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.
Roll Your Own
Foil Capacitors article in the same issue of Popular Electronics magazine,
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. 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.
Reactivating Leaky Electrolytics
Semcor RC-115 reforming a old Mallory 30 MFD 450V electrolytic capacitor sold
by Lafayette Radio. Note that the original University of Ohio web page is
gone, so the hyperlink now goes to
The Wayback Machine on Archive.org.
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 electrolytics?
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 January 20, 2022
(updated from original post on 11/24/2014)