[EE] "X" marks the spot

[Bob Blick]

By mistake I put an electrolytic capacitor in backwards. A very generic 100uF, 50V cap exposed to 16V with the equivalent of about 700 ohms in series with it. It lasted about 30 minutes, then went off with a bang. You can maybe see the damaged heatshrink where the can hit an immovable object.

Please note the scored cross on the top of the can. Isn't that supposed to split and protect me from its rapid self-disassembly? Yes, I was right there, close at hand, trying to figure out why all the voltages were wrong. Perhaps their die for the venting "X" was worn out after 20 million caps. I guess that's what I get when I pay USD 0.03 for caps off of Aliexpress instead of USD 0.11 at Digi-Key :)

I guess I learned a lesson in false economy today. I didn't lose an eye, but I'm going to change my buying habits a little. Obviously I made a mistake putting the cap in wrong, but if I'd used a quality cap perhaps I'd have only been startled with a scary hiss instead of a projectile. Take heed! How many lives do you really have?

Cheerful regards,

Bob

[Brent Brown]

On 26 Feb 2018 at 1:36, Bob Blick wrote:

> By mistake I put an electrolytic capacitor in backwards. A very
> generic 100uF, 50V cap exposed to 16V with the equivalent of about
> 700 ohms in series with it. It lasted about 30 minutes, then went
> off with a bang. You can maybe see the damaged heatshrink where the
> can hit an immovable object.
>
> Please note the scored cross on the top of the can. Isn't that
> supposed to split and protect me from its rapid self-disassembly?
> Yes, I was right there, close at hand, trying to figure out why all
> the voltages were wrong. Perhaps their die for the venting "X" was
> worn out after 20 million caps. I guess that's what I get when I pay
> USD 0.03 for caps off of Aliexpress instead of USD 0.11 at Digi-Key

Perhaps it's a matter of interpretation. The X means "not this end", and the arrows
define the direction of thrust... ;-)

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[Richard Pope]

Brent,
Nope. That X is a weak spot in the casing and it is put there by
the manufacturer as a safety valve so that the capacitor won't go
ballistic if the capacitor should fail. What happened to Bob was not
supposed to occur. I have had Capacitors fail, including a couple that I
have also put in backwards over the years and I have had only one go
ballistic. The others opened at the top. Those had gone pop as there
were pieces of the insides blown all over the place but at least those
pieces would not have been dangerous except for a few minor burns.
GOD Bless and Thanks,
rich!

On 2/25/2018 7:49 PM, Brent Brown wrote:
> On 26 Feb 2018 at 1:36, Bob Blick wrote:
>
>> By mistake I put an electrolytic capacitor in backwards. A very
>> generic 100uF, 50V cap exposed to 16V with the equivalent of about
>> 700 ohms in series with it. It lasted about 30 minutes, then went
>> off with a bang. You can maybe see the damaged heatshrink where the
>> can hit an immovable object.
>>
>> Please note the scored cross on the top of the can. Isn't that
>> supposed to split and protect me from its rapid self-disassembly?
>> Yes, I was right there, close at hand, trying to figure out why all
>> the voltages were wrong. Perhaps their die for the venting "X" was
>> worn out after 20 million caps. I guess that's what I get when I pay
>> USD 0.03 for caps off of Aliexpress instead of USD 0.11 at Digi-Key
> Perhaps it's a matter of interpretation. The X means "not this end", and the arrows
> define the direction of thrust... ;-)
>


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[Brent Brown]

Richard, sorry, my weak humour makes light of the safety concerns. The last cap
that did this near me was something like 2200uF 25V, a long time ago, and I think it
failed from temperature & ripple. Sounded like a shot gun. It was axial leaded, don't
remember if it had an X or not.

Agreed, the X is there to relieve pressure... they certainly deform and open in caps
that swell & leak. Perhaps there are limits to their effectiveness where a fault
creates a fast internal pressure rise closer to the other end.

> Nope. That X is a weak spot in the casing and it is put there by
> the manufacturer as a safety valve so that the capacitor won't go
> ballistic if the capacitor should fail. What happened to Bob was not
> supposed to occur. I have had Capacitors fail, including a couple that I
> have also put in backwards over the years and I have had only one go
> ballistic. The others opened at the top. Those had gone pop as there
> were pieces of the insides blown all over the place but at least those
> pieces would not have been dangerous except for a few minor burns.
>
> > Perhaps it's a matter of interpretation. The X means "not this end", and the arrows
> > define the direction of thrust... ;-)

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[Richard Pope]

Brent,
I don't think it is funny when people could or are being hurt. That
is just me. Funny to me is a cat hanging onto a pole 2 feet off of the
ground as he looks over the pole with this look on his face that says,
"OK, Now what do I do?".
GOD Bless and Thanks,
rich!

On 2/25/2018 8:33 PM, Brent Brown wrote:
> Richard, sorry, my weak humour makes light of the safety concerns. The last cap
> that did this near me was something like 2200uF 25V, a long time ago, and I think it
> failed from temperature & ripple. Sounded like a shot gun. It was axial leaded, don't
> remember if it had an X or not.
>
> Agreed, the X is there to relieve pressure... they certainly deform and open in caps
> that swell & leak. Perhaps there are limits to their effectiveness where a fault
> creates a fast internal pressure rise closer to the other end.
>
>> Nope. That X is a weak spot in the casing and it is put there by
>> the manufacturer as a safety valve so that the capacitor won't go
>> ballistic if the capacitor should fail. What happened to Bob was not
>> supposed to occur. I have had Capacitors fail, including a couple that I
>> have also put in backwards over the years and I have had only one go
>> ballistic. The others opened at the top. Those had gone pop as there
>> were pieces of the insides blown all over the place but at least those
>> pieces would not have been dangerous except for a few minor burns.
>>
>>> Perhaps it's a matter of interpretation. The X means "not this end", and the arrows
>>> define the direction of thrust... ;-)


