Aluminium electrolytic capacitors are widely used in industrial power supplies and drive DC-link circuits because they provide useful capacitance in a compact form. They are also components whose condition can change with time, temperature and electrical duty, making them relevant when assessing ageing equipment.
What ageing changes
An electrolytic capacitor uses a liquid or gel electrolyte as part of its construction. Over long service periods, changes in the electrolyte and internal interfaces can affect capacitance, equivalent series resistance and the ability to handle ripple current. The rate is not fixed: construction, temperature, voltage stress and operating duty all influence it.
This is why a single age rule is a poor substitute for assessment. Two nominally identical drives can have very different service histories—one operating continuously in a hot enclosure, another lightly loaded in a clean, temperature-controlled space.
Heat and ripple current interact
Ripple current produces internal heating through the capacitor's losses. Higher ambient temperature, restricted airflow or nearby hot components can add to that thermal stress. Drive manufacturers therefore relate maintenance expectations to operating conditions rather than treating calendar age as the only variable.
Cooling-system condition matters indirectly. A failed or obstructed fan can raise the temperature of the whole power assembly, affecting capacitors as well as semiconductors, resistors, connectors and solder joints.
Storage is not the same as operation
Long periods without voltage can affect the oxide layer that forms the capacitor dielectric. Drive manufacturers publish reforming guidance for equipment that has been stored for extended periods. The correct action depends on the equipment and manufacturer instructions; applying full power to long-stored equipment without considering this can be an unnecessary risk.
Storage temperature, humidity and contamination also matter. A spare kept in a controlled store has not experienced the same conditions as a unit left in a damp plant room, even when neither has been running.
Visual appearance has limits
Bulging, leakage or a ruptured pressure vent are clear reasons for concern, but the absence of visible damage does not establish electrical condition. Many changes are internal and require suitable assessment. Conversely, replacing every capacitor on sight can introduce avoidable rework risk if the scope is not justified and the replacement selection is poor.
The surrounding circuit should also be considered. Excessive ripple, power-supply faults or thermal problems can damage capacitors; replacing only the visibly affected part may leave the cause in place.
Use an equipment-specific refurbishment decision
A sensible decision considers service history, environment, capacitor duty, measured condition where appropriate, the consequence of failure and whether access will be difficult after the equipment returns to service. Selected preventative replacement can be valuable, but it should be part of a defined refurbishment scope rather than an automatic age-based rule.
Practical conclusion
Electrolytic capacitors deserve attention because their condition is linked to real electrical and thermal service. They should be assessed in context, using suitable parts and a scope proportionate to the equipment.
References and further reading
Public manufacturer material used for general context. Access and content may change at the source.