[ARC5] Aging Electrolytics

[Roy Morgan]

On Jan 30, 2015, at 5:51 PM, Robert Eleazer <releazer at earthlink.net> wrote:

> I have been wondering.  We all know that electrolytic caps tend to deteriorate with age.  But how about the 600V and 1000V varieties?  Are they less prone to deteriorate?

Bob and other hopefuls-about-electrolytics,

There are available single section electrolytics rated at 500 volts working.  I suspect that any rated above this are actually two caps in series, though I don’t have any real evidence at hand.

Given that, it seems to me that electrolytics rated at 600 or 1000 volts may pose some troubles if you try to reform them.  I can guess as to what might happen if one of the two caps reforms badly and will not come up to voltage, and the second one actually does reform to above rating.  You will have an unbalanced situation that could lead to disaster:  SPLAT!

Many caps we find in amateur and military electronics rated at 600 volts and above are actually oil and paper devices.  These seem to have a very long life and though failures have been reported, they seem to be rare.  These caps don’t get reformed as do electrolytics, nor do they seem to degrade with time due to reversal of the chemistry the electrolytics depend upon.

I have gathered additional information about reforming electrolytics that came from the earlier version of the MIL SPEC on the topic.  I have just found the first, A and B versions of the mil spec.  The B version omits the leakage specs given in the A version, and the original version refers the reader to MIL-C-62 for this and other information.

These are:
MIL-HDBK-1131B
29 October 2008
SUPERSEDING
MIL-HDBK-1131A
14 June 2004

STORAGE SHELF LIFE AND
REFORMING PROCEDURES FOR
ALUMINUM ELECTROLYTIC FIXED CAPACITORS

I did just find the A version:

MIL-HDBK-1131A 14 June 2004
SUPERSEDING
MIL-HDBK-1131
7 July 1999

at  http://everyspec.com/MIL-HDBK/MIL-HDBK-1000-1299/MIL_HDBK_1131_1788/

I also found the MIL-C-62/5B, and MIL-C-62/D which has extensive tables giving leakage current, maximum impedance and dissipation factors.  (By the way, the  highest voltage unit included in the table is rated at 450 VDC with a surge rating of 500 volts.)

If anyone should encounter a leaking oil cap and become alarmed at the dreaded consequences of contact with PCB compounds, I offer my Rule for Radioactive Meters and Tubes as applicable advice:

DON’T BREAK THEM OPEN AND EAT THE INSIDES.

I will be updating my “diatribe” on capacitor reforming with this new-to-me information in the near future.  In the meantime, happy capacitating to all.

Roy


Roy Morgan
RoyMorgan at alum.mit.edu
K1LKY Since 1958