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[Michael Johnston]

Bob,
About 30 years ago I was in a Basic Electronics lab and one of my class
mates did exactly what you described on a breadboard . I was working on
building a typical power supply with a bridge rectifier and a transformer
which had a plug for the 110 side. I heard this big bang and looked over
towards where the sound came from. There was a lot smoke and this awful
smell in the air and a guy who looked pretty confused from what had just
happened. He had put one of the filtering caps in backwards on the
breadboard and it blew up and put a huge hole in his lab book and I think
it ruined the bread too. Michael Johnston

On Sun, Feb 25, 2018 at 8:54 PM, Richard Pope <***@charter.net>
wrote:

> Brent,
> I don't think it is funny when people could or are being hurt. That
> is just me. Funny to me is a cat hanging onto a pole 2 feet off of the
> ground as he looks over the pole with this look on his face that says,
> "OK, Now what do I do?".
> GOD Bless and Thanks,
> rich!
>
> On 2/25/2018 8:33 PM, Brent Brown wrote:
> > Richard, sorry, my weak humour makes light of the safety concerns. The
> last cap
> > that did this near me was something like 2200uF 25V, a long time ago,
> and I think it
> > failed from temperature & ripple. Sounded like a shot gun. It was axial
> leaded, don't
> > remember if it had an X or not.
> >
> > Agreed, the X is there to relieve pressure... they certainly deform and
> open in caps
> > that swell & leak. Perhaps there are limits to their effectiveness where
> a fault
> > creates a fast internal pressure rise closer to the other end.
> >
> >> Nope. That X is a weak spot in the casing and it is put there by
> >> the manufacturer as a safety valve so that the capacitor won't go
> >> ballistic if the capacitor should fail. What happened to Bob was not
> >> supposed to occur. I have had Capacitors fail, including a couple that I
> >> have also put in backwards over the years and I have had only one go
> >> ballistic. The others opened at the top. Those had gone pop as there
> >> were pieces of the insides blown all over the place but at least those
> >> pieces would not have been dangerous except for a few minor burns.
> >>
> >>> Perhaps it's a matter of interpretation. The X means "not this end",
> and the arrows
> >>> define the direction of thrust... ;-)
>
>
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[DrSkip]

I suspect the X is initially weaker than the glue holding the can on, so
rapid pressure increase will break open there. Perhaps over the 30
minutes heat weakened the glue to the point of it being the weak point
for a gradual pressure buildup.

Dr Skip


On 02/25/2018 08:36 PM, Bob Blick wrote:
> By mistake I put an electrolytic capacitor in backwards. A very generic 100uF, 50V cap exposed to 16V with the equivalent of about 700 ohms in series with it. It lasted about 30 minutes, then went off with a bang. You can maybe see the damaged heatshrink where the can hit an immovable object.
>
> Please note the scored cross on the top of the can. Isn't that supposed to split and protect me from its rapid self-disassembly? Yes, I was right there, close at hand, trying to figure out why all the voltages were wrong. Perhaps their die for the venting "X" was worn out after 20 million caps. I guess that's what I get when I pay USD 0.03 for caps off of Aliexpress instead of USD 0.11 at Digi-Key :)
>
> I guess I learned a lesson in false economy today. I didn't lose an eye, but I'm going to change my buying habits a little. Obviously I made a mistake putting the cap in wrong, but if I'd used a quality cap perhaps I'd have only been startled with a scary hiss instead of a projectile. Take heed! How many lives do you really have?
>
> Cheerful regards,
>
> Bob
>
>
>
>

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[p***@roadrunner.com]

High school. Rat's nest of free space wiring. Neon bulbs, capacitors
(relaxation ring oscillator). Powered by half bridge directly from AC line
(no transformer). Main supply cap probably 50uF @ 200V or so. Short circuit.
Small rocket dragging 115VAC / 160VDC all around the workbench. Much
excitement.

- - Bob Ammerman
RAm Systems

-----Original Message-----
From: piclist-***@mit.edu [mailto:piclist-***@mit.edu] On Behalf Of
DrSkip
Sent: Monday, February 26, 2018 12:09 AM
To: ***@mit.edu
Subject: Re: [EE] "X" marks the spot

I suspect the X is initially weaker than the glue holding the can on, so
rapid pressure increase will break open there. Perhaps over the 30 minutes
heat weakened the glue to the point of it being the weak point for a gradual
pressure buildup.

Dr Skip


On 02/25/2018 08:36 PM, Bob Blick wrote:
> By mistake I put an electrolytic capacitor in backwards. A very generic
100uF, 50V cap exposed to 16V with the equivalent of about 700 ohms in
series with it. It lasted about 30 minutes, then went off with a bang. You
can maybe see the damaged heatshrink where the can hit an immovable object.
>
> Please note the scored cross on the top of the can. Isn't that
> supposed to split and protect me from its rapid self-disassembly? Yes,
> I was right there, close at hand, trying to figure out why all the
> voltages were wrong. Perhaps their die for the venting "X" was worn
> out after 20 million caps. I guess that's what I get when I pay USD
> 0.03 for caps off of Aliexpress instead of USD 0.11 at Digi-Key :)
>
> I guess I learned a lesson in false economy today. I didn't lose an eye,
but I'm going to change my buying habits a little. Obviously I made a
mistake putting the cap in wrong, but if I'd used a quality cap perhaps I'd
have only been startled with a scary hiss instead of a projectile. Take
heed! How many lives do you really have?
>
> Cheerful regards,
>
> Bob
>
>
>
>

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[David C Brown]

Many years ago at [company name withheld] we had a batch of several
hundred faulty electolytics which had to be disposed of. We had great
fun making a mortar - a piece of copper tube with a wooden plug with a nail
through it - and having a target shooting contest.

