Capacitors Age, and Sometimes Fail

An aluminum electrolytic capacitor is a wear-out component: its capacitance falls and its equivalent series resistance rises as the electrolyte dries over time, and the rate depends on the core temperature and the ripple. Most capacitor problems are therefore either normal aging that is faster than expected or a specific stress such as over-voltage, reverse voltage or excessive ripple. This article presents a method for diagnosing the common issues in Nippon Chemi-Con capacitors, so an engineer can move from symptom to root cause quickly.

Capacitance Loss

Capacitance loss is expected with age, and the datasheet specifies how much change is allowed after the endurance test. If the loss is faster than expected, check the operating conditions: the applied voltage against the rating with margin, the polarity, the ripple margin and the case temperature. Over-voltage and reverse voltage accelerate the aging, and excessive ripple dries the electrolyte faster. Measure the capacitance and the ESR over time to establish the aging rate, and compare it with the estimated life.

Overheating

A hot capacitor is usually carrying too much ripple, sitting near a heat source, or starved of airflow. Check the ripple current against the rating at the measured case temperature, check the local ambient near the capacitor, and check the airflow. Recheck the derating for the temperature and the frequency, and improve the layout if the capacitor is in the shadow of a heat sink or next to hot magnetics.

Venting and Failure

Venting, where the safety vent opens and electrolyte escapes, usually follows an over-voltage, a reverse voltage, an over-temperature or excessive ripple. Check the applied voltage against the rating with margin, confirm the polarity of every capacitor in the bank, and verify the ripple and the temperature are within limits. In a bank, a single failure often points to an imbalance: if one capacitor carries more than its share of the ripple or sees a higher voltage, it ages faster and fails first. Verify the sharing across the bank.

Connection and Mounting Problems

A loose connection heats the terminal and can damage the capacitor. For a screw terminal, confirm the tightening torque and the busbar flatness, and check the contact area. For a snap-in terminal, confirm the hole spacing fits the terminal layout and that the solder joint or press fit is sound. A high contact resistance shows up as a hot terminal at load, so measure the terminal temperature and compare it with the case.

A Systematic Method

Work from the simple to the complex: check the applied voltage and polarity first, then the ripple and the case temperature, then the bank sharing, then the connections and the layout. Keep a reference capacitor that is known good, and record the capacitance and the case temperature of each new design on the bench, so a later change is immediately visible. BeiLuo supplies genuine Nippon Chemi-Con capacitors with import declaration, certificate of origin and RoHS documents, and our FAE team can help you diagnose a problem and choose a design change that resolves the root cause.