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From: Bill Sloman <bill.sloman@ieee.org>
Newsgroups: sci.electronics.design
Subject: Re: heating a cap
Date: Sat, 5 Oct 2024 21:56:04 +1000
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On 5/10/2024 5:44 am, john larkin wrote:
> On Fri, 04 Oct 2024 18:00:51 +0100, Cursitor Doom <cd@notformail.com>
> wrote:
> 
>> On Thu, 03 Oct 2024 16:36:24 -0700, john larkin <jl@glen--canyon.com>
>> 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.
>>
>> That's a hell of sweeping conclusion to come to based on a test of
>> just one random electrolytic!
> 
> It's more data than no experiment would provide.

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

> Elecs seem to explode from internal steam pressure, which sounds
> fairly predictable.
> 
> But other people here could try it too.

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

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

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

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

A rather sweeping generalisation.

-- 
Bill Sloman, Sydney