[Milsurplus] [ARC5] Cool New DC-DC Converter

[Peter Gottlieb]

What do you mean by "power factor" in this context?

I have heard (can't remember sources) that the best way to revive old 
electrolytics was to apply the current limited voltage, starting low (maybe 1/3 
of rated) and gradually increasing to rated as current decreases then letting 
sit at rated until current stabilizes, a day or so.  I think there is an 
applications booklet from an electrolytic manufacturer floating around which 
gives a good description of the process, can't remember if what is described is 
closer to your method or what I described.

A lot of the older stuff I've recently been resurrecting doesn't even use 
electrolytics, just oil caps, and the low voltage stuff just has tantalums which 
are their own nightmare in terms of reliability.

Peter
kb2vtl


On 3/18/2018 2:40 PM, Bruce Gentry wrote:
> Does anyone know how manufacturers assign or condition new electrolytics for 
> their working voltage?   As long as the power factor is good to begin with, I 
> have had very good results reviving electrolytics that had excessive leakage 
> at or below their operating voltage by applying the rated voltage through a 
> current limiting resistor.  I use no more than 2 milliamps and am patient, 
> reducing the current if needed to prevent heating beyond a temperature 
> pleasent to hold.  A multi section condensor may take a few days to reform, 
> but once they do, the power factor/ESR usually improves as well as capacitance 
> and leakage.
>
>      Bruce Gentry, KA2IVY
>
>
> On 3/18/18 1:08 PM, Dennis Monticelli wrote:
>>   All 'lytics pass current (we call it leakage) as part of their natural 
>> ongoing process of oxide decomposition and reformation.  Operate a 450V cap 
>> at 50V for a long period of time and it will reach a new equilibrium, 
>> eventually becoming a 50V cap.  To use that cap at much higher than 50V 
>> safely would require slowly reforming (re-thickening) of the now very thin 
>> oxide layer until an new (high voltage) equilibrium is reached.
>>
>> We see a version of this situation whenever we power up an old piece of 
>> equipment whose lytics have been dormant for years.  If they haven't dried 
>> out they will properly reform if given the chance. That is why we are careful 
>> to severely limit the current into those caps while we allow the oxides to 
>> slowly reform. Slow growth creates a better quality of oxide and insures that 
>> the negative affects of self-heating are keep at a minimum.
>>
>> Dennis AE6C
>>
>
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