What causes Rail Capacitors to Swell and Split Open?

confused256 · 17th September 2006, 10:54 PM

I have an amplifer and the Rail Voltage Capactors are Swelled big and one looks like it lots its juice. What causes this? The 12 volt supply caps look fine.
Also what cause the filter caps on the output of Class D amplifier to swell?

johndiy · 17th September 2006, 11:00 PM

overvoltage

john

dmitriy167 · 17th September 2006, 11:05 PM

Oh, my. CHANGE ALL OF THEM RIGHT AWAY. They usually do that either when their voltage ratings are exceeded, or when they are connected with opposite polarity. If you don't change them, they will explode. Use higher rated caps as a replacement. If your output filter caps are swelling as well (I assume they're electrolytic), then there is probably something very wrong with the amp. Check it out, or if you don't have the skill, have someone check it out for you. Whatever you do, DON'T TURN IT ON.

pinkmouse · 17th September 2006, 11:13 PM

Quote:

Whatever you do, DON'T TURN IT ON.

Yup. That amp is in serious trouble. One or two caps could possibly be down to age, but all of them? Nah, that has been badly abused.

SuperAudioBuff · 17th September 2006, 11:43 PM

A second possibility is that your bridge rectifier has failed, and/or some other means of AC power is being delivered to the filtering capacitors, at any rate, not good news!!! Change the bridge rectifiers, and capacitors right away, double check your voltage ratings on the caps.

kevinkr · 17th September 2006, 11:53 PM

Is this a car amplifier? Sure looks like one. Excessive battery voltage could be the culprit if the amplifier uses a switching power supply. Also age, heat, poor quality caps, and just running it too hard for very long time periods - subwoofer amps.

Dragance007 · 18th September 2006, 12:27 AM

I have repaired many of computer power units by changing exploded caps....on all lines 5 volt, 12 vols 3.3 volt....i never realy find out why they do that swell thing ??? and actual question that i ask myself is:
Are there special caps just 4 SMPS purposes or they R all the same ?

Leolabs · 18th September 2006, 02:33 AM

Quote:

Originally posted by Dragance007
I have repaired many of computer power units by changing exploded caps....on all lines 5 volt, 12 vols 3.3 volt....i never realy find out why they do that swell thing ??? and actual question that i ask myself is:
Are there special caps just 4 SMPS purposes or they R all the same ?

Yes.There special caps for SMPSs.

clem_o · 18th September 2006, 02:55 AM

Computer motherboards too have this problem. It's supposed to have been caused by a capacitor formula 'leaked out' to a competitor by a disgruntled employee. Apparently the formula was incomplete or not yet finished, causing the electrolytic to be unstable. The result is that capacitors produced using this electrolytic have a tendency to produce excessive internal gasses - failure can happen within low hundreds of hours of operation, versus the normal rated life of a few thousand hours. See this link

http://en.wikipedia.org/wiki/Capacitor_plague

or google "bloated capacitors" and you'll see lots of references to such...

Cheers

rdf · 18th September 2006, 03:35 AM

Heat does that in a computer as well. I just tossed an ATX board with swollen caps adjacent to the CPU cooler. The same brand and value a centimeter away were fine.

17th September 2006, 11:43 PM	#5
SuperAudioBuff diyAudio Member Join Date: May 2004 Location: New York (Upstate)	AC Power??? A second possibility is that your bridge rectifier has failed, and/or some other means of AC power is being delivered to the filtering capacitors, at any rate, not good news!!! Change the bridge rectifiers, and capacitors right away, double check your voltage ratings on the caps.

17th September 2006, 11:53 PM	#6
kevinkr diyAudio Moderator Join Date: Sep 2004 Location: Boston, Massachusetts Blog Entries: 6	Is this a car amplifier? Sure looks like one. Excessive battery voltage could be the culprit if the amplifier uses a switching power supply. Also age, heat, poor quality caps, and just running it too hard for very long time periods - subwoofer amps. __________________ "Extraordinary claims require extraordinary evidence." - Carl Sagan

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17th September 2006, 11:00 PM	#2
johndiy Banned Join Date: Aug 2006	overvoltage john

17th September 2006, 11:05 PM	#3
dmitriy167 diyAudio Member Join Date: Mar 2004 Location: NJ, USA	Oh, my. CHANGE ALL OF THEM RIGHT AWAY. They usually do that either when their voltage ratings are exceeded, or when they are connected with opposite polarity. If you don't change them, they will explode. Use higher rated caps as a replacement. If your output filter caps are swelling as well (I assume they're electrolytic), then there is probably something very wrong with the amp. Check it out, or if you don't have the skill, have someone check it out for you. Whatever you do, DON'T TURN IT ON.

18th September 2006, 12:27 AM	#7
Dragance007 diyAudio Member Join Date: Nov 2002 Location: Yugoslavija	I have repaired many of computer power units by changing exploded caps....on all lines 5 volt, 12 vols 3.3 volt....i never realy find out why they do that swell thing ??? and actual question that i ask myself is: Are there special caps just 4 SMPS purposes or they R all the same ?

18th September 2006, 02:55 AM	#9
clem_o diyAudio Member Join Date: Jun 2005 Location: Manila	Computer motherboards too have this problem. It's supposed to have been caused by a capacitor formula 'leaked out' to a competitor by a disgruntled employee. Apparently the formula was incomplete or not yet finished, causing the electrolytic to be unstable. The result is that capacitors produced using this electrolytic have a tendency to produce excessive internal gasses - failure can happen within low hundreds of hours of operation, versus the normal rated life of a few thousand hours. See this link http://en.wikipedia.org/wiki/Capacitor_plague or google "bloated capacitors" and you'll see lots of references to such... Cheers

18th September 2006, 03:35 AM	#10
rdf diyAudio Member Join Date: Jun 2004 Location: big smoke	Heat does that in a computer as well. I just tossed an ATX board with swollen caps adjacent to the CPU cooler. The same brand and value a centimeter away were fine.