I also remember having a batch of memory board assembled with all the
tantalum capacitors put in the wrong way round. They lasted several weeks
until one night I was awoken by andanguished night shift operator reporting
that small puffs of smoke were being regularly ejected from the machine and
should he shut it down.

__________________________________________
David C Brown
43 Bings Road
Whaley Bridge
High Peak Phone: [phone]
Derbyshire eMail: ***@gmail.com
SK23 7ND web: www.bings-knowle.co.uk/dcb
<http://www.jb.man.ac.uk/~dcb>



*Sent from my etch-a-sketch*

On 26 February 2018 at 12:40, <***@roadrunner.com> wrote:

> High school. Rat's nest of free space wiring. Neon bulbs, capacitors
> (relaxation ring oscillator). Powered by half bridge directly from AC line
> (no transformer). Main supply cap probably 50uF @ 200V or so. Short
> circuit.
> Small rocket dragging 115VAC / 160VDC all around the workbench. Much
> excitement.
>
> - - Bob Ammerman
> RAm Systems
>
> -----Original Message-----
> From: piclist-***@mit.edu [mailto:piclist-***@mit.edu] On Behalf
> Of
> DrSkip
> Sent: Monday, February 26, 2018 12:09 AM
> To: ***@mit.edu
> Subject: Re: [EE] "X" marks the spot
>
> I suspect the X is initially weaker than the glue holding the can on, so
> rapid pressure increase will break open there. Perhaps over the 30 minutes
> heat weakened the glue to the point of it being the weak point for a
> gradual
> pressure buildup.
>
> Dr Skip
>
>
> On 02/25/2018 08:36 PM, Bob Blick wrote:
> > By mistake I put an electrolytic capacitor in backwards. A very generic
> 100uF, 50V cap exposed to 16V with the equivalent of about 700 ohms in
> series with it. It lasted about 30 minutes, then went off with a bang. You
> can maybe see the damaged heatshrink where the can hit an immovable object.
> >
> > Please note the scored cross on the top of the can. Isn't that
> > supposed to split and protect me from its rapid self-disassembly? Yes,
> > I was right there, close at hand, trying to figure out why all the
> > voltages were wrong. Perhaps their die for the venting "X" was worn
> > out after 20 million caps. I guess that's what I get when I pay USD
> > 0.03 for caps off of Aliexpress instead of USD 0.11 at Digi-Key :)
> >
> > I guess I learned a lesson in false economy today. I didn't lose an eye,
> but I'm going to change my buying habits a little. Obviously I made a
> mistake putting the cap in wrong, but if I'd used a quality cap perhaps I'd
> have only been startled with a scary hiss instead of a projectile. Take
> heed! How many lives do you really have?
> >
> > Cheerful regards,
> >
> > Bob
> >
> >
> >
> >
>
> --
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> your membership options at http://mailman.mit.edu/mailman/listinfo/piclist
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[Clint Jay]

Apparently, so I'm told, 47uf capacitors make good .22 air rifle slugs.

On 26 Feb 2018 13:02, "David C Brown" <***@gmail.com> wrote:

> Many years ago at [company name withheld] we had a batch of several
> hundred faulty electolytics which had to be disposed of. We had great
> fun making a mortar - a piece of copper tube with a wooden plug with a nail
> through it - and having a target shooting contest.
>
> I also remember having a batch of memory board assembled with all the
> tantalum capacitors put in the wrong way round. They lasted several weeks
> until one night I was awoken by andanguished night shift operator reporting
> that small puffs of smoke were being regularly ejected from the machine and
> should he shut it down.
>
> __________________________________________
> David C Brown
> 43 Bings Road
> Whaley Bridge
> High Peak Phone: [phone]
> Derbyshire eMail: ***@gmail.com
> SK23 7ND web: www.bings-knowle.co.uk/dcb
> <http://www.jb.man.ac.uk/~dcb>
>
>
>
> *Sent from my etch-a-sketch*
>
> On 26 February 2018 at 12:40, <***@roadrunner.com> wrote:
>
> > High school. Rat's nest of free space wiring. Neon bulbs, capacitors
> > (relaxation ring oscillator). Powered by half bridge directly from AC
> line
> > (no transformer). Main supply cap probably 50uF @ 200V or so. Short
> > circuit.
> > Small rocket dragging 115VAC / 160VDC all around the workbench. Much
> > excitement.
> >
> > - - Bob Ammerman
> > RAm Systems
> >
> > -----Original Message-----
> > From: piclist-***@mit.edu [mailto:piclist-***@mit.edu] On Behalf
> > Of
> > DrSkip
> > Sent: Monday, February 26, 2018 12:09 AM
> > To: ***@mit.edu
> > Subject: Re: [EE] "X" marks the spot
> >
> > I suspect the X is initially weaker than the glue holding the can on, so
> > rapid pressure increase will break open there. Perhaps over the 30
> minutes
> > heat weakened the glue to the point of it being the weak point for a
> > gradual
> > pressure buildup.
> >
> > Dr Skip
> >
> >
> > On 02/25/2018 08:36 PM, Bob Blick wrote:
> > > By mistake I put an electrolytic capacitor in backwards. A very generic
> > 100uF, 50V cap exposed to 16V with the equivalent of about 700 ohms in
> > series with it. It lasted about 30 minutes, then went off with a bang.
> You
> > can maybe see the damaged heatshrink where the can hit an immovable
> object.
> > >
> > > Please note the scored cross on the top of the can. Isn't that
> > > supposed to split and protect me from its rapid self-disassembly? Yes,
> > > I was right there, close at hand, trying to figure out why all the
> > > voltages were wrong. Perhaps their die for the venting "X" was worn
> > > out after 20 million caps. I guess that's what I get when I pay USD
> > > 0.03 for caps off of Aliexpress instead of USD 0.11 at Digi-Key :)
> > >
> > > I guess I learned a lesson in false economy today. I didn't lose an
> eye,
> > but I'm going to change my buying habits a little. Obviously I made a
> > mistake putting the cap in wrong, but if I'd used a quality cap perhaps
> I'd
> > have only been startled with a scary hiss instead of a projectile. Take
> > heed! How many lives do you really have?
> > >
> > > Cheerful regards,
> > >
> > > Bob
> > >
> > >
> > >
> > >
> >
> > --
> > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> > View/change
> > your membership options at http://mailman.mit.edu/
> mailman/listinfo/piclist
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[RussellMc]

