How Are Your Capacitors Doing?

Industrial electronics use Electrolytic Capacitors on control and power boards, power supplies and elsewhere inside the component. From our experience, unfortunately, capacitors are the most high-fail component in electronic devices. The great news is, a reputable repair facility can bring your component back to life.

VFDs use Electrolytic Capacitors in the DC Bus section. Capacitors store and release energy as needed within a circuit. Larger capacitors generally have higher current load-handling ability and greater charge storage capacity. These properties are well-suited for large VFDs because some A/C motors need a pulse of energy 300 to 500 percent of normal to get them going. A Bus capacitor in a VFD is used for this application. Capacitors are the most high-fail component in electronic devices.

Why Capacitors Go Bad

The caps can go bad due to age or temperature transients. Typically, the function a capacitor is to act as a power supply filter.  It’s comprised of two strips of aluminum foil (called plates) separated by a paper insulator.  The foil and paper are rolled into a cylinder and immersed in an electrolyte solution consisting of an ethyl glycol fluid. This electrolytic moist separator inside can and will dry out if the unit gets too hot, causing it to develop an internal short circuit. The capacitor can fail if its temperature routinely goes above 150 degrees Fahrenheit or below 32.

Also when large amounts of current flow into the capacitor, it causes the electrolyte solution to boil and turn into a gas. Once turned into a gas, pressure builds rapidly until, hopefully, the safety vent plug releases pressure. (Thus, the term “puffy caps”.) This rupture can be dramatic and destructive. Not only is the boiling liquid and gas hot, it is also corrosive and will damage any components covered by the solution. Under controlled laboratory conditions, measurements have been taken during a violent, large capacitor rupture.  The equivalent explosive force of half a hand grenade has been measured. Many of the violent failures have been captured by mad scientist types on video.

The dielectric oxide-insulating layer is created during manufacture.  However, it will deteriorate in the absence of a sufficient rejuvenating voltage, and eventually the capacitor will fail if voltage is not applied.  Maintaining the integrity of the dielectric requires the steady application of power.  When voltage is applied, the oxide layer is rebuilt.  The oxide layer thickness is the crucial factor to determine the voltage rating of the capacitor.  Otherwise, the oxide layer will break down under voltage and cause a spectacular failure.

By applying voltage to the capacitor on a regular basis, the oxide layer is “reformed”, and the integrity of the insulating characteristic is ensured.  In our experience, the maximum time between power ups should be no longer than one year, provided the equipment is kept in a dry location at roughly 70 degrees F. Large temperature swings require less time between power ups.

In conclusion, look through your shelves to see if you have any electronic equipment that has not been powered up in the last 12 months or what equipment is operating in extreme temperature swings. Do you have equipment like this? If the answer is yes, you should seriously consider sending it to a trusted repair facility to be checked out in a controlled environment.

Many repair facilities, like Innovative-IDM repairs offer a free evaluation on all repairs, and can determine if it time to “refresh your caps”.  As a part of any repair we do, we replace all capacitors more than 5 years old, or any showing signs of degradation. Don’t let a faulty cap result in downtime at your facility.

When he’s not collecting on bets, Marc Phelps is manager of the Innovative-IDM repair facility in Houston. You can contact him at [email protected]