Smoking capacitors

jdoorn · 23rd January 2006, 08:01 PM

I built a stereo amplifier using ZapPulse modules running at about 65V.
For the PSU of this project I bought new capacitors, Nippon chemi-con LXG 80V 4700uF through Ebay.
The amplifier ran fine at normal listening levels, but after some time on loud volume one capacitor started smoking.

Assuming this was an incident, I never had any trouble with capacitors, I replaced the component and tested the whole thing for a day at normal volume.
But again, after about 30 minutes music on high volume again one capacitor started smoking. I use 6 caps per module.
I this just a case of a bunch of bad capacitors I have to ditch or could this be caused by something else ?

theAnonymous1 · 23rd January 2006, 08:05 PM

I guess the obvious thing would be to verify the voltage across the cap when it starts to smoke. If the voltage is within the rating of the cap then either the cap is mislabeled or there is some other factor I'm not aware of.

poobah · 23rd January 2006, 08:15 PM

Was it the same capacitor in your layout... and the same channel?

What is the wattage output at "high" volume?

lohk · 23rd January 2006, 08:18 PM

those caps are probably a faulty lot (sadly not uncommon with ebay purchases)

But on the other hand: Watch your psu voltage ripples with a scope with different loads. Maybe your rectifier creates small "surges" which then overload the quite tightly tolerated caps. 65V can quickly become 70V and more if the mains voltage varies, and the rectifiers switching "impulses" do the "rest".

jdoorn · 23rd January 2006, 08:52 PM

The amplifier is not with me at the moment (it's at my brothers house), but in time I will measure it with a scope.
I'am not sure what the output power was, but the speakers are large and rated 4 ohms, he has also a large living room and was alone in the house, fill in the rest....
At this moment I think also of a faulty lot as I have never experienced this kind of problem.

poobah · 23rd January 2006, 08:57 PM

Was it the same capacitor in your layout... and the same channel?

I ask because it could be your layout is favoring one of capacitors...

I'm good with the bad lot thing too... electrolytics, because they age, ESPECIALLY when not in use, are something you really want to buy new if you can manage.

alfsch · 23rd January 2006, 10:23 PM

do not forget supply bumping...
when driving 4 ohm at hi level, voltage may rise...and kill the caps.
whats the idle supply in your set?

Pano · 23rd January 2006, 11:32 PM

Duuuuude! Don't do it. Smoking caps will give you a nasty buzz.

Stick to pakalolo or banana peels, man. Or cigars, if you must.

Bzzzzzzz

23rd January 2006, 08:01 PM	#1
jdoorn diyAudio Member Join Date: May 2004 Location: Purmerend	Smoking capacitors I built a stereo amplifier using ZapPulse modules running at about 65V. For the PSU of this project I bought new capacitors, Nippon chemi-con LXG 80V 4700uF through Ebay. The amplifier ran fine at normal listening levels, but after some time on loud volume one capacitor started smoking. Assuming this was an incident, I never had any trouble with capacitors, I replaced the component and tested the whole thing for a day at normal volume. But again, after about 30 minutes music on high volume again one capacitor started smoking. I use 6 caps per module. I this just a case of a bunch of bad capacitors I have to ditch or could this be caused by something else ?

23rd January 2006, 08:18 PM	#4
lohk diyAudio Member Join Date: Apr 2001 Location: Austria, near Linz	those caps are probably a faulty lot (sadly not uncommon with ebay purchases) But on the other hand: Watch your psu voltage ripples with a scope with different loads. Maybe your rectifier creates small "surges" which then overload the quite tightly tolerated caps. 65V can quickly become 70V and more if the mains voltage varies, and the rectifiers switching "impulses" do the "rest". __________________ /alohka/

23rd January 2006, 11:32 PM	#8
Pano diyAudio Moderator Join Date: Oct 2004 Location: North Carolina Blog Entries: 4	Duuuuude! Don't do it. Smoking caps will give you a nasty buzz. Stick to pakalolo or banana peels, man. Or cigars, if you must. Bzzzzzzz __________________ Take the Speaker Voltage Test!

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23rd January 2006, 08:05 PM	#2
theAnonymous1 diyAudio Member Join Date: Feb 2004 Location: Anonymityville	I guess the obvious thing would be to verify the voltage across the cap when it starts to smoke. If the voltage is within the rating of the cap then either the cap is mislabeled or there is some other factor I'm not aware of.

23rd January 2006, 08:15 PM	#3
poobah diyAudio Member Join Date: Nov 2005	Was it the same capacitor in your layout... and the same channel? What is the wattage output at "high" volume?

23rd January 2006, 08:52 PM	#5
jdoorn diyAudio Member Join Date: May 2004 Location: Purmerend	The amplifier is not with me at the moment (it's at my brothers house), but in time I will measure it with a scope. I'am not sure what the output power was, but the speakers are large and rated 4 ohms, he has also a large living room and was alone in the house, fill in the rest.... At this moment I think also of a faulty lot as I have never experienced this kind of problem.

23rd January 2006, 08:57 PM	#6
poobah diyAudio Member Join Date: Nov 2005	Was it the same capacitor in your layout... and the same channel? I ask because it could be your layout is favoring one of capacitors... I'm good with the bad lot thing too... electrolytics, because they age, ESPECIALLY when not in use, are something you really want to buy new if you can manage.

23rd January 2006, 10:23 PM	#7
alfsch diyAudio Member Join Date: Jan 2002 Location: augsburg	do not forget supply bumping... when driving 4 ohm at hi level, voltage may rise...and kill the caps. whats the idle supply in your set?

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