On 27 February 2018 at 02:02, David C Brown <***@gmail.com> wrote:

> Many years ago at [company name withheld] we had a batch of several
> hundred faulty electrolytic
> ​s​
> which had to be disposed of. We had great
> fun making a mortar - a piece of copper tube with a wooden plug with a nail
> through it - and having a target shooting contest.
>

​Lonnng ago (40+ years) unmarked untested transistors were available frmo
UK in bulk (100/bag?) at low cost.

Uni labs had benches with multiple mains outlets and a common switch for
bench.
Turn OFF bench.
Insert transistors into every mains socket for bench.
Hide besides bench and turn on mains ...

Wham ... - eruption of flames, transistor cans (metal) and bits of lead
wire.

Highly impressive.
A problem was that legs of transistors in some cases lightly welded to
contacts and sockets had to be opened to detach them and remove shrapnel.


Russell
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[mike brown]

I recently had a tantalum fail. It was correctly polarized, but the 16v
rating was exceeded temporarily. It exploded with no warning. Sounded
like a rifle going off in the room.

On Feb 26, 2018 06:46, <***@roadrunner.com> wrote:

> High school. Rat's nest of free space wiring. Neon bulbs, capacitors
> (relaxation ring oscillator). Powered by half bridge directly from AC line
> (no transformer). Main supply cap probably 50uF @ 200V or so. Short
> circuit.
> Small rocket dragging 115VAC / 160VDC all around the workbench. Much
> excitement.
>
> - - Bob Ammerman
> RAm Systems
>
> -----Original Message-----
> From: piclist-***@mit.edu [mailto:piclist-***@mit.edu] On Behalf
> Of
> DrSkip
> Sent: Monday, February 26, 2018 12:09 AM
> To: ***@mit.edu
> Subject: Re: [EE] "X" marks the spot
>
> I suspect the X is initially weaker than the glue holding the can on, so
> rapid pressure increase will break open there. Perhaps over the 30 minutes
> heat weakened the glue to the point of it being the weak point for a
> gradual
> pressure buildup.
>
> Dr Skip
>
>
> On 02/25/2018 08:36 PM, Bob Blick wrote:
> > By mistake I put an electrolytic capacitor in backwards. A very generic
> 100uF, 50V cap exposed to 16V with the equivalent of about 700 ohms in
> series with it. It lasted about 30 minutes, then went off with a bang. You
> can maybe see the damaged heatshrink where the can hit an immovable object.
> >
> > Please note the scored cross on the top of the can. Isn't that
> > supposed to split and protect me from its rapid self-disassembly? Yes,
> > I was right there, close at hand, trying to figure out why all the
> > voltages were wrong. Perhaps their die for the venting "X" was worn
> > out after 20 million caps. I guess that's what I get when I pay USD
> > 0.03 for caps off of Aliexpress instead of USD 0.11 at Digi-Key :)
> >
> > I guess I learned a lesson in false economy today. I didn't lose an eye,
> but I'm going to change my buying habits a little. Obviously I made a
> mistake putting the cap in wrong, but if I'd used a quality cap perhaps I'd
> have only been startled with a scary hiss instead of a projectile. Take
> heed! How many lives do you really have?
> >
> > Cheerful regards,
> >
> > Bob
> >
> >
> >
> >
>
> --
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[Isaac M. Bavaresco]

When I was a kid, in the late 70's, I used to do that on purpose.

I attached small electrolytic caps to wooden sticks, stretched their
legs and inserted into the 220 V outlets. What a bang!

Never got hurt, fortunately. But then I never used big ones. Never found
a trace of their material too.

