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'[EE]: Grease coating + electrolytics = failure'
2002\08\03@095222 by Morgan Olsson

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I think we can learn sometning from why the electric fence unit broke. (my recent post "Urgent ST FJ0916CI datasheet"):

The IC supply radial cased electrilytic cap has become loose because the rubber gasket had expanded and pulled the solder joint broken.  I guess then the PWM got crazy and destroyed the power FET.  The tracks of that is the IC, Power FET, and a resistor got blown.

The original failure reason i tink is that the cirquit board is covered with some grease, and it seems something in the grease diffuses into the gasket which then expands.

I have also found another radial eletrolytic cap on the cirquit board hich has also pushed itself out.

Lesson: Never use grease coating toghether with rubber part components!
(such as electrolytics)

I always use silicone coating.

The unit is twelve years old, but more than ten of them was on the shelf, so it served only one season.

/Morgan

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2002\08\03@135307 by M. Adam Davis

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Are you sure the gasket wasn't pushed (expanded) out by the capacitor
expanding itself?

You can find out by taking the gasket out and seeing if it is still flat
or if it has, indeed, expanded.  My experience has been that when the
electrolytic fails slowly it bulges the can, and I've seen more than one
push the gasket out.

Sometimes it's just the electro (they have a limited life) going bad,
but often another part goes bad and destroys the electro.

-Adam

Morgan Olsson wrote:

{Quote hidden}

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2002\08\03@135802 by Roman Black

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Morgan Olsson wrote:
>
> I think we can learn sometning from why the electric fence unit broke. (my recent post "Urgent ST FJ0916CI datasheet"):
>
> The IC supply radial cased electrilytic cap has become loose because the rubber gasket had expanded and pulled the solder joint broken.  I guess then the PWM got crazy and destroyed the power FET.  The tracks of that is the IC, Power FET, and a resistor got blown.
>
> The original failure reason i tink is that the cirquit board is covered with some grease, and it seems something in the grease diffuses into the gasket which then expands.
>
> I have also found another radial eletrolytic cap on the cirquit board hich has also pushed itself out.


I think it may be heat related. If you have two
electro caps bulged open or exploded open, that is
probably the source of the "greasy" stuff.
The greasy stuff my be corrosive and poisonous. :o)

Am I right in thinking this electric fence unit has
been working non-stop in the summer sun? Might just
be that the heat finally got to the 12 year old caps
and they blew their guts.
-Roman

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2002\08\03@152601 by Tom Messenger

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At 02:52 AM 8/4/02 +1000, you wrote:
>Morgan Olsson wrote:


>> The original failure reason i tink is that the cirquit board is covered
with some grease, and it seems something in the grease diffuses into the
gasket which then expands.
>>
>> I have also found another radial eletrolytic cap on the cirquit board
hich has also pushed itself out.

You may very well be correct, Morgan, in that the grease caused the failure
of the capacitor. In a previous life, I worked at a power supply company.
It was standard practice to run the boards through a vapor degreaser to
remove solder flux.

Someone changed brands of electrolytic capacitors at one point and a rash
of failures resulted. The failures did not happen in house. They occurred
at the customers site, from 1 to 3 months later.

It was determined that the degreaser solvent was being "soaked up" by the
sealing gasket in the end of the capacitor.  Over time, the solvent did 2
things: it caused the gasket to swell up and it slowly destroyed the
dielectric of the cap. The cap slowly lost its capacitance; some went open,
some went shorted, most failed.

Tom M.

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2002\08\03@175520 by Morgan Olsson

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Roman Black wrote:
>I think it may be heat related. If you have two
>electro caps bulged open or exploded open,

Not open, just the rubber bulged out enough, 1mm, to put enough stres to the solder joint to by time pull the pin loose.

>that is probably the source of the "greasy" stuff.

I meant the whole cirquit board, both sides, and other parts are covered by a grease.
It is definitely not coming from the Caps.

Look petroleum based, yellowish and very like lubrication grease...

Adam Davis wrote:
>Are you sure the gasket wasn't pushed (expanded) out by the capacitor
>expanding itself?

Dissassembled one, and the inner seem clean and OK.
I can easily make a scar in the gasket with my nail!

>Sometimes it's just the electro (they have a limited life) going bad,
>but often another part goes bad and destroys the electro.

According to my capacitance meter both caps were well within spec.

/Morgan

>Morgan Olsson wrote:
>
>> The original failure reason i tink is that the cirquit board is covered with some grease, and it seems something in the grease diffuses into the gasket which then expands.
>>
>> I have also found another radial eletrolytic cap on the cirquit board hich has also pushed itself out.

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2002\08\04@131237 by Peter L. Peres

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There are types of grease additives, solvents and other organic substances
that cause synthetic plastics and rubbers to fail, including by puffing
up. Until you will know what that grease contained there will be no way to
know if it killed your parts. My suggestion: take a new capacitor of the
same kind, put some grease on it, and seal it in a small box for a few
months (maybe in a warm place). Then inspect it.

There is a REASON for not using just any conformal coating off the shelf
without testing over time. Same for solvents, oil, grease, etc. More
serious firms have people who run these tests and compile lists of
'tested' supplies.

Peter

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2002\08\05@182105 by Welch, Ken

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have seen condition where the cleaning solvent has penetrated the rubber
seal ("bung") of an electrolytic...this causes a chemical breakdown of the
electrolyte -- then the part was sealed with conformal coating and "canned"
-- preserving the degraded part

the condition now is like a small (or large) time bomb.  internal pressure
will eventually cause a catastrophic failure and the breakdown of the
electrolyte produces hydrogen...all it needs is a spark -- as when the unit
has to be replaced...

under the right conditions -- like when you're hanging in your climbing
harness at the top of a telephone pole - this can keep electronics a
exciting profession...or at least require clean underwear...

Ken

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