[ARC5] Aging Electrolytics

[Richard Knoppow]

On 1/30/2015 6:07 PM, Kenneth G. Gordon wrote:
> On 30 Jan 2015 at 19:35, David C. Hallam wrote:
>
>> Only as a last resort would I consider reforming old electrolytics.
>> Compare the cost of rewinding a power transformer to $35/40 of a new
>> capacitor.
>>
>> David
>> KW4DH
> I'm with you on this: unless there is some sort of dire emergency, any
> electrolytic which shows significant leakage is tossed.
>
> Heck, if they even LOOK old, out they go.
>
> It is not worth the effort, nor the worry.
>
> I have an ESR meter, and I use it when needed.
>
> Ken W7EKB
>
         ESR may not always be the right criterion.  Rather leakage, or 
parallel resistance may be the right thing to look for. Electrolytics 
have fairly high ESR even when new. Of course the lower the better, but 
leakage is often critical.   Its possible for a capacitor of any type to 
measure low ESR but still be leaky.  ESR is measured using AC, it is the 
equivalent of Q for a capacitor, leakage is measured with DC, an ideal 
capacitor should not pass DC at all, practical ones have some equivalent 
parallel resistance because nothing is a perfect insulator, but it 
should be low enough not to cause problems to the circuit the cap is 
used in.
        Leakage may not show up with low voltages so its usually 
recommended that , at least for electrolytic caps, it be measured at 
something approaching operating or rated voltage.  I have found for 
paper caps an ohm meter capable of reading high values of resistance, 
for instance a Hewlett-Packard 410B or C or an -hp- 412, will usually 
indicate when leakage is excessive.  For some caps something like a 
"megger" is better.   Both high ESR and leakage are bad.

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