[ARC5] Reforming Electrolytics attached as PDF

[Richard Knoppow]

    It should be understood that there is both series and 
parallel resistance in a capacitor. ESR may be less important 
than parallel resistance, which is also called leakage.
    All electrolytic capacitors have leakage and it is the 
leakage that ruins them when it becomes too low. ESR, also called 
Dissipation Factor, is a measure of the Q of a capacitor while 
parallel resistance or leakage measures the amount of DC is passes.
    Ageing without voltage may reduce the thickness of the 
dielectric layer. This will lower the effective voltage rating of 
the capacitor and may raise its capacitance, but may not affect 
its leakage. A high leakage capacitor of any kind may measure OK 
for both value and ESR so both kinds of measurement are 
necessary. The leakage is measured by testing for current through 
the cap. An ideal capacitor should not pass any DC current. 
Practical electrolytics always have some. The old capacitor 
checkers of the sort with a magic eye indicator were leakage 
testers. They usually have a variable DC source for electrolytics 
and a means, often the eye tube, for indicating leakage current.
     I don't think reforming will help leakage.
     A typical impedance bridge does NOT measure leakage although 
it may give a value for parallel resistance. These two are 
confusing because they use the same name for different things. An 
impedance bridge may indicate either series or parallel 
resistance depending on its configuration and range but, unless 
it of the kind that has a DC source for the capactor it will not 
indicate leakage resistance.
     Leakage may not be apparent with a low test voltage because 
it may be due to break down of the dielectric at some voltage. 
However, it may show up even with a conventional ohm meter when 
it reaches high value. I have bad electrolytics that show bad on 
a Hewlett-Packard 410-B VTVM ohm range and also show bad on a 
General Radio Megohm meter and also on an old Eico capacitor 
tester. They are just bad.
     Storage in a capacitor is another way of measuring leakage. 
ESR will not affect the rate at which a charge is lost, that is 
due to parallel resistance. It is partly a property of the 
electrolytic and partly of the insulation of the capacitor body. 
Good non-electrolytic caps can hold a charge for years.
     There are other properties of capacitors such as dielectric 
absorption AKA voltage recovery, which can be critical in some 
applications and unimportant in others. This is the effect of a 
capacitor not fully discharging when shorted. After the terminals 
are opened again some voltage, often considerable appears across 
them. This can be very important in capacitors intended for 
timing and low frequency applications. Mica caps have a lot of 
absorption, paper is low in absorption and plastic has very 
little. It is of no importance in the usual applications for 
electrolytic caps.



On 3/19/2018 10:43 AM, Kenneth G. Gordon wrote:
> On 19 Mar 2018 at 10:06, Bob kb8tq wrote:
> 
>>      His method is to reform the electrolytic VERY SLOWLY, with a B+ source limited to
>>      FIVE MA., while monitoring the Cap voltage.
> 
> This is EXACTLY what that military document I posted says: 5 mA, no more, over a long
> period of time.
> 
> Some of us use 1 mA, which may actually be too low. Testing is required.
> 
> I also have and use an ESR meter.
> 
> Ken W7EKB

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