Re: heating a cap

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