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X-capacitor failure modes?

J

Joerg

Jan 1, 1970
0
Folks,

This afternoon I took the old HP-4191A apart. Yesterday in the middle of
some measurements it went pop-pop-pop, loud, like firecrackers. I ran
over and turned it off, upon which the popping stopped. An immense
amount of light-gray smoke wafted out and it had an odd stench to it.
The stench lingered for hours.

I can't find any source and upon powering it up the analyzer worked
fine. That was before I changed anything. As if it had repaired itself.
The only thing I could see is a crack in the plastic of the X-capacitor.
Snipped the thing out, measured, has almost 0.28uF capacitance (27% more
than stated) and no leakage current. There is another X-cap and two
Y-caps inside a canned IEC receptacle but those can't be the culprits
because that is on the line side of the power switch.

Is it possible that an X-cap self-heals to the point where you can
barely see a thing, yet release a serious plume of smoke? It is a Rifa
GPF-series film cap 0.22uF/250VAC with all kinds of agency logos on there.
 
K

Klaus Bahner

Jan 1, 1970
0
Folks,


I can't find any source and upon powering it up the analyzer worked
fine. That was before I changed anything. As if it had repaired itself.
The only thing I could see is a crack in the plastic of the X-capacitor.

I've once had a fluorescent lamp which produced popping sounds for some
time and also smelled a bit of burned plastics. Was hard to localize
where it came from hence it took some time to find the culprit.

It turned out to be an X-capacitor, which also had a crack in the
housing. Had to look carefully, because besides the rather unimpressive
crack, it looked just fine.
Is it possible that an X-cap self-heals to the point where you can
barely see a thing, yet release a serious plume of smoke? It is a Rifa

No idea. I didn't made any measurements on it, just replaced it. Thus I
don't know whether it self-healed or not.

Regards,
Klaus
 
S

Spehro Pefhany

Jan 1, 1970
0
Folks,

This afternoon I took the old HP-4191A apart. Yesterday in the middle of
some measurements it went pop-pop-pop, loud, like firecrackers. I ran
over and turned it off, upon which the popping stopped. An immense
amount of light-gray smoke wafted out and it had an odd stench to it.
The stench lingered for hours.

I can't find any source and upon powering it up the analyzer worked
fine. That was before I changed anything. As if it had repaired itself.
The only thing I could see is a crack in the plastic of the X-capacitor.
Snipped the thing out, measured, has almost 0.28uF capacitance (27% more
than stated) and no leakage current. There is another X-cap and two
Y-caps inside a canned IEC receptacle but those can't be the culprits
because that is on the line side of the power switch.

Is it possible that an X-cap self-heals to the point where you can
barely see a thing, yet release a serious plume of smoke? It is a Rifa
GPF-series film cap 0.22uF/250VAC with all kinds of agency logos on there.

It's possible.. the old Philips 630VDC (I think the AC rating was
250VAC on those) Polyester caps from that era were explicitly claimed
to be self-healing. I don't think I ever accidentally tested it, but I
would have expected less drama (but if it formed an arc track
internally, then an arc might have become self-sustaining). I would
have expected more leakage, but maybe it burned back.

Did it smell more like burning polyester than burning transformer?

If I had it, I would stick it on my "classic" Hi-pot tester and see
where it breaks over.

I guess you could dissect it and see what the insides look like,


Best regards,
Spehro Pefhany
 
J

Joerg

Jan 1, 1970
0
Spehro said:
It's possible.. the old Philips 630VDC (I think the AC rating was
250VAC on those) Polyester caps from that era were explicitly claimed
to be self-healing. I don't think I ever accidentally tested it, but I
would have expected less drama (but if it formed an arc track
internally, then an arc might have become self-sustaining). I would
have expected more leakage, but maybe it burned back.

Did it smell more like burning polyester than burning transformer?

