WREC Reforms Electrolytic Capacitors

"Don't crush that capacitor, hand me the pliers!"


One of the first tasks of the PDP-1 Restoration Project at the Computer History Museum is to test (and if necessary, repair) the power supplies. A key concern is the electrolytic capacitors.

Without use, electrolytic capacitors go bad. This problem commonly occurs with large electrolytics in linear power supplies. However, they can usually be "reformed" by gradually bringing up the voltage and watching the current.

WREC automates this process using serial ports to control SCPI-programmable power supplies. WREC will ramp the voltage, at each step setting an appropriate current limit, and waiting for the leakage current to drop to an acceptable level.

Initially, only the Agilent E3631A triple-output power supply is supported, because that's the only one I have. The E3631A has three power supplies:

max voltage max current
6.0V 5.0A
+25.0V 1.0A
-25.0V 1.0A

The +/-25V supplies share a common ground. In principle WREC can use this power supply to reform three capacitors simultaneously. However, since most of the capacitors to be reformed have rated voltages of 20V or 25V, I normally expect to only reform two at a time.

WREC should work with only very minor modifications with other SCPI-programmable power supplies with serial interfaces. I haven't yet looked into making it control IEEE-488 (GPIB, HPIB) SCPI power supplies, but that shouldn't be too difficult either.

Release Notes for WREC release 0.01

WREC release 0.01 has been hard-coded to use only the +25V supply of the E3631A. It needs a bit more code to negate the voltage when programming and monitoring the negative supply.

In release 0.01, the capacitor parameters are hard-coded in wrec.c. Future releases will parse options on the command line.


WREC is made available under the terms of the Free Software Foundation's General Public License, Version 2.

Source code is available for download.

WREC development uses the Subversion revision control system. Instructions for access to the Subversion repository for Altogether are found at http://svn.brouhaha.com/, and there is a web interface to browse the repository at http://svn.brouhaha.com/viewcvs/wrec.

Related web pages

Last updated January 7, 2004

Copyright 2003, 2004 Eric Smith


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