Using rotary gaps, there's always the concern about "re-firing" of the gap
after if fires, while the gaps are still aligned. This is more likely to occur
if the break rate is high and the capacitor is small and the electrodes are
very wide and the rotary RPM is low. However at 100 or 120 bps using
relatively large capacitors, re-firing is much less likely to occur. I remember
an experiment where Alan Jones used large square steel plates for his
stationary electrodes and the coil ran fine. These plates were about
1" square and maybe 1/4" thick. There was no re-firing problem. I think
this pretty much cured his ablation problem. Also D.C. Cox used
tungsten electrodes that were about 1" in diameter for his fixed electrodes
in some of his museum coils, and they held up well.
John
-----Original Message-----
From: Steve White <steve.white1@xxxxxxxxx>
To: Phillip Strauss <pstrauss1947@xxxxxxxxx>; Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Sent: Fri, Aug 18, 2017 7:39 pm
Subject: Re: [TCML] Electrode erosion
The one place that I scrimped, out of ignorance, when I built my 8.6" coil was the electrode size. My flying electrodes are only 1/8 inch but oddly enough they show no visible sign of erosion even after many runs. I assume that is because of the excellent air cooling at 3600 RPM combined with the fact that each one fires at 1/4 the frequency of the stationary electrodes thus giving them more time to cool. I also have the flying electrodes mounted in brass bolts which also helps with the cooling and carries a lot of the current. It is the stationary electrode erosion that I am trying to mitigate, even though it is not unreasonable. My stationary electrodes are 5/16". Some day I may rebuild my RSG to incorporate larger electrodes although the current setup is perfectly acceptable at 4800 watts (20 amps at 240 volts).----- Original Message -----From: "Phillip Strauss via Tesla" <tesla@xxxxxxxxxx>To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>Sent: Thursday, August 17, 2017 7:32
:25 AMSubject: Re: [TCML] Electrode erosionHello Steve,I have found that a minimum diameter of 3/8" pure tungsten can cope with just about anything you can throw at it. I have used them as flying electrodes as well as stationaries and wear is absolutely minimal.Pure 1/4" tungstens on the rotor of Phil Tuck's coil to which you alluded survived pretty well before their finning days pulling between 30 and 40A. Copper fins should hold up perfectly well at a least in our experience.Have recently used 1/2" stationary and 3'8" flying electrodes in 40mm diameter copper rod columns with no finning and even prolonged runs at 40A on a large coil show virtually no wear. Did experiment with copper tungsten but ablation was severe.Best of luck,Phillip. _____________________________________________________________________________14 Broad Street, Stamford, Lincs PE9 1PG Tel: 01780 753008 From: Steve White <steve.white1@xxxxxxxxx> To: Tesla Coil List <tesla@xxxxxxxxxx> Sent: Thursday
, 17 August 2017, 13:09 Subject: [TCML] Electrode erosion In an attempt to reduce the erosion of my stationary RSG tungsten electrodes, I machined on my lathe a set of small heat sinks that mount 1/2" away from the spark gap firing point. They are similar to those shown on the "hvtesla.com" web site except mine are made from aluminum instead of copper. The problem is that the high temperature seems to be pitting the face of the heat sinks facing the spark gap. I note that aluminum melts at 1200 degrees F and copper melts at 1900 degrees F.In an attempt to correct this pitting problem I have ordered a set of aluminum nitride sheets. Each is 1.5" x 1.5" x 1 mm. Aluminum nitride is a ceramic which melts at 4000 degrees F. My idea is to attach these small sheets to the face of the heat sink closest to the spark gap in order to prevent the pitting (melting) of the aluminum. I then wondered if attaching copper sheets to the aluminum would have done the job since copper's melting
point is higher.Does anyone using copper heat sinks on the stationary tungsten electrodes have a problem with the copper pitting (melting)?_______________________________________________Tesla mailing listTesla@pupman.comhttp://www.pupman.com/mailman/listinfo/tesla
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