod.org/Projects/electrum/construction/pages/rtarygap.html
This amazing beast uses EIGHT gaps in series! With this, I also want to
bring another interesting fact into discussion: The "opening speed" of the
gaps! So it seems, we have 2 variables to play with:
1. mechanic dwell time, which seems to be the same, no matter of the number
of gaps used. Only disc speed is important and
2. "opening time", here comes the number of gaps into play. The more gaps,
the higher the opening speed, which is by the way not intuitive for me. Greg
Leyh states, that one single gap has an opening speed of 430feet/sec or Mach
0,4. His design uses 8 gaps, so 8 x 0,4 = Mach 3,2 total opening speed. By
the way, I can not find the reason, why he used 4 discs with only 2 gaps
each.
Woulnd't it have been much easier, to use only 2 discs, with each 4 gaps?
Both would give a total of 8 gaps, the same dwell time and opening speed.
Big advantage: You have to mess arround with only 2 instead of 4 discs on
the shaft.
Regards,
Stefan
----- Original Message -----
From: "David Rieben" <drieben@xxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Monday, October 20, 2014 8:20 PM
Subject: [TCML] Number of stationary electrodes & gap spacing in RSG
> Hi Phil and Stefan,
>
> First of all, congratulations to both of you on a pristine design for your
> coils. Both systems would still be downright pretty if they never made the
> first spark :-))
>
> Now as far as rotary gap spacing and such, please allow me to share my
> personal experience in this matter. My coil is the Green Monster and is of
> the generic AC driven from a typical 14.4 kV pole pig with an ASYNC rotary
> gap (about the simplest rotary gap driven coil system- I like keeping it
> as simple as possible). Now I had originally ran with a single 10.5" dia.
> X 1/2" thick G-10 disc with 8 flying tungsten electrodes and just 2
> mounted (1/2" dia) stationary tungsten electrodes. Now my rotary gap isn't
> nearly as pristine and precision made as either of yours but I was still
> able to get sufficiently close spacing between the flying and stationary
> electrodes to get steady and reliable firing without stationary/flying
> electrodes crash. I then decided to try out 4 stationary electrodes as
> opposed to 2. After modifying for this setup, I was still able to get
> reasonably reliable firing across 4 gap points as opposed to 2, but there
> was a new issue that I had not had with the 2 gap points. Since my flying
> electrodes were now each seeing 2 firings per revolution, as opposed to
> one, they were now getting hot enough during operation that they were
> actually blistering the G-10 material around them on the disc, in spite of
> the generous airflow generated by whirling at ~3000 rpm! Also, it actually
> seemed as if the output sparks were ever so slightly weaker at a giving
> power input setting than they were with just 2 gap points. I ended up
> installing 3/8" shaft collar sleeves on each (3/8" dia) tungsten flying
> electrode to help add a bit of thermal mass as well as increased surface
> area. This did seem to keep them a "wee-bit" cooler, but there still
> seemed to be a slight decrease in the coil's output.
>
> Long story short, I ended up going back to the original 2-gap point design
> and the flying electrodes are now running notably cooler (I left the added
> shaft collars in place since they also help anchor the flying electrodes
> in place). The gap spacing tolerance is also less critical and the output
> sparks are now back to like they originally were ;-)
>
> I recall reading somewhere in one of the old TCBA newsletters that it was
> possible to "over quench" a spark gap to the point that the coil's output
> deteriorates, since every gap in a series gap system wastes some of the
> energy that ultimately ends up in the output sparks (maybe Richard Hull?)
> I know it seems strange that there would be a noticeable difference in the
> output of a multi-kilowatt pole pig driven coil system with just the
> addition of 2 extra seriesed gaps and maybe it was just my imagination,
> but it sure seemed that the output was not quite as bright with 4 gaps as
> opposed to 2. May work a little different for a DC res. charging system
> though, as I have no personal experience with this type of setup.
>
> David Rieben
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