[ARC5] Capacitor Tests

[Peter Gottlieb]

That depends on how often it is energized. Temperature effects on life are frequently time dependent, so if you run the unit one hour a day the effects will occur over a very different time scale than if the unit is on 24/7. As well, there is a thermal time constant, so the capacitor will start from ambient temperature and warm up each time so for the first 15 minutes (for example) the capacitor will be at some temperature between room temperature and it’s ultimate equilibrium temperature. 


Peter

> On Jan 9, 2019, at 9:33 AM, Dennis Monticelli <dennis.monticelli at gmail.com> wrote:
> 
> When decided whether to replace vintage 'lytics I always consider the heating effects of the leakage upon life.  If a cap has 400V across it and leaks 5mA, it's internal temperature would be 2W.  That old cap is not going to last long under those conditions so may as well replace it now vs later.
> 
> Dennis AE6C
> 
>> On Wed, Jan 9, 2019 at 12:15 AM Robert Downs via ARC5 <arc5 at mailman.qth.net> wrote:
>> 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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