[ARC5] NOS Electrolytics

Mon Jun 2 14:42:54 EDT 2014

> John and all,
>
> I think your reforming process is very sound.  A resistor and fixed
> voltage
> that keeps the power dissipation within the cap to <500mW (for the large
> caps) is sufficient.  Better quality cap testers can be used to reform
> too.
>  There is really no excuse for not doing it because it is easy.

Agreed! It can also help prevent collateral damage, both to the cap and
other circuit components.

> When I reform I like to put a current meter in series (as you do with your
> HP supply) to observe what is going on.  As the reforming takes place the
> current does not undertake a steady and smooth decline.  It is often
> erratic.  Others may have noticed this too.  This is because the process
> of
> regrowing the oxide is not uniform across the roll of layers.  You can
> even
> observe the current increasing after a decline and then declining once
> again only a fraction of a minute later.  Old caps tend to be more
> erratic.

Yes,I observer short-term (seconds) variation of maybe 10% - 20%.

>  Once formed this behavior stops, so as long as the residual leakage is
> reasonable vs the number of uF you probably now have a good cap.  A check
> of the dissipation factor (i.e. ESR) wouldn't hurt but is not really
> necessary.

Agreed, although a C checkis not a bad idea.

> Many of you already know the following but it bears repeating for those
> readers who don't.  Leakage in a 'lytic is a normal part of the dielectric
> maintenance process.  The cap is losing and regrowing atomic layers
> continuously as part of a self-repairing equilibrium state.  This is
> normal
> and healthy as long as the amount is proportional to what one would expect
> for the uF's and voltage rating.  In fact, if you don't have some leakage,
> then you don't have a functioning electrolytic capacitor.  EIA has
> published standards for electrolytic leakage and modern cap datasheets
> give ranges (*Electric Radio* published a chart a number of years back
but I do
> not remember the issue).  For example, a 47uF 400V cap has an allowance of
> about 800uA.  1500uF at 100V has an allowance of 2.3mA.

The latter number was also in the manual for the Sencor LC102.

> If you're at or under the allowance, the cap is deemed OK.

Initially the leakage on my 1500uF @ 100 VDC was >10mA; after roughly a
day on the supply, it is down to roughly 60uA...  well below the 2.4mA
spec.

> Like John found, it seems to be
> the rule rather than the exception that old NOS (even only 10 to 20 years
> old) benefit from reforming or one risks heat damage from a prolonged
> current surge at the hands of the equipment's circuitry.

Exactly.

Best,

-John

===================
>
> Dennis AE6C
>
>
>
>
> On Sun, Jun 1, 2014 at 3:08 PM, J. Forster <jfor at quikus.com> wrote:
>
>> The supply I use is regulated w/ adjustable current limit (HP 6209B).
>>
>> You can use any old adjustable supply and a DMM and current limiting
>> resistor.
>>
>> I set the supply voltage to the rated DCWV of the cap and set the
>> current
>> limit to keep the dissipation <0.5 W.
>>
>> If you're doing the resistor setup, monitor the current and jack up the
>> voltage intermittantly.
>>
>> These caps are about 2" long, and 7/8" OD, axial lead. After a while the
>> DO get very slightly warm.
>>
>> IMO,it's a very good idea to keep the power limited to avoid any
>> overheating the guts of the cap.
>>
>> -John
>>
>> ==================
>>
>>
>>
>>
>> > John:
>> >
>> > What voltage should be used to reform caps?
>> > I've got a lot of them with label voltages between 10 and 330 V.
>> >
>> > I have a table showing measured ESR on a bunch of caps at:
>> > http://www.prc68.com/I/Capacitors.shtml#Tbl
>> > On the page is also a procedure for measuring super caps
>> >
>> > I sell a combined ESR & Capacitance meter that's made in Russia.  See:
>> > http://www.prc68.com/I/ESRmicro.shtml
>> > I've made a number of repairs using this meter where there was no
>> > documentation.
>> >
>> > Have Fun,
>> >
>> > Brooke Clarke
>> > http://www.PRC68.com
>> > http://www.end2partygovernment.com/2012Issues.html
>> > http://www.prc68.com/I/DietNutrition.html
>> >
>> > Kenneth G. Gordon wrote:
>> >> On 1 Jun 2014 at 14:12, J. Forster wrote:
>> >>
>> >>> I want them to reform some before judging.
>> >> OK.
>> >>
>> >>>>> I've not measured the ESR or C as yet.
>> >>>> Oh. OK. I have at least two ESR meters here and have found them
>> >>>> invaluable.
>> >>> I've never been a real fan. I can measure it on a GR bridge.
>> >> Well, the two I have, a Dick Smith kit, and one I bought off eBay,
>> work
>> >> very
>> >> well, are quick, and have other uses too.
>> >>
>> >> I have a couple of bridges, including a really beautiful military
>> one,
>> >> but they
>> >> take too long to set up for a single use.
>> >>
>> >> If I were going to use it to test a bunch of caps, I would use it,
>> but
>> >> otherwise it
>> >> is too much trouble,
>> >>
>> >> Ken W7EKB
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