bulger

A bulger is an electrolytic capacitor whose casing has swollen outward, typically at the top or sides. The bulge signals that internal pressure has built up inside the component, usually from gas generation caused by electrolyte breakdown or overheating. This deformation is a clear warning sign that the capacitor is degrading and will likely fail within hours or days.

Electrolytic capacitors, especially aluminum electrolytics, generate hydrogen and other gases when their electrolyte decomposes. This happens when the capacitor operates beyond its voltage rating, exceeds its temperature limit (usually 85°C or 105°C for common types), or simply ages past its design life. As pressure accumulates inside the sealed aluminum or steel can, the casing yields at its weakest point, most often where the top is sealed. The bulge starts small but grows visibly as internal pressure increases.

Bulging capacitors are usually spotted during visual inspection of circuit boards, particularly in power supplies, LED drivers, and audio amplifiers where electrolytics work hard. A bulger that ruptures violently can spray caustic electrolyte or, in rare cases, cause the can to split. This makes bulged capacitors a fire and safety hazard in equipment still in service. Some designs include a safety vent on the top that opens before the case deforms, making a bulge less likely but not impossible.

The term bulger is informal shop language rather than formal engineering nomenclature. Datasheet terminology refers to the same failure mode as 'case expansion' or 'leakage current overstress'. In failure analysis, a bulged capacitor indicates the circuit subjected it to stress beyond design envelope, whether through overvoltage, sustained high ripple current, poor thermal management, or simple age-related electrolyte drying.

Finding a bulger on a board means the capacitor must be replaced immediately, and the circuit should be inspected for the root cause: a failed voltage regulator, a thermally choked enclosure, or a design margin that was too thin. Ignoring bulged capacitors leads to further component damage and potential catastrophic failure of the entire device.