There was a plague of failures a decade ago. But the same symptom is not only from bad manufacturing. I believe abuse, bad circuit designs also causes the problem. Newer equipment, in operation about a year, showing inflated capacitors that may got inflated suddently or may have been developing the inflation along some time.

What causes do you attribute for such to each; to sudden and to slow inflation ? When several failing/failed capacitors are in parallel, most show the dome or rupture or nothing visually, and there is usually no clues of heat rose in them. And very often seen in boards with inductor circuits nearby.

----> https://duckduckgo.com/?t=ffab&q=inflated+capacitors&iax=images&ia=images

 

Bad caps (mainly still from bad manufacturing) is a plague that still haunts us, it's just not as bad as before IMO. I've replaced the exact same junk brand cap voltage and capacity with quality caps from OEMS like Panasonic with never an additional capacitor failure.

 

Thanks.
If I want to bulge, leak, explode an electrolytic capacitor, what should I do to it other than if the voltage is not exceeded ?

 

Cause the Capacitor to create excessive HEAT and it will fail every time.
Capacitors generate HEAT because of a too-high ESR rating for the particular application.
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Thanks.
OK. 'cause the capacitor to create its own heat' - How is that done ? -That not being environmental heat or poor equipment dissipation-

 

At constant DC voltage, ESR has no effect because there is zero current.
With AC, ESR consumes power which is dissipated as heat.

 

All quality Electrolytics have 2 "Maximum-Current-Ratings",
usually the first one is at ~120hz,
and the second one may be at ~1000hz, or even somewhere around ~10,000hz.
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Here is a datasheet for a series of Nichicon electrolytic capacitors that have a claimed withstand of 3,000 hours (or 125 days) at maximum rated ripple current and temperature.

Nichicon are supposed to be quite a good brand; if you operate electrolytic capacitors close to their limits in terms of ripple current and/or temperature, don’t expect them to last 25 years.

https://docs.rs-online.com/13fd/0900766b813cd37a.pdf

 

A key factor is cap death is ripple. Poorly designed power supplies can destroy caps even if the voltages appear well within specs. Check the datasheet of the caps for ripple current maximum and measure the ripple in the current being fed to them.

 

 

A really violent capacitor explosion that I was asked to evaluate and repair happened with a high intensity flash system that was very conservatively designed. The 450 volt cap was run at about 400 volts, adequate margin. It was also a PHOTOFLASH cap 3 inches in diameter and 5 inches tall. But it exploded from heat. A flaw developed in the trigger circuit and so it started firing the high power flash tube as fast as the supply could recharge, which was about once per second. So after a very few minutes the very high discharge current thru the internal resistance evaporated the plastic part and the aluminum case burst rather violently, it also damaged the steel housing a bit. So capacitor ESR is very real and can lead to overheating and damage.

 

Thanks.
If I want to bulge, leak, explode an electrolytic capacitor, what should I do to it other than if the voltage is not exceeded ?

Connect it backwards. Wear goggles.

 

Repeated Very rapid charge and discharge were the culprits for the unit I had to evaluate.

 

As a kid I wanted to take a car radio and power it from a 12V transformer and a selenium rectifier. It had bad hum and I wanted to filter out that hum. I had NO IDEA what I was doing. Someone said to use a filter cap. So I found an electrolytic cap rated at 16 volts. And I don't remember how many farads it was. I tried it on the 12V half wave rectified DC - no luck. I tried it on the 12V secondary - no luck. I tried it on the 120VAC primary. BOOM! I have no idea what happened to the guts of the cap but I remember finding the empty shell. So I would guess that I over voltage'd it. Yeah, in fact, I'm SURE that's what I did.

So I don't know what would cause a cap to swell suddenly or over a long period of time. But my first guess would be over voltage. But I'm sure there's more to it than just that.

 

As a kid I wanted to take a car radio and power it from a 12V transformer and a selenium rectifier. It had bad hum and I wanted to filter out that hum. I had NO IDEA what I was doing. Someone said to use a filter cap. So I found an electrolytic cap rated at 16 volts. And I don't remember how many farads it was. I tried it on the 12V half wave rectified DC - no luck. I tried it on the 12V secondary - no luck. I tried it on the 120VAC primary. BOOM! I have no idea what happened to the guts of the cap but I remember finding the empty shell. So I would guess that I over voltage'd it. Yeah, in fact, I'm SURE that's what I did.

So I don't know what would cause a cap to swell suddenly or over a long period of time. But my first guess would be over voltage. But I'm sure there's more to it than just that.

Excess leakage current will cause a correctly rated capacitor to heat, and that will often lead to swelling, or leakage,or bursting.

 

So I don't know what would cause a cap to swell suddenly or over a long period of time. But my first guess would be over voltage. But I'm sure there's more to it than just that.

Excess current,
As is seen in bi-polar electrolytic used as start caps in an induction motor when the centrifugal SW fails etc.

 

Excess current,
As is seen in bi-polar electrolytic used as start caps in an induction motor when the centrifugal SW fails etc.

Ultimately it is ALWAYS excess current, although certainly the reason for the excess current may vary quite a lot.