From: Paul
Date: Thu, 31 May 2001 00:25:07 +0100
Subject: Re: [TSSP] Racing arc clues
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 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? 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. 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. 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. 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. 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.