January 1956 Popular Electronics
Wax nostalgic about and learn from the history of early electronics. See articles
published October 1954 - April 1985. All copyrights are hereby acknowledged.
Unlike the article on making your own foil capacitors, this one advising how to 'reactivate' leaky capacitors
might be of use to a lot more people. The process is called 'reforming,' and consists of applying a DC voltage
to the faulty capacitor, beginning at a very low voltage, and then slowly raising the voltage until the rated
working voltage (WVDC) is reached. Doing so, if the capacitor is not beyond rehabilitation, will reconstitute
the oxide layer that serves as the dielectric. This particular item was presented as the answer to a question
posed by a reader of Popular Electronics. A Google search on "reform
capacitor" will turn up more detail about the procedure. Most people recommend against reforming unless
you have no other option, as this writer from India might have faced at the time.
See all articles from
Reactivating Leaky Electrolytics
Semcor RC-115 reforming a old Mallory 30 MFD 450V electrolytic capacitor sold by Lafayette Radio. Please visit
the University of Ohio web page where this article resides.
Making purchases of electrolytic capacitors through the post is quite
risky, as nearly half of the stuff you receive may turn out to be leaky
due to long storage. Is there any method of re-activating such leaky
A. H. Purti
It is frequently possible to rehabilitate electrolytic capacitors
which have become excessively leaky after long periods of inactivity.
The process is known as "reforming" and consists of rejuvenating the
insulating film in the capacitor. To accomplish this, a variable-voltage
d.c. power supply having good regulation is necessary. With the voltage
set very low, the capacitor is connected across the supply and the voltage
gradually increased over a period of several minutes until it is equal
to the working voltage rating of the capacitor. The voltage is held
at this point for several minutes, or until the leakage current has
decreased to its normal value. During this process, the leakage current
should be checked frequently. If it is allowed to rise too high, the
capacitor may be permanently damaged.
Posted November 24, 2014