[Explanation of the Causes of Capacitor Failure] Failure of a DC Capacitor in an AC Circuit
A Must-Read Guide for Circuit Designers: 15 Examples of Causes and Countermeasures for Capacitor Failures
The rated voltage is set with a margin, taking into account factors such as AC frequency, voltage waveform, voltage fluctuations, and operating temperature!
The film capacitor in the power circuit shorted and caught fire. In this case, a film capacitor with a vapor-deposited electrode designed for DC was used in an AC circuit. The effective value of the AC voltage and the DC rated voltage of the capacitor were almost the same. As a result, a voltage exceeding the rated voltage continued to be applied to the capacitor, leading to a short circuit and fire. [Countermeasures] - Change to a film capacitor suitable for AC - Set the rated voltage of the capacitor with an adequate margin, considering AC frequency, voltage waveform, voltage fluctuations, and operating temperature - If the DC voltage contains an AC component, it is necessary to choose a capacitor with a DC rated voltage higher than the peak voltage *For more details, please refer to the PDF document or feel free to contact us.
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Please be aware of the following: - When using film capacitors in high-frequency circuits, the capacitors may self-heat. - If self-heating is significant, it may lead to failure. - As the frequency increases, the current flowing through the film capacitor also increases, which reduces the allowable voltage. - When using capacitors with special waveforms, the effective value varies depending on the waveform, so caution is needed when selecting the rated voltage. *For more details, please refer to the PDF document or feel free to contact us.
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If you see the following symptoms in a capacitor, it is faulty: ■ The case is swollen (bulging) ■ There are cracks in the case ■ There is a gap between the case and the sealing part ■ The pressure valve has activated (the pressure valve has opened) ■ The case has burst ■ It is hot or generating heat ■ Smoke is coming out ■ There is liquid leakage ■ There are unusual sounds ■ There is an unusual smell *For more details, please refer to the PDF document or feel free to contact us.
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AIC tech handles Aluminum electrolytic capacitors and Film capacitors for industrial market. Our capacitors have a history of more than 70 years and have their origins in technological development in Japan. AIC tech delivers high-value, precision capacitors tailored for power electronics—from renewable energy and industrial systems to transportation, ICT/IoT, healthcare, and infrastructure. Please feel free to contact us if you have any requests.
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