The aluminum electrolytic capacitor is a common component found in nearly every electronic device. You will certainly encounter these devices in school. They are a miracle of modern technology, packing a large amount of charge into a compact, low-cost package. Unfortunately, they do have a limited operational life as described in the Lifetime @ Temp specification.
Must-know facts about polarized electrolytic capacitors
There are a few must-know facts about aluminum electrolytic capacitors:
Capacitor safety precautions
The aluminum electrolytic capacitor will hold a charge for a long time. This presents a safety hazard as unpowered equipment can still deliver an electric shock. Be sure to discharge the capacitor according to the manufacturer’s suggested procedures. Also, be sure to incorporate bleeder resistors, especially for high voltage applications. One of the worst electrical shocks I received was from a photoflash capacitor bank.
Capacitor polarity precautions
The aluminum oxide dielectric is polarity dependent. Incorrect installation will destroy the capacitor. This could range from boiling of the electrolyte with steam exiting the capacitor’s vent to a full explosion where the “guts” of the capacitor are blown out of the case with pieces of aluminum foil strewn over the enclosure. We should all wear safety goggles as a preventative safety measure when working on electronics. As a rule, the negative terminal of the capacitor is marked. Be sure to consult the datasheet as there may be exceptions.
Capacitor degradation and the importance of rejuvenation
The aluminum oxide dielectric degrades with time to the point where the structure is degraded in terms of capacitance and the ability to withstand voltage. Full application of voltage to a degraded capacitor can lead to its destruction. Slow application of current can often restore the capacitor to full health. For example, large Variable Frequency Drives (VFD) have a reforming procedure to restore the capacitor. Search the web to find examples of VFD capacitor restoration.
Precautions for recapping vintage electronics
Capacitors have a finite life. People will often restore vintage audio and guitar equipment by “recapping” the device. This will often restore the equipment to full operation. However, take it slow as it is very easy to make a mistake. Do not replace all capacitors at once, instead replace a few at a time and then test the results. This will limit your troubleshooting to the small areas you just repaired as opposed to the entire device.
Looking forward to continuing the conversation on this forum.
Best wishes,
Aaron Dahlen
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About this author
Aaron Dahlen, LCDR USCG (Ret.), serves as an application engineer at DigiKey. He has a unique electronics and automation foundation built over a 27-year military career as a technician and engineer which was further enhanced by 12 years of teaching (interwoven). With an MSEE degree from Minnesota State University, Mankato, Dahlen has taught in an ABET-accredited EE program, served as the program coordinator for an EET program, and taught component-level repair to military electronics technicians. Dahlen has returned to his Northern Minnesota home and thoroughly enjoys researching and writing articles such as this.