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From: John Robertson <jrr@flippers.com>
Newsgroups: sci.electronics.design
Subject: Re: heating a cap
Date: Fri, 4 Oct 2024 07:09:26 -0700
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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 ;-#)#

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