A New Method for Testing Electrolytic Capacitors to Compare Life Expectancy

Abstract

Power system applications, such as street lighting, typically have a 10 year warranty. When these systems include electrolytic capacitors, it is important to choose a supplier that meets these requirements. Traditional lifetime testing of electrolytic capacitors to ascertain their life expectancy requires specialized equipment, is time consuming, labor intensive, and for most OEMs, is ultimately cost prohibitive. Electrolytic capacitors with the same capacitance and voltage ratings from different suppliers may be rated to the same lifetime, but historical data confirms that they can have significantly different operational expected lives. An accelerated testing methodology is needed to compare the reliability of electrolytic capacitors from different suppliers. DfR has developed an approach that reduces test times from thousands of hours to several weeks by taking advantage of two key behaviors of electrolytics. The first involves the rate at which capacitors lose electrolyte, which is fairly predictable at a given temperature and electrical stress. The second key behavior is the dependence of the equivalent series resistance (ESR) of electrolytic capacitors on the volume of liquid electrolyte. The approach that will be described in this paper will demonstrate a means of comparing the time to failure for comparable capacitors from different suppliers under the same conditions. Case studies will demonstrate how this method avoids the extended testing that is typically required.

An Overview of Condition Monitoring Techniques for Capacitors in DC-Link Applications

“…4(a) shows the average weight loss of an Al-Cap (Nichicon PW series, 450 V/68 F), Fig. 4(b) gives the relationship between weight loss and RESR changes [108]. It is found that the weight of capacitors decreases with the degradation of capacitors, the critical weight loss can be defined at a 200% increase in RESR.…”

“…3(b) lists some commonly used parameter acquisition methods. It is found that industrial instruments including weighting meters [108], [109], X-ray image meters [110], optical inspection meter [111], acoustic detection meter [112], thermography meter [113], etc., are widely used to obtain non-electrical parameters. Moreover, internal temperature sensors [114] and internal pressure sensors [115] are employed to obtain the internal temperature and pressure of capacitors.…”

“…Citation information: DOI 10.1109/TPEL.2020.3023469, IEEE Transactions on Power Electronics Average weight loss of a type of Al-Cap (Nichicon PW series, 450 V/68 F) [108]. (b) Weight loss versus RESR changes of this type of Al-Cap [108]. (c) X-ray images of a healthy Al-Cap and a failure Al-Cap [109].…”

Design for Accelerated Testing of DC-Link Capacitors in Photovoltaic Inverters Based on Mission Profiles

“…This will accelerate the wear-out of the capacitor, and thus decrease the capacitor lifetime and its reliability [11]. Therefore, the reliability of the dc-link capacitor in PV inverters has been investigated in several aspects such as design for reliability [12], lifetime analysis [13]- [15], and testing [16].…”

“…Conventionally, the reliability testing of the dc-link capacitor is done under a constant electrical stress (e.g., ripple current/voltage and bias voltage) and/or environmental stress (e.g., ambient temperature) condition. For instance, a rated (constant amplitude) ripple current, rated bias voltage, and rated ambient temperature are applied to the capacitor during the accelerated lifetime testing in [16] and [17]. Similar testing condition is also considered in [18]- [20], but the ripple current is not applied during the test.…”