From: mystuffs@orwell.net (Metlicka Marc)
Date: Thu, 31 May 2001 00:42:50 -0400
Subject: Re: [TSSP] Racing arc clues
all, (pure speculation on my part too follow) Paul wrote: > > Lots of informative comments from all, and I don't see any that > I disagree with. > > John's comments are thought provoking... > > As you increase the toroid size, a higher topvolts is required > for breakout, and eventually a toroid size is reached at which > the secondary will break down before the topload breaks out. this makes good sense. > > This implies that for a given secondary there is a maximum > tolerable toroid size. Below this size, the system will always > break out from the top (assuming correct tuning). Above this > size, you risk damage to the secondary. Associated with this > would be a maximum voltage capability, and consequently a > maximum wallplug power for any given BPS. Would be nice to know > how to calculate these limits for a given coil. To do so, we > would need to know at what voltage gradient the secondary > breaks down. Is this a function of the wire size, insulation, > smoothness of surface coating, and a host of things, or is > there is more simple recipe? it would seem that there would be all of these factors and maybe more involved, lets look at wire size: if a coil is wrapped with a larger wire size and the 5-1 rule is held, then there is less turns in a given area. these lesser turns would have a higher turn to turn potential, so if the potential of one turn and the turn that is 1" away gets high enough then the arc will try to equalize it? (i think the mpeg's are showing some of this) so a too large topload would breach the threshold, so to speak. this could be lessened by the use of a better insulated wire, but not eliminated, or by adding more turns in a given area? smoothness of coating is a given, inclusions or lumps would cause a focal point for the field to condense in one area, causing corona breakdown of above threshold (once started, easier path of equalization) this is shown well by a breakout point on the toroid, or in one of my cases, a hole in the toroid. > > Following from this is the question: Can we do anything to > maximise the 'tolerable toroid size' by suitable choice of > primary design, by way of ensuring that the secondary voltage > gradient remains as smooth as possible at all times when the > secondary voltage is high. this question leads me too a question: in the case of too high a coupling, is it just the field that intersects the secondary from the primary? or could it be that the field from the upper side of the primary "and" the field from the lower side of the primary are interacting with the secondary? i have heard comments on the pupman list about energy losses by the primary field intersecting metal objects under the primary, but what happens when the lower field is brought into play on the secondary? if the parting line between fields is brought above the bottom turn of the secondary (or close there) wouldn't a form of bipolar coil be introduced? if as ed's comment shows more current as needing less coupling, could it actually be a "tighter doughnut" shaped field? also, if primary field shape does cause a "localized" strong point, inducing a more concentrated energy to the windings, then i would think this could be enough to create unequal gradients, so primary field shapes might have to be given more "visualization" and thought? (remember the twice the distance-twice the voltage-half the current) uniform gradient suggestion paul? > > I wonder if optimising for max tolerable toroid size as defined > above is the same as optimising for maximum voltage .. hmm thinking > aloud .. no its not, the former implies you're willing to crank up > the input power as much as is necessary to achieve breakout, > whereas the latter is all about getting the max voltage at the > top for some fixed bang energy. > > The notion of a max tolerable toroid, and its associated > max power and max volts, is quite appealing - these seem to define > a firm set of upper limits for a given coil. Is something like this > in common use amongst coilers? It sounds like one of the first > things you'd want to know about a coil. i personally try larger toploads until i only get 1-2 streamers breaking out at once, with a rough toroid like tape coated duct, this can be larger then a smooth toroid. at least this is what i'm seeing in the setting up and refining of the topload breakout threshold voltage experiments. (still getting setup for consistent readings by the way, very soon to come though) so field density, or at least a condensing thereof is in effect again. > > As for sharp points on the primary and secondary, well I think > they have specific causes in weaknesses in construction and 'battle > damage' and they can surely be identified as such without too much > difficulty. I think we should focus our attention on the racing > arcs that do not have an obvious cause. i think not only voltages but currents could be interchanged as possible causes, very tricky indeed. > > We will need to distinguish between racing arcs that form when a > properly adjusted coil is driven right to its limits, and those that > occur when the coil is badly tuned or over-coupled. The former > is surely our main concern, since the latter can be fixed by > adjustment and if the problem persists, it is one of the former > category. > > To summarise, we can attempt to maximise the performance of a coil, > in terms of a largest tolerable toroid, by engineering its secondary > voltage gradient for maximum uniformity. To do this we do not need > to know just what the secondary breakdown limit actually is. i think i would now like to wind a duplicate coil to my 3k coil, but with a much thicker wire. then push more and more current into each to see what the effect of putting more turns in a given area may show? marc > > If, in addition, we also knew the breakdown voltage gradient of > the secondary, we could in principle calculate this maximum toroid > size. > > -- > Paul Nicholson, > Manchester, UK. > --
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.