VFD DC-Bus Capacitor Life Calculator

Exponentially: each 10 K above the 85 °C reference halves expected life, and each 10 K below roughly doubles it (the electrolytic-capacitor 10-degree Arrhenius rule used across capacitor datasheets (life doubles per 10 K below rated temperature)). A sustained 20 K overshoot quarters the life — which is why a 'small' cooling problem is never small over the years.

Three signals: rising DC-bus ripple (many drives display or log it — trend it yearly), visible bulging or vented cans at inspection, and increasing nuisance undervoltage trips during ride-through events. Drive makers publish preventive replacement intervals (commonly 7–12 years, temperature-dependent) — this calculator adjusts that interval for your real panel temperature. Reforming applies to long-stored drives: power them up annually or the caps degrade unpowered.

It is the engineering linearisation of the Arrhenius equation over the normal operating window, adopted by the relevant standards because it matches test data well within ±20–30 °C of the reference. Far outside that window (or where a different failure mechanism takes over, e.g. mechanical wear) the rule loses authority — treat extreme extrapolations as indicative only.

The hot-spot (the hottest point of the insulation/material), because chemistry happens at the hottest spot. If you can only measure surface or ambient, add the typical rise for your equipment class — datasheets usually state hot-spot rise over ambient at rated load — and remember intermittent peaks age the asset during the peak hours, not the average.