[Boatanchors] Capacitor Reforming

[Jim Wilhite]

This topic has as many facets as a diamond.  When I acquire a new radio that 
has not had the electrolytic changed, I change them anyway.

Reason!  The electrolytic has a paste that dries over time even without use. 
Most of the radios that we have been used or nearing the 50 year mark if not 
over, therefore subjected to additional heat which dries the paste.

It is very important that the caps do their job, and in some cases can cause 
the loss of a choke or transformer.  So to prevent the loss of a component 
that may be irreplaceable or expensive to acquire, I replace them.

Many of them will reform, but in my experience, over a year or so they dry 
and leak excessive current.  Caps are cheap comparatively so I change them. 
If you have a good checker like the TO 6 or a way to measure leakage, try 
them then run the radio for a year and test again.  Don't just test one time 
and forget.  I open every radio I have yearly for a preventative maintenance 
check.  If I have changed the electrolytic, I skip them, if not I check 
them.

73  Jim
W5JO




> In a message dated 2/13/2006 1:51:58 PM Eastern  Standard Time,
> kulow at epix.net writes:
> <snip>
>> Here is a common  scenario, I’m at 50V and leakage
>> current is 2mA, I increase to 100V and  leakage
> goes to
>> 10-12mA then gradually over the next minute  drops
> back to
>> 2mA. Am I watching the reforming process  take
> place? Am I
>> “pushing” the process too fast? All input  welcome.
>>
>> Dave, WW8S
>
> I have a Sprague TO-6 and the manual  is quite
> helpful on
> this topic.  I think BAMA has it for  download.  Well
> worth
> the download time.
>
> Anyway, according to  the manual, when reforming a
> 'lytic,
> keep the current down below 10 mA to  prevent
> overheating.
> The table of acceptable leakage shows that a  /new/
> 80 mF,
> 450 WVDC 'lytic should have a maximum leakage
> current of
> 3.5 mA.  Leakage goes up with age.  To quote,
> "Capacitors
> with a leakage current of more than 15 mA should
> almost
> always be  discarded."
>
> Depending on how old the 'lytic is, it could take an
> hour
> or more to fully reform.  Be patient!
>
> 73
> Bob WA2UEH