High school. Rat's nest of free space wiring. Neon bulbs, capacitors
(relaxation ring oscillator). Powered by half bridge directly from AC line
(no transformer). Main supply cap probably 50uF @ 200V or so. Short circuit=
..
Small rocket dragging 115VAC / 160VDC all around the workbench. Much
excitement.

- - Bob Ammerman
RAm Systems

-----Original Message-----
From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf Of
DrSkip
Sent: Monday, February 26, 2018 12:09 AM
To: piclist@mit.edu
Subject: Re: [EE] "X" marks the spot

I suspect the X is initially weaker than the glue holding the can on, so
rapid pressure increase will break open there. Perhaps over the 30 minutes
heat weakened the glue to the point of it being the weak point for a gradua=
l
pressure buildup.

Dr Skip


On 02/25/2018 08:36 PM, Bob Blick wrote:
> By mistake I put an electrolytic capacitor in backwards. A very generic
100uF, 50V cap exposed to 16V with the equivalent of about 700 ohms in
series with it. It lasted about 30 minutes, then went off with a bang. You
can maybe see the damaged heatshrink where the can hit an immovable object.
>
> Please note the scored cross on the top of the can. Isn't that=20
> supposed to split and protect me from its rapid self-disassembly? Yes,=20
> I was right there, close at hand, trying to figure out why all the=20
> voltages were wrong. Perhaps their die for the venting "X" was worn=20
> out after 20 million caps. I guess that's what I get when I pay USD=20
> 0.03 for caps off of Aliexpress instead of USD 0.11 at Digi-Key :)
>
> I guess I learned a lesson in false economy today. I didn't lose an eye,
but I'm going to change my buying habits a little. Obviously I made a
mistake putting the cap in wrong, but if I'd used a quality cap perhaps I'd
have only been startled with a scary hiss instead of a projectile. Take
heed! How many lives do you really have?
>
> Cheerful regards,
>
> Bob
>
>
>
>

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