Hi Stefan, all,
Well I did leave a caveat in my statement about the performance "drop-off" with my 4-gap vs. 2-gap setup - I stated that "it may have just been my imagination" ;-) I may also should've added that "YMMV". ;-)) Like I said though, this was just my personal observation and only mine. Btw, I at one time had also employed a 3-gap blown stationary gap in series with my main 2-gap rotary gap for the suppression of the "ring of fire" and poor quenching (noted by a muffled "popping" sound that could be heard over the ambient noise of the sparks) of my rotary. I have since changed my input ballast to the transformer and since doing this, the ring of fire problem has disappeared, even with only the 2-gap rotary for spark commutation. I just decided to give the 4-gap setup a try after switching over to my current ballast and this was when I made these "observations". Btw, the ballast that I am now using is completely "homemade" - 2 "C" core halves from a dead soldier x-ray tranny that is wound on each of the 2 "legs" with ~100 or so turns of #8 THNN copper cable, which are paralleled. I adjusted the spacing between the core halves by carefully ramping up 240 volts via a variac into the ballast and adjust the core spacing so that it was drawing right at 100 amps when "shorting" a 240 volt input. This has proven to be my best performing ballast with my system to date.
David
Sent from my iPhone
> On Oct 21, 2014, at 6:45 AM, Teslalabor <teslalabor@xxxxxxxxxxx> wrote:
>
> 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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