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We report measurements on the breakdown strength of plastics used in stereo lithography for rapid prototyping. Three epoxy-based photopolymer resins commonly used for stereo lithography were the focus of this work. Test samples were manufactured with an electrically smooth geometry to minimize field enhancements. The thickness of the stressed region in the samples was nominally 1 or 2 mm. Samples were tested to failure by applying a ramped and held voltage pulse at discrete levels up to a maximum of 240 kV. We confirmed the uniform field distribution of the sample geometry with electrostatic modeling and calculated the electric field stress at failure as a simple voltage/thickness ratio. These results are compared with values obtained for several typical materials often used in high voltage applications (acrylic, nylon, etc.). We find that the failure threshold for the SLA materials can be a factor of 2-3 below that of the standard materials.

Marx generators have been built with a wide span of physical size and output capability, ranging from circuit board scale devices of a few stages up to systems capable of producing many Megavolts and occupying entire buildings. Our focus in this paper is the development of a capability to explore compact Marx generator (CMG) devices, where we arbitrarily define a CMG to be an apparatus consuming less than 0.5 m/sup 3/ (excluding the charging and control systems). We report the development of a laboratory system that incorporates a shielded test stand with battery-powered high voltage charging supplies and a computer based control system with a graphical user interface. We briefly discuss a demonstration of the test bed capability with results from a modular CMG we have constructed.

Thermal models for large can aluminum electrolytic capacitors have existed for a number of years for screw terminal products. These models have various shortcomings in their ability to handle the effects of package size, roll diameter and the mechanical details of assembly. An improved model was introduced recently which more accurately accounts for these internal parameters. This paper extends the use of that model to improved constructions which allow much more ripple current with no more internal heating than standard capacitors. An approximate empirical relationship has been developed to estimate conduction of heat from the roll to the terminals. In addition, the external environment of the capacitor has been considered since dissipation of heat necessarily involves transfer of the energy away from the capacitor. Studies have been conducted on the effect of air flow on the package-to-ambient thermal resistance. The use of external heat sinking is shown to be effective, especially when air flow is available and the heat sinks are integrated with the capacitor package to minimize the thermal resistances in the heat flow path. In these cases, the external thermal resistances can be reduced by more than 50%.

In prior studies we have reported considerable progress in improving the heat dissipation due to ripple current for large aluminum electrolytic capacitors [elcaps]. Due to these enhanced thermal construction techniques, elcaps are now commercially available with very high ripple current ratings at moderate cost. In those same studies, some effort was devoted to the improvement of the heat dissipation from the elcap into the external environment. This paper extends that work. A number of attempts have been made to enhance the removal of heat from the exterior of large elcaps with varying degrees of acceptance. We describe several approaches to external heat removal including an active heat removal system, which can deliver total thermal resistances around 1 C/Watt with a minimum of additional required space. It is believed that these approaches will be useful to those equipment designers who place a high priority on achieving the greatest possible circuit densities without resorting to liquid cooling.