Judging by the smell I was almost sure it was the transformer. But it's
encapsulated and the only place smoke could come out is a small hole
where all its wires tunnel out. But there was not smoke residue anywhere.

The X-cap sits right in the open, so that is one of the very few parts
that could spew stuff without leaving traces.

If I had it, I would stick it on my "classic" Hi-pot tester and see
where it breaks over.

I guess you could dissect it and see what the insides look like,

Maybe I'll do that, I kept it. But first my wife wants me to barbecue
chicken wings, bratwurst and peppers. And when I pulled that analyzer
out of the rack she remarked "Don't put that back in before cleaning
back there!". It's running for 2h now, sans problems, with a new X-cap.
While I cleaned the lab bench, rack and all that.
 
J

Joerg

Jan 1, 1970
0
Klaus said:
I've once had a fluorescent lamp which produced popping sounds for some
time and also smelled a bit of burned plastics. Was hard to localize
where it came from hence it took some time to find the culprit.

It turned out to be an X-capacitor, which also had a crack in the
housing. Had to look carefully, because besides the rather unimpressive
crack, it looked just fine.

Ah, ok, so it could indeed be the X-cap then. I was impressed how much
smoke it let off. The whole room (size of a bedroom) was full of smoke.

[...]
 
M

Martin Riddle

Jan 1, 1970
0
Folks,

This afternoon I took the old HP-4191A apart. Yesterday in the middle of
some measurements it went pop-pop-pop, loud, like firecrackers. I ran
over and turned it off, upon which the popping stopped. An immense
amount of light-gray smoke wafted out and it had an odd stench to it.
The stench lingered for hours.

I can't find any source and upon powering it up the analyzer worked
fine. That was before I changed anything. As if it had repaired itself.
The only thing I could see is a crack in the plastic of the X-capacitor.
Snipped the thing out, measured, has almost 0.28uF capacitance (27% more
than stated) and no leakage current. There is another X-cap and two
Y-caps inside a canned IEC receptacle but those can't be the culprits
because that is on the line side of the power switch.

Is it possible that an X-cap self-heals to the point where you can
barely see a thing, yet release a serious plume of smoke? It is a Rifa
GPF-series film cap 0.22uF/250VAC with all kinds of agency logos on there.

They are Self-Healing to the point that they don't pose a safety risk.
<http://www.kemet.com/kemet/web/home...ege Presentations/$file/EvoxRifaRFIandSMD.pdf>

Cheers
 
J

Jasen Betts

Jan 1, 1970
0
I can't find any source and upon powering it up the analyzer worked
fine. That was before I changed anything. As if it had repaired itself.
The only thing I could see is a crack in the plastic of the X-capacitor.
Snipped the thing out, measured, has almost 0.28uF capacitance (27% more
than stated) and no leakage current. There is another X-cap and two
Y-caps inside a canned IEC receptacle but those can't be the culprits
because that is on the line side of the power switch.

Is it possible that an X-cap self-heals to the point where you can
barely see a thing, yet release a serious plume of smoke? It is a Rifa
GPF-series film cap 0.22uF/250VAC with all kinds of agency logos on there.

They're supposed to self heal

Smoke has low density, you can fit a lot of smoke precursor into a small space.

if it's got a crack it should definately be replaced, why not do some
destructive testing and see if it can withstand the test voltage
required and if it makes the right sort of wrong smell.
 
M

Martin Riddle

Jan 1, 1970
0
Doesn't the UL standard prohibit "excessive" amounts of smoke? But
those Rifa parts are pretty ancient.


Best regards,
Spehro Pefhany

Some smoke is ok, It is the flame and sustained smoking that throw red
flags for UL. X caps fail open, so they should not smoke for long.

If Joerg left the power on long enough, he probably would not have
seen flames or more smoke.

I would have had a 'Oh sh... moment and turned the power off too" ;D

Cheers
 
S

Spehro Pefhany

Jan 1, 1970
0
Some smoke is ok, It is the flame and sustained smoking that throw red
flags for UL. X caps fail open, so they should not smoke for long.

