Re: {Collins} (no subject)



AMEN Dennis..  Knowledge is power.  Many folks that "reform" are doing it
way wrong.

Bill

-----Original Message-----
From: Collins [mailto:collins-bounces+wcarns=austin.rr.com@xxxxxxxxxxxxx] On
Behalf Of Dennis Monticelli via Collins
Sent: Thursday, October 26, 2017 3:28 PM
To: Glen Zook <gzook@xxxxxxxxx>
Cc: collins <collins@xxxxxxxxxxxxx>
Subject: Re: {Collins} (no subject)

You can generally tell if the quality of the reformed oxide is decent by
observing the reforming process.  The slower the regrowth the denser and
higher quality of oxide gets created.  I usually limit regrowth rates to
only a mA or so, start with a low voltage and watch the current meter.  You
will notice that the regrowth is not uniform.  It will surge for a while and
then drop off, surge again, and then drop off as the pinholes in the old
oxide are filled (old depleted aluminum oxide is very irregular).
After complete reforming the current draw should be fairly low.  50uA is
outstanding, but up to 500uA is OK at rated voltage. I am speaking of
typical value old HV caps like a 40uF.  At this point, the current draw
should be steady.  You are now at an equilibrium of oxide tear-down vs
replacement.  This is normal.  It's how an electrolytic cap works.  If the
equilibrium current is still jumpy or the value of the current high (like a
mA or more), you have a reformed cap that probably won't hold up well.

For classic equipment I usually attempt a patient reformation first.  My
equipment is not fancy: A Heathkit IT-11 and an external current meter (my
Simpson VOM).

Just my two cents worth.

Dennis AE6C

On Thu, Oct 26, 2017 at 1:09 PM, Glen Zook via Collins <
collins@xxxxxxxxxxxxx> wrote:

> My experiences are that "reforming" a capacitor is only postponing the 
> replacement and for how long, nobody knows.  Most "reformed" 
> capacitors do not last all that long and when they do "give up the 
> ghost" the result is not pretty.  Often, when the capacitor goes bad, 
> it "takes out" a lot more components with it and the chances are that 
> replacing those components is going to be a lot more added expense 
> than replacing the capacitor in the first place.  Basically, pay me a
little now or pay met a LOT more later!
>
>
> Replacement electrolytic capacitors are not expensive when purchased 
> from suppliers such as Mouser.
>
>  Glen, K9STH
> Website: http://k9sth.net
>
>       From: Jim Warner via Collins <collins@xxxxxxxxxxxxx>
>  To: W2HX <w2hx@xxxxxxxx>; 'collins' <collins@xxxxxxxxxxxxx>
>  Sent: Thursday, October 26, 2017 9:55 AM
>  Subject: Re: {Collins} (no subject)
>
> On 10/25/2017 10:23 PM, W2HX via Collins wrote:
> "you bring up the resulting B+ until you see capacitor leakage"
>
> Yes. This is the point where I power down the unit under test, note 
> the capacitor working values and form factor, assess cosmetic impact, 
> then determine whether to replace or repack the original housing with 
> a modern and reliable equivalent.
> I've had terrible luck "reforming" capacitors. Win the battle, but 
> inevitably wind up losing the war.
>
>
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