[ARC5] Capacitor Tests

[Robert Downs]

One thing that is important to consider when testing electrolytic capacitors
is the vintage of the capacitor.  If you apply current day criteria to
vintage components, you may do a bunch of unnecessary replacements.  The
Operator's manual on the ZM-3A/U Analyzer (Capacitor) which was in service
from the 1950's through the 1970's says that electrolytics when tested at
their rated operating voltage shall have a DC leakage current no more than 5
mA.  The Sprague TO-6 manual is more detailed but in general, the results
would be similar.  In general, current day standards would reject all
vintage capacitors, so don't use them.

Robert Downs


-----Original Message-----
From: arc5-bounces at mailman.qth.net [mailto:arc5-bounces at mailman.qth.net] On
Behalf Of Richard Knoppow
Sent: Tuesday, January 8, 2019 19:06
To: arc5 at mailman.qth.net
Subject: Re: [ARC5] Capacitor Tests

    I left something out that may make this clearer. Leakage is a 
measure of how much direct current a capacitor will pass. Of 
course, an ideal capacitor will not pass any DC. Electrolytics 
normally pass some, other types should not pass any. It is 
possible for a capacitor to measure correctly for value and for 
series resistance but still have considerable leakage. Most 
capacitor bridges and many meters do not indicate leakage so will 
show a capacitor as good when it isn't. Most capacitor checkers 
will show leakage. Leakage is important where a cap is used as a 
coupling  cap because it will disturb the bias on the following 
stage. Also in decoupling, i.e. by-pass caps, its supposed to 
short the AC to ground without affecting the DC, if it leaks it 
will pull down the DC source to some degree. That is why leaky 
caps can ruin AGC circuits.


-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL
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