heating a cap

X-Ray it?

Joe

Caps have vents...eventually the electrolyte with evaporate and outgas and you are left with a slug of aluminum foil.

I've seen many thousands of caps fail over the decades, you don't want to push them above 85c (even if rated at 105c) unless you like short lifetimes. Heck even caps that are never over 50c will dry out eventually - 20 to 30 years in many cases. Seals aren't perfect.

I assume SMD electrolytics are the same.

Let's not talk about stress testing tantalum caps - "Bang!".

John ;-#)#

The usual MnO2 tantalums actually detonate, and a bit of peak current will set them off. The polymer tantalums don't detonate.

Is there a reason to use polymer tants? I like tantalums for their just-right ESR for some voltage regulators, and I think the polymer tants are lower.

If you want low ESR, may as well use a polymer aluminum.

You're not 'heating a cap'.

You're applying voltage overstress to failure, using a current limited source.

This tells you precisely nothing.

Were you earing safety glasses?

Are you sure you want to advertize this increasingly erratic behavior?

RL

Some alpos are hybrid, i.e. they have water as well as polymer. I don’t think they make hybrid polymer tants.

Cheers

Phil Hobbs

That's a hell of sweeping conclusion to come to based on a test of just one random electrolytic!

"Actually detonate" - this is really just a steam explosion we're talking about here, though, John? It doesn't involve the breaking apart and re-combination of molecular bonds.

As I understand it, a current spike can heat up a tiny bit, and then an exothermic chemical reaction takes over. MnO2 is the oxidizer and tantalum is the fuel.

For reliable operation, make sure the available current is limited, namely don't use tants on power busses.

LM317s and output tants seem to work well.

Felt hot to me.

But it didn't fail.

Told me a lot. Why elect to not learn things?

No earrings, and my normal glasses.

Experimenting with parts is admittedly a bizarre thing for an engineer to do. Sorry.

I once tried heating a large electrolytic salvaged from a valve TV. With a blowtorch. The side started to bulge, then it split. A large flame maybe 1m long emerged, coloured a brilliant green. I was wearing safety glasses. John

It's more data than no experiment would provide.

Elecs seem to explode from internal steam pressure, which sounds fairly predictable.

But other people here could try it too.

Film caps fail suddenly at some large multiple of rated voltage. Ceramics too, but some start leaking first.

Is seems like elecs start to leak seriously at about 1.5x rated voltage and die from overheating.

You could get similar results from a bottle of vodka.

Legg seems to have a problem on the groups with anyone who isn't an out-and-out Commie. Just ignore him.

There's no reason to not destroy parts. They don't have feelings.

But you'd learn a lot more if you had a better idea of what you were doing.

They could also read up a bit on the chemistry of the particular sort of electrolytic capacitor they were putting under stress.

There are lots of different ceramic capacitors, from NPO to XR7. Some people would be more specific.

A rather sweeping generalisation.

If you need a high temperature cap, these work and they're not horribly expensive...

I know people who are terrified of running parts anywhere near abs max. I run some parts at 2x abs max voltage or power. Pushing parts is the way to get performance, especially speed. Some work fine at 4x.

Test them, blow up a few, define your own abs max. But only when there is a big payoff.

I'm pushing a lot of HMC659's (15 GHz distributed amplifiers) to about

I reall want to absorb joules when a power supply is back-driven by a load, like decelerating a motor for instance. So I want caps with a lot of mass, or MOVs that can get very hot before they die.

The environment won't be very hot, but the cap (or MOV) will.

Well, personally speaking, I've derived a great deal of satisfaction from doing so over the years.