when caps blow, what happens?

[chico]

Hi there I have been repairing electronics a lot lately and I see electrolytic caps blow and take out other components. I understand that caps often blow closed but why would that effect any other component?

 

[4pyros]

It depends on how the cap is used. If it is a blocking cap it may pass DC into parts that can not take it.

 

[davenn]

It depends on how the cap is used. If it is a blocking cap it may pass DC into parts that can not take it.

or conversely if is a smoothing cap across a power supply then there will be components wont react well to lots of AC on the DC rail

Dave

 

[KeepItSimpleStupid]

It might not be the caps fault. I knew someone who used a model train transformer to power a 12 V automotive device. basically firecrackers.

 

[Vizier87]

.........or the cap might have boosted voltage and that blew out other components.

 

[cowboybob]

Or, in a very spectacular show of capacitor guts, blow up. Especially electrolytics.

Specifically, what happened that caused you to ask the question?

 

[chico]

I was looking at a number of monitors which had broken inverters.

I discovered that all of them had blown caps, but in all cases the inverter also had busted pump-transistors for the high-current high-side FET.
I beleive that the caps took out the transistors since it seems to me the transistors are over spec'd quite a bit.

 

[cowboybob]

When an electrolytic blows it often does so with a enormous current surge (sacrificing itself to save the fuse). This surge will manifest itself in every component with an electrical link to the cap(s) and experience off-scale current spike(s).

And since they are more likely to experience a short (by virtue of their construction) than non-electrolytic caps, they do seem to stay shorted when the smoke clears.

The rule of thumb in the restoration/repair biz is always, first thing, replace ALL caps. ALL caps! Don't even plug it in to power. Ain't worth it.

I don't envy you having to track down every last component that got fried in the disaster.

If I'm understanding you situation correctly, you might want to check (whether they're tube type monitors or not) any flybacks or their equivalents. As they age their propensity to short rises sharply (which may have been involved with the cap failures). And those puppies are not cheap.

 

[Mikebits]

Tantalum caps will go out with a blaze of glory, often burning through the PCB. Tantalum is very hot when it burns. Also standard electrolytic s make nice rockets when they are connected backwards.

 

[KeepItSimpleStupid]

There was a MAJOR capacitor manufacturing problem/sub quality some time ago. I forget which brand. Some searching and you may be able to find it. It could be one of THOSE.

 

[4pyros]

Look under "bad caps" But I think it mostly was mother boards.
A Taiwan manufacturer stole a bad formula and the caps dry up and sometimes explode.
Look here;
https://en.wikipedia.org/wiki/Capacitor_plague

 

[4pyros]

From Silicon Chip
https://www.siliconchip.com.au/cms/A_30328/printArticle.html

"Industrial espionage?
The story describing how the electrolytes came to be faulty reads like a lot of fiction. It begins in Japan, at a major capacitor manufacturer. A materials scientist for the Japanese company resigned and went to work for a Chinese capacitor manufacturer. While there, he reproduced one of the electrolytes used in his former employer's premium (low-ESR) aluminium electrolytic products.

Staff working with the scientist then defected, taking the secret electrolyte formula with them. They used the formula to manufacture their own electrolyte, which they subsequently flogged to major Taiwanese capacitor manufacturers at bargain prices. Unfortunately, their reproduction of the formula was flawed and the rest is history."

 

[jpanhalt]

There are two rules in business:
1) Never tell everything you know;

John

 

[chico]

I have actually found those blown components on all the inverters I have come across to date (not that many really).
I just found it weird that blown caps result in other blown components but now i know why it happens.

 

[MrAl]

Hi,

I've seen large electrolytics blow out their top and bend 1/4 inch thick copper buss bars with no problem. Overvoltage does it, and the more energy stored in the cap the more energy can be released during the failure. Since energy in a cap is proportional to the square of the voltage, the explosion gets 4 times worse for every doubling of the voltage.
The caps i was talking about where 400vdc if i remember right, probably 10000uf each, in a bank of maybe 8. It was a long time ago so i dont remember all the details...used in a high current three phase DC power supply with hefty rectifier diodes to match.