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Large aluminum electrolytic capacitors are usually selected by considering factors such as cost effectiveness (more ripple current or capacitance per dollar), space effectiveness (less volume per dollar), and performance (more useful life at actual application temperature and voltage). These factors have been addressed in recent years as most major manufacturers have responded with improvements in ripple current ratings, new electrolyte systems, high capacitance foils, and rigorous cost controls. The focus of this paper is some of the constructional and application factors affecting the performance of large electrolytic capacitors. An aluminum electrolytic capacitor must be considered as a complete system since the internal failure mechanisms are multiple and complex in their interactions. It is also shown that the choices made by the circuit designer can be informed and improved by understanding the tradeoffs between different capacitor series, circuit design parameters and equipment design enhancements. This understanding can result in designs that are both reliable and cost-effective.

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%.