C878BF34300AA4J Datasheet, PDF (7/10 Pages) Kemet Corporation – Motor Run Capacitors

Motor Run Capacitors
C87 Series, Cylindrical Aluminum Case, Overpressure Protection 420 VAC/470 VAC
Dissipation Factor
Dissipation factor is a complex function involved with the inefficiency of the capacitor. The tgδ may change up and down with increased
temperature. For more information, please refer to Performance Characteristics.
Sealing
Hermetically Sealed Capacitors
When the temperature increases, the pressure inside the capacitor increases. If the internal pressure is high enough, it can cause a
breach in the capacitor which can result in leakage, impregnation, filling fluid or moisture susceptibility.
Resin Encased/Wrap & Fill Capacitors
The resin seals on resin encased and wrap and fill capacitors will withstand short-term exposure to high humidity environments without
degradation. Resins and plastic tapes will form a pseudo-impervious barrier to humidity and chemicals. These case materials are
somewhat porous and through osmosis can cause contaminants to enter the capacitor. The second area of contaminated absorption
is the lead-wire/resin interface. Since resins cannot bond 100% to tinned wires, there can be a path formed up to the lead wire into the
capacitor section. Aqueous cleaning of circuit boards can aggravate this condition.
Barometric Pressure
The altitude at which hermetically sealed capacitors are operated controls the voltage rating of the capacitor. As the barometric
pressure decreases, the susceptibility to terminal arc-over increases. Non-hermetic capacitors can be affected by internal stresses due
to pressure changes. This can be in the form of capacitance changes or dielectric arc-over as well as low insulation resistance. Heat
transfer can also be affected by altitude operation. Heat generated in operation cannot be dissipated properly and can result in high RI2
losses and eventual failure.
Radiation
Radiation capabilities of capacitors must be taken into consideration. Electrical degradation in the form of dielectric embitterment can
take place causing shorts or opens.
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