If Joerg left the power on long enough, he probably would not have
seen flames or more smoke.

I would have had a 'Oh sh... moment and turned the power off too" ;D

Cheers

Presumably his immediate objective was to interrupt the proximate
cause of the popping and smoking rather than to fully test those
ancient capacitors to UL standards. ;-)


Best regards,
Spehro Pefhany
 
P

Phil Allison

Jan 1, 1970
0
"Joerg"
Is it possible that an X-cap self-heals to the point where you can
barely see a thing, yet release a serious plume of smoke?

** Yep.

It is a Rifa GPF-series film cap 0.22uF/250VAC with all kinds of agency
logos on there.

** I have been in the room twice when one of them blew itself up - RIFA
brand both times.

The first one was years ago inside a fan heater and the second in a portable
TV late last year.

Filled the room with yucky smelling smoke and set off the alarm.



.... Phil
 
L

legg

Jan 1, 1970
0
Folks,

This afternoon I took the old HP-4191A apart. Yesterday in the middle of
some measurements it went pop-pop-pop, loud, like firecrackers. I ran
over and turned it off, upon which the popping stopped. An immense
amount of light-gray smoke wafted out and it had an odd stench to it.
The stench lingered for hours.

I can't find any source and upon powering it up the analyzer worked
fine. That was before I changed anything. As if it had repaired itself.
The only thing I could see is a crack in the plastic of the X-capacitor.
Snipped the thing out, measured, has almost 0.28uF capacitance (27% more
than stated) and no leakage current. There is another X-cap and two
Y-caps inside a canned IEC receptacle but those can't be the culprits
because that is on the line side of the power switch.

Is it possible that an X-cap self-heals to the point where you can
barely see a thing, yet release a serious plume of smoke? It is a Rifa
GPF-series film cap 0.22uF/250VAC with all kinds of agency logos on there.

Never heard of Rifa GPF.

In fact, if it's Rifa, and manufactured since 1980, it's part type
will begin with the letter P, even after their amalgamation with Evox.

Metalized paper PM (or PZ), metalized polyester PH.

Perhaps you've mistaken the brand?

The 4191A was first released in 1980.

Interesting thing about the older Rifa parts, was that their outer
layer was transparent - an overstress or corona can often be seen, as
well as heard, but usually only in locations that are subject to the
attentions of overly zealous test technicians with manually adjustible
hipot equipment.

RL
 
J

Joerg

Jan 1, 1970
0
Spehro said:
Presumably his immediate objective was to interrupt the proximate
cause of the popping and smoking rather than to fully test those
ancient capacitors to UL standards. ;-)

Yep. The smoking was quite intense, had to open the windows and leave
the lab area to avoid coughing. Plus the odor was really nasty.
 
J

Joerg

Jan 1, 1970
0
legg said:
Never heard of Rifa GPF.

In fact, if it's Rifa, and manufactured since 1980, it's part type
will begin with the letter P, even after their amalgamation with Evox.


Maybe it's PME. The label says this:

Rifa GPF
40/085/56
PME 271 M 622

Then also "CM1" rotated 90 degrees on the right. No Evox mention on there.

Metalized paper PM (or PZ), metalized polyester PH.

Perhaps you've mistaken the brand?

No, says Rifa on there and has the logo.

The 4191A was first released in 1980.

The service manual is from 1980 but I believe the machine itself was
built around 1985. It's a good system. Ok, had its quirks. A big
electrolytic in it gave up once. Then they had screwed up the backup
battery charger but since I fixed that it doesn't lose calibration data
anymore. The plastic component clamp levers for the 16092A probe head
are wimpy and, predictably, one snapped in half. Still usable but one
has to have strong fingernails. Other than that it has served me well.

