From: "Barton B. Anderson"
Date: Sun, 12 May 2002 11:20:14 +0000
Subject: Re: [TSSP] Topload breakout potentials
Hi Paul, Forgive my tardyness. I ran into problems last night. Analog am meter had died. I got caught up in trying to fix it (big mistake - time for a new one). Paul wrote: > Bart's coil stands out from the other two for its inexplicable > breakout. > I'm probably demonstrating my ignorance of the primary charging > circuits, but doesn't that make for something like > 180/110 * 14.4 * sqrt(2) = circa 33kV. Where does the 15.3 kV come > from? Obviously I don't understand how the primary charge is set up. > I guess the ballasting and gap settings modify my naive picture. 180/240 * 14.4*sqrt(2) = 15.3kV. It's 240v input for 14.4kV out. After bypassing the broken current meter, I ran the coil as is at several different voltages. I got racing arcs every time and multiple streamers, relatively short. I then detuned out about 7% to turn 14 from 13. Still got racing arcs, however, brighter. Streamers off top load were longer, brighter, and fewer. I then left the tap at 14 and lowered the toroid to center at 70" above ground. This puts the sec top winding about an inch below the toroid center (quite a bit of shielding at this point). This pulls the detune to 10.7%. Low and behold, no racing arcs. Streamers I would say were 1 long streamer, very bright, and staying in the air for a longer duration before quenching. I couldn't go any further than 6 feet (that's where the streamer meets the wall). I then tuned to turn 13 (which is 3.2% deturned). No racing arcs, but streamers were shorter). Notice here, I didn't change coupling. Greater shielding has stopped the racing arcs this time. Normally, I would have raised the secondary to remove the racing arcs. It appears from this test that greater shielding allows higher coulping? As far as the voltage gradient, I don't know what to say about that. I know it's only 20.3kVp at 240 input. For example, applying 120 to the HV terminals, I measure 2v on the LV terminals (60:1). My pig is 2 hv terminals and 3 low voltage terminals (center tap not used). 240 is applied to the two outer low voltage terminals. One hv terminal is at "RF ground" (David Rieben and I run this config to prevent floating and keep the inner turn of the primary at the same potential as the bottom secondary winding). With 180V applied, there can't be more than 15.3kVp to the cap. BTW, I'm running 240 bps and using John Freau's phase adjustment circuit (works excellent John). Take care, Bart > I've got Bart's coil down at 15.3kV across 61nF into a secondary Cee > of 45pF, so we'd expect a (tuned) peak topvolts of > 15.3 kV * sqrt( 61nF/45pF) = 560 kV. > The model reports 460kV and the primary tuning for 13 turns just > seems a couple of percent on the *high* side. Maybe I haven't got > the model tuned quite the same as the real coil? If the real coil > was in tune, the 560 kV would give 14.5kV/cm on the toroid - an > improvement but still well short of the 26kV/cm we expect. Why are > we 50% out? Either > > a) We don't have a good representation of Bart's setup. > b) The model is predicting the wrong topvolts. > c) Tcap is predicting the wrong topload surface V/cm/V. > d) The 26kV/cm threshold isn't right.
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.