Cheers,

Isaac



Em 26/02/2018 09:40, ***@roadrunner.com escreveu:
> High school. Rat's nest of free space wiring. Neon bulbs, capacitors
> (relaxation ring oscillator). Powered by half bridge directly from AC line
> (no transformer). Main supply cap probably 50uF @ 200V or so. Short circuit.
> Small rocket dragging 115VAC / 160VDC all around the workbench. Much
> excitement.
>
> - - Bob Ammerman
> RAm Systems
>
> -----Original Message-----
> From: piclist-***@mit.edu [mailto:piclist-***@mit.edu] On Behalf Of
> DrSkip
> Sent: Monday, February 26, 2018 12:09 AM
> To: ***@mit.edu
> Subject: Re: [EE] "X" marks the spot
>
> I suspect the X is initially weaker than the glue holding the can on, so
> rapid pressure increase will break open there. Perhaps over the 30 minutes
> heat weakened the glue to the point of it being the weak point for a gradual
> pressure buildup.
>
> Dr Skip
>
>
> On 02/25/2018 08:36 PM, Bob Blick wrote:
>> By mistake I put an electrolytic capacitor in backwards. A very generic
> 100uF, 50V cap exposed to 16V with the equivalent of about 700 ohms in
> series with it. It lasted about 30 minutes, then went off with a bang. You
> can maybe see the damaged heatshrink where the can hit an immovable object.
>> Please note the scored cross on the top of the can. Isn't that
>> supposed to split and protect me from its rapid self-disassembly? Yes,
>> I was right there, close at hand, trying to figure out why all the
>> voltages were wrong. Perhaps their die for the venting "X" was worn
>> out after 20 million caps. I guess that's what I get when I pay USD
>> 0.03 for caps off of Aliexpress instead of USD 0.11 at Digi-Key :)
>>
>> I guess I learned a lesson in false economy today. I didn't lose an eye,
> but I'm going to change my buying habits a little. Obviously I made a
> mistake putting the cap in wrong, but if I'd used a quality cap perhaps I'd
> have only been startled with a scary hiss instead of a projectile. Take
> heed! How many lives do you really have?
>> Cheerful regards,
>>
>> Bob
>>
>>
>>
>>
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[Isaac M. Bavaresco]

I never noticed any glue in the caps I have disassembled when I was a
kid. They seemed to be sealed by pressure of the waist in the metal can
around the rubber stopper.

Cheers,

Isaac



Em 26/02/2018 02:08, DrSkip escreveu:
> I suspect the X is initially weaker than the glue holding the can on, so
> rapid pressure increase will break open there. Perhaps over the 30
> minutes heat weakened the glue to the point of it being the weak point
> for a gradual pressure buildup.
>
> Dr Skip
>
>
> On 02/25/2018 08:36 PM, Bob Blick wrote:
>> By mistake I put an electrolytic capacitor in backwards. A very generic 100uF, 50V cap exposed to 16V with the equivalent of about 700 ohms in series with it. It lasted about 30 minutes, then went off with a bang. You can maybe see the damaged heatshrink where the can hit an immovable object.
>>
>> Please note the scored cross on the top of the can. Isn't that supposed to split and protect me from its rapid self-disassembly? Yes, I was right there, close at hand, trying to figure out why all the voltages were wrong. Perhaps their die for the venting "X" was worn out after 20 million caps. I guess that's what I get when I pay USD 0.03 for caps off of Aliexpress instead of USD 0.11 at Digi-Key :)
>>
>> I guess I learned a lesson in false economy today. I didn't lose an eye, but I'm going to change my buying habits a little. Obviously I made a mistake putting the cap in wrong, but if I'd used a quality cap perhaps I'd have only been startled with a scary hiss instead of a projectile. Take heed! How many lives do you really have?
>>
>> Cheerful regards,
>>
>> Bob
>>
>>
>>
>>

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[Dr Skip]

That would make sense too, since the coefficient of expansion for the aluminum can is greater than the plastic or rubber base, which might even soften slightly or deform rather than unglue if it was a crimp or friction fit.

Dr Skip



On February 26, 2018 12:56:30 PM EST, "Isaac M. Bavaresco" <***@gmail.com> wrote:
>I never noticed any glue in the caps I have disassembled when I was a
>kid. They seemed to be sealed by pressure of the waist in the metal can
>around the rubber stopper.
>
>Cheers,
>
>Isaac
>
>
>
>Em 26/02/2018 02:08, DrSkip escreveu:
>> I suspect the X is initially weaker than the glue holding the can on,
>so
>> rapid pressure increase will break open there. Perhaps over the 30
>> minutes heat weakened the glue to the point of it being the weak
>point
>> for a gradual pressure buildup.
>>
>> Dr Skip
>>
>>
>> On 02/25/2018 08:36 PM, Bob Blick wrote:
>>> By mistake I put an electrolytic capacitor in backwards. A very
>generic 100uF, 50V cap exposed to 16V with the equivalent of about 700
>ohms in series with it. It lasted about 30 minutes, then went off with
>a bang. You can maybe see the damaged heatshrink where the can hit an
>immovable object.
>>>
>>> Please note the scored cross on the top of the can. Isn't that
>supposed to split and protect me from its rapid self-disassembly? Yes,
>I was right there, close at hand, trying to figure out why all the
>voltages were wrong. Perhaps their die for the venting "X" was worn out
>after 20 million caps. I guess that's what I get when I pay USD 0.03
>for caps off of Aliexpress instead of USD 0.11 at Digi-Key :)
>>>
>>> I guess I learned a lesson in false economy today. I didn't lose an
>eye, but I'm going to change my buying habits a little. Obviously I
>made a mistake putting the cap in wrong, but if I'd used a quality cap
>perhaps I'd have only been startled with a scary hiss instead of a
>projectile. Take heed! How many lives do you really have?
>>>
>>> Cheerful regards,
>>>
>>> Bob
>>>
>>>
>>>
>>>
>
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[RussellMc]

​
On 26 February 2018 at 14:36, Bob Blick <***@outlook.com> wrote:

> By mistake I put an electrolytic capacitor in backwards. A very generic
> 100uF, 50V cap exposed to 16V with the equivalent of about 700 ohms in
> series with it. It lasted about 30 minutes, then went off with a bang. You
> can maybe see the damaged heatshrink where the can hit an immovable object.
>

I've seen a few fail over the centuries.
Most 'offensive'. long long long ago, was a largish one which gave me a
good faceful of shredded paper plus "goo".
As I recall (ages since last one) they do usually fail at the X.

