Re: heating a cap

john larkin <JL@gct.com> wrote:

On Fri, 4 Oct 2024 07:09:26 -0700, John Robertson <jrr@flippers.com>
wrote:
 

On 2024-10-03 4:36 p.m., john larkin wrote:

I got a small (under 1" long) aluminum electro cap, 220 uF 63v, and
cranked up the voltage. It started drawing a bunch of current at 105
volts, got hot, and folded back to 80 mA at 87v.
 
It got too hot to touch in a couple of minutes, after roughly 500
joules. Freeze spray let it go back up to 100 volts or so.
 
None of that seemed to damage it, so an electrolytic cap sort of has a
built-in MOV.
 

 
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.
 
 

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

--
Dr Philip C D Hobbs  Principal Consultant  ElectroOptical Innovations LLC /
Hobbs ElectroOptics  Optics, Electro-optics, Photonics, Analog Electronics