Interesting thing about the older Rifa parts, was that their outer
layer was transparent - an overstress or corona can often be seen, as
well as heard, but usually only in locations that are subject to the
attentions of overly zealous test technicians with manually adjustible
hipot equipment.

This cap developed a crack across one of the flat sides. Considering the
loud pops and the amount of smoke I'd have expected a total meltdown but
other than the crack I can't see any damage.
 
J

Joerg

Jan 1, 1970
0
Jasen said:
They're supposed to self heal

Smoke has low density, you can fit a lot of smoke precursor into a small space.

if it's got a crack it should definately be replaced, why not do some
destructive testing and see if it can withstand the test voltage
required and if it makes the right sort of wrong smell.

It is rated 250VAC and I gave it 300VAC from my "Australia test setup".
No popping, no smell. But who knows, the suspect area might have already
vaporized itself.
 
P

Phil Hobbs

Jan 1, 1970
0
Maybe it's PME. The label says this:

Rifa GPF
40/085/56
PME 271 M 622

Then also "CM1" rotated 90 degrees on the right. No Evox mention on there.



No, says Rifa on there and has the logo.



The service manual is from 1980 but I believe the machine itself was
built around 1985. It's a good system. Ok, had its quirks. A big
electrolytic in it gave up once. Then they had screwed up the backup
battery charger but since I fixed that it doesn't lose calibration data
anymore. The plastic component clamp levers for the 16092A probe head
are wimpy and, predictably, one snapped in half. Still usable but one
has to have strong fingernails. Other than that it has served me well.



This cap developed a crack across one of the flat sides. Considering the
loud pops and the amount of smoke I'd have expected a total meltdown but
other than the crack I can't see any damage.

I had a very nice hand-wired Krohn-Hite filter croak itself a year or so
back--the clamp on one of the 'computer-grade' filter caps was loose,
and the cap worked its way down through the chassis till it shorted to
the bottom of the case. (No fish paper there, for some silly reason.)

This resulted in clouds of transformer smoke filling the lab, which was
a shame, because it was a really nice box and the transformer was an
irreplaceable custom job. It even had completely separate power
supplies for the two channels, to prevent crosstalk.

Good thing I'm nuts about turning all the lab power off when I'm not
there--it could have happened any time at all.

Cheers

Phil Hobbs



--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510 USA
+1 845 480 2058

hobbs at electrooptical dot net
http://electrooptical.net
 
J

Joerg

Jan 1, 1970
0
Phil said:
I had a very nice hand-wired Krohn-Hite filter croak itself a year or so
back--the clamp on one of the 'computer-grade' filter caps was loose,
and the cap worked its way down through the chassis till it shorted to
the bottom of the case. (No fish paper there, for some silly reason.)

This resulted in clouds of transformer smoke filling the lab, which was
a shame, because it was a really nice box and the transformer was an
irreplaceable custom job. It even had completely separate power
supplies for the two channels, to prevent crosstalk.

Good thing I'm nuts about turning all the lab power off when I'm not
there--it could have happened any time at all.

Still, watch those X-caps in them boat anchors where you now have so
many of. I have seen these golden-clear plastic caps in many of them. My
lab has pretty good line spike filtering and the cap ran at less than
50% of its rated voltage yet it decided to blow. Problem is, things such
as this impedance analyzer can be unattended for long periods of time
when you run an experiment. Same with a spectrum analyzer when it runs a
baseline scan over a 100MHz swath with 1Hz BW. You don't want to come
back from lunch only to see trucks with flashing blue lights surrounding
your building because a fire alarm went off.
 
A

Anthony Stewart

Jan 1, 1970
0
X class caps have improved a lot with fusible links built into thin metal foil pattern so that less heat damage to vaporizing toxic plastic with only fractional loss of capacitance with many fuse links in the entire rolled metalized layer.

Check out Panasonic's design of X class PU and PE caps.

I don't know the MSDS of your part, but smoke from molten PVC wire insulation caused more lethal risk than the radiation at Three Mile Island.
 
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