An equally strong-all-over cylinder will preferentially split along the
long side as stress is double the material stress in that mode compared
with blowing the end off - which is why equal strength material boilers
fail along the sides (fortunately) and wound advanced pressure cylinders
have diagonal wraps to equalise stresses (so you never know where it will
blow).

So (although an ecap is probably not marvellously well modelled by a
pressurised cylinder) the X is needed to reduce the strength by a factor of
about 2 to blow the end out..

In Bob's case it evidently failed to do so BUT the base seal was weaker
again that the side.
So ...

Tantalums are generally more fun.
The best I've seen made a foul smell for a while (source then unknown),
then smoked profusely, then started shrieking, a jet of flame was added and
then it exploded competently.

A large capacity (I think) Tantalum in a DEC PDP11 power supply had a
metal case. A hole was blown in the side near one end and a ball of metal
rolled freely along the interior and was just too large to exist the hole.


Russell
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[Neil]

Resending with link as prev reply with attachment didn't make it through.
Did the same thing last month... reverse cap and I was very close. It
was 99% a nichicon, as that's what I get from Mouser, and yet the pop
was violent.

http://orlandorobotbuilders.com/stuff/Popped-Cap.jpg

Cheers,
-Neil.


On 2/25/2018 8:36 PM, Bob Blick wrote:
> By mistake I put an electrolytic capacitor in backwards. A very generic 100uF, 50V cap exposed to 16V with the equivalent of about 700 ohms in series with it. It lasted about 30 minutes, then went off with a bang. You can maybe see the damaged heatshrink where the can hit an immovable object.
>
> Please note the scored cross on the top of the can. Isn't that supposed to split and protect me from its rapid self-disassembly? Yes, I was right there, close at hand, trying to figure out why all the voltages were wrong. Perhaps their die for the venting "X" was worn out after 20 million caps. I guess that's what I get when I pay USD 0.03 for caps off of Aliexpress instead of USD 0.11 at Digi-Key :)
>
> I guess I learned a lesson in false economy today. I didn't lose an eye, but I'm going to change my buying habits a little. Obviously I made a mistake putting the cap in wrong, but if I'd used a quality cap perhaps I'd have only been startled with a scary hiss instead of a projectile. Take heed! How many lives do you really have?
>
> Cheerful regards,
>
> Bob
>
>
>
>

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[Bob Blick]

You got confetti and streamers from yours, and close to New Years Eve, too :)

Friendly regards, Bob

________________________________________
From: piclist-***@mit.edu <piclist-***@mit.edu> on behalf of Neil
Sent: Monday, February 26, 2018 8:11 AM
To: Microcontroller discussion list - Public.
Subject: Re: [EE] "X" marks the spot

Resending with link as prev reply with attachment didn't make it through.
Did the same thing last month... reverse cap and I was very close. It
was 99% a nichicon, as that's what I get from Mouser, and yet the pop
was violent.

http://orlandorobotbuilders.com/stuff/Popped-Cap.jpg

Cheers,
-Neil.


On 2/25/2018 8:36 PM, Bob Blick wrote:
> By mistake I put an electrolytic capacitor in backwards. A very generic 100uF, 50V cap exposed to 16V with the equivalent of about 700 ohms in series with it. It lasted about 30 minutes, then went off with a bang. You can maybe see the damaged heatshrink where the can hit an immovable object.
>
> Please note the scored cross on the top of the can. Isn't that supposed to split and protect me from its rapid self-disassembly? Yes, I was right there, close at hand, trying to figure out why all the voltages were wrong. Perhaps their die for the venting "X" was worn out after 20 million caps. I guess that's what I get when I pay USD 0.03 for caps off of Aliexpress instead of USD 0.11 at Digi-Key :)
>
> I guess I learned a lesson in false economy today. I didn't lose an eye, but I'm going to change my buying habits a little. Obviously I made a mistake putting the cap in wrong, but if I'd used a quality cap perhaps I'd have only been startled with a scary hiss instead of a projectile. Take heed! How many lives do you really have?
>
> Cheerful regards,
>
> Bob

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[RussellMc]

​
On 27 February 2018 at 05:11, Neil <***@narwani.org> wrote:

> Resending with link as prev reply with attachment didn't make it through.
> Did the same thing last month... reverse cap and I was very close. It
> was 99% a nichicon, as that's what I get from Mouser, and yet the pop
> was violent.
>


I think I've got a 6.3V 47,000 uF (47 mF in Olin's terms) downstairs.
I wonder how that would go on 60 fps 4K video.
Or rather faster vvv low resolution XACTI.
Or both :-)

Russell
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[RussellMc]

A friend in Canada who I sent a copy of part of this thread to responded:

Hi Russell,



I recall in 7th grade, I used to bring a bag of little radial ceramic
capacitors and a 90V battery to class. I would charge them up, then slip
them into my classmates clothing, like down their collars. When they would
later move, they would get a little shock from the cap leads contacting
their neck, and would let out a yelp. Of course the teacher would scold
these puzzled kids.



Yes we also used to hook up a line cord to large electrolytic capacitors in
the electronics lab, and hang them out the window into the yard used by the
power mechanics students. Then plug said cord in and the caps would blow
up.



This electronics lab had a large, scary sign that read, “DANGER, 10,000
OHMS”



We made a contact print of the school’s master key in the darkroom of the
graphics shop, then filed copies of the key from it in metal shop. The
teachers knew we had keys, but we were responsible A students, and they
didn’t really care. That was 1973.



High school was a lot of fun, and surprisingly nobody got hurt.



Cheers,



Jeff
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[Justin Richards]

“DANGER, 10,000
OHMS”

Love it. Might put that up in my workshop, or perhaps a t-shirt.

On 27 February 2018 at 07:43, RussellMc <***@gmail.com> wrote:

> A friend in Canada who I sent a copy of part of this thread to responded:
>
> Hi Russell,
>
>
>
> I recall in 7th grade, I used to bring a bag of little radial ceramic
> capacitors and a 90V battery to class. I would charge them up, then slip
> them into my classmates clothing, like down their collars. When they would
> later move, they would get a little shock from the cap leads contacting
> their neck, and would let out a yelp. Of course the teacher would scold
> these puzzled kids.
>
>
>
> Yes we also used to hook up a line cord to large electrolytic capacitors in
> the electronics lab, and hang them out the window into the yard used by the
> power mechanics students. Then plug said cord in and the caps would blow
> up.
>
>
>
> This electronics lab had a large, scary sign that read, “DANGER, 10,000
> OHMS”
>
>
>
> We made a contact print of the school’s master key in the darkroom of the
> graphics shop, then filed copies of the key from it in metal shop. The
> teachers knew we had keys, but we were responsible A students, and they
> didn’t really care. That was 1973.
>
>
>
> High school was a lot of fun, and surprisingly nobody got hurt.
>
>
>
> Cheers,
>
>
>
> Jeff
> --
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[Christopher Head]

On February 26, 2018 3:43:59 PM PST, RussellMc <***@gmail.com> wrote:
>I would charge them up, then
>slip
>them into my classmates clothing, like down their collars.
>
>Yes we also used to hook up a line cord to large electrolytic
>capacitors in
>the electronics lab, and hang them out the window
>
>we were responsible [
] students

Riiiiiight ;)

Wish I had had that sort of fun in HS though. Wasn’t bad, but nothing like that.

--
Christopher Head

[a***@stfc.ac.uk]

> I recall in 7th grade, I used to bring a bag of little radial ceramic capacitors and
> a 90V battery to class. I would charge them up, then slip them into my
> classmates clothing, like down their collars. When they would later move,
> they would get a little shock from the cap leads contacting their neck, and
> would let out a yelp. Of course the teacher would scold these puzzled kids.

During my time as an electronics apprentice, the factory I worked at assembled stereo amplifiers which used a 40V 220uF capacitor as the bootstrap capacitor in the output stage. The supplied capacitors were made by Philips, who were one of the few major component suppliers in NZ at that stage.

However we had some apprentices who were of a wicked mind-set, who realised that the 8uF 350V Philips capacitors used in the high voltage inverter of the marine radios we made were the same case size, and if you didn't notice that the blue sleeve on it was a little paler than the other capacitors you wouldn't notice the difference in a box of them, especially as the box tended to be at the back of the bench. So a pair of apprentices would charge an 8u 350V cap to around 500V using the insulation tester, then one would come and talk to one of the women assembling the PCBs for the amplifiers and distract them while a second apprentice would come and drop the charged capacitor in the box of capacitors she was fitting to the PCBs. Inevitably at some point the charged capacitor would be handled with resulting shock. After this happened a couple of times the women on the assembly line got very wary of any apprentice coming and talking to them, and would carefully look through thei!
r box of capacitors looking for any that were different.

Russell earlier said ...
> Tantalums are generally more fun.
> The best I've seen made a foul smell for a while (source then unknown),
> then smoked profusely, then started shrieking, a jet of flame was added and
> then it exploded competently.
>
> A large capacity (I think) Tantalum in a DEC PDP11 power supply had a metal
> case. A hole was blown in the side near one end and a ball of metal rolled
> freely along the interior and was just too large to exist the hole.

This would have been a wet tantalum by the sound of it.

I may have written both the following stories in the past, but they bear repeating as warnings.

But a colleague had an almost life changing with a tantalum exploding. We had a new printer come in from our OEM and it was dead on arrival. So colleague pulled the back panel off and pulled the PCB assembly out. All the wiring to the motors and print heads was long enough to allow this to happen and leave everything operational while testing and fault finding. He had the power on and was bending over looking at the PCB when a teardrop tantalum whizzed past his ear, having launched itself off the PCB. It was in a circuit that had switching regulators that allowed around 30V to the stepper motors while running but dropped it down to about 5V to limit the holding current while the motors weren't turning. I suspect the cap was put into circuit backwards and lasted long enough to get through final test at the factory but having had reverse voltage on it died during transit. Finally getting voltage on it again it became a little rocket that left its leads in the PCB. Colleague wa!
s lucky he didn't lose an eye.

But the other capacitor incident I remember was when we had a new minicomputer delivered to run in the companies bureau for customer use. No-one was quite ready for it so we left it running a memory test as a burn in exercise. The card cage had about 20 slots but there was only the processor, memory, disk interface, tape interface and one I/O card, but the power supply was a 5V 300A switch mode to handle the potential fully loaded card cage. I had my pager go off with a call that the new machine was "on fire". By the time I had reached the bureau the machine had been turned off, but the description of smoke coming out the ventilation at the top of the rack seemed a bit over the top ...

Investigation showed that a 100n ceramic capacitor had decided it want a gender change into a resistor - as ceramic caps are well known for doing, not so much these days, but quite common in the past. The power supply had said 'you want to be a resistor, I can supply all the current you want'. The result was a charred hole in the PCB about 1.5" diameter. However there was a problem - we had purchased the machine with minimum memory fitted and then added memory chips as this gave us the full card capacity much cheaper than buying it fully populated, so we couldn't return the card under warranty. The upshot was that someone (not me) was given the job of fixing it which he did by filling the charred hole with epoxy that using Inforex wire to remake the connection (anyone else here deal with Inforex key to disk/tape systems in the past?). The inforex wire is like fine enamelled wire wrap wire.




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[Dwayne Reid]

Hi there, Bob.

My experience is that if you do what you did, the capacitor will
often eject the can from the remainder of the capacitor.

Many years ago, one of my buddies worked at a shop that did car audio
device repairs. The most common failure they had at that time was a
10uF 25V capacitor. These failed by the dozens of non-working units - per day!

In the far corner of their shop was a ceiling-mounted PA horn that
was universally despised by everyone. My buddy took an old 24Vac 15
or 20 Amp transformer and attached sturdy wires with alligator
clips. He then set up a mickey-mouse mortar tube made of brass -
this was semi-fixed in place but adjustable. The tube was just
larger in diameter than these 10uF capacitors.

24 Vac with essentially an unlimited amount of current will cause
some very nice thermal events to small electrolytic
capacitors. Namely: a decently-loud BANG followed by the aluminum
case being ejected quite forcefully!

Everyone took turns using this rig to fire defective capacitors at
that obnoxious PA speaker.

Anyway, this has stuck in my mind for eons now. Bottom line: assume
that the can will be ejected should you do something really bad to
electrolytic capacitors!

dwayne


At 06:36 PM 2/25/2018, Bob Blick wrote:
>By mistake I put an electrolytic capacitor in backwards. A very
>generic 100uF, 50V cap exposed to 16V with the equivalent of about
>700 ohms in series with it. It lasted about 30 minutes, then went
>off with a bang. You can maybe see the damaged heatshrink where the
>can hit an immovable object.
>
>Please note the scored cross on the top of the can. Isn't that
>supposed to split and protect me from its rapid self-disassembly?
>Yes, I was right there, close at hand, trying to figure out why all
>the voltages were wrong. Perhaps their die for the venting "X" was
>worn out after 20 million caps. I guess that's what I get when I pay
>USD 0.03 for caps off of Aliexpress instead of USD 0.11 at Digi-Key :)
>
>I guess I learned a lesson in false economy today. I didn't lose an
>eye, but I'm going to change my buying habits a little. Obviously I
>made a mistake putting the cap in wrong, but if I'd used a quality
>cap perhaps I'd have only been startled with a scary hiss instead of
>a projectile. Take heed! How many lives do you really have?
>
>Cheerful regards,
>
>Bob


--
Dwayne Reid <***@planet.eon.net>
Trinity Electronics Systems Ltd Edmonton, AB, CANADA
780-489-3199 voice 780-487-6397 fax [phone] Toll Free
www.trinity-electronics.com
Custom Electronics Design and Manufacturing

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[John Gardner]

I finally got around to electrolytic "field-expedient" grenades a few

years ago - 10 uF 50V tantalum, plugged into a breadboard (inad-

vertently).

Very impressive - Possibly a lot more impressive with a stiffer Vcc...


...


On 2/26/18, Dwayne Reid <***@planet.eon.net> wrote:
> Hi there, Bob.
>
> My experience is that if you do what you did, the capacitor will
> often eject the can from the remainder of the capacitor.
>
> Many years ago, one of my buddies worked at a shop that did car audio
> device repairs. The most common failure they had at that time was a
> 10uF 25V capacitor. These failed by the dozens of non-working units - per
> day!
>
> In the far corner of their shop was a ceiling-mounted PA horn that
> was universally despised by everyone. My buddy took an old 24Vac 15
> or 20 Amp transformer and attached sturdy wires with alligator
> clips. He then set up a mickey-mouse mortar tube made of brass -
> this was semi-fixed in place but adjustable. The tube was just
> larger in diameter than these 10uF capacitors.
>
> 24 Vac with essentially an unlimited amount of current will cause
> some very nice thermal events to small electrolytic
> capacitors. Namely: a decently-loud BANG followed by the aluminum
> case being ejected quite forcefully!
>
> Everyone took turns using this rig to fire defective capacitors at
> that obnoxious PA speaker.
>
> Anyway, this has stuck in my mind for eons now. Bottom line: assume
> that the can will be ejected should you do something really bad to
> electrolytic capacitors!
>
> dwayne
>
>
> At 06:36 PM 2/25/2018, Bob Blick wrote:
>>By mistake I put an electrolytic capacitor in backwards. A very
>>generic 100uF, 50V cap exposed to 16V with the equivalent of about
>>700 ohms in series with it. It lasted about 30 minutes, then went
>>off with a bang. You can maybe see the damaged heatshrink where the
>>can hit an immovable object.
>>
>>Please note the scored cross on the top of the can. Isn't that
>>supposed to split and protect me from its rapid self-disassembly?
>>Yes, I was right there, close at hand, trying to figure out why all
>>the voltages were wrong. Perhaps their die for the venting "X" was
>>worn out after 20 million caps. I guess that's what I get when I pay
>>USD 0.03 for caps off of Aliexpress instead of USD 0.11 at Digi-Key :)
>>
>>I guess I learned a lesson in false economy today. I didn't lose an
>>eye, but I'm going to change my buying habits a little. Obviously I
>>made a mistake putting the cap in wrong, but if I'd used a quality
>>cap perhaps I'd have only been startled with a scary hiss instead of
>>a projectile. Take heed! How many lives do you really have?
>>
>>Cheerful regards,
>>
>>Bob
>
>
> --
> Dwayne Reid <***@planet.eon.net>
> Trinity Electronics Systems Ltd Edmonton, AB, CANADA
> 780-489-3199 voice 780-487-6397 fax [phone] Toll Free
> www.trinity-electronics.com
> Custom Electronics Design and Manufacturing
>
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