Hi Doug,
Multiple spark gaps, as opposed to single spark gaps, facilitate better quenching by dividing the generated thermal energy into smaller portions at each gap. Too much thermal energy for a gap to dissipate within the given time constant effectively kills arc quenching, which shuts off the resonant switching, and consequently, the spark output of the coil. Of course, such added thermal dissipation features, such as forced air flow, can facilitate much increased quenching for a given gap design, too. However, each gap also introduces its own resistive losses to the flow of resonant tank currents, too, so when you have too many seriesed gaps in proportion to the power of your system, these additional losses end up being subtracted from the spark output as well. Kind of a balancing act.
As an example, my multiple kVA, pole pig driven ARSG system started with a simple rotary gap with 8 flying electrodes and 2 larger, 1/2" diameter x 3" long, heat sunk, stationary tungsten electrodes (effectively 2 operational series gaps, when firing). The naturally generated wind currents generated by their ~3000 rpm rotation seemed to provide adequate quenching, even at 12 to 15 kVA throughput! When I introduced a second pair of stationary electrodes, for a total of 4 stationary electrodes and effectively 4 gaps, when firing, it seemed that although it was not that noticeable, the output was slightly diminished and less smooth (although still handily over 10 ft discharges). The real problem though was that now the 8 flying electrodes on the rotary disc were no longer staying cool enough from the generated wind flow of their movement to prevent them from actually starting to blister the neighboring G-10 material of the rotary disc! Each flying electrode was now indeed seeing 2 firings per rotation instead of one but, each firing should also have had only half the thermal energy to dissipate, since the spark was being commutated 4 ways per firing, as opposed to 2! Yet, there was obviously more resistive gap losses to contend with, and consequently more heat, which manifested itself as the new symptom of blistered G-10 in my rotary disc, and also a slightly rougher and reduced spark output from the coil. I ended up adding aluminum shaft collars to the 3/8" diameter x 2" long flying tungsten electrodes on each side of the disc, to introduce more thermal mass to them. This did improve the excessive heat buildup problem, but I also finally ended up going back to the 2 stationary electrodes and my spark output seemed to improve once again.
If it ain't broke, don't fix it!
David
Doug <doug11642@xxxxxxxxxxx> wrote:
> How does it benefit the TC to have multiple spark-gaps?
>Doug Johnson
>_______________________________________________
>Tesla mailing list
>Tesla@xxxxxxxxxx
>http://www.pupman.com/mailman/listinfo/tesla
_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla