Badcaps.net Forum
Go Back   Badcaps Forums > Welcome to the Badcaps.net Tech Forum! > Frequently Asked Questions (No Posting)
Register FAQ Calendar Search Today's Posts Mark Forums Read

 
Thread Tools Display Modes
Old 08-21-2006, 03:49 AM   #1
Tom41
Badcaps Veteran
 
Tom41's Avatar
 
Join Date: Oct 2005
City & State: Leeds
My Country: England
Line Voltage: 230VAC 50Hz
Posts: 307
Default Why does a cap vent?

Like the title suggests, what exactly causes a cap to vent? Does it heat up and 'boil' the electrolyte? Does electrolysis occur and produce gas?

I vented a cap recently - by pumping 20v into the 10v-rated cap on reversed polarity and the pic in my avatar shows the result. It 'exploded' with a load of smoke. The cap was very hot afterwards, so maybe it boiled?

Last edited by Tom41; 08-21-2006 at 03:51 AM..
Tom41 is offline   Reply With Quote
Old 08-21-2006, 04:06 AM   #2
Topcat
The Boss Stooge
 
Topcat's Avatar
 
Join Date: Oct 2003
City & State: Salem, MO
My Country: United States
Line Voltage: 240V @ 60Hz
I'm a: Professional Tech
Posts: 12,635
Default Re: Why does a cap vent?

The theory is that of a pressure cooker. They heat, things expand, have no place to expand to, and poof.....they vent. They do it faster with shoddier brands, as the electrolyte is water-based, and evaporates at temps a lot lower than good ones.
__________________
<--- Badcaps.net Founder & Owner

Badcaps.net Services:

Premade Capacitor Kits
Badcaps.net Capacitor Master List


Motherboard Repair Services


If you've come here in search of replacement capacitors or repair services, please use the links above.
----------------------------------------------
Badcaps.net Forum Members Folding Team
http://folding.stanford.edu/
Team : 49813
Join in!!
Team Stats
Topcat is offline   Reply With Quote
Old 08-21-2006, 06:45 AM   #3
gonzo0815
Badcaps Veteran
 
Join Date: Feb 2006
City & State: Germany
Posts: 1,595
Default Re: Why does a cap vent?

I think it is the H2, wich is generated by a chemicall reaction of H2O and AL if no inhibiting additive is in the elektrolyt. The H2 would be collected at the top of the cap, abd if the pressure is high enough the safety vent will burst.
gonzo0815 is offline   Reply With Quote
Old 08-21-2006, 07:01 AM   #4
kc8adu
Super Moderator
 
kc8adu's Avatar
 
Join Date: Nov 2003
City & State: dayton ohio
My Country: U.S.A!
Line Voltage: 12vdc,120/240vac,480vac 3ph on my bench
I'm a: Professional Tech
Posts: 8,288
Default Re: Why does a cap vent?

Quote:
Originally Posted by Tom41
Like the title suggests, what exactly causes a cap to vent? Does it heat up and 'boil' the electrolyte? Does electrolysis occur and produce gas?
both. electrolysis starts the bulging.as it dries out esr rises and heating occurs.as the vent opens and more electrolyte is lost the cap looses capacitance and goes open.
kc8adu is offline   Reply With Quote
Old 08-21-2006, 09:20 AM   #5
whiz
Member
 
Join Date: Aug 2006
City & State: Athens,Greece
Posts: 46
Default Re: Why does a cap vent?

some stupid questions

1)What is the "X" mark or the "T" mark on the top of the caps? is this the escape door?

2)The electrolyte is it corrosive for our skin? is it dangerous to smell it?

3)do we know the chemicals it contains?

4) The thin metal film inside the cap what is it? aluminium or some other metal?



thank you...
whiz is offline   Reply With Quote
Old 08-21-2006, 09:39 AM   #6
PeteS in CA
Badcaps Veteran
 
PeteS in CA's Avatar
 
Join Date: Aug 2005
City & State: San Jose, CA
My Country: USA, Unsure of Planet
Line Voltage: 120VAC, 60Hz & 115VAC, 400Hz
I'm a: Professional Tech
Posts: 2,889
Default Re: Why does a cap vent?

1)What is the "X" mark or the "T" mark on the top of the caps? is this the escape door?

It's an intentional "weak" spot in the can. It make it less likely that the whole can will launch like a little rocket. The scorings vent at a fairly predictable pressure - electrolyte vapor and/or hydrogen. BTW, electrolytes with significant water content are not peculiar to crap caps: e.g. all Rubycon low impedance caps have significant water content, but Rubycon (the other two 'cons and Panasonic also) knows what to add to stabilize the electrolyte.

2)The electrolyte is it corrosive for our skin? is it dangerous to smell it?

As a whole, no, though I wouldn't use electrolyte as soap or a beverage.

3)do we know the chemicals it contains?

The basic ingredients are known publicly.

4) The thin metal film inside the cap what is it? aluminium or some other metal?

Aluminum
__________________
PeteS in CA

Power Supplies should be boring: No loud noises, no bright flashes, and no bad smells.

Where might is right
There is no right.
- Sophocles in "Antigone"
****************************
All that is gold does not glitter,
Not all those who wander are lost;
- J.R.R. Tolkien, The Fellowship of the Ring
****************************
To kill personal responsibility, initiative or success, punish it by taxing it. To encourage irresponsibility, improvidence, dependence and failure, reward it by subsidizing it.
PeteS in CA is offline   Reply With Quote
Old 08-21-2006, 04:20 PM   #7
whiz
Member
 
Join Date: Aug 2006
City & State: Athens,Greece
Posts: 46
Default Re: Why does a cap vent?

Quote:
Originally Posted by PeteS in CA
It's an intentional "weak" spot in the can. It make it less likely that the whole can will launch like a little rocket.
quite interesting effect if they could lift off...

thank you for the analysis...do you know any good sites so i can read
about the composition of electrolyte?
whiz is offline   Reply With Quote
Old 09-19-2006, 03:35 AM   #8
VILE DISRUPTION
Member
 
Join Date: Jun 2006
City & State: Queensland,Australia
Posts: 47
Default Re: Why does a cap vent?

probably google. try "capacitor electrolyte" or something.
VILE DISRUPTION is offline   Reply With Quote
Old 09-19-2006, 11:09 AM   #9
gonzo0815
Badcaps Veteran
 
Join Date: Feb 2006
City & State: Germany
Posts: 1,595
Default Re: Why does a cap vent?

Think this i somehow a secret wich is kept closed to the public. As today to mutch well skilled competitors in low cost countries are waiting for the proper rezept.
gonzo0815 is offline   Reply With Quote
Old 09-19-2006, 12:01 PM   #10
arneson
Badcaps Veteran
 
Join Date: Sep 2005
City & State: SWF
Posts: 1,258
Default Re: Why does a cap vent?

The write ups Iv'e read on this go quickly over my head but detail the tweaking of test solutions. Adding stabilizers, nuetralizers and removing water.
Lots of graphs and math. I don't think the prefered formular is secret but any improvements would certainly be, unless HP taps the phone.
__________________
Jim
arneson is offline   Reply With Quote
Old 12-29-2006, 12:28 PM   #11
PedroDaGr8
Senior Member
 
Join Date: Oct 2006
Posts: 130
Default Re: Why does a cap vent?

Quote:
Originally Posted by arneson
The write ups Iv'e read on this go quickly over my head but detail the tweaking of test solutions. Adding stabilizers, nuetralizers and removing water.
Lots of graphs and math. I don't think the prefered formular is secret but any improvements would certainly be, unless HP taps the phone.
Any chance that you could send me some of these, or the links / names etc. I am trying to find out as much of this as I can inorder to try and put together a plain english article on why capacitors vent (initially I was going to do some research but the Hillman et al. article is quite good on the research).
PedroDaGr8 is offline   Reply With Quote
Old 01-02-2007, 12:09 AM   #12
davmax
Badcaps Veteran
 
davmax's Avatar
 
Join Date: Dec 2005
City & State: Perth Western Australia
Posts: 886
Default Re: Why does a cap vent?

I have used thsi reference before: http://industrial.panasonic.com/www-...ABA0000TE4.pdfBasically the internal cap pressure is claimed to be caused by excessive hydrogen. Good electrolyte formulae absorb the hydrogen whilst the bad cap brands have used an incorrect formula and excess hydrogen is the result. Too much and pop goes the vent.
__________________
Gigabyte EP45-DS3L Ultra Reliable (Power saver)
Intel E8400 (3000Mhz) Bios temps. 4096Mb 800Mhz DDR2 Corsair XMS2 4-4-4-12
160Gb WD SATAII Server grade
Nvidia 8500GT 256Mb
160Gb WD eSATAII Server grade for backup.
Samsung 18x DVD writer
Pioneer 16x DVD writer + 6x Dual layer
33 way card reader
Windows XP Pro SP3
Thermaltake Matrix case with 430W Silent Power
17" Benq FP737s LCD monitor
HP Officejet Pro K5300 with refillable tanks
davmax is offline   Reply With Quote
Old 01-03-2007, 01:34 PM   #13
PedroDaGr8
Senior Member
 
Join Date: Oct 2006
Posts: 130
Default Re: Why does a cap vent?

Quote:
Originally Posted by davmax
I have used thsi reference before: http://industrial.panasonic.com/www-...ABA0000TE4.pdfBasically the internal cap pressure is claimed to be caused by excessive hydrogen. Good electrolyte formulae absorb the hydrogen whilst the bad cap brands have used an incorrect formula and excess hydrogen is the result. Too much and pop goes the vent.
Nice article, covers a wide range of failure modes.
The mode of failure for the tiawanesse capacitors was investigated by Hillman et al. Article It appears to be more complex than this. The good electrolytes actually prevent the H2 generation in the first place. It seems that the bad electrolytes are usually marked by pH>=6 while the good ones are have a pH of around 2-4, bad electrolytes also seem to be lacking in phosphate ions compared to the good electrolyte. The reason that the pH is important, is that it degrates the aluminum oxide dielectric layer. Which I explain the mechanism in detail in this thread http://www.badcaps.net/forum/showthread.php?t=3047
The dielectric degredation is characterized by a gradually rising capacitance value (as the dielectric layer gets thinner and thinner) until there is a sudden spontaneous drop (dielectric layer is gone, now have highly conductive electrolyte bridging to plates).
PedroDaGr8 is offline   Reply With Quote
Old 12-07-2007, 05:18 AM   #14
mbutts
New Member
 
mbutts's Avatar
 
Join Date: Dec 2007
City & State: midwest usa
Posts: 2
Default Re: Why does a cap vent?

Very informative thread!

on a side note

Eons ago when I was in college I was doing a lab project. I had an axial cap on a breadboard in a circuit and was attempting to take a voltage reading. The DVM counted down toward zero volts. Just be for it hit that magical number there was a very loud pop followed by small quantities of white hair like debris floating in the air. I had inadvertently put a cap in backwards and it blew up. One end of the cap was still on the breadboard, the other had shot to the ceiling and bounced back down on the bench top. Needless to say I got the attention of the rest of the lab. I picked up the piece off the bench and burnt the heck out of my fingers. Since then, it has been down hill with my love affair of bad caps and I replace them every opportunity I get.
__________________
Puppy Linux user
mbutts is offline   Reply With Quote
Old 12-07-2007, 06:54 AM   #15
PCBONEZ
Grumpy Old Fart
 
PCBONEZ's Avatar
 
Join Date: Aug 2005
City & State: Phoenix, AZ
My Country: USA
Line Voltage: 120V 60Hz
I'm a: Professional Tech
Posts: 10,630
Default Re: Why does a cap vent?

Bit of caution as to:
>>>>>>>>>>
3)do we know the chemicals it contains?
<<<<<<<<<<

The answers I see are pertaining to the low ESR caps this site is about.
I agree, those aren't especially nasty chemicals.

But other types of caps indeed have very some nasty stuff inside.
[off the top of my head.]
- The electrolyte in Tantalum foil capacitors may be as much as 40% sulfuric acid.
- Old oil filled caps may contain PCB's.

.
__________________
Mann-Made Global Warming.
- We should be more concerned about the Intellectual Climate.

-
Be who you are and say what you feel, because those who mind don't matter and those who matter don't mind.

- Dr Seuss
-
You can teach a man to fish and feed him for life, but if he can't handle sushi you must also teach him to cook.
-
PCBONEZ is offline   Reply With Quote
Old 12-07-2007, 07:07 AM   #16
PCBONEZ
Grumpy Old Fart
 
PCBONEZ's Avatar
 
Join Date: Aug 2005
City & State: Phoenix, AZ
My Country: USA
Line Voltage: 120V 60Hz
I'm a: Professional Tech
Posts: 10,630
Default Re: Why does a cap vent?

>>>>>>>
by pumping 20v into the 10v-rated cap on reversed polarity
<<<<<<<

Most "on site topic" caps are rated for 1v max on reverse polarity.
-
Reverse polarity strips the oxide layer off the aluminum.
(Due to electrolysis in the wrong direction.)
The oxide layer is the bulk of the dielectric (insulator) between the plates.
When it's gone the cap is effectively shorted internally. (Or partially so.)
More current. More heat. More gasses?. Thermal expansion?(electrolyte)
~Pop~
.
PCBONEZ is offline   Reply With Quote
Old 01-08-2013, 01:18 PM   #17
DRHCREEK
New Member
 
Join Date: Jan 2013
City & State: Arden Hills, MN
My Country: USA
Line Voltage: 120VAC 60HZ
I'm a: Professional Tech
Posts: 1
Default Re: Why does a cap vent?

Years ago while working on tube television chassis inside a wooden console, I saw an aluminum can electrolytic launch the can into the top of the wooden console. It planted itself into the wooden top enough to cause the top of the furniture to require refinishing.
Caps in those televisons were 400+ uf's at up to 600 volts. They became grenades if installed incorrectly. Be very careful about ploarity when installing any cap.
DRHCREEK is offline   Reply With Quote
Old 01-09-2013, 05:15 AM   #18
Hondaman
Badcaps Veteran
 
Hondaman's Avatar
 
Join Date: Sep 2008
City & State: Clarksville, Indiana
My Country: USA
Line Voltage: 120V 60Hz
I'm a: Forum Junkie
Posts: 758
Smile Re: Why does a cap vent?

Seven years ago, my vocational school teacher had his own HVAC business in the daytime and taught us at night. He told us a story once about a capacitor that blew on a rooftop air conditioning unit. He bent down to pick up a tool and heard it explode. It is a good thing he bent down.

(I don't know why a capacitor the size of a 330 or 354 milliliter cola can would be mounted on its side, 5 or 6 feet above the surface of the roof. And I presume the power was off when it blew. What could cause such a time delay before the explosion?)

Anyway, the top blew. The contents struck the cover panel of the neighboring air conditioning unit (because it was laying on its side). It was a hot mess.

(Why would the capacitor blow after power was removed?)

It is a good thing my teacher bent down when he did!

(He also told us about the time he was working on a rooftop unit at a small corner food store [Dayton Ohio, probably late 1970s]. He came down from the roof to take a break and discovered that someone had brutally murdered the two workers and put their bodies in the freezer while he was working up there.)

Anyway, be safe out there!

Last edited by Hondaman; 01-09-2013 at 05:17 AM..
Hondaman is offline   Reply With Quote
Old 07-10-2013, 03:54 PM   #19
Uniballer
Badcaps Veteran
 
Join Date: Jul 2013
City & State: Buffalo, NY
My Country: USA
I'm a: Knowledge Seeker
Posts: 332
Default Re: Why does a cap vent?

Quote:
Originally Posted by Hondaman View Post
And I presume the power was off when it blew. What could cause such a time delay before the explosion?
I would assume the power was on. There are plenty of things an HVAC guy may want to do to a rooftop compressor with the power on (e.g. measuring refrigerant pressures).
Uniballer is offline   Reply With Quote
Old 07-11-2013, 11:35 PM   #20
Hondaman
Badcaps Veteran
 
Hondaman's Avatar
 
Join Date: Sep 2008
City & State: Clarksville, Indiana
My Country: USA
Line Voltage: 120V 60Hz
I'm a: Forum Junkie
Posts: 758
Default Re: Why does a cap vent?

Maybe the power was on, I'm not sure. The teacher gave the impression that "it wasn't supposed to happen", so I assumed the power was off and the cap was discharging. Please wear safety glasses around high voltage. And don't wear jewelry (wedding ring) which could cause a short or get tangled up with parts when working on stuff.

Last edited by Hondaman; 07-11-2013 at 11:36 PM..
Hondaman is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump



Badcaps.net Technical Forums 2003 - 2019
Powered by vBulletin ®
Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
All times are GMT -6. The time now is 04:56 PM.
Did you find this forum helpful?