Hello
The material with which the old capacitors were made were not as effective as today's ones and the manufacturers certified their life cycle in an interval reduced to a few years of operation. Often the internal electrolyte is no longer able to form that thin layer of insulating oxide that acts as a dielectric. For this reason, if the gelatinous substance has dried completely, it is no longer possible to attempt a possible recovery.
The first method is probably safer. In practice, the component must be subjected to an increasing voltage over time until the nominal value is reached. This elevation can be done very slowly so that it is completed in about 24 hours. It is advisable to insert a resistance of a few ohms, in case the capacitor is short-circuited. After recharging, a discharge must be carried out, using a resistor in parallel to the capacitor, with which to short-circuit the component. The process has to repeat itself over and over again. The gradual increase in voltage does not have to be automatic but can also be determined by the adjustment of a manual potentiometer. This method contributes to the reformation of the thin oxide layer of the reinforcements. It does not have to be done hastily but it is necessary to spend a lot of time on the discharge and charge cycles.
Another method more abrupt than the previous one is this: the capacitor must be subjected directly to its nominal voltage, that is the one shown on the plate by means of a limiting resistor to avoid any type of short circuit. The duration of the treatment can be, for example, 1 minute. Then you have to unload it with the help of a resistor. You have to repeat the whole operation many times.
Giovanni Di Maria
